The Grüneisen parameter and Poisson coefficient for glassy organic polymers and inorganic glasses

The Grüneisen lattice parameter has been calculated from the data on the Poisson coefficient for amorphous polymers and glasses. For glassy polymers, the thermodynamic Grüneisen parameter characterizes anharmonicity averaged over intrachain and other vibrational modes, the Grüneisen lattice parameter defines anharmonicity of interchain interactions provided by intermolecular interactions. In the case of alkali silicate glasses, the Grüneisen lattice parameter reflects the anharmonicity of vibrations of ionic sublattice that is formed by alkali-metal ions and nonbridging oxygen atoms.     

Coefficient of transverse deformation and anharmonism of lattice oscillations in quasi-isotropic solids

The dependence of the Grüneisen parameter γ _D on the anharmonism of lattice oscillations is controlled by γ₃ that appears to be a single-value function of the Poisson coefficient. In terms of γ _D -γ₃ relationship, all solids can be grouped into different structural types. Within each group, the above relationship is linear. The nature of correlation between the Grüneisen parameter and the Poisson coefficient is discussed.     

Elastic Moduli: a Tool for Understanding Chemical Bonding and Thermal Transport in Thermoelectric Materials

The elastic behavior of a material can be a powerful tool to decipher thermal transport. In thermoelectrics, measuring the elastic moduli—directly tied to sound velocity—is critical to understand trends in lattice thermal conductivity, as well as study bond anharmonicity and phase transitions, given the sensitivity of elastic moduli to the chemical bonding. In this review, we introduce the basics of elasticity and explain the origin of high-temperature lattice softening from a bonding perspective. We then review elasticity data throughout classes of thermoelectrics, and explore trends in sound velocity, anharmonicity, and thermal conductivity. We reveal how experimental sound velocities can improve the accuracy of common thermal conductivity models and present a critical discussion of Grüneisen parameter estimates from elastic moduli. Readers will be equipped with tools to leverage elasticity measurements or calculations to accurately interpret thermal transport trends.     

Anharmonicity and the elementary event of plastic deformation of amorphous polymers and glasses

The critical displacement of an excited atom (group of atoms) corresponding to the maximum in the interatomic attraction force plays an important part in the elementary event of plastic deformation of glassy solids. As a result of considerable departure of the excited kinetic unit from the equilibrium position and the nonlinearity of the interatomic interaction force, the microdeformation in the elementary event turns out to be a function of the degree of anharmonicity (Grüneisen parameter).     

The first-principle studies of the elastic,electronic, and vibrational properties of L-alanine

The calculation in the present work is conducted with the help of CRYSTAL’17 package using PBE method, including gradient approximation and taking into account van der Waals forces as well as the B3LYP hybrid functional. Crystal structure and chemical bond, elastic properties, equation of state, structural properties under pressure, and vibrational properties are studied. The elastic constants of single crystal and polycrystalline properties are obtained; anisotropic nature of the crystal is determined. The impact of hydrostatic compression up to pressure of 7.5 GPa on the L-alanine properties is studied. The effect of taking into account the forces of intermolecular interaction on the accuracy of calculation of lattice constants and intermolecular distances is shown. The atom charges and bond overlap population in molecules are determined within the framework of the Mulliken scheme. The total and partial density of states is calculated and it is established that the transition from valence band to conduction band is performed by electrons from oxygen atoms to carbon atoms of the –COO group. The average value of the tensor component of the polarizability, permittivity, and piezoelectric stress coefficients were 40.67 Å³, 2.08, and ? 4.25 pm/V, relatively. The obtained dependence of the lattice constants demonstrated occurrence of intersection within pressure interval of about 1.8 GPa, the fact that has earlier been established experimentally. It has been shown that C–C and C–N intramolecular distances reduce with pressure increase, as for the –COO group, C1–O1 distances decrease, while C1–O2 distances increase. The mode Grüneisen parameters, obtained from ab initio calculations for the first time, revealed the increase in the vibration frequency of the –NH₃ group, while other vibration frequencies decrease with increasing pressure.

