Pressure Derivative Of Bulk Modulus Research Articles

Computational investigations of mechanical and vibrational properties of quaternary semiconductor alloys MgxZn1-xSySe1-y

Physical properties like elastic constants, pressure derivative of bulk modulus, pressure derivative of elastic constants and acoustic wave velocities in different directions for Mg x Zn 1-x S , Mg x Zn 1-x Se and ZnS y Se 1-y semiconductor ternary alloys and Mg x Zn 1-x S y Se 1-y quaternary alloys with different concentrations of x and y are studied using our previously proposed potential based on the pseudopotential formalism. It is noticed from the present study that the physical properties under investigations depend on concentrations x and y of constitute compounds. The present results of various physical quantities of compounds presented here are compared with the available experimental data and other theoretical estimations and showed roughly reasonable agreement. The numerical values of same quantities for ternary alloys and MgZnSSe quaternary alloys were reported first time and hence such results may be useful for comparison purpose in future with either the experimental or the theoretical work.

Some physical properties of In x Ga1−x N y As1−y semiconducting quaternary alloys obtained using pseudopotential method

The cohesive energy, bulk modulus, elastic constants, pressure derivative of bulk modulus and pressure derivative of elastic constants for In x Ga1−x N y As1−y semiconducting quaternary alloys have been investigated based on pseudopotential formalism. A reasonable agreement of presently investigated numerical data with the available experimental data and other such theoretical values has been observed.

Phase transitions of serpentine in the lower mantle

Phase transformations in natural serpentine and chlorite have been studied at 25–50GPa and 900–1280°C by in-situ X-ray diffraction measurements using the multianvil apparatus with sintered diamond anvils. Antigorite was found to transform to a phase assemblage including phase H, at pressures above about 35–40GPa corresponding to those in the upper part of the lower mantle. The zero pressure bulk modulus K0 of phase H was determined to be 160GPa, assuming its pressure derivative K′=4. The thermal stability of phase H is significantly enhanced by a solid solution with a δ-AlOOH component, suggesting that aluminous phase H in cold slabs would deliver a certain amount of water into the deepest part of the lower mantle.

Half-metallic ferromagnetism in Be1−x V x Te alloys: an Ab-initio study

First-principles calculations of the structural, elastic, electronic, magnetic and thermodynamic properties of zinc blende Be1−x V x Te alloys (x = 0, 0.25, 0.50, 0.75 and 1) based on spin-polarized density functional theory are performed using full-potential augmented plane wave method, within the spin generalized gradient approximation for the exchange–correlation potential. The equilibrium structural parameters such as lattice constant (a 0 ), bulk modulus (B 0 ) and first pressure derivative of bulk modulus (\( B^{\prime } \)) are optimized for all alloys. The elastic constants C 11, C 12, C 44 and anisotropy coefficients are also estimated. The calculations of the band structure and the density of states demonstrate that all Be1−x V x Te (x = 0.25, 0.50, 0.75 and 1) alloys are complete half-metals. The investigation of the band structure and the density of states demonstrate that Be0.75V0.25Te alloy is entirely half-metal, whereas Be0.50V0.50Te and Be0.25V0.75Te alloys are nearly half-metal. The estimation of the s(p)–d exchange splitting constants N 0α (conduction band) and N 0β (valence band), as obtained through the density of states, have been used to indicate the magnetic behavior of the compounds. From the total magnetic moment, it is observed that the p–d hybridization reduces the local magnetic moment of V atom from its free space charge of 3µ B and generates small local magnetic moments on the nonmagnetic Be and Te sites. Lastly, based on the quasi-harmonic Debye model, the obtained macroscopic thermodynamic properties, such as thermal expansion coefficient, heat capacities and Debye temperate, are presented in detail.

