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Microsegregation formed during solidification is of great importance to material properties. The conventional Lever rule and Scheil equation are widely used to predict solute segregation. However, these models always fail to predict the exact solute concentration at a high solid fraction because of theoretical assumptions. Here, the dynamics of microsegregation during polycrystalline solidification of refined Al-Cu alloy is studied via two- and three-dimensional quantitative phase-field simulations. Simulations with different grain refinement level, cooling rate, and solid diffusion coefficient demonstrate that solute segregation at the end of solidification (i.e. when the solid fraction is close to unit) is not strongly correlated to the grain morphology and back diffusion. These independences are in accordance with the Scheil equation which only relates to the solid fraction, but the model predicts a much higher liquid concentration than simulations. Accordingly, based on the quantitative phase-field simulations, a new analytical microsegregation model is derived. Unlike the Scheil equation or the Lever rule that respectively overestimates or underestimates the liquid concentration, the present model predicts the liquid concentration in a pretty good agreement with phase-field simulations, particularly at the late solidification stage.

The search for new two-dimensional monolayers with diverse electronic properties has attracted growing interest in recent years. Here, we present an approach to construct MA2Z4 monolayers with a septuple-atomic-layer structure, that is, intercalating a MoS2-type monolayer MZ2 into an InSe-type monolayer A2Z2. We illustrate this unique strategy by means of first-principles calculations, which not only reproduce the structures of MoSi2N4 and MnBi2Te4 that were already experimentally synthesized, but also predict 72 compounds that are thermodynamically and dynamically stable. Such an intercalated architecture significantly reconstructs the band structures of the constituents MZ2 and A2Z2, leading to diverse electronic properties for MA2Z4, which can be classified according to the total number of valence electrons. The systems with 32 and 34 valence electrons are mostly semiconductors. Whereas, those with 33 valence electrons can be nonmagnetic metals or ferromagnetic semiconductors. In particular, we find that, among the predicted compounds, (Ca,Sr)Ga2Te4 are topologically nontrivial by both the standard density functional theory and hybrid functional calculations. While VSi2P4 is a ferromagnetic semiconductor and TaSi2N4 is a type-I Ising superconductor. Moreover, WSi2P4 is a direct gap semiconductor with peculiar spin-valley properties, which are robust against interlayer interactions. Our study thus provides an effective way of designing septuple-atomic-layer MA2Z4 with unusual electronic properties to draw immediate experimental interest., The discovery of a new two-dimensional van der Waals layered MoSi2N4 material inspires many attentions. Here, the authors report intercalation strategies to explore a much wider range of MA2Z4 family and predict amount of materials accessible to experimental verifications with emergent topological, magnetic or Ising superconductivity properties.

The discovery of topological quantum states marks a new chapter in both condensed matter physics and materials sciences. By analogy to spin electronic system, topological concepts have been extended into phonons, boosting the birth of topological phononics (TPs). Here, we present a high-throughput screening and data-driven approach to compute and evaluate TPs among over 10,000 real materials. We have discovered 5014 TP materials and grouped them into two main classes of Weyl and nodal-line (ring) TPs. We have clarified the physical mechanism for the occurrence of single Weyl, high degenerate Weyl, individual nodal-line (ring), nodal-link, nodal-chain, and nodal-net TPs in various materials and their mutual correlations. Among the phononic systems, we have predicted the hourglass nodal net TPs in TeO3, as well as the clean and single type-I Weyl TPs between the acoustic and optical branches in half-Heusler LiCaAs. In addition, we found that different types of TPs can coexist in many materials (such as ScZn). Their potential applications and experimental detections have been discussed. This work substantially increases the amount of TP materials, which enables an in-depth investigation of their structure-property relations and opens new avenues for future device design related to TPs., Topological phononic (TP) materials are attracting wide attentions and it is more difficult to seek TP materials compared to electronic materials. Here, the authors present a high-throughput screening and data-driven approach to discover 5014 TP materials and further clarify the mechanism for the occurrence of various TPs.

The realization of multifunctional two-dimensional (2D) materials is fundamentally intriguing, such as the combination of piezoelectricity with a topological insulating phase or ferromagnetism. In this work, a Janus monolayer SrAlGaSe4 is built from the 2D MA2Z4 family with dynamic, mechanical and thermal stabilities, which is piezoelectric due to the lack of inversion symmetry. The unstrained SrAlGaSe4 monolayer is a narrow gap normal insulator (NI) with spin orbital coupling (SOC). However, the NI to topological insulator (TI) phase transition can be induced by biaxial strain, and a piezoelectric quantum spin Hall insulator (PQSHI) can be achieved. More excitingly, the phase transformation point is only about 1.01 tensile strain, and the nontrivial band topology can hold until the considered 1.16 tensile strain. Moreover, Rashba spin splitting in the conduction bands can exist in a PQSHI due to the absence of a horizontal mirror symmetry and the presence of SOC. For monolayer SrAlGaSe4, both in-plane and very weak out-of-plane piezoelectric polarizations can be induced with the application of uniaxial strain. The calculated piezoelectric strain coefficients d11 and d31 of monolayer SrAlGaSe4 are −1.865 pm V−1 and −0.068 pm V−1 at 1.06 tensile strain as a representative TI. In fact, many PQSHIs can be realized from the 2D MA2Z4 family. To confirm that, similar to SrAlGaSe4, the coexistence of piezoelectricity and topological orders can be realized by applying strain (about 1.04 tensile strain) in the CaAlGaSe4 monolayer. This study suggests that Janus monolayer SrAlGaSe4 is a pure 2D system for a PQSHI, enabling future studies exploring the interplay between piezoelectricity and topological order, which can lead to novel applications in electronics and spintronics.

Using ab initio density functional approach, we analyze the trapping behavior of Hydrogen atom in a series fcc structure metals (M = Ni, Cu and Al). From the calculations we found that the potential trapping sites in all these three metals is strongly correlated with the electron charges distribution and the swelling of the nH-Vac cluster is largely determined by the transferring charges of the metal atoms around the vacancy. According to our results, in both intrinsic metals and the metal with monovacancy the hydrogen atoms are always prone to be trapped at the interstitial site with large pre-existed charges and the growth of nH-Vac cluster greatly depends on the charges supplying by the surrounding metal atoms. By our calculations the deficit charges supplying by the nearby metal atoms always accompany a strain energy increment which forbid the nH-Vac swelling. This mechanism is identified in all these three fcc metals. We also found that the formation of hydrogen molecule at the center of the vacancy can only be identified in Aluminum no matter the trapping sites around the vacancy are fully occupied or not. But in Ni and Cu with the same fcc structure H2 molecule are not popular.

