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Thermoelectric materials have attracted extensive attention because they can directly convert waste heat into electric energy. As a brand-new method of alloying, high-entropy alloys (HEAs) have attracted much attention in the fields of materials science and engineering. Recent researches have found that HEAs could be potentially good thermoelectric (TE) materials. In this study, special quasi-random structures (SQS) of PbSnTeSe high-entropy alloys consisting of 64 atoms have been generated. The thermoelectric transport properties of the highest-entropy PbSnTeSe-optimized structure were investigated by combining calculations from first-principles density-functional theory and on-the-fly machine learning with the semiclassical Boltzmann transport theory and Green–Kubo theory. The results demonstrate that PbSnTeSe HEA has a very low lattice thermal conductivity. The electrical conductivity, thermal electronic conductivity and Seebeck coefficient have been evaluated for both n-type and p-type doping. N-type PbSnTeSe exhibits better power factor (PF = S2σ) than p-type PbSnTeSe because of larger electrical conductivity for n-type doping. Despite high electrical thermal conductivities, the calculated ZT are satisfactory. The maximum ZT (about 1.1) is found at 500 K for n-type doping. These results confirm that PbSnTeSe HEA is a promising thermoelectric material. [ABSTRACT FROM AUTHOR]

Recently, transition metal dichalcogenide photocatalysts have been substantially explored as efficient catalysts for water splitting. This paper systematically investigates the electronic structure and related properties of four, hitherto uninvestigated, Janus MoSSe/Ga 2 SSe vdW heterostructures using first-principles calculations. The results indicate that two out of the four heterostructures exhibit a type-II energy band arrangement, which facilitates the effective separation of electron-hole pairs in space. Additionally, the electrostatic potential, charge density difference and Bader charges analyses indicate that charge transfer in the interfacial region creates a built-in electric field that effectively inhibits electron and hole complexation, and that one out of the four heterostructures corresponds to a direct Z-scheme heterojunction. The optical absorption coefficients show that the MoSSe/Ga 2 SSe vdW heterostructures have a broad absorption range from visible to ultraviolet. These findings suggest that the Janus SMoSe/SGa 2 Se and SMoSe/SeGa 2 S vdW heterostructures could be suitable for photocatalytic water decomposition. The SMoSe/SGa 2 Se and SMoSe/SeGa 2 S vdW heterostructures have high corrected solar-to-hydrogen (STH) efficiency of 11.84% and 10.13%, respectively. [Display omitted] • Two Janus MoSSe/Ga 2 SSe vdW heterostructures are found type-II heterojunctions. • One of the type-II heterojunctions is a candidate as direct Z-scheme photocatalyst. • The built-in electric field can promote the separation of charge carriers. • Heterostructures band positioning are suitable for water splitting. • The heterostructures exhibit a broad absorption range from visible to ultraviolet. [ABSTRACT FROM AUTHOR]

In this work, the thermoelectric properties of Cu‐Sb system compounds have been investigated to understand their relation with the electronic structures. The approach used is a theoretical one that combines the density functional theory, the Boltzmann transport theory, and the quantum theory of atoms in molecules. The results show that the Seebeck effect in metallic systems originates from the existence of various types of chemical bonds. However, this feature is not sufficient enough to generate effective thermoelectric effect. As in semi‐conducting compounds, the intrinsic driving force for thermoelectric effect remains the variation of the density of states near the Fermi level. [ABSTRACT FROM AUTHOR]

The electronic and transport properties of Mg2Si are calculated using the density-functional and semi-classical Boltzmann transport theories. A detailed comparison of the efficiency of the Perdew, Burke, and Ernzerhof (PBE) and the modified Becke-Johnson (m-BJ) exchange potentials on the prediction of these properties is presented. We show that the m-BJ potential is able to predict the Mg2Si thermoelectric properties with better agreement with the experimental data than the PBE potential. These findings are correlated with a small modification of the valence orbitals of the materials and the opening of the gap. [ABSTRACT FROM AUTHOR]

Abstract: This work is an investigation on the phase formation in Al–Cu thin film systems. This investigation was carried out on eight samples with different Cu/Al thickness ratios (0.29, 0.56, 0.71, 0.87, 1.07, 1.26, 1.58 and 2.38). The corresponding compositions of these samples are 29, 44, 50, 55, 60, 64, 69 and 77at.% Cu. The samples were prepared by sputtering and characterized using in situ resistance measurements, and in-situ X-ray Diffraction (XRD). The sequence of phase formation was evidenced from this study. In addition, the energies of activation of Al2Cu and Al4Cu9 were calculated using simulations of the XRD and resistivity results, and the resistivity values of AlCu, Al2Cu3 and Al4Cu9 were determined at room temperature. [Copyright &y& Elsevier]

Abstract: This work is an investigation on the phase formation in Al–Fe thin film systems. This investigation was carried out on four samples with different Al/Fe thickness ratios (1.4, 3.13, 4 and 7). The samples were prepared by sputtering and characterized using in situ resistivity measurements and in-situ X-Ray Diffraction (XRD) measurements. The sequence of phase formation was evidenced from this study. Whatever the composition of the sample, the reaction between Al and Fe at around 300 °C leads to the formation of the metastable phase Al6Fe. The subsequent phases depend on the composition of the sample. Except for the sample with the highest content in Al, the end phases observed at 600 °C correspond to those reported in the phase diagram for the corresponding compositions at the same temperature. The energies of activation of Al6Fe, Al5Fe2 and AlFe were determined from in-situ resistance measurements by using Kissinger method and resistivity values were measured at room temperature for AlFe, Al5Fe2 and Al83Fe17. [Copyright &y& Elsevier]

