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Sr 2 V 2 O 7 (SVO) microwave dielectric ceramics were fabricated through a conventional solid-state synthesis method and sintered at 900–1000 °C for 10 h. The crystal structures and morphologies of the SVO samples were examined via X-ray diffraction and scanning electron microscopy. These analyses revealed that the SVO sample sintered at 950 °C exhibited high crystallinity and a triclinic crystal system. Through the lens of lattice dynamics, the phonon characteristics of the SVO samples were investigated via Raman spectroscopy and far-infrared spectroscopy to elucidate the dielectric response mechanics and microstructural origins of these responses. Raman spectra were classified into three sections corresponding to the vibration of Sr2+ ions, the V–O or V–O–V telescopic vibration, and the internal elongation of the tetrahedral structure composed of V–O, respectively. The inherent dielectric properties obtained from the far-infrared spectra were analyzed using a four-parameter semi-quantum model with the assistance of the Focus software. This analysis aligned with the measured property values. The relationships between the crystal structures and the dielectric properties were established using the Raman modes. Particularly, the SVO sample sintered at 950 °C exhibited excellent dielectric properties, characterized by a dielectric constant (ε r) of 9.49, a quality factor (Q × f) of 35,189 GHz, and a resonant frequency (f) of 12.48 GHz. [ABSTRACT FROM AUTHOR]

Exploring superconducting materials stands as a pivotal pursuit in condensed matter physics, particularly, the investigation of superconductivity in two-dimensional metal hydrides is of paramount importance due to its intriguing nature. Our study focuses on elucidating the metallic state of van der Waals layered TM-H (TM = Ti, Zr, Hf) compounds, a key factor in predicting their superconducting (SC) characteristics. Leveraging an evolutionary algorithm rooted in density functional theory, we predicted the structures of hydrides, including Ti 2 H 2 , Ti 2 H 4 , Zr 2 H 2 , Zr 2 H 4 , Zr 2 H 5 , Hf 2 H 2 , Hf 2 H 4 , Hf 2 H 5 , and determined their energetically stable structures. Along with exploring the potential for SC, we conducted a comprehensive examination of relevant electronic properties. A significant aspect addressed was the influence of anharmonic phonon properties in determining the stochastic self-consistent harmonic approximation. These findings underscore the pivotal role of anharmonicity in determining the SC of two-dimensional metal hydrides. [Display omitted] • A variety of atomic configurations of hydrogen are unveiled in the discovery of novel two-dimensional monolayers featuring transition metals. • Enhancing T c relies significantly on the impact of quantum fluctuations and anharmonic corrections. • The SSCHA method renormalizes an analytical expression for lattice dynamics, ensuring stabilization at finite temperatures. • Hf 2 H 5 exhibits superconductivity with a notable T c of 10.3 K. [ABSTRACT FROM AUTHOR]

The conversion of heat into electricity using the thermoelectric effect is a crucial issue to tackle the ever-increasing global energy consumption. Cu 2 Se is one of the high-performance thermoelectric materials due to its liquid-like atomic structure, which minimizes the phonon-derived thermal conductivity. Nevertheless, the unambiguous atomic structure of the low-temperature phase, α -Cu 2 Se, remains controversial. By employing a combination of theoretical approaches including an evolutionary algorithm for structural searching, density functional theory, and lattice dynamics, the α -Cu 2 Se phase is proposed to crystalize in the dynamically stable triclinic Cu 2 Se structure (s.g. P1) which can be regarded as a monoclinic polymorph (s.g. P2 1 /c †) through slight distortion. The corresponding heat capacity (C V) and Debye temperature (Θ D) are 0.37 J/g K and 276 K, respectively, indicating low thermal conductivity in the material. The semiconducting P1 phase possesses an indirect gap of 1.0 eV. Additionally, based on the Boltzmann transportation theory, fundamental thermoelectric parameters around the transition temperature (300–500 K) are investigated. Beyond the semiconducting phase, a novel metallic phase identified as the triclinic P 1 ̄ phase is also discovered, exhibiting a two-dimensional (2D) crystal geometry. [ABSTRACT FROM AUTHOR]

We address the existence of non-trivial closed invariant ideals for positive operators defined on Banach lattices whose order is induced by an unconditional basis. In particular, for band-diagonal positive operators such existence is characterized whenever their matrix representations meet a positiveness criteria. For more general classes of positive operators, sufficient conditions are derived proving, particularly, the sharpness of such results from the standpoint of view of the matrix representations. The whole approach is based on studying the behavior of the dynamics of infinite matrices and the localization of the non-zero entries. Finally, we generalize a theorem of Grivaux regarding the existence of non-trivial closed invariant subspaces for positive tridiagonal operators to a more general class of band-diagonal operators showing, in particular, that a large subclass of them have non-trivial closed invariant subspaces but lack non-trivial closed invariant ideals. [ABSTRACT FROM AUTHOR]

Pure BiFeO 3 (BFO), Sr-doped Bi 0.97 Sr 0.03 FeO 3 (BSFO) and Sr, Co co-doped Bi 0.97 Sr 0.03 Fe 0.8 Co 0.2 O 3 (BSFCO) samples have been prepared via a tartaric acid-assisted sol-gel technique. Investigation of the structure, lattice dynamics, magnetization and hyperfine interaction have been performed through X–ray diffraction (XRD), transmission electron microscope (TEM), Raman spectroscopy (RS), vibrating sample magnetometer (VSM) and Mössbauer spectroscopy (MS). The TEM images show that the particle sizes of BFO, BSFO and BSFCO are respectively 11.4, 12.1 and 8.8 nm. The XRD analysis reflects a structural phase transition from rhombohedral R 3 c structure in case of BFO and BSFO samples to two phase coexistence (rhombohedral R 3 c and trigonal R–3m:R) in case of BSFCO sample. This structural phase transition has been strongly confirmed by the alterations in the vibration modes observed in Raman spectra (expansion, shift, merge, and reduced intensity). Second order vibration modes, corresponding to the two-phonon scattering in the range 650–1000 cm−1, have been recorded for all samples. Investigation of magnetic properties reveals that pure and Sr doped samples possess considerably high magnetic saturations (Ms = 5.61 and 5.79 emu/g respectively). Additionally, BSFCO sample shows enhancement in Ms (Ms rises to 8.26 emu/g). Suppression of spiral spin structure caused by the small nano-size has been assumed. The destruction of the spiral spin has been also suggested through M össbauer studies. The hyperfine parameters reveal that only Fe3+ is observed in two different nonequivalent trigonal distorted octahedral environments. The outcome of this work suggests the potentiality of Sr, Co co-doping to improve the structure and ferromagnetism of BiFeO 3 ceramic making it feasible to be employed in enormous applications. [ABSTRACT FROM AUTHOR]