The systematic investigation on the U–H binary system up to 300 GPa has been performed by means of first-principles calculations in combination with the variable-composition evolutionary algorithm. Twenty uranium hydrides, including UHx (x = 1, 2, 3, 4, 5, 6, 7, 8, 9, 17), U2Hy (y = 3, 5, 7, 13, 15, 17), U3H8, U3H10, U4H5 and U4H9 have been found under different pressures. Besides thirteen compounds that are in nice agreement with previously reported structural search, new uranium hydrides in terms of the derived convex hull of the formation enthalpies have also been found in the present investigation. These seven novel compounds including Cmcm-UH3, Fmmm-UH4, R 3 ‾ m-U2H7, Pm–U2H15, Cm–U3H8, C2–U4H9 and C2/m-U4H5, are found to be dynamically and thermodynamically stable, and their stable pressure range has been determined. At last, the electronic and mechanical properties of these seven novel structures have further been calculated.

By means of first-principles calculations, we have proposed an ab initio modeling to establish a formula between the hydrogen evolution rate and its overpotential of hydrogen evolution reaction (HER), relating with three different rate determining mechanisms, when Volmer reaction, Tafel reaction and Heyrowsky reaction are the rate determining steps of the entire reaction, respectively. Within this modeling, the free energy ( Δ G H * ) of the adsorbed hydrogen atom and the concentration of hydrogen ions in the solution have been correlated to the exchange current density. The hydrogen evolution modeling has been validated by available experimental results. Furthermore, by combining the previously proposed first-principles modeling of the anodic dissolution and this modeling of the HER in the electrochemical corrosion, the polarization curves of the 18 crystallographic surfaces of pure Mg have been theoretically derived. It has been found that in a neutral solution ( p H = 7 ) the corrosion current densities (icorr) of the 18 crystallographic surfaces range from 10 − 3.477 to 10 − 0.455 A/cm2 and their corresponding corrosion potentials (Ecorr) range from −1.36 to −0.892 VSHE, respectively. The base (0001) surface exhibits a lower corrosion rate of 10 − 3.345 A/cm2, whereas the crystal (21 3 ¯ 0) surface has a fast corrosion rate of 10 − 0.455 A/cm2. The calculations even reveal that except for Ag, all the other alloying elements considered here accelerate the rates of the cathodic HER. In agreement with theoretical results, the experimentally measured polarization curves of the Mg-1Zn and Mg-2Sn alloys verify that both Zn and Sn additions accelerate the rate of the HER of Mg.

Several n- and p-type Half-Heusler (HH) thermoelectric materials (Ti0.5Zr0.5NiSn-based and NbFeSb-based) have been processed by high-pressure torsion (HPT) to improve their thermoelectric performance via a drastic reduction towards ultra-low thermal conductivity. This reduction occurs due to grain refinement and a high concentration of deformation-induced defects, i.e. vacancies and dislocations as inferred by this severe plastic deformation and documented via SEM and TEM investigations. In most cases the figure of merit, ZT, and the thermo-electric conversion efficiency were enhanced up to η ∼ 10% for the thermally stable HPT-processed sample. Raman spectroscopy, backed by DFT calculations, proves that HPT induces a stiffening of the lattice and as a consequence, a blue-shift of the lattice vibrations occurs. Furthermore for all investigated specimens Vickers hardness values after HPT were significantly higher, whereas the change in the elastic moduli was less than 5% in comparison to the HP reference sample.

In crystalline solids, to computationally determine atomic migration energy barrier is a highly time consuming challenge within the framework of Density Functional Theory (DFT). Through first-principle calculations, here we have proposed a simple, high-throughput formula to fast, effectively calculate atomic migration energy barrier for fcc metals through three basic parameters of materials, the equilibrium volume ( V 0 ), the bulk modulus ( B 0 ) and the Poisson's ratio (ν). This formula is useful not only for the ideal strain-free lattices but also for the uniaxially strained lattices. It has been further validated by a series of fcc metals when compared with both available experimental or theoretical data and DFT-derived data obtained by Nudged Elastic Band (NEB) method. Moreover, we have investigated the effect of uniaxial deformation on the diffusion behavior of vacancy in fcc metals. Our calculations revealed that in fcc metals under uniaxial tensile deformation, vacancy prefers to diffuse along the direction that is perpendicular to the uniaxial tensile deformation.

An experimental observation was reported that TiO2 nanoparticles promote α-Al2O3 direct growth on nickel aluminide by skipping the metastable-to-stable alumina transformation during the oxidation process. Mechanically, this direct growth of α-Al2O3 can be attributed to the fact that both α-Al2O3 and rutile-TiO2 nanoparticles share the well-matching sublattice of oxygen among their energetically favorable interfaces of (0 1 ¯ 0)TiO2//(000 1 ¯ )Al2O3, (0 1 ¯ 0)TiO2//( 1 ¯ 2 1 ¯ 0)Al2O3 and (001)TiO2//(10 1 ¯ 0)Al2O3. The work paves a new route to the controlling direct thermal growth of α-Al2O3 on the substrates of MxAly (M = Ni, Co, Fe)-based alloys by spreading the seed of a selected oxide which possesses the well-matching oxygen sublattice to α-Al2O3.

By means of ab initio molecular dynamics (AIMD), the evolution of local atomic structures of the U116Nb12 liquid alloy during solidification from 2600 K to 600 K was systemically investigated in terms of the pair correlation function, structure factor, bond angle distribution, coordination number, the Honeycutt-Anderson (HA) and Voronoi index as well as diffusivity and viscosity. The distinctly linear dependence of the mean square displacements (MSDs) as a function of time indicates that the equilibrium configurations are derived from our AIMD simulations. The equations of the volumetric expansion, thermal diffusion and viscosity of the U116Nb12 liquid alloy are presented, respectively. The most abundant structures in the U116Nb12 liquid alloy are those having HA indices of 1551, 1541, 1431, 1441 and 1661. The Voronoi analysis reveals that the distributions of local atomic structures at high temperature are homogeneous, whereas Voronoi polyhedra trend to form , , , , , and with the larger fraction at low temperature. The analysis of chemical short-range order and structural properties suggests that the icosahedra and bcc-type clusters play the dominant roles upon cooling and, the addition of Nb in the U116Nb12 liquid alloy is indeed beneficial to occurrence of the local atomic structural evolution.