Abstract: This work is an investigation on the phase formation in Al–Cu–Fe thin film systems. This investigation was carried out on four samples with different Al/Cu/Fe thickness ratios. The samples were prepared by sputtering at room temperature and characterised using in-situ resistivity measurements, and in-situ X-Ray Diffraction (XRD) measurements from room temperature up to 600 °C. The sequence of phase formation was evidenced for all the samples studied in this work. Whatever the composition, the first reaction occurs at the Al/Cu interface at around 200 °C and leads to the formation of Al2Cu. The nature of the following phases depends on the Al/Cu/Fe thickness ratios. Since at the end of the heat treatment, the sample has reached its equilibrium state, this work also brings new information on the Al–Cu–Fe ternary phase diagram. Resistivity values at room temperature of the ternary single phase materials, α-Al23CuFe4 and ω-Al7Cu2Fe, are reported for the first time. [Copyright &y& Elsevier]

Abstract: We present density-functional theory (DFT) calculations on the electronic structures of Zn1−xCdxSb solid solution for , 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, and 1.0. The electronic band structures, energy gaps, Bader’s charges, and electron localization functions were calculated. We show that the energy gaps and Bader’s charges exhibit peculiar behaviour for the alloy, which agrees with previously reported data. The plot of the electron localization functions shows that the Sb–Zn and Sb–Cd bonds are ionic in nature while the Sb–Sb bonds are covalent. [Copyright &y& Elsevier]

Abstract: A peculiar behaviour was already reported in literature from experimental investigations in the Zn1−x Cd x Sb solid solution around x =0.5. This behaviour was assumed to be linked to an ordering in the phase; however this assumption was never confirmed. The aim of this work was to understand this behaviour from a theoretical point of view. DFT calculations were performed to calculate the energy and the lattice parameters for all the possible structures of Zn1−x Cd x Sb with several compositions (x =0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1.0). The results show that an ordering appears in the most stable structure for x =0.5. This ordering consists in stacked planes each containing only one chemical species. [Copyright &y& Elsevier]

Abstract: The thermodynamic assessment is made for the Sb–Zn system using the CALPHAD approach (calculation of phase diagram). The liquid phase, the intermediate compounds of SbZn, Sb3Zn4 (three modifications of ɛ, δ and δ′) and Sb2Zn3 (two modifications of η and ξ) and the terminal phases of rhombohedral-Sb and hcp-Zn are taken into consideration in this optimization. Liquid phase is described by a substitutional solution model with Redlich–Kister polynomials. The intermediate compounds are treated as stoichiometric. Two terminal phases are taken as unary phases according to literature. A set of self-consistent thermodynamic parameters is obtained and the calculated phase diagram and thermodynamic properties are presented and compared with experimental data obtained from literature. [Copyright &y& Elsevier]

Owing to their low lattice thermal conductivity, many compounds of the n(PbTe)-m(Bi 2 Te 3 ) homologous series have been reported in the literature with thermoelectric (TE) properties that still need improvement. For this purpose, in this work, we have implemented the band engineering approach by applying biaxial tensile and compressive strains using the density functional theory (DFT) on various compounds of this series, namely Bi 2 Te 3 , PbBi 2 Te 4 , PbBi 4 Te 7 and Pb 2 Bi 2 Te 5 . All the fully relaxed Bi 2 Te 3 , PbBi 2 Te 4 , PbBi 4 Te 7 and Pb 2 Bi 2 Te 5 compounds are narrow band-gap semiconductors. When applying strains, a semiconductor-to-metal transition occurs for all the compounds. Within the range of open-gap, the electrical conductivity decreases as the compressive strain increases. We also found that compressive strains cause larger Seebeck coefficients than tensile ones, with the maximum Seebeck coefficient being located at −2%, −6%, −3% and 0% strain for p-type Bi 2 Te 3 , PbBi 2 Te 4 , PbBi 4 Te 7 and Pb 2 Bi 2 Te 5 , respectively. The use of the quantum theory of atoms in molecules (QTAIM) as a complementary tool has shown that the van der Waals interactions located between the structure slabs evolve with strains as well as the topological properties of Bi 2 Te 3 and PbBi 2 Te 4 . This study shows that the TE performance of the n(PbTe)-m(Bi 2 Te 3 ) compounds is modified under strains. [ABSTRACT FROM AUTHOR]

