Volume Thermal Expansion Coefficient Research Articles

High temperature structure and vibrational properties of ScXO4 (X= V5+ and P5+): A comparative study

ScVO4 and ScPO4 represent the zircon (xenotime) type structures with smallest trivalent cations, and that enable them to host both transition metal and rare-earth ions for applied optical materials. Thus, their crystal chemistry and thermophysical properties becomes relevance for their application in non-ambient conditions. In this report, high temperature crystal chemistry and vibrational properties of ScVO4 and ScPO4, as observed from in situ high temperature powder XRD and Raman spectroscopic studies, are reported. The comparative analyses of the results indicate that, though both are isostructural, they show drastically different thermal expansion behavior. In case of ScVO4, the c-axis shows significantly larger expansion compared to a-axis, while in ScPO4 the thermal expansion along and a and c-axes are more or less similar. At ambient condition, the thermal expansion anisotropy in ScPO4 and ScVO4 are 1.02 and 3.97, respectively. Additionally, ScPO4 shows relatively lower coefficient of volume thermal expansion compared to ScVO4, (αv = 23.64 × 10−6 K−1 for ScPO4 and 26.09 × 10−6 K−1 for ScVO4), and is contributed by the expansion of ScO8 units in their structures. The thermal expansion coefficients of ScO8 unit in ScPO4 and ScVO4 are 36.3 × 10−6 K−1 and 39.1 × 10−6 K−1, respectively. Temperature evolution of Raman modes indicates weakening of all the modes, except a symmetric stretching mode, with increasing temperature. The anharmonic analyses of the Raman modes indicate that implicit contributions in ScVO4 and ScPO4 are appreciably higher than the explicit contributions, and hence the changes in mode wavenumbers with volume play dominating role in governing their thermal expansion behaviors. Further, it is concluded that ScPO4 is characterized by more or less like rigid unit cell compared to ScVO4.

Ab initio predictions of pressure-dependent structural, elastic, and thermodynamic properties of GaMF3 (M = Ca, and Sr) halide perovskites

The structural, elastic, and thermodynamic characteristics of the GaCaF3 and GaSrF3 halide perovskites have been predicted for the first time, using ab initio pseudopotential plane wave calculations. The equilibrium lattice parameters are in good agreement with previously documented results. Both compounds exhibit substantial thermodynamic and mechanical stability. The single-crystal and polycrystalline elastic properties and related properties have been examined. GaCaF3 exhibits higher hardness than GaSrF3. The temperature dependence of the lattice parameter, bulk modulus, volume thermal expansion coefficient, heat capacity, and Debye temperature, have been computed using ab initio calculations combined with the quasi-harmonic Debye model.

Phase diagram and physical properties anisotropy of strontianite

The physical properties and anisotropy of carbonates at high pressure are fundamental to understanding the deep carbon cycle and storage. Here, we redraw the phase diagram of strontianite (SrCO3) by first-principles calculations combined with lattice dynamics and study its physical properties and anisotropy at high pressure. The results show that there are only Pnma and Pmmn phases in SrCO3 in the entire Earth's mantle, and there is no R3m phase. The SrCO3 polymorphs have a large elastic anisotropy. SrCO3 polymorphs are a kind of carbonate with high density, low wave velocity, and low wave velocity anisotropy. The linear thermal expansion coefficient of SrCO3-Pmmn was obtained for the first time by using the linear elastic compression coefficient combined with the volume thermal expansion coefficient. The results are of great significance for understanding the high-pressure behavior of Sr-carbonates.