Inorganic chalcogenides are traditional high-performance thermoelectric materials. However, they suffer from intrinsic brittleness and it is very difficult to obtain materials with both high thermoelectric ability and good flexibility. Here, we report a flexible thermoelectric material comprising highly ordered Bi2Te3 nanocrystals anchored on a single-walled carbon nanotube (SWCNT) network, where a crystallographic relationship exists between the Bi2Te3 < $$\bar{1}2\bar{1}0$$ > orientation and SWCNT bundle axis. This material has a power factor of ~1,600 μW m−1 K−2 at room temperature, decreasing to 1,100 μW m−1 K−2 at 473 K. With a low in-plane lattice thermal conductivity of 0.26 ± 0.03 W m−1 K−1, a maximum thermoelectric figure of merit (ZT) of 0.89 at room temperature is achieved, originating from a strong phonon scattering effect. The origin of the excellent flexibility and thermoelectric performance of the Bi2Te3–SWCNT material is attributed, by experimental and computational evidence, to its crystal orientation, interface and nanopore structure. Our results provide insight into the design and fabrication of high-performance flexible thermoelectric materials. Bi2Te3 materials suffer from brittleness, limiting their application for thermoelectric harvesting. By depositing ordered nanocrystals onto single-wall carbon nanotubes, a flexible material is formed that achieves ZT of 0.89 at room temperature.

The septuple-atomic-layer $\mathrm{VSi_2P_4}$ with the same structure of experimentally synthesized $\mathrm{MoSi_2N_4}$ is predicted to be a spin-gapless semiconductor (SGS). In this work, the biaxial strain is applied to tune electronic properties of $\mathrm{VSi_2P_4}$, and it spans a wide range of properties upon the increasing strain from ferromagnetic metal (FMM) to SGS to ferromagnetic semiconductor (FMS) to SGS to ferromagnetic half-metal (FMHM). Due to broken inversion symmetry, the coexistence of ferromagnetism and piezoelectricity can be achieved in FMS $\mathrm{VSi_2P_4}$ with strain range of 0\% to 4\%. The calculated piezoelectric strain coefficients $d_{11}$ for 1\%, 2\% and 3\% strains are 4.61 pm/V, 4.94 pm/V and 5.27 pm/V, respectively, which are greater than or close to a typical value of 5 pm/V for bulk piezoelectric materials. Finally, similar to $\mathrm{VSi_2P_4}$, the coexistence of piezoelectricity and ferromagnetism can be realized by strain in the $\mathrm{VSi_2N_4}$ monolayer. Our works show that $\mathrm{VSi_2P_4}$ in FMS phase with intrinsic piezoelectric properties can have potential applications in spin electronic devices., 6 pages,7 figures

The six-membered ring (SMR) is a common structure unit for numerous material systems. These materials include, but are not limited to, the typical two-dimensional materials such as graphene, h-BN, and transition metal dichalcogenides, as well as three-dimensional materials such as beryllium, magnesium, MgB2 and Bi2Se3. Although many of these materials have already become ‘stars’ in materials science and condensed-matter physics, little attention has been paid to the roles of the SMR unit across a wide range of compositions and structures. In this article, we systematically analyze these materials with respect to their very basic SMR structural unit, which has been found to play a deterministic role in the occurrence of many intriguing properties and phenomena, such as Dirac electronic and phononic spectra, superconductivity and topology. As a result, we have defined this group of materials as SMR inorganic materials, opening up a new perspective on materials research and development. With their unique properties, SMR materials deserve wide attention and in-depth investigation from materials design, new physical discoveries to target-wizard applications. It is expected that SMR materials will find niche applications in next-generation information technology, renewable energy, space, etc., The authors defined SMR materials, which possess extensive six-membered-ring structural units and rich structural lattices, chemistry and physics, suitable for niche applications in next-generation information technology, renewable energy, space, etc.

By means of first-principles calculations and a modeling analysis, we have predicted that traditional two-dimensional graphene hosts four types of topological phononic Dirac points (DPs) and a phononic nodal ring (PNR) in its phonon spectrum. In the phonon spectrum of graphene, there exist four types of DPs, DP1, DP2, DP3, and DP4, with both DP1 and DP2 located at the Brillouin zone (BZ) corners $K$ and ${K}^{\ensuremath{'}}$, DP3 located along the $\mathrm{\ensuremath{\Gamma}}\text{\ensuremath{-}}K$ line, and DP4 located along the $\mathrm{\ensuremath{\Gamma}}\text{\ensuremath{-}}M$ line, as well as the PNR surrounding the centered $\mathrm{\ensuremath{\Gamma}}$ point in the ${q}_{x,y}$ plane. The calculations further reveal that Berry curvatures are vanishingly zero throughout the whole BZ, except for the positions of these four Dirac phonons, at which the nonzero singular Berry curvatures appear with a Berry phase of $\ensuremath{\pi}$ or $\ensuremath{-}\ensuremath{\pi}$, confirming its topological nontrivial nature. The topologically protected nontrivial phononic edge states have been also evidenced along both the zigzag-edged and armchair-edged boundaries. These results may pave the way for further studies of the topological phononic properties of graphene, such as phononic destructive interference with a suppression of backscattering and intrinsic phononic quantum Hall-like effects.

Based on first-principles calculations, we predict that the superconductor ${\mathrm{MgB}}_{2}$ with an ${\mathrm{AlB}}_{2}$-type centrosymmetric lattice hosts the so-called phononic topological Weyl nodal lines (PTWNLs) in its bulk phonon spectrum. These PTWNLs can be viewed as countless Weyl points (WPs) closely aligned along the straight lines in the $\ensuremath{-}H--K--H$ direction within the three-dimensional Brillouin zone (BZ) and are always paired with opposite Berry phase. Their topologically nontrivial natures are confirmed by the calculated Berry curvature distributions on the planes perpendicular to these lines. These lines are unique, because they are located exactly at the high-symmetry boundary of the BZ protected by the mirror symmetry and, simultaneously, are straightly transverse to the whole BZ, differently from known classifications, including nodal rings, nodal chains or nets, and nodal loops. On the $(10\overline{1}0)$ crystal surface, the PTWNL-induced drumhead-like nontrivial surface states appear within the rectangular area confined by the projected lines of the PTWNLs. Moreover, when the mirror symmetry is broken, the double-degenerate PTWNLs are further lifted to form a pair of WPs with opposite chirality. Our results pave the way for future experimental study of topological phonons on ${\mathrm{MgB}}_{2}$ and highlight similar results in a series of isostructural ${\mathrm{AlB}}_{2}$-type metallic diborides.