Phonons play a pivotal role in the lattice dynamics and thermal transport properties of AlN epilayers. Revealing the phonon anharmonicity and epilayer-substrate interactions is the most fundamental step to develop high-performance AlN-based optoelectronic devices. We systematically report the temperature-dependent behavior of phonons in AlN epilayers grown on sapphire substrates in the temperature range of 4 – 870 K. The nonlinear frequency redshifts (softening) of the two main phonon modes, E 2 (high) and A 1 (LO), are fitted by our proposed formula with robust generalizability. Strikingly, the weakly anomalous phonon behavior of AlN epilayers and bulk AlN was observed below 100 K, which may be attributed to the negative thermal expansion of AlN crystals. More pronounced phonon softening due to substrate induced strain effect was observed in AlN epilayers than in bulk AlN. This stronger temperature dependence in AlN epilayers can be used as a non-invasive thermal probe to determine the local temperature variation of AlN-based devices. Combined with first-principles calculations, the frequency redshift and linewidth broadening of E 2 (high) and A 1 (LO) modes are further quantified by a physical model involving thermal expansion, phonon anharmonic effects, and substrate effects. Our findings shed insight into phonon-phonon interactions in AlN and provide an indicator for its extreme device applications. This process can also be fundamentally applicable to other emerging epitaxial films and 2D materials. Additionally, the biaxial stress coefficient and pure temperature coefficient of the E 2 (high) mode determined by the contribution of substrate-induced strain effects to the phonon frequency shift are −6.63 ± 0.27 cm−1/GPa and −0.0217 cm−1/K, respectively. These coefficients provide critical information for accurately assessing the impact of temperature and stress on device reliability. [ABSTRACT FROM AUTHOR]

In this study, we present a model designed to unravel the statistical complexities of pedestrian crossing times and related physical quantities in a unique pedestrian intersection, specifically a double intersecting diagonal crossing. Our model employs an agent-based stochastic process based on a lattice gas dynamics to describe a four-species interaction on an underlying square lattice representing the intersection. This model incorporates four static floor fields guiding each species within the scenario. Our findings emphasize the critical role that the density of highly driven pedestrians plays in the statistics of crossing times by triggering the transition from a normal distribution for low densities to a uniform distribution for a crowded scenario. In the steady state, we mapped the system mobility and showed that an anomalous mobile phase emerges when considering a scenario with high density of poorly driven pedestrians. To monitor these phenomena, we focus on two variables: directed mobility and average distance between agents. We conclude our analysis by overcoming a crucial limitation of the lattice gas model with the introduction of viscosity effects among pedestrians. We observe that mixed state regime emerges as the system presents a mobile-to-immobile phase transition when viscosity effects faints. Our research sheds light on the nuanced dynamics of scramble intersections, contributing to a deeper understanding of urban mobility challenges. • Investigation of Pedestrian Dynamics at Scramble Intersections. • Modeling Incorporating Orientation Factor and viscosity effects. • Analysis of Crossing Time Statistics and Congestion Patterns. • Computational Simulation Employing Asynchronous Dynamics within the Framework of Monte Carlo Simulations. [Display omitted] [ABSTRACT FROM AUTHOR]

The TiB 4 RM (RM = Cr, Mo, W) tetraborides are promising hard materials, however, other physical properties of these tetraborides are currently unknown. Here, the structural, electronic, dynamical, mechanical and thermal properties of the TiB 4 RM are thoroughly investigated from the first-principles calculations. These compounds are thermodynamically, mechanically, and dynamically stable, and the sequence of stability is TiB 4 Mo > TiB 4 Cr > TiB 4 W. These compounds are brittle-hard materials, and the order of hardness is TiB 4 Cr > TiB 4 Mo > TiB 4 W. The TiB 4 W has the highest bulk modulus, and the TiB 4 Cr has the highest shear modulus and Young's modulus. The electronic density of states indicates that these compounds are metallic in nature. The electron localization function reveal that the partially metallic bonding nature in addition to covalent and ionic interactions between B and metal (Ti and RM) atoms. The thermal properties indicate that the hexagonal TiB 4 Mo is more suitable for high-temperature applications due to its highest bulk modulus and lowest expansion coefficient under high temperature. In addition, the mechanical properties of TiB 4 RM are compared and analyzed with those of TiB 2 and RM B 2 compounds. • The physical properties of TiB 4 RM (RM = Cr, Mo, W) compounds are studied by DFT. • The lattice dynamics, mechanical, and thermal properties are discussed. • The TiB 4 RM compounds have high hardness and high melting temperature. • The hexagonal TiB 4 Mo is more suitable for high temperature applications. • The results are compared with AlB 2 -type TiB 2 and RM B 2. [ABSTRACT FROM AUTHOR]

The structural, magnetic, and electronic features of Cr 2 InN are investigated using PBE and PBE+U approaches. The computed formation enthalpy and formation energy values indicate that the aforementioned compound could be synthesized experimentally. Cr 2 InN exhibits metallic characteristics as there is no bandgap visible at the Fermi level. The spin polarization calculation in bulk without on-site coulomb interaction reveals a very minute energy difference between ferromagnetic (FM) and antiferromagnetic (AF) ground states, while for U = 1 eV, the results confirm the AF ground state. However, in the supercell calculation, in-plane antiferromagnetic1 (in-AFM1) is more stable than in-AFM2 and FM configurations for the U parameters 0 eV and 1 eV. The inclusion of spin orbit coupling with and without the correlation effect does not have a significant impact on the magnetic properties of Cr 2 InN. The computed elastic constants C i j reveal the mechanical stability of Cr 2 InN. The Voigt–Reuss–Hill approximation is successfully utilized for calculating the Young modulus, shear modulus, and bulk modulus. The Pugh's and Poisson's ratios show that Cr 2 InN is ductile. The anisotropic nature of Cr 2 InN is observed from 2D and 3D plots of elastic moduli and anisotropic indices. The phonon spectra of the present system predict that Cr 2 InN is dynamically stable, as it does not display imaginary frequencies. In addition, the thermal and thermodynamic properties of Cr 2 InN have been calculated, including its melting temperature, minimum thermal conductivity, Debye temperature, entropy, specific heat capacity, free energy, and internal energy. Cr 2 InN might be useful for thermal barrier coatings because it has low values for Young's modulus, minimum thermal conductivity, and lattice thermal conductivity. We hope these theoretical findings offer valuable insights for future experimental research on Cr 2 InN. [ABSTRACT FROM AUTHOR]

Theoretical investigation of hydrogenation processes has applied to magnesium diborides under ambient conditions, which identified two structurally stable phases, i.e, Mg 4 B 6 H 2 and Mg 4 B 4 H 4. These identifications were evaluated through assessments of their lattice dynamics stability using density functional perturbation theory. Both phases exhibit metallic behavior within their electronic band structures. Our findings showcase the significant impact of anisotropic Migdal–Eliashberg calculations, enhancing the superconducting properties within this system and resulting in a notably higher T c of 34 K. Mg 4 B 4 H 4 exhibits superconductivity with a T c of 17 K under atmospheric conditions, as determined by anisotropic Migdal–Eliashberg calculations. Our study underscores the wide range of structural variations achievable through the hydrogenation of MgB 2 and highlights the crucial importance of hydrogen atom placement within these structures. In addition, the calculation result indicates the influence of band dispersion characteristics on Fermi velocity, a factor attributed to both anharmonicity and harmonicity, which plays a pivotal role in determining the superconducting properties of these materials. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Experimental validation of MD model on the uniaxial compression test. • Influence of crystallographic orientation on the beginning of plastic deformation. • Influence of size effect on the beginning of plastic deformation. • Influence of stacking fault energy on the beginning of plastic deformation. • These factors determine the plastic deformation of polycrystalline materials. Predicting of the mechanical properties of a polycrystal requires knowledge of the behavior of its individual grains during deformation and their mutual influence on each other. The self-similarity of deformation processes at different scales in crystalline solids allows using of molecular dynamics simulations to analyze the deformation of individual grains of a polycrystal, treating them as single crystals. We have studied the patterns of slip and twinning deformation caused by differences in stacking fault energy, crystal morphology, crystallographic orientation and shear conditions towards the lateral surfaces. It was found that in addition to the stacking fault energy and the crystallographic direction of compression, the crystallographic orientation of the lateral faces and the boundary conditions on them must be taken into account. They affect the accumulation of dislocations, the types of formed dislocations, low-mobile and immobile dislocation complexes, and the shear propagation in the crystal. The changes in shear conditions towards the lateral faces explain the size effect of the grain size/thickness ratio on mechanical properties under uniaxial strain. [ABSTRACT FROM AUTHOR]