Investigation of the anisotropic thermal expansion of PbIn6Te10 crystal by high temperature x-ray diffraction measurements

The PbIn6Te10 crystal, an IR laser frequency conversion material, grown via the Bridgman method with dimensions ϕ35 mm × 90 mm in a four-zone furnace, was subject to the investigation of its thermal expansion behavior using high-temperature x-ray diffraction in the range of 25–450 °C. Based on the obtained data, the average thermal expansion coefficients of 15.21 × 10−6 K−1 for α a and 6.44 × 10−6 K−1 for α c were determined utilizing the least square method. The study revealed that the linear and volume thermal expansion coefficients of PbIn6Te10 crystals satisfy the relationships α a > α c > 0, α V = 2α a + α c , and α a increased while α c decreased with increasing temperature, accentuating a substantial anisotropy in thermal expansion between the crystal’s principal axes. A detailed exploration pinpointed that the variations in the PbTe6 octahedron primarily governed the changes in the PbIn6Te10 unit cells, with further investigation uncovering its association with variations in the nearest neighboring bonds, which is mainly related to Pb-Te4 and Pb-Te2 bonds. Additionally, the determination of temperature-dependent anisotropic thermal expansion coefficient α was complemented by calculating Grüneisen parameter γ using Quasi-harmonic Debye model. Remarkably, these parameters also exhibited anisotropic behaviors ( γ⊥ increases with temperature whereas γ// decreases, α ⊥ > α ∥), contributing additional insights into the crystal thermal characteristics.

Search for new apatite-like phases for lead utilization based on crystal structure and thermal expansion

Apatites, being one of the most numerous mineral-like families of compounds, are considered as a matrix for binding lead ions, which is dangerous for the biosphere. The crystal-chemical (composition, structure) and thermophysical aspects (thermal expansion) are considered as the basis for analysing the properties of this kind of material. It is suggested that substances of the composition Pb5(AIVO4)2(BVIO4), Pb5(AIVO4)(CVO4)2 can be a perspective form of lead binding materials based on compounds with the structure of apatite (AIV = Si, Ge; BVI = S, Cr; CV = P). Such compounds, as it was shown by DTA and HTXRD experiments, are distinguished by the absence of polymerphism and the abnormal ordering of structure. Also, they have relatively low values of thermophysical indicators (the rate of change of linear thermal expansion coefficients is 0.02?0.03?106 K-1; values of the volume thermal expansion coefficients are 40?70?106 K-1). Compounds Pb5(SiO4)(PO4)2 (a = 9.78782(16) ?, c = 7.31084(16) ?, V = 606.555(23) ?3, R-bragg = 4.694 %) and Pb5(GeO4)(PO4)2 (a = 9.87697(12) ?, c = 7.33136(11) ?, V = 619.388(17) ?3, R-bragg = 1.730 %) were obtained, identified and crystallographically characterised for the first time.

First-principles calculations on electronic, superconducting, mechanical, and thermodynamic properties for the superhard compound Tc2C under pressure

This study presents a theoretical investigation on the electronic, superconducting, mechanical, and thermodynamic properties of the superhard compound Tc2C up to 100 GPa. The investigation is conducted via the first-principles plane-wave pseudopotential method. Furthermore, to treat the exchange-correlation potential for the total energy calculations, the revised Perdew–Burke–Ernzerhof formulation stemming from the generalized gradient approximation is employed. The results suggest that Tc2C is a potential hard compound due to the robust covalent bonding between Tc and C atoms. Moreover, the electronic structure and electron–phonon coupling reveal that Tc2C is a superconducting material with Tc of 0.59 K at 0 GPa. Additionally, using the quasi-harmonic Debye model, the variation of crucial structural parameters, such as the volume thermal expansion coefficient, heat capacity, and isothermal bulk modulus and its pressure derivatives, is predicted in terms of temperature and pressure. The results demonstrate that temperature and pressure have contrasting effects on the volume thermal expansion coefficient and heat capacity, and the effect of temperature is larger than that of pressure, especially at low temperatures. The isothermal bulk modulus decreases with increasing temperature but increases with increasing pressure. The first and second pressure derivatives of the isothermal bulk modulus for Tc2C are not the assumed constants in the equation of state study at high pressures and temperatures. To our knowledge, this study presents the first quantitative theoretical prediction of the pressure and temperature dependence of the thermodynamic parameters for Tc2C, which is essential for understanding the basic physical properties of similar transition metal carbides.