Due to the volume expansion effect during charge and discharge processes, the application of transition metal oxide anode materials in lithium-ion batteries is limited. Composite materials and carbon coating are often considered feasible improvement methods. In this study, three types of TiO2@Fe3O4@C microspheres with a core–double-shell structure, namely TFCS (TiO2@Fe3O4@C with 0.0119 g PVP), TFCM (TiO2@Fe3O4@C with 0.0238 g PVP), and TFCL (TiO2@Fe3O4@C with 0.0476 g PVP), were prepared using PVP (polyvinylpyrrolidone) as the carbon source through homogeneous precipitation and high-temperature carbonization methods. After 500 cycles at a current density of 2 C, the specific capacities of these three microspheres are all higher than that of TiO2@Fe2O3 with significantly improved cycling stability. Among them, TFCM exhibits the highest specific capacity of 328.3 mAh·g−1, which was attributed to the amorphous carbon layer effectively mitigating the capacity decay caused by the volume expansion of iron oxide during charge and discharge processes. Additionally, the carbon coating layer enhances the electrical conductivity of the TiO2@Fe3O4@C materials, thereby improving their rate performance. Within the range of 100 to 1600 mA·g−1, the capacity retention rates for TiO2@Fe2O3, TFCS, TFCM, and TFCL are 27.2%, 35.2%, 35.9%, and 36.9%, respectively. This study provides insights into the development of new lithium-ion battery anode materials based on Ti and Fe oxides with the abundance and environmental friendliness of iron, titanium, and carbon resources in TiO2@Fe3O4@C microsphere anode materials, making this strategy potentially applicable. [ABSTRACT FROM AUTHOR]

This study combined inorganic α-hemihydrate gypsum (α-HHG) with organic polyacrylamide (PAM) hydrogel to create a novel α-HHG/PAM composite material. Through this facile composite strategy, this fabricated material exhibited a significantly longer initial setting time and higher mechanical strength compared to α-HHG. The effects of the addition amount and the concentration of PAM precursor solution on the flowability of the α-HHG/PAM composite material slurry, initial setting time, and mechanical properties of the hardened specimens were investigated. The structural characteristics of the composite material were examined using XRD, FE-SEM, and TGA. The results showed that the initial setting time of the α-HHG/PAM composite material was 25.7 min, which is an extension of 127.43% compared to that of α-HHG. The flexural strength and compressive strength of the oven-dried specimens were 23.4 MPa and 58.6 MPa, respectively, representing increases of 34.73% and 84.86% over values for α-HHG. The XRD, FE-SEM, and TGA results all indicated that the hydration of α-HHG in the composite material was incomplete. The incompleteness is caused by the competition between the hydration process of inorganic α-HHG and the gelation process of the acrylamide molecules for water, which hinders some α-HHG from entirely reacting with water. The enhanced mechanical strength of the α-HHG/PAM composite material results from the tight interweaving and integrating of organic and inorganic networks. This study provides a concise and efficient approach to the modification research of hemihydrate gypsum. [ABSTRACT FROM AUTHOR]

The thermoelectric (TE) properties of the BaM2Ge4X6 compounds, where M = Rh and X = S, Se, Te, were investigated by computational approaches using density-functional theory and semi-classical Boltzmann theory for electronic transport. It was found that these compounds bear good TE properties, in particular BaRh2Ge4Te6, for which the figure of merit was estimated to reach 1.51 at 300 K. As this compound has not yet been proved to be stable, we also investigated BaRh2Ge4S4Te2 by assuming that replacing tellurium by sulphur could stabilize the tellurium-containing structure. It was found that the TE properties are good. The quantum theory of atoms in molecules was used to investigate the nature of the chemical interactions that prevail in these compounds. A wide variety of interactions were evidenced, from van der Waals interactions to ionic and polar-covalent ones, which could explain the good TE performance of these compounds. [ABSTRACT FROM AUTHOR]

Two-dimensional MX2 (M = Mo, W; X = S, Se, Te) homo- and heterostructures have attracted extensive attention in electronics and optoelectronics due to their unique structures and properties. In this work, the layer-dependent electronic and optical properties have been studied by varying layer thickness and stacking order. Based on the quantum theory of atoms in molecules, topological analyses on interatomic interactions of layered MX2 and WX2/MoX2, including bond degree (BD), bond length (BL), and bond angle (BA), have been detailed to probe structure-property relationships. Results show that M-X and X-X bonds are strengthened and weakened in layered MX2 compared to the counterparts in bulks. X-X and M-Se/Te are weakened at compressive strain while strengthened at tensile strain and are more responsive to the former than the latter. Discordant BD variation of individual parts of WX2/MoX2 accounts for exclusively distributed electrons and holes, yielding type-II band offsets. X-X BL correlates positively to binding energy (Eb), while X-X BA correlates negatively to lattice mismatch (lm). The resulting interlayer distance limitation evidences constraint-free lattice of vdW structure. Finally, the connection between microscopic interatomic interaction and macroscopic electromagnetic behavior has been quantified firstly by a cubic equation relating to weighted BD summation and static dielectric constant. [ABSTRACT FROM AUTHOR]

In recent years, layered chalcogenides have attracted interest for their appealing thermoelectric properties. We investigated the Ge2Sb2Te5 compound in two different stacking sequences, named stacking 1 (S1) and stacking 2 (S2), wherein the Ge and Sb atomic positions can be interchanged in the structure. The compound unit cell, comprising nine atoms, is made of two layers separated by a gap. We show, using the quantum theory of atoms in molecules, that the bonding across the layers has characteristics of transit region bonding, though with a close resemblance to closed-shell bonding. Both S1 and S2 are shown to bear a similar small gap. The full determination of their thermoelectric properties, including the Seebeck coefficient, electrical conductivity and electronic and lattice thermal conductivities, was carried out by solving the Boltzmann transport equation. We show that stacking 1 exhibits a larger Seebeck coefficient and smaller electrical conductivity than stacking 2, which is related to their small electronic gap difference, and that S1 is more suitable for thermoelectric application than S2. Moreover, under certain conditions of temperature and doping level, it could be possible to use S1-Ge2Sb2Te5 as both a p and n leg in a thermoelectric converter. Under biaxial, tensile and compressive strains, we observe that the thermoelectric properties are improved for both S1 and S2. Furthermore, the increase in the power factor of S1 in the cross-plane direction, namely perpendicular to the gap between the layers, shows that strains can counteract the electronic transport hindrance due to the gap. [ABSTRACT FROM AUTHOR]