In order to elucidate the role of various M -alloying additions in the fcc-type γ phase of nickel-based superalloys, we have performed a comprehensive and systematical computation on all 3 d -, 4 d - and 5 d - M alloying additions substituting in the Ni lattice using the same standard of the first-principles calculations within the framework of the density functional theory. The results show that the substitution enthalpies of Sc, Ti, V, Mn, Fe, Co, Zn, Zr, Nb, Hf, Ta, and Pt are negative, while the others elements have positive substitution enthalpies. To further explore the contributions of various factors to the substitution enthalpy, we have attempted to divide the substitution enthalpy into two parts. The first one is the mechanical deformation energy caused by the atomic volume change because of the M -alloying additions substituting in fcc Ni and the other one is the chemical and magnetic energy through electronic hybridizations and local magnetic interactions. It is found that the substitution enthalpy is a consequence of the balancing of these two contributions. Furthermore, we have attempted to correlate their mechanical deformation energies with metallic atomic radii of substitutional M -alloying addition with respect to Ni, and the chemical and magnetic energies with transferred charges between M -alloying addition and Ni, which are indeed associated with the so-called electronegativity difference.

By means of ab initio molecular dynamics (AIMD) simulations, Nudged Elastic Band (NEB) method and cluster expansion (CE) combined with the Monte Carlo (MC) techniques, we have investigated that the elemental interactions and local structural dynamics in the melt and γ phase of U-Nb alloy and hydrogen diffusion behavior in γ-U-Nb alloy. It has been found that the aggregation of Nb atoms inherited from melt to γ phase plays a significant role in improving mechanical property and protecting γ-U-Nb alloy from hydrogen damage. The analyses of chemical short-range order parameters attest that there exists the similarity of element interactions between the melt and γ phase of U-Nb alloy. The U-Nb pairs in both melt and γ phase exhibit the repulsive interactions, whereas the attractive U-U and Nb-Nb interactions exits. These results demonstrate that the U and Nb atoms prefer to stay in their own shells to form the localized clusters in both melt and γ phase of U-Nb alloy. Furthermore, the analyses of hydrogen diffusion behavior in γ-U-Nb alloy, our NEB calculations have further proved that the hydrogen atoms prefer to be trapped by Nb atoms and, this trend is further reinforced by the aggregation of Nb atoms. It implies that, once Nb is added into U alloys, the Nb addition plays an important role in slowing down the diffusion of hydrogen atoms in γ-U-Nb alloy. The uniform distribution of Nb clusters helps to avoid the occurrence of excessive local hydrogen concentration.

Topological nodal line (DNL) semimetals, formed by a closed loop of the inverted bands in the bulk, result in the nearly flat drumhead-like surface states with a high electronic density near the Fermi level. The high catalytic active sites associated with the high electronic densities, the good carrier mobility, and the proper thermodynamic stabilities with $\Delta G_{H^*}$$\approx$0 are currently the prerequisites to seek the alternative candidates to precious platinum for catalyzing electrochemical hydrogen (HER) production from water. Within this context, it is natural to consider whether or not the DNLs are a good candidate for the HER because its non-trivial surface states provide a robust platform to activate possibly chemical reactions. Here, through first-principles calculations we reported on a new DNL TiSi-type family with a closed Dirac nodal line consisting of the linear band crossings in the $k_y$ = 0 plane. The hydrogen adsorption on the (010) and (110) surfaces yields the $\Delta G_{H^*}$ to be almost zero. The topological charge carries have been revealed to participate in this HER. The results are highlighting that TiSi not only is a promising catalyst for the HER but also paves a new routine to design topological quantum catalyst utilizing the topological DNL-induced surface bands as active sites, rather than edge sites-, vacancy-, dopant-, strain-, or heterostructure-created active sites.

Topological materials are a new and rapidly expanding class of quantum matter. To date, identification of the topological nature of a given compound material demands specific determination of the appropriate topological invariant through detailed electronic structure calculations. Here we present an efficient criterion that allows ready screening of potential topological materials, using topological insulators as prototypical examples. The criterion is inherently tied to the band inversion induced by spin-orbit coupling, and is uniquely defined by a minimal number of two elemental physical properties of the constituent elements: the atomic number and Pauling electronegativity. The validity and predictive power of the criterion is demonstrated by rationalizing many known topological insulators and potential candidates in the tetradymite and half-Heusler families, and the underlying design principle is naturally also extendable to predictive discoveries of other classes of topological materials.

By means of the first-principles calculations, the lattice parameters, electronic structures, phonon dispersions, and mechanical properties of the rare earth metal borocarbide YB 2 C have been theoretically investigated. The dynamically stability of the layered tetragonal YB 2 C has been evidenced based on the frozen phonon method. We have found that the covalent bonding between B-2 p , C-2 p and Y-5 d orbitals are responsible for the strong interlayer interactions based on the calculated electronic structures and ELF images. The estimated hardness of P 4 2 / mbc -YB 2 C is around 23.46 GPa which is comparable with the well-known ultra-incompressible oP 6-OsB 2 . Additionally, the analysis of the ideal shear and tensile strength of YB 2 C reveals the importance of covalent bonds between Y and B/C layer which help to enhance the resistance under deformation.

International audience; The equiaxed dendritic growth of Al-Cu alloys in nearly isothermal temperature field under continuous cooling condition is studied using in situ and real-time observation of experiments by synchrotron X-ray radiography and large-scale quantitative two-dimensional (2D) phase-field (PF) simulations. It is revealed that the equiaxed dendritic morphology and the secondary dendritic arm spacing (SDAS) in the 2D PF simulations are in a reasonable agreement with the experimental data. Increasing the cooling rates results in a smaller SDAS, as predicted by the analytical Kattamis-Flemings model. The transformation kinetics of solid fraction can be described by the Johnson-Mehl-Avrami-Kologoromov (JMAK) theory, but quantitative differences between the experiments and 2D PF simulations are significant. The maximum solute concentration Cmax in liquid is approximately equal to the equilibrium concentration, which depends on the undercooling rather than the cooling rate. But the minimum solute concentration Cmin in solid decreases with the cooling rate, thus leading to a larger segregation ratio SR = Cmax/Cmin. Moreover, the liquid gravity-driven natural convection is considered in simulations. The liquid flow slightly increases the SDAS but has no apparent effect on solid fraction, and the segregation ratio is slightly reduced by the liquid convection, which could be attributed to the almost same Cmax and enlarged Cmin.

