Effect of A-site cation radius on thermodynamic properties of ARuO3 (A = Ca, Sr, and Ba)

The thermodynamic properties of alkaline earth ruthenate ARuO₃ (A?=?Ca, Sr, and Ba) perovskites have been investigated for the first time by means of a modified rigid ion model at temperature 1 K?≤?T?≤?300 K. As strong electron–phonon interactions are present in these compounds, the lattice contribution to the specific heat deserves proper attention. The values of specific heat calculated by us have shown remarkably good agreement with corresponding experimental data. We have found that in ARuO₃ (A?=?Ca, Sr, and Ba) ruthenate family, Debye temperature increases inversely with the ionic radius of the alkaline earth A cations. In addition, the results on the temperature dependence of thermal expansion coefficient (α), cohesive energy (?), molecular force constant (f), Reststrahlen frequency (υ), Debye temperature (θ _D), and Grüneisen parameter (γ) are also reported.     

高压下TiAl3结构及热动力学性质的第一性原理研究

采用平面波赝势密度泛函理论研究了钛铝系金属间化合物TiAl₃的结构性质, 计算值与实验值及其他理论值相符合. 通过准谐德拜模型研究了TiAl₃的热动力学性质, 计算得到了相对体积(V/V₀)与压强和温度的关系, 以及不同温度和压强下的热膨胀系数和热容. 与TiAl的计算结果进行对比, 发现随着温度的升高, TiAl的热膨胀系数增大的速度高于TiAl₃, 且随着压强的增大温度效应减弱; TiAl₃的热容值近似为TiAl的热容值的2倍. 关键词： 结构性质 热动力学性质 第一性原理 高压     

Elastic and thermodynamic properties of AVO3 (A=Sr, Pb) perovskites

We have investigated the elastic and thermodynamic properties for the perovskite type metavanadate SrVO₃ and the multiferroic PbVO₃, probably for the first time by the means of a Modified Rigid Ion Model (MRIM). We present the elastic constants (C_11,C_12,C₄₄) and other elastic properties like Bulk modulus (B), Young′s modulus (E), shear modulus (G), Poisson′s ratio (σ) and wave velocity (υ_l, υ_s, υ_m). Besides we have reported the thermodynamic properties molecular force constant (f), Reststrahlen frequency (ν), cohesive energy (?), Debye temperature (θ_D) and Gruneisen parameter (γ). We have also computed the variation of heat capacity (C_P) and there by volume thermal expansion coefficient (α) in a wide temperature range. We found that the computed properties reproduce well with the available data in literature. To our knowledge some of the properties are reported for the first time.     

Influence of temperature and composition on cohesive and thermal properties of mixed crystal manganites

We have investigated the influence of temperature and composition on cohesive and thermal properties of the doped manganites: Eu_1−xY_xMnO₃ (0.0≤x≤1.0) by using a modified rigid ion model (MRIM). Theoretically, MRIM provides arguably the most realistic interaction potential to treat these properties. We have also computed the specific heat variations with temperatures for these manganites. The computed results obtained from MRIM have presented proper interpretation of the experimental data on Eu_1−xY_xMnO₃.     

Effect of heavy cation doping on thermal properties of LaMnO3

Effect of heavy cation doping (Ca²⁺ at the A-site) on the thermal properties of perovskite LaMnO₃ has been investigated using the Rigid Ion Model (RIM)). As strong electron-phonon interactions are present in these compounds, the lattice part of the specific heat deserves proper attention. The specific heat of magnetoresistance compound La_0.25Ca_0.75MnO₃ as a function of temperature (10 K ≤ T ≤ 300 K) is reported. Our results on specific heat are in good agreement with the measured values of specific heat at lower temperatures. In addition, the results on the cohesive energy (ϕ), molecular force constant (f), Restrahalen frequency (ν ₀), Debye temperature (Θ _D) and Gruneisen parameter (γ) are also discussed.      