Ab initio investigation of structural, elastic, and thermodynamic characteristics of tetragonal XAgO compounds (X = Li, Na, K, Rb)

The present research utilizes ab initio computations to examine the thermodynamic, structural, and elastic characteristics of XAgO ternary oxides, where X signifies Li, Na, K, and Rb.The GGA-PBE and GGA-WC functionals were used to calculate the ground-state lattice parameters and atomic position coordinates of the title materials. The calculated results were in good agreement with both experimental measurements and theoretical predictions. This suggests that the GGA-PBE and GGA-WC functionals are accurate for describing the structural properties of the material under study.This study offers computational predictions for the elastic properties of monocrystalline structures and polycrystalline aggregates of XAgO compounds. These predictions encompass various key parameters, including single-crystal elastic constants, Young’s modulus, bulk modulus, Lame coefficients, Poisson’s ratio, shear modulus, and Debye temperature. Additionally, the quasi-harmonic Debye approximation is utilized to explore the temperature-dependent behavior of bulk modulus, Debye temperature, volume thermal expansion coefficient, and isobaric and isochoric heat capacities over an extensive temperature range, while maintaining constant pressures. The results obtained from this model are found to be highly successful in accurately predicting the behavior of these properties.

First-principles calculation of Fe-Mo-Cr alloys based on special quasi-random structure

Mo element has an important effect on ferritic stainless steel. It is of great significance to study the role of the Mo element in the composition design of stainless steel alloys. In this paper, the formation energy, magnetic moment, electronic structure, mechanical and high-temperature mechanical properties of Fe-Mo binary alloys and Fe-Mo-Cr ternary alloys were obtained by density functional theory of first principles. The results showed that the formation energy increases gradually with the increase of Mo content. The alloys have a stable system when the Mo concentration is less than 3.125%. The addition of Cr increases the formation energy, but when Mo content is 3.125%, the formation energy is lower than that of Fe-Mo binary alloys. Fe atoms are ferromagnetic state and Mo atoms are anti-ferromagnetic state, there is an opposite magnetic effect between them. With the increase of Mo concentration, Mo atoms change from anti-ferromagnetic to paramagnetic. Mo atoms become paramagnetic when Mo concentration reaches 100%. Mo element has little effect on the shear modulus of the alloys. The hardness and compressive strength decrease with increasing Mo concentration. The addition of Cr atom also reduces the hardness. Fe-Mo alloys have better thermal stability when Mo concentration is 12.5%. The Cr atom significantly changes the thermodynamic properties of the alloys. The volume thermal expansion coefficient of Fe-Mo-Cr ternary alloys decreases with the increase of Mo concentration, and the highest temperature appears near the Mo concentration of 12.5∼18.75%.

Effects of pressure and temperature on topological electronic materials X2Y3 (X = As, Sb, Bi; Y = Se, Te) using first-principles.

We systematically study the thermal and topological properties of X2Y3 (X = As, Sb, Bi; Y = Se, Te) and the effects of pressure and temperature on their electronic properties using first-principles. We find that the external pressure-induced electronic topological transition occurs at about 5 GPa for Bi2Se3, and the type of band gap tends to become indirect with the increase of pressure. We also investigate the lattice expansion with temperature in quasi-harmonic approximation and further explore the effect of temperature on the volume, band gap, and volumetric thermal expansion coefficient of the studied selenides and tellurides. Finally, we calculate the evolution of the Wannier charge center of X2Y3 to determine their topological invariants, and theoretically suggest that Bi2Se3 changes from a topological to an ordinary insulator when the pressure decreases to -8 GPa; As2Se3 is found to be an ordinary insulator, while all other four compounds are always strong topological insulators at any pressure or temperature.