Macrosegregation is the key issue in the solidification field. Oxygen and its inclusions play the important role in driving the melt flow and the resulting macrosegregation in steel. Here, to reveal the inducing mechanism and quantitative model of oxygen content in real industrial steel ingots, we demonstrate for the first time that there exists the critical oxygen content in triggering the formation of channel-type segregation, the most undesirable macrosegregation type in steel. Our multiscale simulations from density functional theory calculations to multiphase/multicomponent macromodel, clarify the quantitative conditions initializing channel-type segregation and reveal two typical growth modes via oxide flotation. The oxygen content model and criterion to induce the channel onset is built accordingly, which are validated by the numerous full ingot dissections and experimental characterizations including the in situ electrolysis of inclusions, X-ray microtomography, scanning electron microscope, large-scale measurement system of inclusions and chemical analysis. With oxygen controlled below this critical value of 0.0008 wt%, channel disappears. This study quantitatively uncovers the novel role of oxygen in steel, changes the traditional sole concept of cleanliness, and highlights an innovative and controlling-effective route to fabricate homogenized steel.

The mechanism of θ- to α-Al2O3 phase transformation is proved by the “synchro-shear” model through the first-principles calculations. The proposed model is based on a reorganization of oxygen anions sublattice from f.c.c. to h.c.p. which is achieved by series of shears of the oxygen closed-stacking plane (20 1 ) along the direction of [102] and a migration of Al-cations to the near octahedral interstices to form a ‘‘honey comb’’ lattice. On this basis, it is concluded that there is a critical size of ~22.88 nm at which θ-Al2O3 is thermodynamically able to transform to an α form. The obtained data is in a good agreement with the experimental observations.

There have been extensive experimental observations of the anisotropic corrosion behavior of metals and alloys, and their mechanisms were assumed to be correlated with the so-called surface energy or the work function. However, to date, a specified mechanism or theory to interpret anisotropic corrosion behavior remains unclear. Here, we determine the anisotropic anodic dissolution of metals and alloys in corrosive environments by developing a formula to specify the relationship between the electrode potential (U) and the current density (I) by considering the basic parameters of our defined surface energy density ( E s u r f / ρ ) and the work function ( Φ ). Therefore, we build an ab initio model to evaluate the anisotropic anodic dissolution behavior of metals and alloys using the inputs obtained within density functional theory. This theory is further validated in the case of variations in the crystallographic planes of Mg. Moreover, some selected alloying additions such as Ga, Cd, Hg, In, As, and Cr are theoretically elucidated to effectively reduce the anodic dissolution rates of the Mg matrix to some extent, in close agreement with available experimental observations. This model is capable of predicting the anisotropic anodic dissolution behavior, providing a promising perspective for designing better corrosion-resistant alloys.

Ultrathin films of $\ensuremath{\beta}$-tungsten $(\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{W})$ is attracting extensive attentions because of its promising application in spintronics due to giant spin Hall effect and its fundamental interest in superconductivity. By means of first-principles calculations, we have elucidated its nontrivial topological nature with multiple Dirac nodal lines in the $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{W}$ metal when spin-orbit coupling (SOC) is ignored. The analysis of electronic structures reveal that its topology is associated with the band inversion between the ${d}_{xz}+{d}_{yz}$ and ${d}_{{z}^{2}}$ orbitals at the $M$ point in its Brillouin zone. By switching on the SOC, these Dirac nodal lines become gapped, as accompanied with the occurrence of 24 massive Dirac fermions at the energy of 87 meV below the Fermi level. Different from the exact gapless Dirac fermions with the linear band crossings, we have identified that these massive Dirac fermions all open a tiny gap of 7 meV. In addition, we have observed the topologically protected nontrivial surface arc states connecting these massive Dirac fermions. The existence of these massive Dirac fermions in the $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{W}$ phase would be important to understand its giant spin Hall effect according to a recent study [Nature 555, 638 (2018)] where massive Dirac fermions were identified to generate Berry-curvature-induced Hall conductivity.

Electrides, with their excess electrons distributed in crystal cavities playing the role of anions, exhibit a variety of unique electronic and magnetic properties. In this work, we employ the first-principles crystal structure prediction to identify a new prototype of A$_3$B electride in which both interlayer spacings and intralayer vacancies provide channels to accommodate the excess electrons in the crystal. This A$_3$B type of structure is calculated to be thermodynamically stable for two alkaline metals oxides (Rb$_3$O and K$_3$O). Remarkably, the unique feature of multiple types of cavities makes the spatial arrangement of anionic electrons highly flexible via elastic strain engineering and chemical substitution, in contrast to the previously reported electrides characterized by a single topology of interstitial electrons. More importantly, our first-principles calculations reveal that Rb$_3$O is a topological Dirac nodal line semimetal, which is induced by the Rb-$s$ $\rightarrow$ O-$p$ band inversion at the general electronic k momentums in the Brillouin zone associated with the intersitial electric charges. The discovery of flexible electride in combining with topological electronic properties opens an avenue for electride design and shows great promises in electronic device applications., 15 pages, 12 figures

Hot corrosion behavior of three nickel-based single crystal superalloys with different key alloying elements (including Re, Cr, Al and Ti) contents in molten Na2SO4 salt at 900 °C was investigated. Comparative study of hot corrosion resistance was conducted on two Re-free superalloys with 12 wt% Cr and different content of Al and Ti. By further adding Re, the experimental alloy with moderate Cr content (8.5 wt%) and Al/Ti > 1 in the present research also exhibited excellent hot corrosion resistance. The influence mechanism of Re on promoting hot corrosion resistance was attempted to be explored in combined with first-principle calculation. In addition, the potential design space of new-developed single crystal superalloys was also proposed.

A new visible-light responsive metallic photocatalyst, nanostructured MoO2, has been discovered. The metallic nature of MoO2 is confirmed by valance X-ray photoelectron spectroscopy spectrum and theoretical calculations. However, MoO2 itself shows only moderate activity due to the serious charge recombination, a general disadvantage of metallic photocatalysts. The findings suggest that its effective charge diffusion length Lp is smaller than 1.0 nm while the separation efficiency ηsep is less than 10%. Therefore, only the periphery of the metallic MoO2 can effectively contribute to photocatalysis. This limitation is overcome by integrating MoO2 in a hydrothermal carbonation carbon (HTCC) matrix (mainly contains semiconductive polyfuran). This simple chemical modification brings two advantages: (i) an internal electric field is formed at the interface between MoO2 and HTCC due to their appropriate band alignment; (ii) the nanostructured MoO2 and the HTCC matrix are intertwined with each other intimately. Their small size and large contact area promote charge transfer, especially under the internal electric field. Therefore, the separation rate of photoexcited charge carrier in MoO2 is greatly enhanced. The activity increases by 2.4, 16.8, and 4.0 times in photocatalytic oxygen evolution, dyes degradation, and photoelectrochemicl cell, respectively. The new approach is helpful for further development of metallic photocatalysts.

