Pressure Dependence Of Elastic Properties Research Articles

Electronic, magnetic, half-Metallic, pressure-induced elastic and curie temperature predictions of Zr2RhTl Heusler alloy: DFT and EFT studies

ABSTRACT The DFT method investigated the total and partial magnetic moments, half-metallic characters, and pressure-dependent elastic properties of Zr2RhTl alloy. According to the ground state properties, the FM phase is more stable in energy than the AFM and NM phases. The Curie temperature value was obtained as 897.43 K with the help of the energy differences of the AFM and FM phases. The total magnetic moment of Zr2RhTl alloy was obtained as 2.00 µB/f.u. Partial magnetic moment values were obtained as 0.810, 0.506, 0.032, and 0.009 µB for Zr1, Zr2, Rh, and Tl atoms, respectively. All these total and partial magnetic moment values and Curie temperatures were supported by the Effective Field Theory (EFT) method. In addition, partial Curie temperatures of Zr2RhTl alloy were calculated by EFT separately for each element. The up-spins of Zr2RhTl alloy show metallic character in both the GGA and GGA + mBJ approximations, while the down-spins have band gaps of 0.698 and 0.699 eV, respectively. Electronic properties were also supported by GGA + U (U = 1, 2, 3 eV) interactions. Therefore, Zr2RhTl alloy is a true half-metallic ferromagnetic material. Zr2RhTl alloy was elastically stable, and the Debye temperature was calculated as 221.496 K at 0 GPa. All calculations obtained using two different methods (DFT and EFT) and two different approximations (GGA and GGA + mBJ) support each other. Therefore, Zr2RhTl alloy proved to be a very suitable material to be used as an alternative for spintronics.

Structure stability, mechanical properties and thermal conductivity of the new hexagonal ternary phase Ti2InB2 under pressure

ABSTRACT Recently, Wang et al. [Nat. Commun. 10 (2019) 2284] report a new compound, Ti2InB2, a stable boron-based ternary phase in the Ti-In-B system. This predicted compound is successfully synthesised using a solid-state reaction route and its space group is confirmed as (No. 187). In this work, the structural stability, mechanical properties, and thermal conductivity of the new hexagonal ternary phase Ti2InB2 under pressure up to 100 GPa have been carried out with first-principles calculations based on density functional theory. Our calculated lattice parameters in the ground state are consistent well with the theoretical prediction data. The calculations of elastic constants and phonon dispersion curves indicate that Ti2InB2 is mechanically and dynamically stable at least up to 100 GPa. Moreover, the pressure dependent elastic properties, such as bulk modulus B, shear modulus G, transverse sound velocity vt , longitudinal sound velocity vl , and Debye temperature Θ, are successfully obtained. It is found that Ti2InB2 behave in brittle manner under pressure up to 100 GPa. Meanwhile, the anisotropy of the directional linear compressibility and the Young’s modulus under pressure are also analysed for the first time. Finally, the minimum thermal conductivity of Ti2InB2 under different pressures are further evaluated by using both Clark’s model and Cahill’s model. The results show that Ti2InB2 exhibits relatively low thermal conductivity in the ground state and is suitable to be used as thermal insulating materials.

Novel elastic evolution of carbide Mo2Ga2C under pressure: Ab initio theoretical investigation

The pressure dependence of elastic properties of Mo2Ga2C is studied via first-principles calculation. The present investigation shows that differing from other MAX phases, in Mo2Ga2C the [Formula: see text] is larger than [Formula: see text], because of the strong Ga–Ga interlayer bonds along [Formula: see text]-axis. Moreover, under pressure, the [Formula: see text] increases more rapidly, originating from the faster strengthening of Ga–Ga bonds. Interestingly, elastic constants [Formula: see text] soften under high pressure (more than 20 GPa). Especially, the calculated phonon structure demonstrates that transverse acoustic (TA) phonon mode also softens under pressure, implying possible phase transition. The reduction of [Formula: see text] and softening of phonon mode are attributed to significantly weakened Mo–Mo interaction in contrast to the strengthening of Ga–Ga bonds under high pressure. Our present results further indicate that Mo2Ga2C is more ductile under pressure.

Pressure dependence of elastic properties of wurtzite ZnO crystal

ABSTRACTWe present the pressure dependence of elastic properties of the wurtzite phase of ZnO undergoing wurtzite to the rocksalt phase transition. A simple Landau theory is developed to describe the structural phase transition between wurtzite to rocksalt phases observed in ZnO. We have defined the necessary order parameter of the wurtzite to the rocksalt phase transition. We present a detailed analysis of the pressure dependence of the elastic and shear constants of the wurtzite phase of ZnO. The theoretical predictions are in the line with experimental results.