Heusler Alloys compounds are a type of intermetallic ternary compound. These compounds exhibit a non-centrosymmetric cubic structure. The crystalline structure characterized by four face centred cubic sublattices that intersect at the positions of the three atoms with an additional vacant site. Typically, X and Y represent alkali metals, transition metals, while Z denotes a foremost group element. The X atom occupies position a 1 while Z resides at a 2 , creating a rock salt lattice arrangement. Typically, there are six modes for distributing the X, Y, and Z atoms across the three sublattices. The interchangeability of atoms at positions a 1 and a 2 results in equivalent configurations due to symmetry. [Display omitted] • To predict the novel multifunctional materials that encloses bulky response by the implementations of stress as well of applied fields. • Intrinsic and strain dependent mechanical, electronic and phonon dynamics of PdScSb half Heusler alloy. Isotropic strain from -12% to +4% has been examined. • Young's, Shear and Bulk moduli, Pugh ratio, Frantsevich ratio and Poisson ratio reflects a decline trend with tensile strain and reveals elevation with compressive strain. • With increase in compressive strain up to -12% the compound exhibits a greater ductile nature. However, with an escalation in tensile strain to +4% the material tends to became more brittle. • Band gap energy declines considerably with rise in tensile strength and increases with escalation in compressive strain. The phonon studies exhibit the positive frequencies which confirm the robust stability of PdScSb alloy. The significant and vital challenge in the field of materials science is to design the novel multifunctional materials that enclose bulky response by the implementations of stress on applied fields. A promptly enhancing prototype for the advancement of such kind of materials is typically based on first principles approach for the elucidation of numerous materials. This manuscript presents a comprehensive exploration on intrinsic and strain dependent mechanical, electronic and phonon dynamics of PdScSb half Heusler compound. The impact of isotropic (compressive to tensile) strain from −12 % to +4 % has been examined. From the computed parameters we noticed that Young's, Shear and Bulk moduli, Pugh ratio, Frantsevich ratio and Poisson ratio reflects a decline trend with tensile strain and reveals elevation with compressive strain. The elastic and mechanical properties, evinced from computed Pugh's parameter and elastic constants, reveal that the alloy is brittle. With increase in compressive strain up to −12 % the compound displays a ductile nature. However, with an escalation in tensile strain to +4 % the material tends to became brittle. From the exploration of band profile, the band gap energy declines considerably with rise in tensile strength and increases with the rise in compressive strain. The mechanical stability of the material is studied in detail at various strain level. The phonon studies exhibit the positive frequencies which confirm the robust stability of PdScSb Heusler material. Hence the present Heusler material exhibits a good performance for spintronics and industrial applicability due to its semiconducting nature under a broader range of isotropic strain. [ABSTRACT FROM AUTHOR]

[Display omitted] • Far IR spectra of CdSe 1−x Te x films are measured using the synchrotron radiation. • DFT calculations of the lattice and molecular dynamics (MD) of the films are conducted. • Experimental infrared spectra of CdSe 1-x Te x films are analyzed using DFT calculations. • Redshift of the optical vibration mode of Cd 108 Te 108 thin film is simulated using MD. Optical reflection spectra of CdSe 1-x Te x thin films deposited on quartz substrates are measured using the synchrotron radiation in the spectral range of 20–500 cm−1. The absorption bands of CdSe, CdTe, CdSe 0.75 Te 0.25 , CdSe 0.5 Te 0.5 , and CdSe 0.25 Te 0.75 films are localized in the range of 20–220 cm−1. The imaginary parts of the dielectric function ε 2 (λ−1) of CdTe 1-x Se x crystals calculated in the framework of the density functional theory are in good agreement with the experimental reflection spectra of CdTe 1-x Se x films. The eigenvectors of the dynamical matrix CdTe 1-x Se x crystals are analyzed for several phonon modes to understand the difference between the frequency dependences of the calculated vibration density of states and the imaginary part of dielectric function ε 2 (λ−1). Small features of the experimental reflective spectra of CdSe 1-x Te x films in the ranges 50–70 cm−1 and 80–120 cm−1 are explained using the analysis of results of the molecular dynamics. During comparative molecular dynamics calculations, it was found that the vibration density of states of a thin CdTe slab with a surface-to-volume number of atoms relation of N S / N V = 0.2, experienced a redshift of approximately 30 cm−1. This shift was observed in comparison with the CdTe single crystal. [ABSTRACT FROM AUTHOR]

The local atomic structure and lattice dynamics of two isostructural layered transition metal dichalcogenides (TMDs), 1T-TiSe 2 and 1T-VSe 2 , were studied using temperature-dependent X-ray absorption spectroscopy at the Ti, V, and Se K-edges. Analysis of the extended X-ray absorption fine structure (EXAFS) spectra, employing reverse Monte Carlo (RMC) simulations, enabled tracking of the temperature evolution of the local environment in the range of 10–300 K. The atomic coordinates derived from the final atomic configurations obtained using the RMC method were used to calculate the partial radial distribution functions (RDFs) and the mean-square relative displacement (MSRD) factors for the first ten coordination shells around the absorbing atoms. Characteristic Einstein frequencies and effective force constants were determined for Ti Se, Ti Ti, V Se, V V, and Se Se atom pairs from the temperature dependencies of MSRDs. The obtained results reveal differences in the temperature evolution of lattice dynamics and the strengths of intralayer and interlayer interactions in TiSe 2 and VSe 2. • The local structure and lattice dynamics were studied in 1T-TiSe 2 and 1T-VSe 2 by X-ray absorption spectroscopy. • The partial radial distribution functions were obtained by reverse Monte Carlo method. • The characteristic Einstein frequencies and the effective force constants were determined. • Anomalous behavior of the mean-square relative displacement was found in the second shell of vanadium. [ABSTRACT FROM AUTHOR]

• Reduced bond lengths in AZ80 alloy boost bonding strength. • Phonon calculations confirms dynamic stability. • Band unfolding aids understanding of effect of alloying elements. Magnesium alloys, particularly in the aluminum-zinc (AZ) series, are widely recognized for their remarkable strength-to-weight ratio. We performed electronic structure, lattice dynamics, and mechanical properties of the AZ80 alloy using first-principles density-functional theory. The influence of dilute alloying by Al/Zn was observed in electronic-structure of AZ80 through hybridization of Mg-(s,p) with Al- p /Zn- d states. The Allen's electronegativity difference between Mg and Al/Zn was found to induce charge transfer mechanism that provides solid-solution strengthening and ductility, in agreement with experiments. The electronic and phononic band-structure was unfolded onto the primitive unit cell of pure Mg to provide key information related to structural distortions and disorder effects. Finally, the dynamic and mechanical stability of AZ80 were confirmed by phonons and Born-Huang criteria, respectively. Collectively, this study provides valuable insights into the fundamental properties of lightweight commercial grade AZ80, essential for application-oriented design of Mg alloys. [ABSTRACT FROM AUTHOR]