     

Universal Scaling of Intrinsic Resistivity in Two‐Dimensional Metallic Borophene

Two‐dimensional boron sheets (borophenes) have been successfully synthesized in experiments and are expected to exhibit intriguing transport properties. A comprehensive first‐principles study is reported of the intrinsic electrical resistivity of emerging borophene structures. The resistivity is highly dependent on different polymorphs and electron densities of borophene. Interestingly, a universal behavior of the intrinsic resistivity is well‐described using the Bloch–Grüneisen model. In contrast to graphene and conventional metals, the intrinsic resistivity of borophenes can be easily tuned by adjusting carrier densities, while the Bloch–Grüneisen temperature is nearly fixed at 100 K. This work suggests that monolayer boron can serve as intriguing platform for realizing tunable two‐dimensional electronic devices.     

First-principles study of the crystal structure and equation of state of naphthaline and anthracene

A first — principles method of density functional theory with a gradient approximation of the exchange-correlation potential in the form of PBE implemented in the PWscf program of the Quantum ESPRESSO software using the Grimme’06 scheme is used to calculate the crystal structure of naphthaline and anthracene at a hydrostatic pressure ranging from 0 GPa to 2 GPa and from 0 GPa to 20 GPa respectively; their equations of states are analyzed. It is shown that under pressure the volume decreases due to voids, and the molecules themselves are practically not deformed. The Grüneisen parameter is calculated in the Slater-Dugdale-MacDonald-Zubarev-Vashchenko model. This parameter decreases from the equilibrium values of 2.356 (anthracene) and 3.226 (naphthaline) with an increase in the pressure. With the use of the Mie-Grüneisen equation under the additional Hugoniot-Renkin condition the impact pressure is calculated, which increases compared to the cold one at a relative compression V/V ₀, below 0.7.     

Melting temperature and anharmonicity of lattice vibrations in solids

A correlation between melting points and Grüneisen lattice constants was found for a number of glass-forming oxides. It was established that, at the melting point, the mean energy of the thermal motion of a kinetic unit equaled the ultimate strain work of the interatomic bond corresponding to the quasi-elastic force maximum.     

The thermal properties of Al–Mg–TM (TM = Sc,Zr): Ab initio study

Ab initio density functional theory (DFT) and density function perturbation theory (DFPT) have been used to investigate the thermal properties of the Al–Mg–Sc, Al–Mg–Zr and Al–Mg–Sc–Zr alloys over a wide range of temperature and pressure. Phonon dispersions are obtained at equilibrium and strained configurations by DFPT. Using the quasiharmonic approximation (QHA) for the free energy, several physical quantities of interest such as thermal Grüneisen parameter, heat capacity at constant pressure and at constant volume, thermal expansion coefficient, entropy, adiabatic bulk modulus and isothermal bulk modulus as a function of temperature and pressure are calculated and discussed. The present results show that the thermal expansion coefficient of the Al–Mg–Sc–Zr is far lower than that of Al–Mg–Sc and Al–Mg–Zr, and the variation features in the adiabatic bulk modulus and isothermal bulk modulus for the Al–Mg–Sc–Zr are also very different from that of Al–Mg–Sc and Al–Mg–Zr.     

Anharmonicity and fragility in lithium borate glasses

Since the physical properties of lithium borate glasses xLi₂O-(1-x)B₂O₃ (0<x< 0.28) vary over a wide range with the composition, this binary system is particularly suitable for studying the relationship between vibrational anharmonicity and fragility. The density, the linear expansion coefficient, the longitudinal and transverse ultrasonic velocities and their respective temperature coefficients of the velocities are measured, from which the vibrational anharmonicity in lithium borate glasses is evaluated with the help of the Grüneisen parameter at the Debye cut-off frequency and the Anderson-Grüneisen parameter: these two parameters plotted vs. composition have the same characteristics with minima at x≈0.08. The fragility is evaluated from the temperature width of the glass transition; the fragility also shows a minimum at x≈0.08. The presence of minima at x≈0.08 is ascribable to the fact that the crosslinking density between six-membered rings in the glass reaches a maximum at this composition. We show that the anharmonic parameters strongly correlate with the fragility metrics. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pressure dependence of the Grüneisen parameter of silver bromide