Study of low-hydrostatic pressure dependent elasticity of porous alumina saturated with various gas media

Poroelasticity describes how the elasticity of porous materials depend on the material properties: porosity, pore saturation medium and its pressure, nature of pore arrangement, and the skeleton material. The primary goal of this study is to investigate the low-hydrostatic pressure dependent elastic properties of porous alumina saturated with different gas media using resonant ultrasound spectroscopy (RUS). RUS is a precise experimental approach for investigating the elastic properties of solid materials which is capable of measurements at different temperatures and hydrostatic pressures. In RUS, the elastic stiffness tensor of crystalline and polycrystalline solids is determined from the vibrational resonance spectra. In this study, we have used commercially available porous alumina ceramic material which has ~40% of porosity and 2 μm of pore diameter. Here we are reporting the variation of elasticity and acoustic attenuation of porous alumina during the low-hydrostatic pressure cycles from 760 torr (1 atm) to 0.1 torr. An experimentally observed discontinuity of elastic stiffness and acoustic attenuation during the pressure region ~150 torr to 0.1 torr will be described by the transition from viscous to molecular flows, quantified by Knudsen number. The effects of saturated gas medium to the elasticity will also be discussed based on the RUS measurements taken during the air, He, and Ar gas saturation.

Study of temperature and pressure dependent elastic properties of porous ceramics

Resonant Ultrasound Spectroscopy (RUS) is a widely used experimental approach to investigate the elastic properties of solid materials at different temperature and pressure. In RUS, experimentally obtained vibrational resonance spectrum of a sample is used to calculate the full elastic tensor of the material. We report here a series of RUS measurements of novel porous ceramics material designed by LG which has applications in high temperature fuel cells. The elasticity and the acoustic damping of a porous material are influenced by its porosity and its saturation fluid. The time dependent elasticity obtained from RUS measurements exhibits a two-step process of stiffening with two distinct time constants. The stiffening-softening behavior during the heating-cooling cycles and the reduction of acoustic damping in the low-pressure conditions were observed depending on the synthesis history of the material.Resonant Ultrasound Spectroscopy (RUS) is a widely used experimental approach to investigate the elastic properties of solid materials at different temperature and pressure. In RUS, experimentally obtained vibrational resonance spectrum of a sample is used to calculate the full elastic tensor of the material. We report here a series of RUS measurements of novel porous ceramics material designed by LG which has applications in high temperature fuel cells. The elasticity and the acoustic damping of a porous material are influenced by its porosity and its saturation fluid. The time dependent elasticity obtained from RUS measurements exhibits a two-step process of stiffening with two distinct time constants. The stiffening-softening behavior during the heating-cooling cycles and the reduction of acoustic damping in the low-pressure conditions were observed depending on the synthesis history of the material.

Temperature- and pressure-dependent elastic properties, thermal expansion ratios, and minimum thermal conductivities of ZrC, ZrN, and Zr(C0.5N0.5)

Abstract We investigated the temperature- and pressure-dependent properties of ZrC, ZrN, and Zr(C0.5N0.5) solid solution using first-principles calculations with Debye–Gruneisen theory. The properties investigated included elastic moduli, thermal expansion coefficients, and thermal conductivities. Equilibrium volumes were determined by obtaining the energy–volume (E–V) curves of ZrC, ZrN, and Zr(C0.5N0.5) at different temperatures and external pressures. We adopted quasi-harmonic and quasi-static approximations to examine the influence of temperature and pressure on the elastic properties. Throughout the temperature and pressure ranges studied, the bulk modulus of the ZrN phase was higher than that of the other two phases, whereas its shear and Young's moduli were lower. An increase in nitrogen content resulted in an increase in the thermal expansion coefficient. The hardness, anisotropic properties, and minimum thermal conductivities of Zr(C0.5N0.5) and ZrC were similar, whereas those of the Zr(C0.5N0.5) phase were somewhat larger. Given its elastic properties, anisotropy, hardness, and minimum thermal conductivity, Zr(C0.5N0.5) is the best of the three phases for extreme environmental applications. Our results provide fundamental and useful information on the ZrC, ZrN, and Zr(C0.5N0.5) phases.