Cohesive and Thermal Properties of Sodium Cyanide-Halide Mixed Crystals

In order to analyse the cohesive and thermal properties of sodium cyanide-halide mixed crystals an Extended Three Body Force Shell Model (ETSM) has been applied by incorporating the effect of translational-rotational (TR) coupling. We have conducted theoretical research on cohesive and thermal properties, such as cohesive energy (, molecular force constant (f), compressibility (), Restrahlen frequency (, Debye temperature (D), Gruneisen parameter (), Moelwyn Hughes constants (F1) and the ratio of volume thermal expansion coefficient (v) to volume specific heat (Cv), as a function of temperature within the temperature range 50K T 300K at concentration x=0, 0.27, 0.58 and 1. The current model computations and the findings of the available experiments are in good agreement. The ETSM is a sufficiently realistic model and may be applied to a variety of other mixed crystals in this family.

Ab initio study of pressure dependence of the structural, elastic and thermodynamic properties of AlXY3 (X = B, C)

ABSTRACT We have investigated the pressure dependence of the structural, elastic and thermodynamic properties of the ternary AlXY3 (X = B, C) compounds through the ab initio pseudopotential plane wave method within the general gradient approximation developed especially for solids. The optimized lattice parameters are in good agreement with the available experimental and theoretical counterparts. Analysis of the monocrystalline elastic constants predicted through the strain–stress technique shows that the studied materials are mechanically stable with strong elastic anisotropy. The calculated polycrystalline moduli highlight that the title compounds exhibit a moderate resistant to external deformations, AlBC3 is in the border between ductility and brittleness and AlCY3 is brittle. The quasi-harmonic Debye model was used to explore the temperature and pressure dependencies of the lattice parameter, bulk modulus, isochore and isobar heat capacities, volume thermal expansion coefficient and Debye temperature.

Physical properties of BaRu2X2 (X = P, As) superconducting compound sunder pressure effects: Ab initio study

We report the results of a detailed ab initio investigation of the pressure effects up to 18 GPa on the structural, elastic and thermodynamic properties of the superconducting compounds BaRu2P2 and BaRu2As2. The exchange-correlation effects were modeled through the PBEsol version of the generalized gradient approximation. The calculated equilibrium lattice parameters are in good agreement with the available experimental counterparts. The lattice parameter c decreases with increasing pressure faster than the lattice parameter a. The computed single-crystal elastic constants (Cij) show that both BaRu2P2 and BaRu2As2 are mechanically stable under pressure effect up to 18 GPa. Pressure dependence of the single-crystal and polycrystalline elastic moduli, and related physical parameters, namely Cij, Young's modulus, shear modulus, bulk modulus, Poisson's ratio, average sound velocity, Debye temperature (θD), minimum thermal conductivity (Kmin), melting temperature (Tm) and Vickers hardness (HV), were successfully calculated for the pressure range 0-18 GPa. The quasi-harmonic Debye model was successfully used to explore the temperature and pressure dependencies of the unit cell volume, bulk modulus, isochoric and isobar heat capacities, volume thermal expansion coefficient and Debye temperature. The good agreement between the results obtained using the quasi-harmonic Debye model and those corresponding deduced from the elastic constants constitutes proof of the reliability of the results obtained.

Phase stability, mechanical, and thermal properties of high‐entropy transition and rare‐earth metal diborides from first‐principles calculations

AbstractThe narrow composition design space of high‐entropy transition metal diborides (HE TMB2) limits their further development. In this study we designed six quaternary and quinary high‐entropy transition metal and rare‐earth diborides (HE TMREB2) and investigated their phase stability using the energy distribution of the local mixing enthalpy of all possible configurations. The results show that both quaternary and quinary HE TMREB2 have higher enthalpic driving forces, which facilitates the formation of single‐phase AlB2‐type structures between TMB2 and REB2. Calculations of elastic constants show that the TMB2 component has the greatest effect on the c44 elastic constant and shear modulus G, while REB2 significantly influences the bulk modulus B. Furthermore, LuB2 and TmB2 substantially affect the elastic modulus anisotropy of HE TMB2. Rare‐earth atoms in HE TMREB2 can enhance the nonharmonic interactions between phonons, which results in a significant hindrance in the thermal transport of low‐frequency phonons as well as an increase in the volume thermal expansion coefficients. Thus, the incorporation of REB2 into HE TMB2 has a significant impact on the phase stability and properties.