For the first time, the Grüneisen parameter of silver bromide is calculated as a function of pressure by using the Callaway integral technique and pressure dependence of the thermal conductivity. The values are reported up to 2.0 GPa at 130 and 292 K. Good agreement between theory and experiment is obtained in the low-pressure region where the latter data exist.     

Pressure dependence of the Grüneisen parameters of KCl,KI, LiF,NaCl, and RbBr

A new expression has been obtained, using the Callaway integral equation for thermal conductivity, which relates the pressure dependence of thermal conductivities, average phonon velocities, and average Grüneisen parameters. Using this technique for the first time, we calculated the pressure dependence of the Grüneisen parameters of KCl, KI, LiF, NaCl, and RbBr at 310 K and zero pressure.     

Anharmonicity of lattice vibrations and the fluctuation volume of amorphous substances near the glass transition temperature

The fraction of the fluctuation volume (in a model of the excited state) at the glass transition temperature depends linearly on the Gruneisen parameter, i.e., the degree of the anharmonicity of lattice vibrations in amorphous polymers and glasses.     

Thermal Expansion Behaviors of Li3AsW7O25: A Case Study for Comparative Debye Temperature for a Large Polyatomic Unit Cell

The thermal expansion behavior of Li₃AsW₇O₂₅ has been studied. The temperature‐dependent development of crystal structural parameters was obtained from Rietveld refinement using neutron time of flight powder diffraction data. Modeling of the lattice thermal expansion was carried out using a Grüneisen first‐order approximation for the zero‐pressure equation of state, where the temperature‐dependent vibrational energy was calculated taking the Debye‐Einstein‐Anharmonicity approach. Temperature‐dependent Raman spectra shed light on some selective modes with unusual anharmonicity. Debye temperatures were calculated using three different theoretical approaches, namely, thermal expansion, mean‐squared isotropic atomic displacement parameter and heat capacity. Similarities as well as discrepancies between the numerical values obtained from different theoretical approaches are discussed.     

First-principles calculations of hydrostatic pressure effects on the structural,elastic and thermodynamic properties of cubic monocarbides XC (X = Ti,V, Cr,Nb, Mo,Hf)

Six transition metal monocarbides (TiC, VC, CrC, NbC, MoC, HfC) with the rock-salt structure were chosen for a detailed comparative ab initio study of their structural, electronic, elastic, and thermodynamic properties at ambient and elevated up to 50 GPa hydrostatic pressures. Special attention was paid to the relation between the elastic and bonding properties and the number of valence electrons in each compound. Elastic anisotropy of the considered carbides was analyzed; the directions in the crystal lattice corresponding to the greatest and smallest Young's moduli values were identified. The calculated values of the elastic constants were used for further estimations of the Debye temperatures, Grüneisen parameters, specific heat capacities and linear coefficients of thermal expansion. Comparison of the calculated results with available experimental and theoretical data for TiC, VC, NbC, HfC yielded good agreement. The specific heat capacities and thermal expansion coefficients for CrC and MoC were calculated for the first time, to the best of the authors' knowledge.     