Elastic and thermal properties of Sr1−xYxCoO3

The elastic and thermal properties of Sr_1?xY_xCoO₃ (0 ≤ x ≤ 0.5) have been investigated, probably for the first time, by using modified rigid ion model. We present the elastic constants (C_11, C_12, C₄₄) and other elastic properties like bulk modulus (B), Young's modulus (Y), shear modulus (G), Poisson's ratio (σ), Lame's parameter (μ, λ), transverse, longitudinal and average wave velocity (υ_t, υ_l and υ_m) and anisotropy parameter (A). Besides, we have reported the thermodynamic properties molecular force constant (f), Reststrahlen frequency (υ), cohesive energy (φ), Debye temperature (θ_D) and Gruneisen parameter (γ). We have also computed the variation of specific heat (C) and volume thermal expansion coefficient (α). The computed results on the elastic and thermodynamic properties are the first report on them. This model is capable of explaining the Cauchy's discrepancy, elastic and thermal properties successfully.     

Influence of temperature on thermal properties of (Sm,Eu) VO3

The bulk modulus and thermal properties of orthovanadates SmVO₃ and EuVO₃ in the temperature range 5 K≤T≤300 K have been investigated using the Modified Rigid Ion Model (MRIM) by incorporating the effect of lattice distortions. The results on the specific heat, cohesive energy, molecular force constant, the reststrahlen frequency and the Gruneisen parameter following the temperature driven structural phase transitions are presented. Our results are in fair agreement with the available experimental data. The specific heat results can further be improved by including the spin and orbital ordering contributions to the specific heat.     

高压下TiC的弹性、电子结构及热力学性质的第一性原理计算

利用基于密度泛函理论的第一性原理平面波赝势方法 并结合准谐徳拜模型研究了NaCl结构的TiC在高压下的弹性性质、电子结构和热力学性质. 计算所得零温零压下的晶格常数、体弹模量及弹性常数与实验值符合得很好. 零温下弹性常数和弹性模量随压强增大而增大. 通过态密度和电荷密度的分析, Ti-C键随压强增大而增强. 运用准谐德拜模型, 成功计算了TiC在高温高压下的体弹模量、熵、热膨胀系数、徳拜温度、 Grüneisen参数和比热容. 结果表明压强对体弹模量、热膨胀系数和徳拜温度的影响大于温度对其的影响. 热容随着压强升高而减小, 在高温高压下, 热容接近Dulong-Petit极限.     

First-principles calculation of elastic and thermodynamic properties of Ni2MnGa Heusler alloy

The equilibrium lattice parameter, heat capacity, thermal expansion coefficient and bulk modulus of Ni 2 MnGa Heusler alloy are successfully obtained using the first-principles plane-wave pseudopotential (PW-PP) method as well as the quasi-harmonic Debye model. We analyse the relationship between bulk modulus B and temperature T up to 800 K and obtain the relationship between bulk modulus B and pressure at different temperatures. It is found that the bulk modulus B increases monotonically with increasing pressure and decreases with increasing temperature. The pressure dependence of heat capacity C v and thermal expansion α at various temperatures are also analysed. Finally, the Debye temperature of Ni 2 MnGa is determined from the non-equilibrium Gibbs function. Our calculated results are in excellent agreement with the experimental data.     

Thermodynamic properties of cubic ZrC under high pressure from first-principles calculations

The elastic and thermodynamic properties of Zirconium carbide (ZrC) are investigated by ab initio plane-wave pseudopotential density function theory method. The obtained lattice constant, elastic constant and bulk modulus B are consistent with the experimental and theoretical data. Through the quasi-harmonic Debye model, the dependences of the normalized volume V/V ₀ and the bulk modulus B on pressure P, as well as the specific heat C _V on the temperature T are obtained successfully. The relationships of the thermal expansion α with temperature and pressure are also investigated, which indicate the temperature hardly has any effect on the thermal expansion α at high pressure. Supported by the National Natural Science Foundation of China (Grant No. 10776022)     

Cu_3N弹性和热力学性质的第一性原理研究

利用基于密度泛函理论的第一性原理全势线性缀加平面波方法,研究了立方反ReO3结构Cu3N在零温(0K)零压下的平衡晶格常数、体弹模量及其对压强的一阶导数,计算结果与其他实验及理论结果基本相符.同时得出Cu3N的弹性常数,Poisson比等,并分析出Cu3N在零温零压下是稳定的.通过准谐Debye模型计算Cu3N的热力学性质,得到了Cu3N的晶格常数、等压比热容、等容比热容、热胀系数与温度和压强之间的关系,同时计算出不同温度不同压强下其体弹模量及Debye温度的值。     

