The Mössbauer effect of Fe57 was used to probe and characterize iron ions adsorbed on the interlayer surfaces of montmorillonite. Measurements were performed with Fe- and Ca-saturated mont-morillonites. At 210°K the intensity of the Fe2+ line was greatly reduced, apparently due to the melting of interlayer water. Neither the structural Fe2+ in Ca-montmorillonite nor the adsorbed Fe3+ in Fe-mont-morillonite were affected by the melting process. From the temperature dependence of the absorption intensity, the effective Debye temperature of all the iron species appears to be approximately the same (θD = 189 ± 5°K). This result allowed for an accurate determination of the population of Fe2+/Fe3+ in various samples.

Rh-rich and Ir-poor erlichmanite–laurite OsS2–RuS2 solid solutions have been discovered at placers in Haraigawa, Misato-machi, Kumamoto, Japan. Microprobe analysis was performed to identify solid solutions containing few sub-components other than Rh. Approximately 10 at.% Rh was found to be present in the solid-solution samples. Structural refinement was performed using four natural samples: Os0.32Ru0.61Rh0.07S2, Os0.49Ru0.43Rh0.08S2, Os0.58Ru0.33Rh0.08S2 and Os0.81Ru0.09Rh0.10S2. The unit-cell parameters for the solid solutions containing Rh from Haraigawa varied from 5.61826(6) to 5.63142(8) Å. The (Os, Ru, Rh)–S distances in the Os1–x–yRuxRhyS2 system were almost constant with a small variation of 0.001 Å. Conversely, the S–S distances varied significantly, with variations approaching 0.1 Å. Rh substitution of Os rather than Ru had a larger impact on the crystal structure. The atomic displacement ellipsoid of both cations and anions was almost spherical, and no elongation along the M–S and S–S bond directions was observed. The bulk Debye temperatures were estimated from the Debye–Waller factor for the sulfide site. The bulk Debye temperatures of pure OsS2 and RuS2 were 688 K and 661 K, respectively, which suggests that the melting point of erlichmanite is higher than that of laurite. The high Debye temperature of OsS2 is inconsistent with the crystallisation of laurite prior to erlichmanite from the primitive magma, which suggests that $f_{\rm S_2}$, rather than temperature, is the main cause of the known crystallisation order. The presence of several percent Rh has a significant effect on the thermal stability of OsS2 and lowers the melting point of the erlichmanite solid solution compared to that of the laurite solid solution.

The elastic constants, elastic modulus, anisotropy, Debye temperature, and sound velocity properties of Mo0.85Nb0.15B3 were investigated by first-principles calculations under pressure based on the generalized gradient approximation (GGA) proposed by Perdew–Burke-Ernzerhof (PBE). Employing the stress-strain method and the Voigt-Reuss-Hill approximations, were calculated the elastic properties of single and polycrystalline crystals; Bulk modulus (B), Young modulus (E), Poisson ratio (ν), Pugh ratio (G/B), Debye temperature and the Cauchy pressure terms. The calculated ν, Cauchy pressure, and Pugh ratio G/B values indicate that Mo0.85Nb0.15B3 shows a transition from brittle to ductile under pressure. Finally, the Density of States decreases as pressure increases.

The stability of the Ti50Pd50-xRux alloy was investigated using first-principles density functional theory within the plane-wave pseudopotential method. Firstly, the Ti50Pd50 gave equilibrium lattice parameter and lowest heats of formation in better agreement with experimental data to within 3%. The heat of formation decreases with an increase in Ru concentration, consistent with the trend of the density of states which is lowered at the Fermi level as Ru content is increased which suggests stability. It was also found that from the calculated elastic constants the structures showed positive shear modulus above 20 at. % Ru, condition of stability. Furthermore, the addition of Ru was found to strengthen the Ti50Pd50-xRux system at higher concentrations. The thermal coefficients of linear expansion for the Ti50Pd31.25Ru18. 75 are higher at low temperature, and that the TiPd-Ru system tends to expand more at low content of 18.75 at. % Ru than at higher content. Partial substitution of Pd with Ru was found more effective as a strengthening element and may enhance the martensitic transformation temperature of the Ti50Pd50 alloy.