'Hundred Talents Project' of the Chinese Academy of Sciences; Key Research Program of Chinese Academy of Sciences [KGZD-EW-T06]; National Natural Science Foundation of China [51474202, 51174188]; Beijing Supercomputing Center of CAS (Shenyang branch); high-performance computational cluster in the Shenyang National University Science and Technology Park; Major Research Plan [91226204]

The strength and hardness of nanostructured materials are significantly enhanced owing to the large amount of grain boundaries (GB) produced by a reduced grain size. The thermal stability of the GB is a key to maintaining the grain size and thus the strength/hardness in nanostructured materials at high temperatures. In this work, coherent domain boundaries (DB) were introduced by compressive processing to sub-divide a complex-structured intermetallic Cr2Nb into nanograins of size down to 2 nm. These DB persisted after an annealing of 10 h at 1273 K. The coherent DB have been investigated by aberration-corrected high-resolution transmission electron microscopy and first-principles calculations. The high thermal stability is evidently a result of low formation energies of the DB.

By summarizing over seven hundred elastic constants of materials with various crystal structures, we have found that the so-called ductile-to-brittle transition originates from the bonding type transition. This can be reflected well by a universal linear relation between Cauchy pressure/bulk modulus (CP/B) and shear modulus/bulk modulus (G/B). In general, G/B of a material will gradually decrease with increasing pressure and temperature, while a significant change in G/B against increasing temperature often corresponds to a certain phase transition, such as magnetic transition, spin flipping, structural phase transition and so on. The present work suggests that the value of G/B for materials can serve as an indicator of bonding type. Importantly, this linear relation is robust for materials under temperature, pressure and with defects. Here we propose that damage tolerance properties can be experimentally measured from the elastic constants of a given material. It is suggested that a material with a value of G/B that varies little with temperature, pressure and defect concentration, potentially exhibits high damage tolerance. These observations shed light on the ductile-to-brittle transition. They may provide a potential tool towards the design of materials, particularly under extreme conditions.

By combining theoretical density functional theory (DFT) and experimental studies, structural and magnetic phase stabilities and electronic structural, elastic, and vibrational properties of the Laves-phase compound ${\mathrm{NbMn}}_{2}$ have been investigated for the C14, C15, and C36 crystal structures. At low temperatures C14 is the ground-state structure, with ferromagnetic and antiferromagnetic orderings being degenerate in energy. The degenerate spin configurations result in a rather large electronic density of states at Fermi energy for all magnetic cases, even for the spin-polarized DFT calculations. Based on the DFT-derived phonon dispersions and densities of states, temperature-dependent free energies were derived for the ferromagnetic and antiferromagnetic C14 phase, demonstrating that the spin-configuration degeneracy possibly exists up to finite temperatures. The heat of formation ${\mathrm{\ensuremath{\Delta}}}_{298}{H}^{0}=\ensuremath{-}45.05\ifmmode\pm\else\textpm\fi{}3.64\phantom{\rule{0.16em}{0ex}}\mathrm{kJ}\phantom{\rule{0.16em}{0ex}}{(\mathrm{mol}\phantom{\rule{0.16em}{0ex}}\mathrm{f}.\mathrm{u}.\phantom{\rule{0.16em}{0ex}}{\mathrm{NbMn}}_{2})}^{\ensuremath{-}1}$ was extracted from drop isoperibolic calorimetry in a Ni bath. The DFT-derived enthalpy of formation of ${\mathrm{NbMn}}_{2}$ is in good agreement with the calorimetric measurements. Second-order elastic constants for ${\mathrm{NbMn}}_{2}$ as well as for related compounds were calculated.

In analogy to various fermions of electrons in topological semimetals, topological mechanical states with two types of bosons, Dirac and Weyl bosons, were reported in some macroscopic systems of kHz frequency, and those with a type of doubly-Weyl phonons in atomic vibrational framework of THz frequency of solid crystals were recently predicted. Here, through first-principles calculations, we have reported that the phonon spectra of the WC-type TiS, ZrSe, and HfTe commonly host the unique triply degenerate nodal points (TDNPs) and single two-component Weyl points (WPs) in THz frequency. Quasiparticle excitations near TDNPs of phonons are three-component bosons, beyond the conventional and known classifications of Dirac, Weyl, and doubly-Weyl phonons. Moreover, we have found that both TiS and ZrSe have five pairs of type-I Weyl phonons and a pair of type-II Weyl phonons, whereas HfTe only has four pairs of type-I Weyl phonons. They carry nonzero topological charges. On the ($10\overline{1}0$) crystal surfaces, we observe topological protected surface arc states connecting two WPs with opposite charges, which host modes that propagate nearly in one direction on the surface.

Thermoelectric materials transform a thermal gradient into electricity. The efficiency of this process relies on three material-dependent parameters: the Seebeck coefficient, the electrical resistivity and the thermal conductivity, summarized in the thermoelectric figure of merit. A large figure of merit is beneficial for potential applications such as thermoelectric generators. Here we report the thermal and electronic properties of thin-film Heusler alloys based on Fe2V0.8W0.2Al prepared by magnetron sputtering. Density functional theory calculations suggest that the thin films are metastable states, and measurements of the power factor—the ratio of the Seebeck coefficient squared divided by the electrical resistivity—suggest a high intrinsic figure of merit for these thin films. This may arise from a large differential density of states at the Fermi level and a Weyl-like electron dispersion close to the Fermi level, which indicates a high mobility of charge carriers owing to linear crossing in the electronic bands. A high intrinsic thermoelectric figure of merit is found for a metastable thin-film Fe2V0.8W0.2Al Heusler alloy.