In this work, we have performed a theoretical calculation to investigate the structural, mechanical, electronic, lattice dynamics, and thermodynamic properties of Ta T Si (T = Rh, Os, Ir) within the full potential linearized augmented plane wave method. Both (a) TaRhSi and (b) TaIrSi exhibit a reduction in the density of states at the Fermi energy, resulting from a pseudogap-like feature nearby the Fermi energy. This reduction is likely to suppresses the superconductivity of TaRhSi and TaIrSi. In contrast, (c) TaOsSi demonstrates a relatively higher density of states at the Fermi energy, which could account for its superconducting properties. [Display omitted] • The full potential linearized augmented plane wave method was used. • The elastic mechanical, electronic, thermodynamic, and lattice dynamics properties. • of TaRhSi and TaOsSi, and TaIrSi, were predicted. • TaRhSi and TaIrSi exhibit a pseudogap-like feature in the density of states nearby. • the Fermi energy. • The elastic anisotropy of TaRhSi and TaOsSi, and TaIrSi were observed. We have performed a theoretical calculation, based on density functional theory, to investigate the structural, mechanical, electronic, lattice dynamics, and thermodynamic properties of Ta T Si (T = Rh, Os, Ir) within the full potential linearized augmented plane wave method. The calculated values of the lattice constant and unit cell volume are in excellent agreement with the available experimental data. The mechanical stability is substantiated by our calculated elastic constants, while the mechanical properties are subsequently derived. The results indicate that the compounds are ductile materials, except for TaRhSi which exhibits quasi-ductile behavior; however, all of them exhibit elastic anisotropy. In addition, the electronic density of states of the Ta T Si (T = Rh, Os, Ir) compounds reveal that all these materials have a metallic character. Moreover, the dynamical stability is confirmed by our calculated phonon spectra. Finally, we present temperature-dependent thermodynamic properties including free energy, internal energy, entropy, and heat capacity. [ABSTRACT FROM AUTHOR]

Low-loss microwave dielectric ceramics are of great significance for fifth-generation telecommunication (5G) devices used for higher frequencies, while reducing the dielectric loss in the microwave band is still a technical challenge. Lattice dynamics and terahertz response are closely related to the polarization of dielectrics, and can be used as effective methods to explore the loss mechanism of microwave dielectrics. Here, Al3+ was doped into the conventional high-permittivity (ε r) Ca 1- x Sm 2 x /3 TiO 3 (x = 0.4) ceramic system, enhancing the Q × f values significantly. Raman spectra, thermally stimulated depolarization currents (TSDC) and terahertz time-domain spectra (THz-TDS) together showed that the stiffness of cation vibration became stronger when z value was larger, indicating a smaller damping of the lattice vibration, and leading to lower extrinsic losses and higher Q × f values. The relationship between lattice dynamics, defect behavior and microwave dielectric loss will provide a significant reference for the development of low-loss microwave dielectric ceramics. • Medium/high- ε r dielectrics of microwave/terahertz devices are developed. • The Q × f values in the microwave and terahertz bands are essentially constant. • Bond strength, defects, lattice vibration and dielectric loss have strong correlation. [ABSTRACT FROM AUTHOR]

Defects can significantly degrade the thermal conductivity of ThO 2 , an advanced nuclear fuel material as well as a surrogate for other fluorite-structured materials. We investigate how point defects in ThO 2 impact phonon mode-resolved thermal transport. By incorporating phonon modes from lattice dynamics, we decompose the trajectory and heat flux to phonon normal mode space and extract key phonon properties, including phonon relaxation times and their contributions to thermal conductivity. We implement two methods. The first method is based on the Green Kubo formalism to resolve the contribution of each phonon mode to thermal conductivity. The second resolves the lifetime of individual phonon modes and the thermal conductivity is calculated using the Boltzmann transport equation within relaxation time approximation. Notably, a lower contribution of acoustic modes is revealed compared to perturbative approaches considering only three-phonon scattering processes. The effects of four types of point defects are evaluated. The strongest impact on a reduction in thermal conductivity is from Th interstitials, followed by Th vacancies. O interstitials/vacancies have a similar impact, albeit smaller than defects on the thorium sublattice. These observations are consistent with previous studies. [ABSTRACT FROM AUTHOR]

• Gas adsorbates exhibit varying vibrational dynamics in different porous ZIF phases. • Thermal conductivities and heat conduction mechanisms of various ZIF-adsorbate systems are evaluated. • Gas dynamics are "fingerprints" to govern the influences of adsorbates on heat transport of MOFs. Understanding the thermal conductivity (κ) of metal-organic frameworks (MOFs) with adsorbates is critical for tailoring their heat dissipation in practical applications. However, a detailed description of how adsorbates influence the heat transport of MOFs is still lacking. In this work, we employ molecular dynamics simulations combined with lattice dynamics calculations to investigate the effect of gas adsorbates on κ of representative crystalline and glassy zeolitic imidazolate frameworks (ZIFs). We identify that the diffusive adsorbate motions in the crystalline ZIFs with large pores can enhance lattice anharmonicity, serving as a source of phonon scattering and significantly suppressing κ. Conversely, the adsorbates with restricted dynamics in limited space (i.e., in the dense ZIF crystals or glasses) behave more like a heat transfer medium and facilitate heat transport. Besides pore size, gas dynamics are also proved to vary upon gas-lattice interaction strength, and dictate if gas adsorbates serve as a heat conduction suppressor or promoter. We anticipate that this governing role of gas dynamics is applicable to a diverse range of MOF-adsorbate systems. As such, our work offers guidance for the practical thermal management of MOF porous materials to ensure their desired storage or separation performance. [Display omitted] [ABSTRACT FROM AUTHOR]

• The physical properties of several complex Fe-Si phases are studied by DFT. • The structural stability is verified by formation enthalpy, phonon and elastic constants. • The magnetic, electronic, and mechanical properties are discussed. • Anomalous phonon behavior is observed in the Fe 24 Si 5 phase. • The Young's modulus, shear modulus and Debye temperature decrease with the increase of Fe/Si ratio. The formation enthalpy, electronic structure, lattice dynamics and elasticity of several complex ordered iron-rich silicides (Fe 11 Si 5 , Fe 13 Si 3 , Fe 17 Si 12 and Fe 24 Si 5) are calculated from the first-principles calculations. It is found that the Debye temperature Θ D of the system decreases with the increase of the ratio of the number of iron atoms to the number of silicon atoms in the same structure. The softening of low-energy acoustic phonons is more obvious with the increase of iron atoms. The elastic constants C 11 and C 44 , Young's modulus E and shear modulus G of the system decrease with the increase of iron atoms. An anomalous phenomenon occurs in the high frequency region of Fe 24 Si 5. The contribution of Fe1 atoms with smaller magnetic moment to the phonon density of states is much larger than that of the Si and other Fe atoms. This indicates that the local metal bond strength between Fe1-Fe1 atoms is stronger. [ABSTRACT FROM AUTHOR]