Prediction of new high pressure structural sequence in thorium carbide: A first principles study

In the present work, we report the detailed electronic band structure calculations on thorium monocarbide. The comparison of enthalpies, derived for various phases using evolutionary structure search method in conjunction with first principles total energy calculations at several hydrostatic compressions, yielded a high pressure structural sequence of NaCl type (B1) → Pnma → Cmcm → CsCl type (B2) at hydrostatic pressures of ∼19 GPa, 36 GPa, and 200 GPa, respectively. However, the two high pressure experimental studies by Gerward et al. [J. Appl. Crystallogr. 19, 308 (1986); J. Less-Common Met. 161, L11 (1990)] one up to 36 GPa and other up to 50 GPa, on substoichiometric thorium carbide samples with carbon deficiency of ∼20%, do not report any structural transition. The discrepancy between theory and experiment could be due to the non-stoichiometry of thorium carbide samples used in the experiment. Further, in order to substantiate the results of our static lattice calculations, we have determined the phonon dispersion relations for these structures from lattice dynamic calculations. The theoretically calculated phonon spectrum reveal that the B1 phase fails dynamically at ∼33.8 GPa whereas the Pnma phase appears as dynamically stable structure around the B1 to Pnma transition pressure. Similarly, the Cmcm structure also displays dynamic stability in the regime of its structural stability. The B2 phase becomes dynamically stable much below the Cmcm to B2 transition pressure. Additionally, we have derived various thermophysical properties such as zero pressure equilibrium volume, bulk modulus, its pressure derivative, Debye temperature, thermal expansion coefficient and Gruneisen parameter at 300 K and compared these with available experimental data. Further, the behavior of zero pressure bulk modulus, heat capacity and Helmholtz free energy has been examined as a function temperature and compared with the experimental data of Danan [J. Nucl. Mater. 57, 280 (1975)].

A comparative study of Burakovsky's and Jacobs's volume dependence Grüneisen parameter for fcc aluminum

We compare two expressions for the volume dependence of the Grüneisen parameter γ for fcc Al presented by Burakovsky and Preston (2004) [3] and Jacobs and Schmid-Fetzer (2010) [4], respectively. It’s found that both calculated results of the melting temperature Tm are in good agreement with experimental data. But the higher order Grüneisen parameters are different. We obtain the values of the third order Grüneisen parameter λ∞ and the pressure derivative of bulk modulus K′∞ at extreme pressure, and the parameter f in the generalized free volume formula for the two models. The results show that the Jacobs’s expression of Grüneisen parameter is more suitable for fcc Al.

Structural phase transition of ternary dielectric SmGdO3: Evidence from angle dispersive x-ray diffraction and Raman spectroscopic studies

High-pressure synchrotron based angle dispersive x-ray diffraction (ADXRD) studies were carried out on SmGdO3 (SGO) up to 25.7 GPa at room temperature. ADXRD results indicated a reversible pressure-induced phase transition from ambient monoclinic to hexagonal phase at ∼8.9 GPa. The observed pressure-volume data were fitted with the third order Birch-Murnaghan equation of state yielding zero pressure bulk modulus B0 = 132(22) and 177(9) GPa for monoclinic (B-type) and hexagonal (A-type) phases, respectively. Pressure dependent micro-Raman spectroscopy further confirmed the monoclinic to hexagonal phase transition at about 5.24 GPa. The mode Grüneisen parameters and pressure coefficients for different Raman modes corresponding to each individual phases of SGO were calculated using pressure dependent Raman mode analysis.

Ab-initio study of structural, electronic and elastic properties of cobalt intermetallic compounds

The structural, electronic, elastic, bonding and thermal properties of CoX (X=Ti, Zr and Hf) have been investigated using ab initio full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA). The ground state and electronic properties such as lattice constant (a0), bulk modulus (B), pressure derivative of bulk modulus (B′) and density of states at Fermi level N(EF) are reported with experimental and available theoretical results. Electronic and bonding patterns of these compounds have been analyzed from band structure, Fermi surfaces and contour plots. The elastic constants (C11, C12 and C44) and mechanical properties are also estimated. From the elastic constant, it is inferred that these compounds are mechanically stable in B2 phase. Ductility for these compounds is further analyzed by calculating the ratio of B/GH and Cauchy’s pressure (C12–C44). Our calculated results reveal that all these compounds are ductile in nature.