The phase diagram of the YbTe-SnTe-Bi 2 Te 3 system was experimentally investigated by using differential thermal analysis (DTA), powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM-EDS) techniques. Four isothermal sections at 300, 800, 900 and 1000 K, the liquidus surface projection, as well as four isopleth sections were constructed from experimental results. Three different solid solubility fields based on SnTe, YbTe and Bi 2 Te 3 , respectively, were observed at 300 and 800 K. No new quaternary compound was detected in the system. The primary crystallization fields and homogeneity ranges of the phases as well as the types and coordinates of all the non- and monovariant equilibria were determined. It was also revealed that the solid solution α 2 based on YbTe is a major phase in the distribution of phase areas in the subsolidus. [ABSTRACT FROM AUTHOR]

A single crystalline layered semiconductor In1.2Ga0.8S3 phase was grown, and by intercalating p-aminopyridine (NH2-C5H4N or p-AP) molecules into this crystal, a new intercalation compound, In1.2Ga0.8S3·0.5(NH2-C5H4N), was synthesized. Further, by substituting p-AP molecules with p-ethylenediamine (NH2-CH2-CH2-NH2 or p-EDA) in this intercalation compound, another new intercalated compound—In1.2Ga0.8S3·0.5(NH2-CH2-CH2-NH2) was synthesized. It was found that the single crystallinity of the initial In1.2Ga0.8S3 samples was retained after their intercalation despite a strong deterioration in quality. The thermal peculiarities of both the intercalation and deintercalation of the title crystal were determined. Furthermore, the unit cell parameters of the intercalation compounds were determined from X-ray diffraction data (XRD). It was found that increasing the c parameter corresponded to the dimension of the intercalated molecule. In addition to the intercalation phases' experimental characterization, the lattice dynamical properties and the electronic and bonding features of the stoichiometric GaInS3 were calculated using the Density Functional Theory within the Generalized Gradient Approximations (DFT-GGA). Nine Raman-active modes were observed and identified for this compound. The electronic gap was found to be an indirect one and the topological analysis of the electron density revealed that the interlayer bonding is rather weak, thus enabling the intercalation of organic molecules. [ABSTRACT FROM AUTHOR]

In this study, lychee-like TiO2@Fe2O3 microspheres with a core-shell structure have been prepared by coating Fe2O3 on the surface of TiO2 mesoporous microspheres using the homogeneous precipitation method. The structural and micromorphological characterization of TiO2@Fe2O3 microspheres has been carried out using XRD, FE-SEM, and Raman, and the results show that hematite Fe2O3 particles (7.05% of the total mass) are uniformly coated on the surface of anatase TiO2 microspheres, and the specific surface area of this material is 14.72 m2 g−1. The electrochemical performance test results show that after 200 cycles at 0.2 C current density, the specific capacity of TiO2@Fe2O3 anode material increases by 219.3% compared with anatase TiO2, reaching 591.5 mAh g−1; after 500 cycles at 2 C current density, the discharge specific capacity of TiO2@Fe2O3 reaches 273.1 mAh g−1, and its discharge specific capacity, cycle stability, and multiplicity performance are superior to those of commercial graphite. In comparison with anatase TiO2 and hematite Fe2O3, TiO2@Fe2O3 has higher conductivity and lithium-ion diffusion rate, thereby enhancing its rate performance. The electron density of states (DOS) of TiO2@Fe2O3 shows its metallic nature by DFT calculations, revealing the essential reason for the high electronic conductivity of TiO2@Fe2O3. This study presents a novel strategy for identifying suitable anode materials for commercial lithium-ion batteries. [ABSTRACT FROM AUTHOR]

In this study, 20Li2O-60V2O5-(20 − x)B2O3-xBi2O3 (x = 5, 7.5, 10 mol%) glass materials have been prepared by the melt-quenching method, and the structure and morphology of the glass materials have been characterized by XRD, FTIR, Raman, and FE-SEM. The results show that the disordered network of the glass is mainly composed of structural motifs, such as VO4, BO3, BiO3, and BiO6. The electrochemical properties of the glass cathode material have been investigated by the galvanostatic charge-discharge method and cyclic voltammetry, and the results show that with the increases of Bi2O3 molar content, the amount of the VO4 group increases, and the network structure of the glass becomes more stable. To further enhance the electrochemical properties, glass-ceramic materials have been obtained by heat treatment, and the effect of the heat treatment temperature on the structure and electrochemical properties of the glass has been studied. The results show that the initial discharge capacity of the glass-ceramic cathode obtained by heat treatment at 280 °C at a current density of 50 mA·g−1 is 333.4 mAh·g−1. In addition, after several cycles of charging and discharging at a high current density of 1000 mA·g−1 and then 10 cycles at 50 mA·g−1, its discharge capacity remains at approximately 300 mAh·g−1 with a capacity retention rate of approximately 90.0%. The results indicate that a proper heat treatment temperature is crucial to improving the electrochemical properties of glass materials. This study provides an approach for the development of new glass cathode materials for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