First-Principles Investigation of Mechanical and Thermodynamic Properties of Nickel Silicides at Finite Temperature

First-principles calculations are performed to investigate lattice parameters, elastic constants and 3D directional Young’s modulus E of nickel silicides (i.e., β-Ni₃Si, δ-Ni₂Si, θ-Ni₂Si, ε-NiSi, and θ-Ni₂Si), and thermodynamic properties, such as the Debye temperature, heat capacity, volumetric thermal expansion coefficient, at finite temperature are also explored in combination with the quasi-harmonic Debye model. The calculated results are in a good agreement with available experimental and theoretical values. The five compounds demonstrate elastic anisotropy. The dependence on the direction of stiffness is the greatest for δ-Ni₂Si and θ-Ni₂Si, when the stress is applied, while that for β-Ni₃Si is minimal. The bulk modulus B reduces with increasing temperature, implying that the resistance to volume deformation will weaken with temperature, and the capacity gradually descend for the compound sequence of β-Ni₃Si > δ-Ni₂Si > θ-Ni₂Si > ε-NiSi > θ-Ni₂Si. The temperature dependence of the Debye temperature ΘD is related to the change of lattice parameters, and ΘD gradually decreases for the compound sequence of ε-NiSi > β-Ni₃Si > δ-Ni₂Si > θ-Ni₂Si > θ-Ni₂Si. The volumetric thermal expansion coefficient αV, isochoric heat capacity and isobaric heat capacity C _p of nickel silicides are proportional to T³ at low temperature, subsequently, αV and C _p show modest linear change at high temperature, whereas C_v obeys the Dulong-Petit limit. In addition, β-Ni₃Si has the largest capability to store or release heat at high temperature. From the perspective of solid state physics, the thermodynamic properties at finite temperature can be used to guide further experimental works and design of novel nickel–silicon alloys.

     

Specific heat and thermal conductivity of superionic conductors in the superionic phase

The temperature dependences of the specific heat and the thermal conductivity of crystalline superionic conductors LnF₃ (Ln = La, Ce, Pr), Li₂B₄O₇ and α-LiIO₃ in the superionic phase have been investigated experimentally. The specific heat C _p and the thermal conductivity K are observed to increase monotonically over a wide range of temperatures above the Debye temperature Θ_D. This increase is attributed to the relaxational interaction of high-frequency phonons with two-level systems. Fiz. Tverd. Tela (St. Petersburg) 39, 1548–1553 (September 1997)     

Phase stability,mechanical and thermodynamic properties of orthorhombic and trigonal MgSiN2: an ab initio study

Structural stability and mechanical and thermodynamic properties of the orthorhombic and trigonal MgSiN₂ polymorphs (or-MgSiN₂ and tr-MgSiN₂) were investigated through density functional theory and quasi-harmonic Debye model (QHDM). Our calculations show that or-MgSiN₂ is energetically the stable polymorph at low pressure, in agreement with previous experimental and theoretical study. Under pressure, a crystallographic transition from the orthorhombic structure to the trigonal one occurs around 25, 17.45 and 19.05 GPa as obtained from the generalized gradient approximation of Perdew-Wang (GGA-PW91), the generalized gradient approximation parameterized recently by Perdew et al (GGA-PBEsol) and the local density approximation developed by Ceperley and Alder and parameterized by Perdew and Zunger (LDA-CAPZ), respectively. Single-crystalline and polycrystalline elastic constants and related properties, namely Vickers hardness, acoustic Grüneisen parameter, minimum thermal conductivity, isotropic sound velocities and Debye temperature, were numerically estimated for both or-MgSiN₂ and tr-MgSiN₂. We have showed that the hardness of tr-MgSiN₂ is comparable to that of the harder materials like c-BN and B₆O. Temperature and pressure dependencies of volume, bulk modulus, thermal expansion, Grüneisen parameter, heat capacities and Debye temperature were investigated using QHDM.     