First-principles thermoelasticity and stability of pyrite-type FeO2 under high pressure and temperature

The pyrite-type FeO2 was proposed recently as a new structure that exists in the deep Earth. Taking into account the influence of temperature, we investigated the stability and elastic properties of pyrite-type FeO2 under high pressure. The obtained lattice constants and bulk modulus agree well with the available experimental and theoretical data. We found the stability of pyrite-type FeO2 is greatly affected by temperature and pressure. For example, pyrite-type FeO2 is predicted to be both mechanically and thermodynamically unstable when temperature is beyond 1700 K at 300 GPa. The stable boundary of pyrite-type FeO2 is obtained at high pressure and temperature. Furthermore, the pressure dependences of elastic properties of pyrite-type FeO2 are investigated for the first time. It is found that the values of C44 and shear modulus G are nearly invariable with the increasing pressure and temperature.

First-principles calculations for transition phase, mechanical and thermodynamic properties of ZnS under extreme condition

The structural and mechanical properties of ZnS in both B3 and B1 phases have been investigated by the generalized gradient approximation (GGA) within the plane-wave pseudopotential density functional theory (DFT). The obtained lattice parameters and bulk modulus of ZnS for both B3 and B1 structures are well in line with the available theoretical and experimental results. Using the enthalpy–pressure data, we have predicted that the phase transition pressure of ZnS from B3 to B1 is 17.26 GPa, which is in good agreement with previous experimental values. The hydrostatic pressure-dependent elastic properties of the two structures, such as bulk modulus, shear modulus and Young’s modulus, are discussed. Then, the mechanical characteristics of ZnS, including ductile/brittle behavior and elastic anisotropy of the two cubic single-crystal structures, are investigated in details. Furthermore, the thermodynamic properties of ZnS under extreme condition are explored by quasi-harmonic Debye modeling. The calculated results show that the ductility and elastic anisotropy increase with pressure clearly except the ductility of B1. Besides, the temperature and pressure dependencies of the heat capacity and the Debye temperature are obtained and analyzed in the wide ranges.

Investigation of polymorphism for amorphous and semi-crystalline poly (-ethylene terephthalate-) using high-pressure Brillouin spectroscopy

High-pressure Brillouin spectroscopy was applied to clarify quantitatively the physical and mechanical differences of a polymer with distinct structures consisting of the same elements. The pressure dependences of elastic properties, Young’s modulus, the shear modulus, the bulk modulus, and Poisson’s ratio for an amorphous poly (-ethylene terephthalate-) [(-PET-)] and a semi-crystalline PET were compared for pressures up to 11 GPa. A collapse of the free volume for the two PETs was ascertained at the different values of the pressure with different slopes for the elastic properties, Young’s modulus, the shear modulus, and the bulk modulus. Although the Poisson’s ratios of a semi-crystalline PET increased linearly with increasing pressure, those of an amorphous PET were almost constant. The P-V equation of state (EOS) for an amorphous PET was also determined, and isothermal bulk moduli extracted from the Birch-Murnaghan and the Vinet EOSs were 6.3 ± 0.2 GPa and 6.7 ± 0.1 GPa, respectively.

Elastic properties and equation of state for polycarbonate by high-pressure Brillouin spectroscopy

Although the conventional vibrational spectroscopic techniques of Raman and infrared spectroscopy are generally used to analyze the material properties of polymers, the physical and mechanical information that can be obtained through these techniques is very scarce. Since elastic information and equation of state are important for the application of polymers, we carried out Brillouin spectroscopy coupled with a diamond anvil cell. The pressure dependence of elastic properties for an amorphous polycarbonate with and without pressure medium was investigated for pressure up to 11 GPa. A substantial collapse of free volume under the anisotropic pressure was ascertained with the different slopes of elastic constants, Young's moduli, and bulk moduli at low and high pressures. From the Brillouin frequency shifts, we extracted C11 and C12 elastic constants, Young's moduli, shear moduli, bulk moduli, Poisson's ratios, and their pressure dependences. P–V isotherms were then constructed and fitted to two semi-empirical equations of state to extract the isothermal bulk modulus and its pressure derivative.