Anharmonic phonon scattering study in MnPS3 crystal by Raman spectroscopy

Phonons play a vital role in lattice dynamics, so a better understanding of anharmonic phonon scattering in van der Waals material MnPS3 is of great significance for its potential applications. Here, we employed Raman spectrum, in situ x-ray diffraction, and first-principles calculations for detailed research. The volume thermal expansion coefficient of MnPS3 was reported. Through the symmetric phonon scattering model, it is confirmed that cubic phonon processes play a major role in P2, P3, P4, and P5 peaks, while quartic phonon processes play an indispensable role in most peaks. The covalent bond was found to be more susceptible to anharmonic phonon scattering than ionic bonds, which is reflected in the wavenumber redshift. Moreover, asymmetric phonon scattering channels also play a meaningful role. Different cubic phonon scattering channels greatly influence the fitting results, and various quartic phonon scattering channels are diverse in highly nonlinear linewidth broadening.

Low-temperature thermal expansion of the topological material candidates [formula omitted]-PtBi[formula omitted] and [formula omitted]-PdBi[formula omitted

We report on the low-temperature (T< 120 K) thermal expansion of the bismuth-based topological semimetal β-PtBi2 and topological superconductor β-PdBi2 candidates. The linear thermal-expansion coefficient of tetragonal β-PdBi2 shows a pronounced anisotropy between the a- and c-axis while the volume thermal-expansion coefficient αV (β-PdBi2) is considerable larger than αV (β-PtBi2). The coefficient αV (β-PtBi2) nearly matches the experimental specific heat, from which a Debye temperature θD=199 K is obtained. On the other hand, αV (β-PdBi2) reasonably fits the Debye model with θD=138 K, extracted from the low-temperature specific heat. An almost constant Grüneisen parameter Γ≈ 2 is obtained for both compounds. No magnetostriction is observed in any of both compounds up to μ0H=16 T. We compare our results with other Bi-based topological materials.

Ab initio study of the pressure dependence of mechanical and thermodynamic properties of GeB2O4 (B = Mg, Zn and Cd) spinel crystals

Ab initio full-potential (linearized) augmented plane-wave plus local orbitals (FP-(L)APW + lo) calculations are performed to study the hydrostatic pressure dependence of the mechanical and thermodynamics properties of GeMg2O4, GeZn2O4, and GeCd2O4 cubic spinels. The calculated equilibrium structural parameters using both the local density approximation and the generalized gradient approximation are well consistent with the available theoretical and experimental data in the literature. The monocrystalline elastic constants are predictet using the energy-strain scheme. The polycrystalline elastic moduli are determined from the monocrystalline elastic constants through the Voigt-Reuss-Hill approximations. To understand the mechanical behavior of the investigated compounds, assessments of their mechanical stability, ductility/brittleness, sound velocities, elastic anisotropy, pressure-dependent elastic constants, and Debye temperature are made. Regarding thermodynamic properties, temperature dependence of the lattice parameter, bulk modulus, isochoric and isobaric heat capacities, volume thermal expansion coefficient, and Debye temperature at different fixed pressures are explored through the quasi-harmonic Debye model coupled with the FP-(L)APW + lo approach.

High-Temperature Behavior, Oxygen Transport Properties, and Electrochemical Performance of Cu-Substituted Nd1.6Ca0.4NiO4+δ Electrode Materials

In this study, Nd1.6Ca0.4Ni1−yCuyO4+δ-based electrode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) are investigated. Materials of the series (y = 0–0.4) are obtained by pyrolysis of glycerol-nitrate compositions. The study of crystal structure and high-temperature stability in air and under low oxygen partial pressure atmospheres are performed using high-resolution neutron and in situ X-ray powder diffraction. All the samples under the study assume a structure with Bmab sp.gr. below 350 °C and with I4/mmm sp.gr. above 500 °C. A transition in the volume thermal expansion coefficient values from 7.8–9.3 to 9.1–12.0 × 10−6, K−1 is observed at approximately 400 °C in air and 500 °C in helium.The oxygen self-diffusion coefficient values, obtained using isotope exchange, monotonically decrease with the Cu content increasing, while concentration dependence of the charge carriers goes through the maximum at x = 0.2. The Nd1.6Ca0.4Ni0.8Cu0.2O4+δ electrode materialdemonstrates chemical compatibility and superior electrochemical performance in the symmetrical cells with Ce0.8Sm0.2O1.9, BaCe0.8Sm0.2O3−δ, BaCe0.8Gd0.19Cu0.1O3−δ and BaCe0.5Zr0.3Y0.1Yb0.1O3−δ solid electrolytes, potentially for application in IT-SOFCs.