A comparative photoluminescence study on Mn-Free GaAs/AlAs and Mn-containing Ga1-xMnxAs/AlAs quantum wells (QWs) grown on various orientations by MBE

Optical properties of diluted magnetic semiconductor Ga_0.999Mn_0.001As/AlAs quantum well structures grown on (1?0?0?), (1?1?0), (3?1?1)B and (4?1?1)B by molecular beam epitaxy are reported. Temperature-dependent spectral photoluminescence (PL) measurement was performed at temperatures between 15 and 300 K. The PL measurements showed that band gap of the alloy decreases with increasing lattice temperature regardless the growth orientations. S-shaped temperature dependence has been observed in the samples grown on (1?0?0), (3?1?1)B, (4?1?1)B orientations. PL emission energy is fitted with Varshni and Bose–Einstein Approximation to determine Debye temperature (β), (Θ_E) and thermal expansion coefficient (α), the exciton–phonon coupling strength (a_B).     

Thermodynamic properties of OsB under high temperature and high pressure

The energy-volume curves of OsB have been obtained using the first-principles plane-wave ultrasoft-pseudopotential density functional theory (DFT) within the generalized gradient approximation (GGA) and local density approximation (LDA). Using the quasi-harmonic Debye model we first analyze the specific heat, the coefficients of thermal expansion as well as the thermodynamic Grüneisen parameter of OsB in a wide temperature range at high pressure. At temperature 300 K, the coefficients of thermal expansion α_V by LDA and GGA calculations are 1.67×10⁻⁵ 1/K and 2.01×10⁻⁵ 1/K, respectively. The specific heat of OsB at constant pressure (volume) is also calculated. Meanwhile, we find that the Debye temperature of OsB increases monotonically with increasing pressure. The present study leads to a better understanding of how the OsB materials respond to pressure and temperature.     

Structural,elastic, thermodynamic and electronic properties of LuX (X = N,Bi and Sb) compounds: first principles calculations

ABSTRACT

The structural, electronic, elastic and thermodynamic properties of LuX (X = N, Bi and Sb) based on rare earth into phases, Rocksalt (B1) and CsCl (B2) have been investigated using full-potential linearized muffin-tin orbital method (FP-LMTO) within density functional theory. Local density approximation (LDA) for exchange-correlation potential and local spin density approximation (LSDA) are employed. The structural parameters as lattice parameters a₀, bulk modulus B, its pressure derivate B’ and cut-off energy (E_c) within LDA and LSDA are presented. The elastic constants were derived from the stress–strain relation at 0 K. The thermodynamic properties for LuX using the quasi-harmonic Debye model are studied. The temperature and pressure variation of volume, bulk modulus, thermal expansion coefficient, heat capacities, Debye temperature and Gibbs free energy at different pressures (0–50 GPa) and temperatures (0–1600 K) are predicted. The calculated results are in accordance with other data.     

First-principles calculations of elasticity and thermodynamic properties of LaNi5 crystal under pressure

This paper investigates the equilibrium lattice parameters, heat capacity, thermal expansion coefficient, bulk modulus and its pressure derivative of LaNi 5 crystal by using the first-principles plane-wave pseudopotential method in the GGA-PBE generalized gradient approximation as well as the quasi-harmonic Debye model. The dependences of bulk modulus on temperature and on pressure are investigated. For the first time it analyses the relationships between bulk modulus B and temperature T up to 1000 K, the relationship between bulk modulus B and pressure at different temperatures are worked out. The pressure dependences of heat capacity C v and thermal expansion α at various temperatures are also analysed. Finally, the Debye temperatures of LaNi 5 at different pressures are successfully obtained. The calculated results are in excellent agreement with the experimental data.     

Low temperature thermal properties of mixed crystal KBrKI

The low temperature specific heat and thermal conductivity of KBr_0.53I_0.47 mixed crystal are measured. This material is known to have compositional fluctuations on a scale of order 1000 Å. The thermal properties, however, are well described by the Debye model and show no indication of glass-like thermal behavior.