First-principles study of high-pressure stability, structure, and elasticity of FeS2 polymorphs

The pressure-dependent elastic properties of the Fe–S system are important to understand the dynamic properties of the Earth’s interior. We have therefore undertaken a first-principles study of the structural and elastic properties of FeS2 polymorphs under high pressure using a method based on plane-wave pseudopotential density function theory. The lattice constants, elastic constants, zero-pressure bulk modulus, and its pressure derivative of pyrite are in good agreement with the previous experiments and theoretical approaches; the lattice constants of marcasite are also consistent with the available experimental data. Calculations of the elastic constants of pyrite and marcasite have been determined from 0 to 200 GPa. Based on the relationship between the calculated elastic constants and the pressure, which can provide the stability of mineral, it would appear that pyrite is stable, whereas marcasite is unstable when the pressure rises above 130 GPa. Static lattice energy calculations predict the marcasite-to-pyrite phase transition to occur at 5.4 GPa at 0 K.

Modeling the pressure sensitivity of uncemented sediments using a modified grain contact theory: Incorporating grain relaxation and porosity effects

We develop a modified grain contact theory to better describe the pressure-dependent elastic properties of uncemented sediments. The Hertz-Mindlin (HM) theory typically predicts shear moduli that are much higher than observed laboratory measurements, resulting in inaccurate estimates of the dry bulk to shear modulus ratio [Formula: see text]. The HM theory further predicts that the [Formula: see text] ratio is constant with pressure, whereas ultrasonic core measurements typically show an increasing [Formula: see text] ratio as effective pressure decreases. Laboratory data also suggest that the dry bulk and shear moduli variation with effective pressure is greater than the cube-root power law predicted by the HM theory. We introduce two new pressure-dependent calibration parameters to account for the shortcomings in effective medium theory, and we develop a new method to predict pressure-dependent elastic properties. Our calibration parameters agree with the results of published granular dynamics simulations, and they incorporate grain relaxation and porosity effects not included in existing effective medium theories. Our new model provides improved fits to laboratory data when compared with existing models, and it can be used for improved prediction of elastic properties as a function of effective pressure. Our new theory can also be used to model uncemented sediments with values of Poisson’s ratio [Formula: see text], where many existing grain contact and effective medium theories currently fail.

Structural and elastic properties of Ce2O3 under pressure from LDA+U method

We investigate the structural and elastic properties of hexagonal Ce2O3 under pressure using LDA+U scheme in the frame of density functional theory (DFT). The obtained lattice constants and bulk modulus agree well with the available experimental and other theoretical data. The pressure dependences of normalized lattice parameters a/a0 and c/c0, ratio c/a, and normalized primitive volume V/V0 of Ce2O3 are obtained. Moreover, the pressure dependences of elastic properties and three anisotropies of elastic waves of Ce2O3 are investigated for the first time. We find that the negative value of C44 is indicative of the structural instability of the hexagonal structure Ce2O3 at zero temperature and 30 GPa. Finally, the density of states (DOS) of Ce2O3 under pressure is investigated.

First principles investigation of temperature and pressure dependent elastic properties of ZrC and ZrN using Debye–Gruneisen theory

We investigated the effects of temperature and pressure on the elastic properties of ZrC and ZrN using first-principles calculations and quasi-harmonic Debye–Gruneisen theory. Three expressions, the Slater, Dugdale–MacDonald (DM), and free volume expressions, were employed in the Debye–Gruneisen theory to obtain the Gruneisen parameter, γ. The DM expression agreed well with the experimental measurements of the ZrN volume expansion. The volume expansion of ZrC, on the other hand, did not agree well with any expression investigated here. ZrC calculations, therefore, require a modified expression. Variations in the Debye temperature, the Gruneisen parameter, the bulk (B), shear (G), and Young’s (E) moduli were calculated as a function of temperature and pressure. The temperature-dependent properties at room pressure agreed well with previous experimental results and other calculated results; however, the pressure effects at the various temperatures were not easily compared with the results from other experimental and computational results because their effects on the elastic properties of ZrC and ZrN remain largely unknown.

First principles investigations on elastic and electronic properties of BaHfN2 under pressure

We investigate the elastic and electronic structure properties of BaHfN2 under pressure by performing the generalized gradient approximation (GGA) and local density approximation (LDA) correction scheme in the frame of density functional theory (DFT). The pressure dependences of the normalized lattice parameters a/a0 and c/c0, the ratio c/a, and the normalized primitive volume V/V0 of BaHfN2 are also obtained. The obtained lattice constants and bulk modulus agree well with the available experimental and other theoretical data. The pressure dependences of elastic properties are investigated for the first time. It is found that, as the pressure increases, the elastic constants C11, C33, C66, C12 and C13 increase, the variation of elastic constant C44 is not obvious. At 40GPa, the tetragonal structure BaHfN2 transfers to another structure at zero temperature. Moreover, our compressional and shear wave velocities VL=5.87km/s and VS=3.12km/s as well as the Debye temperature Θ=451.7K at 0GPa are obtained. The pressure dependences of the band structures, energy gap and density of states are also investigated.