This is the second in a series of three papers in which we study a lattice gas subject to Kawasaki conservative dynamics at inverse temperature β > 0 in a large finite box Λ β ⊂ Z 2 whose volume depends on β. Each pair of neighboring particles has a negative binding energy − U < 0 , while each particle has a positive activation energy Δ > 0. The initial configuration is drawn from the grand-canonical ensemble restricted to the set of configurations where all the droplets are subcritical. Our goal is to describe, in the metastable regime Δ ∈ (U , 2 U) and in the limit as β → ∞ , how and when the system nucleates, i.e., grows a supercritical droplet somewhere in Λ β. In the first paper we showed that subcritical droplets behave as quasi-random walks. In the present paper we use the results in the first paper to analyze how subcritical droplets form and dissolve on multiple space–time scales when the volume is moderately large , namely, | Λ β | = e Θ β with Δ < Θ < 2 Δ − U. In the third paper we consider the setting where the volume is very large , namely, | Λ β | = e Θ β with Δ < Θ < Γ − (2 Δ − U) , where Γ is the energy of the critical droplet in the local model, i.e., when Λ β has a fixed volume not depending on β and particles can be created and annihilated at the boundary, and use the results in the first two papers to identify the nucleation time. We will see that in a very large volume critical droplets appear more or less independently in boxes of moderate volume, a phenomenon referred to as homogeneous nucleation. Since Kawasaki dynamics is conservative , i.e., particles move around and interact but are preserved, we need to control non-local effects in the way droplets are formed and dissolved. This is done via a deductive approach : the tube of typical trajectories leading to nucleation is described via a series of events, whose complements have negligible probability, on which the evolution of the gas can be captured by a coarse-grained Markov chain on a space of droplets, which we refer to as droplet dynamics. [ABSTRACT FROM AUTHOR]

The clique graph kG of a graph G has as its vertices the cliques (maximal complete subgraphs) of G , two of which are adjacent in kG if they have non-empty intersection in G. We say that G is clique convergent if k n G ≅ k m G for some n ≠ m , and that G is clique divergent otherwise. We completely characterise the clique convergent graphs in the class of (not necessarily finite) locally cyclic graphs of minimum degree δ ≥ 6 , showing that for such graphs clique divergence is a global phenomenon, dependent on the existence of large substructures. More precisely, we establish that such a graph is clique divergent if and only if its universal triangular cover contains arbitrarily large members from the family of so-called "triangular-shaped graphs". [ABSTRACT FROM AUTHOR]

In this study, the manganites Nd 0.5 Ca 0.5 MnO 3 , Nd 0.5 Sr 0.5 MnO 3, and Pr 0.5 Ca 0.5 MnO 3 were investigated using infrared spectroscopy. The experiments were conducted under standard conditions at room temperature, and the infrared spectra of the compounds were analyzed within the wavenumber range of 400–4000 cm−1. The observed frequencies primarily correspond to the Mn–O–Mn metal-oxygen bonds that form the MnO 6 octahedron. Additionally, in the Nd 0.5 Ca 0.5 MnO 3 and Pr 0.5 Ca 0.5 MnO 3 compounds containing calcium, extra frequencies corresponding to Ca–O bonds were also detected. • The obtained results allow us to obtain information about the atomic dynamics of Nd(Pr) 0.5 Ca(Sr) 0.5 MnO 3 compounds. [ABSTRACT FROM AUTHOR]

[Display omitted] • The most stable defect compensation model is constructed using lattice dynamics. • H i is bonded to an O ion forming hydroxyl (0.99 Å) in both systems. • (V K + H i). have large formations and are therefore unstable. • It is expected to produce absorption with peaks around 167 nm and 179 nm. • It is expected to produce luminescence with peaks around 623 nm and 867 nm. The electronic structures, defect formations, defect transition levels and optical properties for V K + H i defect models in KDP crystals have been studied based on DFT. Lattice dynamics methods give the most reasonable compensation mechanism for V K , namely compensation with the third-nearest H i neighbor from V K for the paraelectric (PE) phase and compensation with the fourth-nearest neighbor H i from V K for the ferroelectric (FE) phase. The defect formation energies indicate that the (V K + H i) x (The superscript represents the charged state, the 'x' represents neutral, '" represents −1 charge state and '.' represents +1 charge state.) is the main defect type in this kind of defect cluster and a self-trapped electron is located at H i in the (V K + H i)′ system. For (V K + H i) x system, one electron is accommodated in V K. There is not a new defect state in the band gap. The H i bonds with the O ion (0.99 Å) form a hydroxyl. For (V K + H i)′ system, the hydroxyl is broken, the H i exists in an atomic form and introduces new defect states in the band gap. As the large relaxation energy leads to a large Huang-Rhys factor, the Stokes red shifts will significantly affect the optical properties. A broad ultraviolet (UV) absorption band and emission band range from UV to visible are obtained originating from the defect cluster. We believe that the far-violet absorption peaks (167 nm and 179 nm) caused by defect cluster V K + H i can significantly impact the optical damage threshold of the KDP. [ABSTRACT FROM AUTHOR]

This study investigates the impact of nanostructuring and Ba substitution on the thermoelectric performance and lattice dynamics of cubic SrSi 2. The solubility limit of Ba in α-SrSi 2 is investigated under varied synthesis conditions, revealing a notable increase beyond previous reports. Mechanical alloying enables a remarkable enhancement, surpassing the conventional solubility limit of 13–14 %at. Ba. After spark plasma sintering (SPS), secondary phases appear above 22 % at. Ba, extending the solubility limit to 22 % at. Ba. High-pressure sintering at 1 GPa further extends this limit to 40 % at. Ba with excellent relative density. Raman and infrared spectroscopy were explored and unveil shifts in lattice dynamics, impacting phonon scattering and indicating a reduction in lattice thermal conductivity. From the electrical resistivity and Seebeck coefficient we were able to determine the evolution of the bandgap with the Ba content which led to an increase of the power factor by about 10 %. Increasing of Ba content also led to a strong decrease of the thermal conductivity leading to an increase of the figure of merit by 68 % compared to pure cubic SrSi 2. [Display omitted] • Ball milling combined with SPS increased Ba solubility from 13 % at. up to 40 % at. • Raman and IR spectroscopy reveal changes in the lattice dynamics with Ba content. • Power factor increases with increasing Ba content up to 10 % for 7 % at. substitution. • Total thermal conductivity reaches 1.96 W.m−1.K−1 by nanostructuring and alloying. • By nanostructuring and Ba substitution the figure of merit increased by 140 %. [ABSTRACT FROM AUTHOR]