Nb-based silicides are promising ultrahigh-temperature materials. However, the structural stability and mechanical properties of Nb-based silicides are markedly influenced by Nb3Si phase. Therefore, the improvement of the stability and mechanical properties of Nb3Si is a great challenge. To solve these key problems, in this work, we apply the first-principles calculations to investigate the influence of transition metals (TM = Mo, Re, Ta, W, Pt, and Ir) on the structural stability, mechanical, and thermodynamic properties of Nb3Si. Two possible doped sites: Nb site and Si site are considered. We find that these alloying elements not only can stabilize the Nb3Si phase but also effectively improve the mechanical properties of Nb3Si. The calculated electronic structure shows that high elastic modulus is attributed to the formation of the TM–Si bond. Importantly, these alloying elements improve the heat capacity of Nb3Si due to the vibration of TM atoms under high temperature. Therefore, our calculated results predict that alloying elements of Re and Ir are beneficial for improving the overall performances of Nb3Si.

Some time ago, we reported the synthesis of bixbyite-type V2O3, a new metastable polymorph of vanadium sesquioxide. Since, a number of investigations followed, dealing with different aspects like electronic and magnetic properties of the material, the deviation from ideal stoichiometry or the preparation of nanocrystals as oxygen storage material. However, most of the physical properties were only evaluated on a theoretical basis. Here, we report the lattice dynamics and physical properties of bixbyite-type V2O3 bulk material, which we acquired from physical property measurements and neutron diffraction experiments over a wide temperature range. Besides attributing different possible orientations of the magnetic moments for V1 and V2 to the identified antiferromagnetic (AFM) ground state with a Néel temperature of 38.1(5) K, we use a first order Grüneisen approximation to determine lattice-dependent parameters for the relatively stiff cubic lattice, and, amongst others identify the Debye temperature to be as low as 350 ± 65 K.

The present study focuses on a quantitative analysis of electrical resistivity in monovalent-doped manganites La1−xAgxMnO3 (x = 0.05 and 0.1). The electrical resistivity data in the ferromagnetic (FM) metallic phase are analyzed by considering a temperature-independent inelastic scattering of the electrons (due to domain and grain boundaries, defects, etc.) and other temperature-dependent elastic scattering mechanisms (electron–electron, electron–phonon, and electron–magnon). The Debye and Einstein temperatures are deduced from the model Hamiltonian containing potential energy contribution from the long-range Coulomb, van der Waals (vdW) interaction, and short-range repulsive interaction up to the second-neighbor ions. The electron–phonon scattering partially describes the reported FM metallic resistivity behavior with temperature for La1−xAgxMnO3 (x = 0.05 and 0.1). The T2 and T4.5 terms accounting for electron–electron and electron–magnon interactions are essential for the correct description of resistivity. The Mott–Ioffe–Regel criterion for metallic conductivity is valid, and kFl ∼ 1, εFτ ∼ 1.

The Debye temperature of wurtzite aluminum nitride (AlN) was determined by the Rietveld refinement method based on the room-temperature X-ray powder diffraction data. The refined lattice parameters are a = 3.11139(1) Å, c = 4.978 43(3) Å; the refined positional parameter for N is z = 0.384 59(33) Å; and the refined temperature factors of Al and N were 0.442(12) Å2 and 0.559(33) Å2, respectively. Using this refined temperature factor, the Debye temperature was evaluated as 971 K through the Debye approximation.

Density-functional theory (DFT) simulations are applied to obtain elastic, strength, and EOS properties of actinide metals under extreme conditions. In this presentation, we will show our recent study on temperature effects of the properties of solids of actinide metals. For example of low temperature uranium (U) solids, elastic constants are calculated directly from the DFT total energy for the ground-state phase in a wide pressure range. For higher temperature U solids, we are applying a recent scheme to calculate temperature-dependent phonon dispersions through the self-consistent ab initio lattice dynamics (SCAILD) technique. This scheme is particular important for the higher temperature phases that the elasticity cannot be analogously obtained because of its mechanical instability at lower temperatures. From these SCAILD phonon dispersions we then extract the elastic constants from the slopes approaching the Γ point. In addition, the phonon density of states of U obtained from SCAILD/DFT calculations have been used to parameterize a double Debye model for its ion-thermal free energy. We will discuss the ramification of this new Debye model on our development of multi-phase uranium EOS.