This paper reports a Density Functional Theory (DFT) investigation of the electron density and optoelectronic properties of two-dimensional (2D) MX2 (M = Mo, W and X = S, Se, Te) subjected to biaxial strains. Upon strains ranging from −4% (compressive strain) to +4% (tensile strain), MX2 bilayers keep the same bandgap type but undergo a non-symmetrical evolution of bandgap energies and corresponding effective masses of charge carriers (m*). Despite a consistency regarding the electronic properties of Mo- and WX2 for a given X, the strain-induced bandgap shrinkage and m* lowering are strong enough to alter the strain-free sequence MTe2, MSe2, MS2, thus tailoring the photovoltaic properties, which are found to be direction dependent. Based on the quantum theory of atoms in molecules, the bond degree (BD) at the bond critical points was determined. Under strain, the X-X BD decreases linearly as X atomic number increases. However, the kinetic energy per electron G/ρ at the bond critical point is independent of strains with the lowest values for X = Te, which can be related to the highest polarizability evidenced from the dielectric properties. A cubic relationship between the absolute BD summation of M-X and X-X bonds and the static relative permittivity was observed. The dominant position of X-X bond participating in this cubic relationship in the absence of strain was substantially reinforced in the presence of strain, yielding the leading role of the X-X bond instead of the M-X one in the photovoltaic response of 2D MX2 material. [ABSTRACT FROM AUTHOR]

A thermodynamic assessment of the binary Ga–Ti system was performed based on the evaluation of the literature and our experimental results. Diffusion couple and alloy samples with appropriate compositions were prepared and analyzed by electron probe microanalysis and X-ray diffraction to determine the stability of intermetallic compounds. The Ga-rich part of phase diagram was checked by differential thermal analyses. The subreguler solution model was used to describe the solution phases liquid (L), b.c.c. (β), h.c.p. (α1) and f.c.c. (γ1). The compound energy model was employed to describe compounds with homogeneity ranges of Ti3Ga (α2), Ti5Ga4(ρ) and TiGa(γ2). The compounds Ti2Ga, Ti5Ga3, Ti2Ga3, TiGa2 and TiGa3 were treated as stoichiometric phases. A set of thermodynamic parameters was obtained and the calculated phase diagram was presented. [Copyright &y& Elsevier]

By combining density functional theory, quantum theory of atoms in molecules and transport properties calculations, we evaluated the thermoelectric properties of Sb-S system compounds and shed light on their relationships with electronic structures. The results show that, for Sb2S3, the large density of states (DOS) variation induces a large Seebeck coefficient. Taking into account the long-range weak bonds distribution, Sb2S3 should exhibit low lattice thermal conductivity. Therefore, Sb2S3 is promising for thermoelectric applications. The insertion of Be atoms into the Sb2S3 interstitial sites demonstrates the electrical properties and Seebeck coefficient anisotropy and sheds light on the understanding of the role of quasi-one-dimensional structure in the electron transport. The large interstitial sites existing in SbS2 are at the origin of phonons anharmonicity which counteracts the thermal transport. The introduction of Zn and Ga atoms into these interstitial sites could result in an enhancement of all the thermoelectric properties. [ABSTRACT FROM AUTHOR]

Two-dimensional MX (M = Ga, In; X = S, Se, Te) homo- and heterostructures are of interest in electronics and optoelectronics. Structural, electronic and optical properties of bulk and layered MX and GaX/InX heterostructures have been investigated comprehensively using density functional theory (DFT) calculations. Based on the quantum theory of atoms in molecules, topological analyses of bond degree (BD), bond length (BL) and bond angle (BA) have been detailed for interpreting interatomic interactions, hence the structure–property relationship. The X–X BD correlates linearly with the ratio of local potential and kinetic energy, and decreases as X goes from S to Te. For van der Waals (vdW) homo- and heterostructures of GaX and InX, a cubic relationship between microscopic interatomic interaction and macroscopic electromagnetic behavior has been established firstly relating to weighted absolute BD summation and static dielectric constant. A decisive role of vdW interaction in layer-dependent properties has been identified. The GaX/InX heterostructures have bandgaps in the range 0.23–1.49 eV, absorption coefficients over 10−5 cm−1 and maximum conversion efficiency over 27%. Under strain, discordant BD evolutions are responsible for the exclusively distributed electrons and holes in sublayers of GaX/InX. Meanwhile, the interlayer BA adjustment with lattice mismatch explains the constraint-free lattice of the vdW heterostructure. [ABSTRACT FROM AUTHOR]

The present work systematically clarifies the influence of the atomic mixing and the atomic order (i.e. atomic constituent distribution or site occupancy preference on inequivalent sites of a crystal) on the molar volume of the binary sigma phase. We calculated the molar volumes of 21 binary sigma compounds with different atomic order by using EMTO-CPA (Exact Muffin-Tin Orbitals - Coherent Potential Approximation) method. The calculation results follow a similar trend as the experimental data. Moreover, the calculated molar volumes with respect to the composition of the sigma phase in disordered states show that the sigma compounds do not comply with the linear volume-composition relationship. This is due to the influence of the atomic mixing and the deviation can be either negative or positive depending on the tendency of electron loss or gain of the two constituent elements. Additionally, we compared the molar volume difference (ΔVm = V disorder -V order ) between the hypothetically disordered and ordered states of the binary sigma compounds. The results indicate that the effect of the atomic order on the molar volume of the sigma phase depends on the size difference and the electron configurations of the two constituent elements. [ABSTRACT FROM AUTHOR]