This work explores a possibility of improving the mechanical behavior and thermodynamic stability of AlB 2 -type YB 2 through alloying with isostructural VB 2 using first-principles calculations. The analysis derived from the cluster-expansion model suggests Y 0.5 V 0.5 B 2 , whose atomic configuration is represented by periodically alternating YB 2 /VB 2 layers in the ¡0001¿ direction, is the only solution in the pseudo-binary YB 2 –VB 2 system predicted to be stable from the thermodynamic viewpoint. By evaluating the influence of lattice dynamics on the Gibbs free energies of superlattice-structured Y 0.5 V 0.5 B 2 and its constituent compounds within the quasiharmonic approximation, the thermodynamic stability, elastic properties, and hardness at a given pressure and temperature of the three diborides can be accessed. The results reveal, at a given temperature, isotropic compression of the diborides to high pressures enhances the stability of Y 0.5 V 0.5 B 2 measured relative to YB 2 and VB 2 , while raising the temperature at a given applied pressure can increasingly result in a driving force toward separation of Y 0.5 V 0.5 B 2 into YB 2 and VB 2. The thermodynamic stabilization of superlattice-structured Y 0.5 V 0.5 B 2 , despite large distinctions in atomic radius and electronegativity between Y and V, can be explained in terms of band filling induced by introduction of V atoms in YB 2. Within the range of temperatures (0–1200 K) and pressures (0–15 GPa) studied, the band-filling effect is found to result in significant positive deviations in the values of shear strength, stiffness, and hardness of superlattice-structured Y 0.5 V 0.5 B 2 from those evaluated from its constituent compounds using the Vegard's law, respectively, by ∼ 8%, ∼ 5%, and ∼ 25%, and the hardness of superlattice-structured Y 0.5 V 0.5 B 2 is ∼ 40 GPa potentially indicating its superhard nature. These consequences strongly underline the essential impact of band filling on improvement in mechanical behavior and stability of YB 2 through alloying with VB 2 , and also they can be served as guidance for further advancement of hard-coating technology based especially on transition-metal diborides. [Display omitted] • Y 0.5 V 0.5 B 2 in the form of superlattice structure is thermodynamically stable. • Y 0.5 V 0.5 B 2 is potentially a superhard material. • The thermodynamic stability and superhard nature of Y 0.5 V 0.5 B 2 arises from the band-filling effect. [ABSTRACT FROM AUTHOR]

The phonon, dielectric, and infrared reflectance spectra of the II-VI binary chalcogenides with wurtzite structure are carefully investigated using the first-principle linear response theory. The impact of sulfur group elements from S to Te on various characteristics of binary chalcogenides is examined. The results indicate that the phonon vibrational frequencies are influenced by the relative atomic mass. The overall permittivities are primarily determined by the electronic polarization. When Born effective charge approaches the nominal ionic charge, the compounds exhibit ionicity. The modal-oscillator strengths of the chalcogenides decrease from top to bottom within the same group of elements corresponding to an increase in relative atomic mass. In binary chalcogenides having the identical cation, the resonance absorption peaks experience a frequency decrease when the anions' mass increases. The infrared reflection spectrum shows red-shifts with decreasing electronegativity of the anions. The reststrahlen band-widths of the infrared optical mode are impacted by the splitting of LO/TO. [ABSTRACT FROM AUTHOR]

The physical properties and anisotropy of carbonates at high pressure are fundamental to understanding the deep carbon cycle and storage. Here, we redraw the phase diagram of strontianite (SrCO 3) by first-principles calculations combined with lattice dynamics and study its physical properties and anisotropy at high pressure. The results show that there are only Pnma and Pmmn phases in SrCO 3 in the entire Earth's mantle, and there is no R 3 m phase. The SrCO 3 polymorphs have a large elastic anisotropy. SrCO 3 polymorphs are a kind of carbonate with high density, low wave velocity, and low wave velocity anisotropy. The linear thermal expansion coefficient of SrCO 3 - Pmmn was obtained for the first time by using the linear elastic compression coefficient combined with the volume thermal expansion coefficient. The results are of great significance for understanding the high-pressure behavior of Sr-carbonates. [ABSTRACT FROM AUTHOR]

The crystal structure stability, mechanical, optical and thermodynamic properties of TiBC, Ti 6 Si 2 B and Ti 6 Ge 2 B were predicted using the first principles calculations. The analysis of phonon dispersion curves, formation enthalpies, energy bands, and density of states demonstrate that TiBC, Ti 6 Si 2 B and Ti 6 Ge 2 B exhibit structure stability and metallic properties. The tensile strength of TiBC, Ti 6 Si 2 B and Ti 6 Ge 2 B were simulated, the results showed that the tensile strength of TiBC was the best. Anisotropy was explored by anisotropy index, 3D surface constructions and 2D projections. The order of anisotropy is TiBC > Ti 6 Ge 2 B > Ti 6 Si 2 B. The optical properties showed that TiBC, Ti 6 Si 2 B and Ti 6 Ge 2 B have strong long-wave absorption capacity. Finally, Debye temperature and sound velocity were investigated, the order of Debye temperature is: TiBC > Ti 6 Si 2 B > Ti 6 Ge 2 B. [ABSTRACT FROM AUTHOR]

In this work, we investigate the feasibility of cleaved-gate ferroelectric FET (CG-FeFET) as multi-level cell (MLC) memory devices, by conducting 3-dimensional quantum transport simulations based on time-dependent-Ginzburg–Landau equation, and the non-equilibrium Green's function method. Our results indicate that CG-FeFET can achieve multi-level operations by utilizing different thicknesses of the ferroelectric layer. We analyze the influence of electron–phonon interaction and also verify that CG-FeFET is robust to noise. Furthermore, we identify the critical role of the spacing between two ferroelectric layers in determining the memory window, considering the effects of polarization cancellation and electrostatic coupling. These findings provide valuable insights into designing stable and reliable nonvolatile memory technologies, which could offer potential solutions for high-density memory requirements. • CG-FeFETs enable multi-level memory with different ferroelectric layer thicknesses. • CG-FeFET functions as a stable memory device, maintaining polarization despite noise. • Ferroelectric layer spacing plays a crucial role in determining the memory window. [ABSTRACT FROM AUTHOR]

• AIMD simulation of strained Li 3 OCl anti-perovskite solid-state electrolyte. • Analysis of lithium vibrational amplitude, frequency, and jump trajectory in Li 3 OCl under strain. • Elucidation of tensile strain's enhancement of conductivity via lattice softness and dynamics. • Application of continuous symmetry measures (CSM) to correlate local structural distortion with migration barrier. Utilizing first-principle calculations, this study elucidated the underlying mechanism of elastic strains affecting the Li-ion diffusivity and conductivity in Li 3 OCl anti-perovskite solid-state electrolyte. Strain was shown to modulate the Li-ion vibrational amplitude, attempt frequency and adjacent site jumps, as revealed by ab initio molecular dynamics (AIMD) simulation post-processing. Additionally, analysis of lattice dynamics and phonon behavior under various strain conditions demonstrated that tensile strains soften the lattice and lower the phonon band center frequency, thereby diminishing the energy barriers impeding ion transport. Further, we have systematically investigated strain-induced distortions of the coordination environment via continuous symmetry measures (CSM), assessing the variations at initial and saddle sites along the Li-ion migration routes. And the study of bonding variability under strain provided a deeper understanding of strain-induced conducting behavior. These results underscore insights into the fundamental mechanisms governing ionic transport in Li 3 OCl anti-perovskite under elastic strain, highlighting the potential of strain engineering as a promising avenue for optimizing the performance of solid-state electrolytes in energy storage applications. [ABSTRACT FROM AUTHOR]

The current work presents a theoretical study of the physical properties of several FePt 2 ordered structures through first-principles calculations, including structural, magnetic, electronic, mechanical, phonon and thermal properties. The structural stabilities are certified by the enthalpies of formation, elastic constants, and phonon dispersion relationships. The tetragonal I 4/ mmm structure is energetically favorable compared to other types FePt 2 structures including Cmcm , Immm , P 6 3 / mmc and P 4/ nmm structures. The electronic density of states and the contributions of each d -orbital electron to the magnetic moment are analyzed to understand their magnetism. The bulk modulus B values of these FePt 2 structures are similar, but the Young's modulus E and shear modulus G as well as the elastic anisotropy are quite different. The thermal properties at finite temperature are estimated by the quasi-harmonic approximation. The I 4/ mmm structure has higher isothermal bulk modulus, lower thermal expansion coefficient and weaker thermal expansion anisotropy, which is more suitable for high temperature applications than other structures. Also, the sequence of thermal expansion anisotropy is P 4/ nmm > Immm > Cmcm > I 4/ mmm (≈ P 6 3 / mmc). [ABSTRACT FROM AUTHOR]