Unusual Gruneisen and Bridgman parameters of low-density amorphous ice and their implications on pressure induced amorphization

The low-temperature limiting value of the Grüneisen parameter for low-frequency phonons and the density dependence of the thermal conductivity (Bridgman parameter) of low-density amorphous (LDA) ice, high-density amorphous (HDA) ice, hexagonal ice Ih, and cubic ice Ic were calculated from high-pressure sound velocity and thermal conductivity measurements, yielding negative values for all states except HDA ice. LDA ice is the first amorphous state to exhibit a negative Bridgman parameter, and negative Grüneisen parameters are relatively unusual. Since Ih, Ic, and LDA ice all transform to HDA upon pressurization at low temperatures and share the unusual feature of negative Grüneisen parameters, this seems to be a prerequisite for pressure induced amorphization. We estimate that the Grüneisen parameter increases at the ice Ih to XI transition, and may become positive in ice XI, which indicates that proton-ordered ice XI does not amorphize like ice Ih on pressurization.     

二元Ni-Al合金极端条件下的弹性和热力学性能：全电子准谐波近似

通过在原子尺度上建模来研究Al、NiAl和Ni3Al合金在极端高温和高压下的点阵常数、弹性常数、弹性模量、泊松比和弹性各向异性因子等性质．计算得到的弹性常数均满足相应的力学稳定条件．由于NiAl和Ni3Al具有较高的B／G值,在0～30GPa内都属于延展性材料．通过包含电子热运动对体系吉布斯自由能贡献的全电子准谐近似方法,得到了高温高压下Al、NiAl和Ni3Al合金的热膨胀系数、体积模量、热容和熵等．计算值与已有的实验值和理论值符合较好．     

Thermally induced low-temperature relaxation of plastic deformation in glassy organic polymers and silicate glasses

A deep analogy between the processes of low-temperature thermally induced relaxation of plastic deformation in amorphous polymers and inorganic glasses is observed. The results of the calculation of the activation energy and activation volume of this relaxation process in terms of the excited state model satisfactorily agree with the experimental data obtained for both epoxy polymer systems and sheet silicate glasses. This evidence allows us to conclude that the initial stage of macroscopic plastic deformation in glassy systems involves small critical displacements of excited atoms (groups of atoms) that are provided by local rearrangements of neighboring particles (entropy fluctuations). In the vicinity of the yield point, the number of excited atoms per unit volume induced by the action of mechanical stresses appears to be quite sufficient (10²⁶–10²⁷ m^?3) for promotion of a marked plastic deformation of glasses and preservation of appreciable amounts of internal energy.     

On the molecular mobility in amorphous polymers, inorganic glasses, and amorphous metal alloys in the glass transition range

The transition of kinetic units (atoms or groups of atoms) in amorphous media from one quasi-equilibrium state to another is determined by fluctuations of both energy and entropy of the system. In the glass transition range of liquids and polymers, the entropic mechanism plays a determining role: the fluctuation of packing of particles turns out to be more important than accumulation of energy. Above the glass transition range, the energy mechanism begins to play a dominant role. The procedure that is currently used to calculate the constant for the Bartenev equation, which relates the relaxation time to the cooling rate at the glass transition temperature, leads to overestimated values. A procedure for the calculation of this parameter was proposed with allowance for the temperature dependence of the entropy of activation in the region of the liquid-glass transition. The use of this equation in the relaxation spectrometry of amorphous polymers, inorganic glasses, and amorphous metal alloys is discussed.     

First‐principles calculations on thermodynamic properties of BaTiO3 rhombohedral phase

The calculations based on the linear combination of atomic orbitals have been performed for the low‐temperature phase of BaTiO₃ crystal. Structural and electronic properties, as well as phonon frequencies were obtained using hybrid PBE0 exchange–correlation functional. The calculated frequencies and total energies at different volumes have been used to determine the equation of state and thermal contribution to the Helmholtz free energy within the quasiharmonic approximation. For the first time, the bulk modulus, volume thermal expansion coefficient, heat capacity, and Grüneisen parameters in BaTiO₃ rhombohedral phase have been estimated at zero pressure and temperatures form 0 to 200 K, based on the results of first‐principles calculations. Empirical equation has been proposed to reproduce the temperature dependence of the calculated quantities. The agreement between the theoretical and experimental thermodynamic properties was found to be satisfactory. © 2012 Wiley Periodicals, Inc.