We have calculated the enthalpy of formation and bulk modulus for 19 typical binary sigma compounds with different atomic order (i.e. atomic constituent distribution or site occupancy preference on inequivalent sites of a crystal structure) based on the experimental site occupancy as well as completely ordered and hypothetically disordered states by using the EMTO-CPA (Exact Muffin-Tin Orbitals - Coherent Potential Approximation) method. The calculation results show that at 0 K the sigma phase in ordered state bears a lower enthalpy of formation and a larger bulk modulus than the ones in less ordered state. [ABSTRACT FROM AUTHOR]

We calculated the atomic volume with respect to the atomic charge of the constituent atoms in the complete set of ordered configurations for several binary sigma systems by using first-principles calculations. The calculation results indicate that both the nearest neighbor (NN) atoms and coordination polyhedron (CP) affect the atomic volume of sigma phases. For a specific atom on a specific site, the more negative the atomic charge, the larger the atomic volume; the more the NN large atoms and the higher the CP symmetry, the larger the space to accommodate the specific atom, thus the larger the atomic volume. [ABSTRACT FROM AUTHOR]

The sigma phase can serve as a prototype of intermetallic phases when investigating the atomic order (i.e. atomic constituent distribution or site occupancy preference on inequivalent sites of a crystal structure), as the sigma phase bears a broad homogeneity range and there are numerous experimental site occupancy data available for the sigma phase. The present work brings new insights into the influencing factors of atomic order in the binary sigma phase. We calculated the atomic volumes and atomic charges of the constituent elements of 32 stoichiometric end-member compounds (i.e. the complete set of ordered configurations) of the binary sigma phase by using first-principles calculations. The calculation results show that besides the size factor and the number of valence electrons, the total number of electron shells is found as the third factor that affects the atomic order of the sigma phase. Moreover, the calculation results indicate that between the two constituent elements, the one with larger atomic size, smaller number of valence electrons or smaller total number of electron shells prefers occupying large coordination number (CN) sites (i.e. 4 f , 8 i 1 and 8 j ) and the other prefers occupying small CN sites (i.e. 2 a and 8 i 2 ). Furthermore, we dissociated the effects of individual influencing factors on atomic order of the sigma phase combining with the measured site occupancies from the literature. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D/2D g-C 3 N 4 /CeO 2 with oxygen vacancy mediated activity was fabricated. • Ce3+/Ce4+ ratio in CeO 2 was modulated through hydrogen gas treatment. • Oxygen vacancy in CeO 2 effectively promoted CH 4 yields of CO 2 reduction. • S-scheme photocatalytic mechanism of g-C 3 N 4 /CeO 2 heterojunction was proposed. CeO 2 sheets (CeO 2 -S) through hydrogen treatment (CeO 2 -S-H 2) have been coupled with carboxylated g-C 3 N 4 (C-g-C 3 N 4) to construct 2D/2D C-g-C 3 N 4 /CeO 2 -S-H 2 heterostructure. The ratio of Ce3+/Ce4+ in CeO 2 -S was increased from 28.2 % to 32.08 % in CeO 2 -S-H 2. Experimental results demonstrated the CO yields in 8 h on 60 %C-g-C 3 N 4 /CeO 2 -S-H 2 were 2.41, 6.83 and 1.72 times of that of pure C-g-C 3 N 4 , CeO 2 -S and CeO 2 -S-H 2. Meanwhile, it also exhibited the highest CH 4 yields of 11.997 μmol/g. Interestingly, CH 4 yields of CeO 2 -S-H 2 were much higher than that of CeO 2 -S, verifying oxygen vacancy introduction can effectively enhance CH 4 production. In addition, 60 %C-g-C 3 N 4 /CeO 2 -S-H 2 heterostructure demonstrated the best ciprofloxacin degradation performance. It is suggested that the synergistic effects of oxygen vacancy introduction and heterojunction construction promoted charges transfer and separation. [ABSTRACT FROM AUTHOR]

The present paper is a detailed study on the deposition of SbSe thin films by electrochemical atomic layer epitaxy (EC-ALE). The related electrochemical aspects have been deeply investigated by means of cyclic voltammetry, anodic potentiodynamic scanning, and coulometry. The UPD layer of Se was obtained by first depositing both UPD Se and a small amount of bulk Se and then stripping the redundant bulk Se in blank solutions. A 'two times rinsing' method was developed to avoid the formation of red Se during the rinsing process. The deposition parameters were determined for the first three EC-ALE cycles, and from these values, a nanofilm containing Sb and Se atoms has been obtained. By scanning electron microscopy and coulometry, it was shown that the deposit is compact and it has a stoichiometry very close to that of SbSe. The Raman spectral analyses show that the deposit is made of SbSe nanoclusters. [ABSTRACT FROM AUTHOR]