We present a Raman study of the collective vibrations arising from the homogeneous bundling of single-walled carbon nanotubes and analyze the dependence of their vibrational coupling on the tube diameter using two systems, single-walled carbon nanotube coils and a monochiral carbon nanotube film. We report on two breathing-like modes for quasi-infinite bundles, compared to the single radial breathing mode characteristic for isolated tubes. The exciton-phonon coupling in these modes is probed with resonant Raman spectroscopy, revealing the same resonance energy for both breathing-like peaks. Our experimental findings align well with previously reported theoretical studies, demonstrating a 1 / d scaling for all modes, as well as confirming the relative shift of the modes dependent on intertube interaction. These vibrations provide insight into the role of intertube lattice dynamics in two-dimensional THz-range phononic crystals. [Display omitted] [ABSTRACT FROM AUTHOR]

Since the revelation of significant negative thermal expansion (NTE) across an extensive temperature range in cubic ScF 3 , there has been a notable surge of interest in fluorides of the ReO 3 -type structure. However, with the exceptions of ScF 3 , nearly all ReO 3 -type fluorides at low temperature crystallize in a rhombohedral structure in which the thermal expansion becomes strong positive. In this work, we reinvestigated the phase transition mechanism of α -AlF 3 from rhombohedral to cubic phase by combining in situ X-ray diffraction, in situ Raman spectra and first principles calculation. Our research has unveiled that this phase transition is driven by a phonon mode A 1g , which is associated with the tilting of octahedral structures. The α -AlF 3 shows seriously anharmonic lattice dynamics with A 1g phonon mode exhibiting softening behavior even far below the transition temperature. Anharmonic analysis based on Balkanski model suggests that A 1g mode decays into a longitudinal acoustic (LA) phonon and a transverse optical phonon E g , which have large amplitudes and promote the titling of AlF 6 octahedra, final leading to the phase transition to the cubic structure. This finding further indicates the potential for tuning NTE materials through phonon engineering. • Computational and experimental reinvestigation of the temperature-induced phase transition mechanism of α-AlF 3. • Anharmonic analysis of the Balkanski model shows that the phase transition is mainly driven by an anharmonic phonon (A 1g). • Possible decay paths for the A 1g mode include longitudinal acoustic (LA) phonons and transverse optical E g phonons. [ABSTRACT FROM AUTHOR]

• The role of lattice dynamics to minimize the lattice thermal conductivity is investigated in transition metal nitrides. • Lattice parameters and bond lengths are in good agreement with the available experimental study. • Layered structure of Li 2 MN 2 leads to strong anisotropy in transport properties. • Li 2 ZrN 2 exhibits ultralow lattice thermal conductivity despite of large group velocity. This study systematically examines the lattice dynamics of Li 2 MN 2 (M = Zr or Hf), with the aim of unraveling the factors contributing to its unique thermal transport properties using first-principles calculations. Both compounds are found to be energetically and dynamically stable, and our results for their lattice parameters and bond lengths are in good agreement with the available experimental data. The transport properties exhibit strong anisotropic behavior due to the layered structure. Li 2 ZrN 2 possesses a low lattice thermal conductivity (1.52 Wm−1K−1) along the a -axis at 1000 K, owing to the significant reduction in phonon lifetime caused by the rattling behavior of Zr. The present study may provide valuable insights when exploring the role of lattice dynamics in minimizing the lattice thermal conductivity of transition metal nitrides and their prospective energy harvesting applications. [Display omitted] [ABSTRACT FROM AUTHOR]

SiC is essential for next-generation semiconductors and nuclear plant components. Its performance is strongly influenced by its thermal conductivity, which is highly sensitive to its microstructure. Molecular dynamics (MD) simulation is one of the most reliable methods for studying thermal transportation mechanisms in devices with nano-scale microstructures. Nevertheless, owing to inaccurate interatomic potentials, the implementation of MD for studying SiC still presents limitations. This study used the deep potential (DP) methodology to develop two interatomic potential (DP-IAPs) models for studying SiC, based on two adaptively generated datasets within the density functional approximations at the local density and generalized gradient levels. Combined with the LD and MD simulations, the thermal transport and mechanical properties of SiC were systematically investigated. The proposed DP-IAPs can accurately reproduce the structural properties, phonon behaviors, and thermal properties of various SiC polytypes. The two DP-IAPs exhibited extraordinary speed with high accuracy in both simulating the lattice dynamics (LD) and analyzing the scattering rate of phonon transportation. Our proposed methodology paves the way for a systematic approach to model heat transport in SiC-based devices and nuclear grade SiC components using multiscale modeling. [ABSTRACT FROM AUTHOR]

It has generally been believed that the lattice thermal conductivity (κ L) is mainly contributed by acoustic phonons and the contribution of optical phonons can be neglected in crystalline materials. However, in this work, we demonstrate that the contribution of optical phonons play an important role in the complex structural low- κ L oxides. The mode-wised κ L of three representative oxides, MgO, BaHfO 3 and La 2 Zr 2 O 7 , with different structural complexity was calculated using first-principles phonon Boltzmann transport equation (BTE) method. It is found that the contribution of optical phonons become significant as the structural complexity increases. Especially, for La 2 Zr 2 O 7 , the κ L is dominated by optical phonons due to the large density of states. Optical phonons exhibit amorphous-like phonon-phonon scattering characteristics that are different from those of acoustic phonons. Furthermore, calculations for materials other than the three representative oxides were conducted and the results confirmed the validity of our conclusions. [ABSTRACT FROM AUTHOR]

The temperature-dependent (T -dependent) linewidth (Γ G) and frequency shift (Δ ω G) of the G mode provide valuable information on the phonon anharmonicity of graphene-based materials. In contrast to the negligible contribution from electron-phonon coupling (EPC) to the linewidth of a Raman mode in semiconductors, Γ G in pristine graphene is dominated by EPC contribution at room temperature due to its semimetallic characteristics. This leads to difficulty in resolving intrinsic contribution from phonon anharmonicity to Γ G. Here, we probed the intrinsic phonon anharmonicity of heavily-doped graphene by T -dependent Raman spectra based on FeCl 3 -based stage-1 graphite intercalation compound (GIC), in which the EPC contribution is negligible due to the large Fermi level (E F) shift. The Δ ω G and Γ G exhibit a nonlinear decrease and noticeable broadening with increasing temperature, respectively, which are both dominated by phonon anharmonicity processes. The contribution of phonon anharmonicity to Γ G of heavily-doped graphene decreases as the E F approaches to the Dirac point. However, the T dependence of Δ ω G is almost independent on E F and qualitatively agrees with the theoretical result of pristine graphene. These results provide a deeper understanding of the role of phonon anharmonicity on the Raman spectra of heavily doped graphene. [Display omitted] [ABSTRACT FROM AUTHOR]