We study the optical properties of the Ruddlesden-Popper series of iridates Sr$_{n+1}$Ir$_n$O$_{3n+1}$ ($n$=1, 2 and $\infty$) by solving the Bethe-Salpeter equation (BSE), where the quasiparticle (QP) energies and screened interactions $W$ are obtained by the $GW$ approximation including spin-orbit coupling. The computed optical conductivity spectra show strong excitonic effects and reproduce very well the experimentally observed double-peak structure, in particular for the spin-orbital Mott insulators Sr$_2$IrO$_4$ and Sr$_3$Ir$_2$O$_7$. However, $GW$ does not account well for the correlated metallic state of SrIrO$_3$ owing to a much too small band renormalization, and this affects the overall quality of the optical conductivity. Our analysis describes well the progressive redshift of the main optical peaks as a function of dimensionality ($n$), which is correlated with the gradual decrease of the electronic correlation (quantified by the constrained random phase approximation) towards the metallic $n=\infty$ limit. We have also assessed the quality of a computationally cheaper BSE approach that is based on a model dielectric function and conducted on top of DFT+$U$ one-electron energies. Unfortunately, this model BSE approach does not accurately reproduce the outcome of the full $GW$+BSE method and leads to larger deviations to the measured spectra., 13 pages, 8 figures

Topological materials in crystal solids, including topological insulators (TIs), topological crystalline insulators (TCIs), topological Dirac semimetals (DSMs), topological Weyl semimetals (WSMs), topological Dirac or Weyl nodal line semimetals (NLSMs) and beyond, are mainly featured with topological, protected non-trivial surface states, and their bulk phases are insulators or semimetals with the proper presence of Dirac cones, Weyl nodes or Dirac nodal lines around the Fermi level. The author suggests a two-step computational screening strategy of 3D topological materials by mixing chemistry with physics with the considerations of fully filled bands and band inversion., Comment: 3 pages, 1 figure, accepted by National Science Review

We study the effects of dilute La and Rh substitutional doping on the electronic structure of the relativistic Mott insulator Sr2IrO4 using fully relativistic and magnetically noncollinear density functional theory with the inclusion of an on-site Hubbard U. To model doping effects, we have adopted the supercell approach, that allows for a realistic treatment of structural relaxations and electronic effects beyond a purely rigid band approach. Bymeans of the band unfolding technique we have computed the spectral function and constructed the effective band structure and Fermi surface (FS) in the primitive cell, which are readily comparable with available experimental data. Our calculations clearly indicate that La and Rh doping can be interpreted as effective electron and (fractional) hole doping, respectively. We found that both electron and hole doping induce an insulating-to-metal transition (IMT) but with different characteristics. In Sr2-x La-x IrO4 the IMT is accompanied by a moderate renormalization of the electronic correlation substantiated by a reduction of the effective on-site Coulomb repulsion U -J from 1.6 eV (x = 0) to 1.4 eV (metallic regime of x = 12.5%). The progressive closing of the relativistic Mott gap leads to the emergence of connected elliptical electron pockets at (pi/2, pi/2) and less intense features at X on the Fermi surface. The average ordered magnetic moment is slightly reduced upon doping, but the canted antiferromagnetic state is perturbed on the Ir-O planes located near the La atoms. The substitution of Ir with the nominally isovalent Rh is accompanied by a substantial hole transfer from the Rh site to the nearest-neighbor Ir sites. This shifts down the chemical potential, creates almost circular disconnected hole pockets in the FS, and establishes the emergence of a two-dimensional metallic state formed by conducting Rh planes intercalated by insulating Ir planes. Finally, our data indicate that hole doping causes a flipping of the in-plane net ferromagnetic moment on the Rh plane and induces a magnetic transition from the antiferromagnetic (AF)-I to the AF-II ordering.

Bylo provedeno termodynamicke modelovani soustavy Ta-V-Si. Jsou prezentovany fazove stability zakladnich stavů pro vsech devět binarnich sloucenin a pro ternarni intermetalikum tau1, ziskane na podkladě ab initio přistupu. Vypoctene tvorne energie byly zahrnuty do termodynamickeho modelovani prostřednictvim metody CALPHAD. Termodynamicke přemodelovani podsoustav Ta-V a V-Si a výsledna optimalizace poskytly dobrou shodu s experimentalnimi výsledky ve zkoumane teplotni oblasti 1200 - 1500C.

Beryllium is a simple alkali earth metal, but has been the target of intensive studies for decades because of its unusual electron behaviors at surfaces. Puzzling aspects include (i) severe deviations from the description of the nearly free electron picture, (ii) anomalously large electron-phonon coupling effect, and (iii) giant Friedal oscillations. The underlying origins for such anomalous surface electron behaviors have been under active debate, but with no consensus. Here, by means of first-principle calculations, we discover that this pure metal system, surprisingly, harbors the Dirac node line (DNL) that in turn helps to rationalize many of the existing puzzles. The DNL is featured by a closed line consisting of linear band crossings and its induced topological surface band agrees well with previous photoemission spectroscopy observation on Be (0001) surface. We further reveal that each of the elemental alakali earth metals of Mg, Ca, and Sr also harbors the DNL, and speculate that the fascinating topological property of DNL might naturally exist in other elemental metals as well., Comment: 5 pages, 4 figures

Phase relations have been evaluated for the Ta-V-Si system at 1500 and 1200 degrees C. Three ternary phases were found: tau(1)-(Ta,V)(5)Si-3 (Mn5Si3-type), tau(2)-Ta(Ta,V,Si)(2) (MgZn2-type) and tau(3)-Ta(Ta,V,Si)(2) (MgCu2-type). The crystal structure of tau(2)-Ta(Ta,V,Si)(2) was solved by X-ray single crystal diffraction (space group P6(3)/mmc). Atom order in the crystal structures of tau(1)-(Ta,V)(5)Si-3 (Mn5Si3 type) and tau(3)-Ta(Ta,V,Si)(2) was derived from X-ray powder diffraction data. A large homogeneity range was found for tau(1)-(TaxV1-x)(5)Si-3 revealing random exchange of Ta and V at a constant Si content. At 1500 degrees C, the end points of the tau(1)-phase solution (0.082

The Ta-V system is an interesting system exhibiting the existence of Laves phases among elements of the same group in the periodic system, and with an unusual order of stability of Laves phase structures at 0 K. Whereas the hexagonal C14 Laves phase is stable at 0 K and at high temperatures, the C15 structure is the most stable Laves phase at intermediate temperatures. The ab initio calculations of the total energies of formation for both C14 and C15 Laves phases employed two- and three-sublattice models to revise the thermodynamic description of the system published recently. The remodeled Gibbs energies of Laves phases require less fitting parameters than those obtained in previous treatments and the corresponding phase diagrams provide an excellent agreement with the experimental data on the phase stability and phase boundaries found in the literature. The new fitting procedure proposed involves a temperature dependent heat capacity for the C15 structure and allows us to compare the optimized heat capacity differences between the Laves phase and Standard Element Reference structure with those determined experimentally and theoretically. (C) 2010 Elsevier Ltd. All rights reserved.