Abstract: This study reports on preliminary experiments which are required to define the experimental conditions for depositing CoSb3 thin films by the electrochemical atomic layer epitaxy (EC-ALE) method. The underpotential deposition (UPD) of cobalt and antimony on polycrystalline gold substrates has been investigated by means of cyclic voltammetry, anodic potentiodynamic scanning and coulometry. The UPD of Sb on Co-covered Au and of Co on Sb-covered Au have also been studied and compared to those obtained on bare Au substrate. The UPD potential values for both Co and Sb are reported in this paper, and owing to the flexibility of the EC-ALE equipment, new insights on the Co UPD on gold substrate are presented. This study shows that the subsequent alternate deposition of Co and Sb monolayers is feasible and thus that the EC-ALE method can be used to elaborate CoSb3 thin films. [Copyright &y& Elsevier]

Abstract: The La–Mg–Zn phase diagram is experimentally investigated at 595 K, x La > 4% and the corresponding isothermal section is partially determined. This section includes 5 substitutional solid solutions based on the binary compounds (LaMg, LaZn, LaMg3, LaMg10.3 and La2Zn17) and three ternary phase (La8(Mg,Zn)92, La3(Mg,Zn)11 and La4.27Mg2.89Zn30). The enthalpies of mixing in the ternary solid solutions are calculated at 298 K on the basis of tin solution calorimetry experiments. [Copyright &y& Elsevier]

In this study, home-made amorphous TiO2 microspheres with good mono-dispersity and large numbers of mesopores on the surface were used as substrates. The intermediate microspheres were obtained by adding Co/Ni sources with different Co/Ni molar ratios in a water bath and making them react by water bath heating. By calcining the intermediate microspheres deposited on the TiO2 ones, a core–shell structured spherical CoTiO3/NiTiO3 inorganic composite pigment was prepared. The synthesized pigments were characterized by X-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDS), laser particle size (LPS) analysis and colorimetry. The results show that when the calcination temperature is 800 °C and the Co/Ni molar ratio is 0.5:0.5, the pigments consist of a TiO2 core and outer ilmenite CoTiO3/NiTiO3 shell. Moreover, the surface of the product microspheres is smooth, and the particles are of regular sphericity with a uniform particle size of about 1.8 μm. The colorimetric analysis from the samples calcined at 800 °C shows color changes from yellow-green to dark green as the Co/Ni molar ratio increases (0.1:0.9 to 0.9:0.1). A Co/Ni molar ratio that is too high or too low results in the formation of by-products such as Co3O4 or NiO, respectively, which adhere to the product surface and affect the chromaticity of the product. This work has enabled the chromatic modulation of yellow-green inorganic pigments, providing a solution for the preparation of spherical inorganic pigments that are more suitable for industrial inkjet printing. [ABSTRACT FROM AUTHOR]

Abstract: Sequential processing of aluminum and copper followed by reactive diffusion annealing is used as a paradigm for the metalorganic chemical vapour deposition (MOCVD) of coatings containing intermetallic alloys. Dimethylethylamine alane and copper N,N′-di-isopropylacetamidinate are used as aluminum and copper precursors, respectively. Deposition is performed on steel and silica substrates at 1.33kPa and 493–513K. Different overall compositions in the entire range of the Al–Cu phase diagram are obtained by varying the relative thickness of the two elemental layers while maintaining the overall thickness of the coating close to 1μm. As-deposited films present a rough morphology attributed to the difficulty of copper to nucleate on aluminum. Post-deposition annealing is monitored by in situ X-ray diffraction, and allows smoothening the microstructure and identifying conditions leading to several Al–Cu phases. Our results establish a proof of principle following which MOCVD of metallic alloys is feasible, and are expected to extend the materials pool for numerous applications, with innovative thin film processing on, and surface properties of complex in shape parts. [Copyright &y& Elsevier]

Abstract: This work deals with the investigation of the phase formation in thin film systems corresponding to the Al10Cu10Fe phase composition. The samples were prepared by sputtering at room temperature. They were subsequently characterized using in situ resistance measurements, and in situ X-ray diffraction measurements from room temperature up to 600°C. The first reaction occurs at the Al/Cu interface. The iron starts to take part into the phase formation for temperatures higher than 400°C. At the end of the heat treatment, the sample is constituted of Al10Cu10Fe, only. This result is in agreement with the stable phase at the temperature of interest corresponding to the nominal composition of the sample. The activation energy of the phase formation of Al10Cu10Fe was determined from the in situ resistance measurements both by using simulation and Kissinger''s method. Resistivity value of the Al10Cu10Fe phase was also determined at room temperature. [Copyright &y& Elsevier]

Abstract: A thermodynamic optimization of the La–Zn system is carried out using the CALPHAD (CALculation of the PHAse Diagram) method. This new assessment takes into account the latest experimental values of enthalpies of formation reported in literature. The solution phases (liquid, bcc-La, fcc-La, dhcp-La and hcp-Zn) are modelled as substitution solutions using the Redlich–Kister equation. Nine intermediate phases are considered in this assessment, namely LaZn, LaZn2, LaZn4, LaZn5, LaZn7, La3Zn22, La2Zn17, LaZn11 and LaZn13 and are treated as stoichiometric compounds. [Copyright &y& Elsevier]

Literature results on the La-Mg binary system are critically reviewed. It is shown that most recent experimental results are not in agreement with the previously published assessments of the system. Thus, an experimental re-investigation of this phase diagram is required. Several alloys are synthesized from pure constitutive elements and characterized using X-ray diffraction, scanning electron microscopy, and differential thermal analysis. This study clarifies the phase equilibria in the La-Mg system. These results combined with the recent study of the enthalpies of formation of the intermediate compounds of this system provide a sound basis for the Calphad optimization of the system. [ABSTRACT FROM AUTHOR]