Elastic and electronic properties of YNi 2B 2C under pressure from first principles

The elastic and electronic structure properties of YNi 2B 2C under pressure are investigated by performing the generalized gradient approximation (GGA) and local density approximation (LDA) correction scheme in the frame of density functional theory (DFT). The pressure dependences of the normalized lattice parameters a/ a 0 and c/ c 0, the ratio c/ a, and the normalized primitive volume V/ V 0 of YNi 2B 2C are also obtained. The lattice constants and bulk modulus obtained are in agreement with the available experimental and other theoretical data. We have also studied the pressure dependences of elastic properties. It is found that, as pressure increases, the elastic constants C 11, C 33, C 66, C 12, and C 13 increase, the variation of elastic constant C 44 is not obvious. Moreover, our compressional and shear wave velocities V L =6.99 km/s and V S =3.67 km/s as well as the Debye temperature Θ=549.7 K at 0 GPa compare favorably with the available experimental data. The pressure dependences of band structures, energy gap and density of states are also investigated.

Pressure dependent elastic properties of diluted magnetic semiconductors: Hg 1− xMn xS ( x=0.02 and 0.07)

A theoretical study of the elastic properties in diluted magnetic semiconductors Hg 1− x Mn x S ( x=0.02 and 0.07) using an effective interionic interaction potential (EIoIP) in which long-range Coulomb interactions, charge transfer mechanism (three body interaction) and the Hafemeister and Flygare type short-range overlap repulsion extending up to the second neighbor ions and the van der Waals (vdW) interaction is considered. Particular attention is devoted to evaluate Poisson's ratio ν, the ratio R S/ B of S (Voigt averaged shear modulus ) over B (bulk modulus), elastic anisotropy parameter, elastic wave velocity, average wave velocity and thermodynamic property as Debye temperature is calculated. By analyzing Poisson's ratio ν and the ratio R S/ B we conclude that Hg 1− x Mn x S is brittle in zinc blende (B3). To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of ductile (brittle) nature of Hg 1− x Mn x S compounds and still awaits experimental confirmations.

Pressure and doping dependent elastic and thermodynamical properties of Ga 1− xIn xP mixed valent compounds

Using a phenomenological lattice model incorporating the long-range Coulomb and charge transfer caused by the deformation of the electron shells of the overlapping ions and the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbor ions and the van der Waals (vdW) interaction, we present a comprehensive study to understand the effects of pressure on the elastic behavior as ductility (brittleness) and thermodynamical properties of Ga 1− x In x P. Estimated phase-transition pressure and the vast volume discontinuity in pressure–volume phase diagram confirm the structural phase transition from zinc blende ( B3) to rock salt ( B1) phase. From the elastic constants the Poisson's ratio ν, the ratio R S/ B of S (Voigt averaged shear modulus) over B (bulk modulus), elastic wave velocity, average wave velocity and thermodynamical property Debye temperature is calculated. The Poisson's ratio ν and the ratio R S/ B allows one to conclude that Ga 1− x In x P is brittle in zinc blende ( B3) and ductile nature is inferred in sodium chloride ( B1) phase. To our knowledge this is the first quantitative theoretical prediction of the doping and pressure dependent elastic properties for mixed valent Ga 1− x In x P compounds and still awaits experimental confirmations.

First-principles calculations for elastic properties of OsB2 under pressure

The pressure dependence of elastic properties of ZnS in zinc-blende (ZB) and wurtzite (WZ) structures are investigated by the generalized gradient approximation (GGA) within the plane-wave pseudopotential density functional theory (DFT). Our results are in good agreement with the available experimental data and other theoretical results. From the high-pressure elastic constants obtained, we find that the ZB and WZ structures of ZnS are unstable when the applied pressures are larger than 15.8 GPa and 21.3 GPa, respectively. The sound velocities along different directions for the two structures are also obtained. It is shown that as pressure increases, the sound velocities of the shear wave decrease, and those of all the longitudinal waves increase. An analysis has been made to reveal the anisotropy and highly noncentral forces in ZnS.