Pressure dependence of the electronic, optical, thermoelectric, thermodynamic properties of CsVO3: first-principles study

ABSTRACT We have studied hydrostatic pressure dependence of the electronic, optical, thermodynamic and thermoelectric properties of CsVO3 via first principles calculations. In addition, temperature dependence of the thermoelectric and thermal parameters was investigated. The calculated equilibrium structural parameters are in excellent agreement with the available experimental counterparts. The calculated phonon-band dispersion curve confirms the dynamic stability of CsVO3 compound in its ground-state. Analysis of the energy band dispersion calculated within the TB-mBJ potential reveals that CsVO3 is a direct bandgap semiconductor with a fundamental bandgap of 3.14 eV. It is found that the bandgap increases with increasing pressure. Analysis of the DOS diagrams and charge density topology shows that the V-O bond is partially covalent and the Cs-O bond is predominantly ionic in nature. Frequency-dependent linear macroscopic optical coefficients, namely absorption coefficient, refractive index, extinction coefficient, reflectivity and optical conductivity, were deduced from the calculated real and imaginary parts of the complex dielectric function under hydrostatic pressure effect. The semi-classic Boltzmann transport theory was used to explore pressure and temperature dependencies of the thermoelectric properties. Pressure and temperature dependencies of the thermal parameters, viz., isochore and isobar heat capacities, lattice thermal conductivity, volume thermal expansion coefficient and Debye temperature, were explored through the quasi-harmonic Debye model.

Thermal Expansion in a diluted Ce system La1–x Ce x Cu6

The thermal expansion of a diluted Ce system La1-x Ce x Cu6 for (0.6 ≤ x ≤ 1) has been measured between 10 and 150 K to reveal the change from the coherent heavy Fermion state (0.9 ≤ x ≤ 1) to the incoherent Kondo state (0 < x ≤ 0.73). The large Ce concentration x dependence of the linear thermal expansion coefficient along b-axis αb (T) suggests that the coupling between the 4f 1 electron and the lattice strain is the largest along the b-axis in the three crystallographic axes. The maximum of the magnetic contribution to the volume thermal expansion coefficient β m(T) at T = 50 K is retained in the x range of 0.6 ≤ x ≤ 1, suggesting the crystalline electric field (CEF) level for x = 1 doesn’t change by the substitution. Furthermore, the upturn in β m(T) below 25 K, which should be a precursor of the maximum at T = 2.5 K reported for x = 1, is retained when we decrease x from 1 to 0.6. Because the ground state for x = 0.6 is the incoherent Kondo state, the robustness of the maximum at T = 50 K and upturn in the current x value implies that β m(T) in 10 ≤ T ≤ 150 K is attributed to the CEF and Kondo effects rather than the formation of the heavy Fermion state.

Thermal Properties of Solids Under Varying Conditions of Pressure and Temperature

A simple theoretical method is developed to study the properties of solids under varying conditions of pressure and temperature. We have considered different types of materials viz. metallic, hydrides, sulphides and coesites. Unit cell volume, coefficient of volume thermal expansion and bulk modulus have been investigated under varying conditions of pressures and temperatures. The results obtained are compared with the available experimental data. A good agreement between theory and experiment demonstrates the suitability of the model used. It is realized that due to simplicity and applicability, it may be used to a large number of materials and may be of current interest to the researchers working in thehigh pressure and temperature science.