In γ -LiAlO 2 ceramic, Li ion diffusion plays a key role both in tritium release as a solid tritium breeder material in nuclear fusion and in phase stability as a matrix material in molten carbonate fuel cells (MCFC). Yet fundamental understanding of the diffusive process in γ -LiAlO 2 is still missing, especially considering the interaction of the lattice dynamics and Li ion motion. Herein, we demonstrated that two specific optical phonon modes are coupled with Li ion diffusion in γ -LiAlO 2 , by investigating the temperature-dependent lattice dynamics via Raman scattering experiments, as well as first-principles calculations and neutron diffraction experiments (ND). The high-temperature ND experiments showed that γ -LiAlO 2 undergoes partial Li ion disordering in Li sublattice at high temperature. Notably, the lattice dynamics studies demonstrated that B 1 mode at 226 cm−1 and A 1 mode at 263 cm−1 are responsible for Li ion motion through the oscillation of Li–O in <010> and <001> direction, respectively. Our results further suggest that the behavior of tritium release and phase stability in γ -LiAlO 2 at elevated temperature may be controlled by tuning the two specific phonon modes through photon/electron-phonon coupling. [ABSTRACT FROM AUTHOR]

In molten carbonate fuel cells (MCFC), α -LiAlO 2 ceramic matrix, at higher temperature or H-rich atmosphere, undergoes an irreversible phase transition of α -LiAlO 2 to γ -phase that causes a large volume change and greatly impacts the lifetime of the cells. In this manuscript, we unravel an unusual coupling property between the lattice dynamic and Li+ ions diffusion for the first time, near the common operating temperature of 923 K. A temperature-dependent lattice dynamics study on α -LiAlO 2 was performed by probing the in-situ Raman spectroscopy. In addition, the phonon density of states was estimated theoretically through first-principles calculations. Notably, in-situ Raman spectroscopy combined with the calculated atom-projected phonons density of states (PDOS) and Bond Valence Energy Landscape (BVEL) calculations demonstrated that the phonon mode E g dominated by oxygen atoms decays into three acoustical phonons that couple with the diffusion of mobile Li+ ions in ab -plane above 600 K. In MCFC environments, large amounts of Li+ ions or H+ ion in the electrolyte will diffuse into the lattice of α -LiAlO 2. This would further enhance the coupling behavior between oxygen atoms and diffusion ion and finally results in the instability of lattice dynamics of oxygen atoms. [ABSTRACT FROM AUTHOR]

High quality Fe 4 Nb 2 O 9 single crystal was grown by optical floating zone method. The magnetization-temperature(M - T) curves, isothermal magnetization curves(M - H) and pyroelectric current-temperature curves of the single crystal along different crystallographic directions were measured. The results of magnetization measurements which shows the Néel temperature T N of around 90 K and the in-plane magnetic structure of Fe 4 Nb 2 O 9 are very consistent with the reported magnetic structure obtained by neutron diffraction. The isothermal magnetization curves along [210] direction show spin flop phase transition and a local ferromagnetic loop under 50 K. The critical field H C of spin flop phase transition is found to be 94 kOe. Pyroelectric current-temperature curves show ferroelectric polarization below about 90 K under zero magnetic field, which has not been reported before in single crystal Fe 4 Nb 2 O 9. At the same time, Fe 4 Nb 2 O 9 shows magnetoelectric coupling effect. With the increase of magnetic field, the polarization increases to over 300 μC/m2 along a axis under applied magnetic field of 70 kOe. [ABSTRACT FROM AUTHOR]

Lattice vibrations play a significant role in the martensitic phase transformation of MgSc alloys, thus in the shape memory effects as well. In this article, the phonon spectra and thermodynamic properties of MgSc alloys with different structures were systemically studied by first-principles methods. The phonon spectra of Mg-18.75 at%Sc and Mg-20.83 at%Sc in austenite phase are fundamentally different, and the experimental martensitic transition behavior of MgSc alloys with different compositions can be well explained by the lattice dynamics. The occurred Fermi surface nesting at specific compositions leads to the appearance of phonon imaginary frequency, thus resulting in the lattice instability. The entropy change and latent heat obtained from harmonic phonon calculations suggests that the MgSc alloys are promising for the application in low-temperature elastocaloric cooling, and that the entropy changes are comparable to the well known cooling materials such as BaTiO 3 and NiTi. • Explain the experimentally observed different martensitic transformation behavior of Mg-18.75 at%Sc and Mg-20.83 at%Sc alloys • Mg-20.83 at%Sc alloy is expected to be a promising candidate materials for elastocaloric cooling at low temperatures compared. • Fermi surface nesting is the physical origin of phonon imaginary frequency and the thermo-elastic martensitic transformation. [ABSTRACT FROM AUTHOR]

Air-stable and Sb/Bi-based perovskite-inspired materials are attractive substitutes for their Pb-based counterparts in optoelectronic applications. The attractive low-energy broadband luminescence phenomenon has been hotly investigated. However, understanding the physical mechanism behind it is still at an early stage. Herein, high-quality Cs 3 SbBiI 9 crystals were synthesized and accompanied with reference Cs 3 Sb 2 I 9 and Cs 3 Bi 2 I 9. The reformed energy band structure can be confirmed by experiment and density functional theory (DFT) calculation. Unexpected broadband near-infrared (NIR) emission has been discovered and is explained by the nonexclusive self-trapped exciton (STE) and defect-induced emission models. Temperature- dependent Raman and PL spectra confirm the diminished Stokes shift and electron-phonon coupling effect in Sb-Bi alloyed crystals driven by the local broken-symmetry. This result provides a basic physical explanation for the controversial photo-physical process in defect-type Bi/Sb alloyed perovskite-inspired family and it will inspire a feasible way to design novel Pb-free perovskites. • Bi was successfully alloyed into the Cs3Sb2I9 by low-cost hydrothermal method. • Lattice dynamics and electron-phonon interaction were carefully studied. • Unexpected broadband near-infrared emission has been discovered. [ABSTRACT FROM AUTHOR]

Nanoporous phenolic-based composites are widely used as lightweight ablative thermal protection materials, but an accurate prediction of the effective thermal conductivity (λ eff) associated with the nanoporous phenolic matrix (NPM) remains a significant challenge. Herein, a series of NPMs with different porosities are prepared, and their thermal conductivities measured experimentally. Precise nanostructure models for NPM are established by measuring the porous structural characteristics. These models have facilitated an accurate predication of λ eff by combining the non-equilibrium molecular dynamics with the Lattice Boltzmann method, with an associated maximum deviation less than 5 %. Furthermore, the effects on λ eff of intrinsic structure such as porosity, particle overlapping, pore and particle size, in addition to environmental factors are investigated. The results demonstrate that changes in λ eff due to porosity are primarily confined to porosity values lower than 50 %. When the degree of particle overlapping is below 0.6, any increase in particle overlapping results in a marked increase in λ eff. In addition, λ eff exhibits a linear relationship with respect to temperature (below 673 K), and a response to changes in pressure is primarily observed within the range 104–107 Pa. This research provides significant insight into the thermal insulation characteristics and mechanisms of NPM, and can serve as a useful guide for the structural optimization of lightweight thermal protection materials. [Display omitted] • A combination of NEMD and LBM is applied to determine the thermal conductivity of NPM. • Excellent thermal insulation of NPM can be achieved by controlling the porosity to a value above 50 %. • The degree of particle overlapping must be kept below 0.6 to ensure better thermal insulation. • Pore size has a greater effect on thermal conductivity than particle size. [ABSTRACT FROM AUTHOR]