The electronic properties of ThO2 single crystals were studied using x-ray photoemission spectroscopy (XPS). The XPS results show that the Th 4f core level is in an oxidation state that is consistent with that expected for Th in ThO2. The effective Debye temperature is estimated from the temperature dependent photoemission intensities of the Th 4f core level over the temperature range of 290 to 360 K. A Debye temperature of 468±32 K has been determined.

Crystal structure of 4H-SiC was refined from room-temperature X-ray powder diffraction data using the Rietveld refinement method. The refined lattice constants were determined to be a=b=3.079 93(0) Å, c=10.082 22(2) Å, and the refined overall temperature factor B=0.383(3) Å2. Using the Debye approximation, the Debye temperature was successfully determined to be 1194.8 K.

We have studied the thermal conductivity of graphene using Callaway’s effective relax-ation time theory and by employing analytical expressions for phonon dispersion relations and vibrational density of states based on the semicontinuum model by Nihira and Iwata. It is found that consideration of the momentum conserving nature of three-phonon Normal pro-cesses is very important for explaining the magnitude as well as the temperature dependence of the experimentally measured results. At room temperature, the N-drift contribution (the correction term in Callaway’s theory) provides 94% addition to the result obtained from the single-mode relaxation time theory, clearly suggesting that the single-mode relaxation time approach is inadequate for describing the phonon conductivity of graphene.

We conducted an investigation into the thermodynamic properties of two stoichiometric CaCu3Ti4O12(CCTO) samples prepared by solid-state reaction and soft chemistry methods to probe the stability of the material relative to simpler oxide constituents (e.g., CaO, CuO, and TiO2) over a wide temperature range. Thermodynamic functions (i.e., heat capacity, formation enthalpies, entropies, and Gibbs free energies) have been measured from near absolute zero to 1100 K using calorimetric methods, including drop solution, low-temperature adiabatic relaxation, and differential scanning calorimetry. In addition, the thermodynamic characteristics of the magnetic-phase transition from the antiferromagnetic to the paramagnetic state are reported. It has been shown that CCTO is very stable relative to constituent oxides and calcium titanate at room temperature and higher, independent of the synthesis route. The enthalpic factor is dominant in the thermodynamics of CCTO, with the entropic factor having almost no effect on the stability of the compound relative to other oxide assemblages. The recommended values for the standard molar enthalpy of formation from constituent oxides and from elements at 298.15 K are −122.1 ± 4.5 and −4155.7 ± 5.2 kJ/mol−1, respectively. The mean of the third law entropy at 298.15 K is 368.4 ± 0.1 J/mol−1/K−1. Based on the thermodynamic data reported, the study confirms the possibility of CCTO decomposition in a reducing atmosphere or CO2 under conditions recently observed in experiments.

The ideal strengths of metals and alloys at finite temperatures have been studied using the statistical moment method. The tensile and shear strengths of the body-centered cubic (bcc) transition metals like Mo and W (refractory metals), and ordered FeAl (B2) and Fe3Al (DO3) alloys are calculated as a function of the temperature. The orthogonal tight-binding method is used for bcc transition elements, while the universal binding-energy relation (UBER)-type of pairwise potentials, derived from ab initio density-functional theory, is used for the FeAl and Fe3Al alloys. We discuss the temperature dependence of the tensile and shear strengths of the metals and alloys in conjunction with those of the second-order elastic constants.

Instrumented indentation is often used in the study of small-scale mechanical behavior of “soft” matters that exhibit viscoelastic behavior. A number of techniques have been used to obtain the viscoelastic properties from quasi-static or oscillatory indentations. This paper summarizes our recent findings from modeling indentation in linear viscoelastic solids. These results may help improve methods of measuring viscoelastic properties using instrumented indentation techniques.