Although doping with appropriate heteroatoms is a powerful way of increasing visible light absorption of wide-bandgap metal oxide photocatalysts, the incorporation of heteroatoms into the photocatalysts usually leads to the increase of deleterious recombination centers of photogenerated charge carriers. Here, a conceptual strategy of increasing visible light absorption without causing additional recombination centers by constructing an ultrathin insulating heterolayer of amorphous boron oxynitride on wide-bandgap photocatalysts is shown. The nature of this strategy is that the active composition nitrogen in the heterolayer can noninvasively modify the electronic structure of metal oxides for visible light absorption through the interface contact between the heterolayer and metal oxides. The photocatalysts developed show significant improvements in photocatalytic activity under both UV-vis and visible light irradiation compared to the doped counterparts by conventional doping process. These results may provide opportunities for flexibly tailoring the electronic structure of metal oxides.

Increasing visible light absorption of classic wide-bandgap photocatalysts like TiO2 has long been pursued in order to promote solar energy conversion. Modulating the composition and/or stoichiometry of these photocatalysts is essential to narrow their bandgap for a strong visible-light absorption band. However, the bands obtained so far normally suffer from a low absorbance and/or narrow range. Herein, in contrast to the common tail-like absorption band in hydrogen-free oxygen-deficient TiO2 , an unusual strong absorption band spanning the full spectrum of visible light is achieved in anatase TiO2 by intentionally introducing atomic hydrogen-mediated oxygen vacancies. Combining experimental characterizations with theoretical calculations reveals the excitation of a new subvalence band associated with atomic hydrogen filled oxygen vacancies as the origin of such band, which subsequently leads to active photo-electrochemical water oxidation under visible light. These findings could provide a powerful way of tailoring wide-bandgap semiconductors to fully capture solar light.

The Mg-Si-O system is the major Earth and rocky planet-forming system. Here, through quantum variable-composition evolutionary structure explorations, we have discovered several unexpected stable binary and ternary compounds in the Mg-Si-O system. Besides the well-known SiO2 phases, we have found two extraordinary silicon oxides, SiO3 and SiO, which become stable at pressures above 0.51 TPa and 1.89 TPa, respectively. In the Mg-O system, we have found one new compound, MgO3, which becomes stable at 0.89 TPa. We find that not only the (MgO)x(SiO2)y compounds, but also two (MgO3)x(SiO3)y compounds, MgSi3O12 and MgSiO6, have stability fields above 2.41 TPa and 2.95 TPa, respectively. The highly oxidized MgSi3O12 can form in deep mantles of mega-Earths with masses above 20 M+ (M+:Earth's mass). Furthermore, the dissociation pathways of pPv-MgSiO3 are also clarified, and found to be different at low and high temperatures. The low-temperature pathway is MgSiO3 -> Mg2SiO4 + MgSi2O5 -> SiO2 + Mg2SiO4 -> MgO + SiO2, while the high-temperature pathway is MgSiO3 -> Mg2SiO4 + MgSi2O5 -> MgO + MgSi2O5 -> MgO + SiO2. Present results are relevant for models of the internal structure of giant exoplanets, and for understanding the high-pressure behavior of materials., 24 pages, 6 figures

Phase relations in the title system are evaluated for the isothermal sections at 1500 and 1200 °C.

By means of hybrid density functional theory we investigate the evolution of the structural, electronic, and magnetic properties of the colossal magnetoresistance (CMR) parent compound LaMnO3 under pressure. We predict a transition from a low-pressure antiferromagnetic (AFM) insulator to a high-pressure ferromagnetic (FM) transport half metal (tHM), characterized by a large spin polarization (approximate to 80-90%). The FM-tHM transition is associated with a progressive quenching of the cooperative Jahn-Teller (JT) distortions which transform the Pnma orthorhombic phase into a perfect cubic one (through a mixed phase in which JT-distorted and regular MnO6 octahedra coexist), and with a high-spin (S = 2, m(Mn) = 3.7 mu(B)) to low-spin (S = 1, m(Mn) = 1.7 mu(B)) magnetic moment collapse. These results interpret the progression of the experimentally observed non-Mott metalization process and open up the possibility of realizing CMR behaviors in a stoichiometric manganite.

The evolution of the magnetic ordering temperature of the 4d(3) perovskites RTcO(3) (R = Ca, Sr, Ba) and its relation with its electronic and structural properties has been studied by means of hybrid density functional theory and Monte Carlo simulations. When compared to the most widely studied 3d perovskites the large spatial extent of the 4d shells and their relatively strong hybridization with oxygen weaken the tendency to form Jahn-Teller like orbital ordering. This strengthens the superexchange interaction. The resulting insulating G-type antiferromagnetic ground state is characterized by large superexchange coupling constants (26-35 meV) and Neel temperatures (750-1200 K). These monotonically increase as a function of the R ionic radius due to the progressive enhancement of the volume and the associated decrease of the cooperative rotation of the TcO(6) octahedra.

Electrical resistivity, specific-heat, and NMR measurements classify noncentrosymmetric Mo(3)Al(2)C (beta-Mn type, space group P4(1)32) as a strong-coupled superconductor with T(c)=9 K deviating notably from BCS-type behavior. The absence of a Hebbel-Slichter peak, a power-law behavior of the spin-lattice relaxation rate (from (27)Al NMR), an electronic specific heat strongly deviating from BCS model and a pressure enhanced T(c) suggest unconventional superconductivity with possibly a nodal structure of the superconducting gap. Relativistic density-functional theory calculations reveal a splitting of degenerate electronic bands due to the asymmetric spin-orbit coupling, favoring a mix of spin-singlet and spin-triplet components in the superconducting condensate, in absence of strong correlations among electrons.

Combining experiments and ab initio models we report on ${\mathrm{SrPt}}_{4}{\mathrm{Ge}}_{12}$ and ${\mathrm{BaPt}}_{4}{\mathrm{Ge}}_{12}$ as members of a novel class of superconducting skutterudites, where Sr or Ba atoms stabilize a framework entirely formed by Ge atoms. Below ${T}_{c}=5.35$ and 5.10 K for ${\mathrm{BaPt}}_{4}{\mathrm{Ge}}_{12}$ and ${\mathrm{SrPt}}_{4}{\mathrm{Ge}}_{12}$, respectively, electron-phonon coupled superconductivity emerges, ascribed to intrinsic features of the Pt-Ge framework, where Ge-$p$ states dominate the electronic structure at the Fermi energy.