Abstract: We investigated in this work the stability of the Higher Manganese Silicides (HMS). Several alloys in the composition range 62–66at.% Si were prepared from their constitutive elements by arc-melting. The prepared alloys were then analysed by in situ X-ray diffraction measurements and Electron Probe Micro-Analyser (EPMA). The whole results allow us to suggest that whatever the composition is, only Mn27Si47 is stable for the temperatures 500°C and 800°C. At higher temperatures, the studied samples undergo two phase transformations which consecutively lead to the formation of Mn15Si26 and Mn11Si19. Mn4Si7 was never evidenced in the present work. It is shown for the first time in this work that Mn27Si47 is the only HMS stable phase at room temperature. [Copyright &y& Elsevier]

This paper reports first-principles calculations on PbBi 2 Te 2 S 2 , PbBi 2 Te 2 Se 2 and PbBi 2 Te 4 monolayers. The strain effects on their electronic and thermoelectric properties as well as on their stability have been investigated. Without strain, the PbBi 2 Te 4 monolayer exhibits highest Seebeck coefficient with a maximum value of 671 μ V/K. Under tensile strain the highest power factor are 12.38 × 10 11 Wm − 1 K − 2 s − 1 , 10.74 × 10 11 Wm − 1 K − 2 s − 1 and 6.51 × 10 11 Wm − 1 K − 2 s − 1 for PbBi 2 Te 2 S 2 , PbBi 2 Te 2 Se 2 and PbBi 2 Te 4 at 3%, 2% and 1% tensile strains, respectively. These values are 85.9%, 55.0% and 3.3% larger than those of the unstrained structures. [ABSTRACT FROM AUTHOR]

This work deals with the deposition of a Sb 2 Se 3 thin film on a Pt substrate using Electro-Chemical Atomic Layer Epitaxy (EC-ALE). We first investigated the UPD of selenium on a Pt substrate. Two routes have been evidenced to get a UPD layer of Se, either the polarization of the Pt-substrate at around 0.35 V in the Se solution or the deposition of full UPD Se together with bulk deposition of Se and dissolution of the latter one at lower potentials. The following investigation on the electrochemical behavior of antimony on selenium-covered platinum electrode by cyclic voltammetry and anodic potentiodynamic studies led us to choose the two-steps procedure for the Se deposition. After an optimization of the deposition parameters, the alternate deposition of Sb and Se elements to form the Sb 2 Se 3 compound by EC-ALE on platinum substrate has been performed. The stoichiometry of the deposited film has been evaluated by coulometry and it has been confirmed by atomic force microscopy (AFM). • The electrochemical behavior of Sb on a Se-covered Pt electrode is investigated. • The alternate deposition of Sb and Se on Pt by using EC-ALE method is performed. • The stoichiometry of the deposited film is evaluated by coulometry. • The formation of Sb 2 Se 3 compound is confirmed by atomic force microscopy (AFM). [ABSTRACT FROM AUTHOR]

The formation of the sigma phase in technologically important materials influences greatly their mechanical properties. Fundamental knowledge on the sigma phase is demanded to understand the phase stability and reasonably control its precipitation. The present work clarifies the atomic bonding characteristics of the binary sigma phase including A -Al (A = Nb, Ta) and transition metal systems (TM-TM) based on the electronic density of states (DOS) and electron localization function (ELF) calculated by using first-principles methods. We show that the atomic bonds of the binary sigma phase exhibit both metallic and covalent characters. The completely ordered A 66.7 Al 33.3 (A = Nb, Ta) sigma compounds bear higher stability than their counterparts with atomic disordering. Besides, for a TM-TM sigma compound, the constituent atom with more electron shells or less valence electrons presents stronger electronic stability. When increasing its atomic occupancy on a specific site, the atomic bonding on the site becomes stronger. • Atomic bonds of the sigma phase exhibit both metallic and covalent characters. • Ordered A 66.7 Al 33.3 (A = Nb, Ta) sigma compoundsbear higher stability than their counterparts with atomic disordering. • For a transition metal sigma system, constituent atom with more electron shells or less valence electrons bonds more strongly. [ABSTRACT FROM AUTHOR]

Platinum is the most employed electrocatalyst for the reactions taking place in energy converters, such as the oxygen reduction reaction in proton exchange membrane fuel cells, despite being a very low abundant element in the earth's crust and thus extremely expensive. The search for more active electrocatalysts with ultra-low Pt loading is thus a very active field of investigation. Here, surface-limited redox replacement (SLRR) that utilizes the monolayer-limited nature of underpotential deposition (UPD) was used to prepare ultrathin deposits of Pt, using Te as sacrificial metal. Cyclic voltammetry and anodic potentiodynamic scanning experiments have been performed to determine the optimal deposition conditions. Physicochemical and electrochemical characterization of the deposited Pt was carried out. The deposit comprises a series of contiguous Pt islands that form along the grain interfaces of the Au substrate. The electrochemical surface area (ECSA) of the Pt deposit obtained after 5 replacements, estimated to be 18 m2/g, is in agreement with the ECSA of extended surface catalysts on flat surfaces. [ABSTRACT FROM AUTHOR]