Structural, elastic, and lattice dynamic stability of yttrium selenide (YSe) under pressure: A first principle study

Structural, elastic, and lattice dynamical stability of YSe has been investigated as a function of pressure through first principles electronic band structure calculations. The comparison of enthalpies of rocksalt type (B1) and CsCl type cubic (B2) structures determined as a function of pressure suggests that the B1 phase will transform to B2 structure at ∼32 (30 GPa at 300 K obtained from comparison of Gibbs free energy at 300 K). The transition is identified to be of first order in nature with a volume discontinuity of ∼6.2% at the transition pressure. Furthermore, the theoretically determined equation of state has been utilized to derive various physical quantities, such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus. The single crystal elastic constants have been predicted at various pressures for both the B1 and B2 structures using the energy strain method. The activation barrier between B1 and B2 phases calculated at transition point is ∼19.7mRy/formula unit. Our lattice dynamic calculations show that both the B1 as well as B2 structures are lattice dynamically stable not only at ambient pressure but also at transition pressure. The B1 phase becomes lattice dynamically unstable at ∼112 GPa, i.e., much beyond the transition pressure. The effect of temperature on volume and bulk modulus of the YSe in B1 phase has also been examined.

Volume Dependence of Thermodynamic Properties for Solids at high Temperatures

Abstract A new computing model on the volume dependence of the product αKT of the thermal expansion coefficient α and the isothermal bulk modulus KT is proposed straightforward in this paper. Based on this revised formula, the volume dependence of Grüneisen parameter, entropy, Anderson-Grüneisen parameter, and first pressure derivative of bulk modulus, respectively, are thus investigated. The calculated results agree well with the previous work for magnesium oxide, sodium chloride, lithium, sodium, and potassium.

Ab initio calculations of B2 type RHg (R = Ce, Pr, Eu and Gd) intermetallic compounds

Spin polarized ab initio calculations have been carried out to study the structural, electronic, elastic and thermal properties of RHg (R = Ce, Pr, Eu and Gd) intermetallic compounds in B2 structure. The calculations have been performed by using both generalized gradient approximation (GGA) and local spin density approximation (LSDA). The calculated value of lattice constant (a0) for these compounds with GGA is in better agreement with the experimental data than those with LSDA. Bulk modulus (B), first-order pressure derivative of bulk modulus and magnetic moment (μB) are also presented. The energy band structure and electron density of states show the occupancy of 4f states for light as well as heavy rare earth atom. The elastic constants are predicted from which all the related mechanical properties like Poisson’s ratio (σ), Young’s modulus (E), shear modulus (GH) and anisotropy factor (A) are calculated. The ductility or brittleness of these compounds is predicted from Pugh’s rule (B/GH) and Cauchy pressure (C12 − C44). The Debye temperature (θD) is estimated from the average sound velocity, which have not been calculated and measured yet.

High-pressure structural stability of the ductile intermetallic compound, ErCu

High-pressure angle dispersive X-ray diffraction measurements up to 23.6 GPa have been carried out on the ductile intermetallic compound, ErCu. Our measurements show that the ambient CsCl structure (SG: Pm-3m) is stable up to the highest pressure of the present measurements. A second-order Birch-Murnaghan equation of state fit to the pressure, volume data yielded a bulk modulus of 67.6 GPa with the pressure derivative of bulk modulus fixed at 4.

Electronic Band Structure and Metallization of Aluminium Nitride (AlN) under High Pressure

One basic problem in solid state physics, material chemistry, geosciences and even in planetology, is the precise electronic properties of the materials present in objects. The uniqueness of aluminium nitride (AlN) and its special role in human society is closely related to its structural stability at extreme pressures. In this paper, the results of a full potential linear muffin-tin orbital (FP-LMTO) study on the electronic properties of cubic zinc blende type group III-V semiconductor aluminium nitride (AlN) under pressure are presented. The equilibrium lattice constant, bulk modulus, pressure derivative of bulk modulus and the phase transition pressure from ZnS to NaCl is predicted from the total energy calculations. The ground state properties and band gap values are compared with the experimental results. At normal pressure AlN is indirect bandgap semiconductor with bandgap value 4.56eV. When the pressure is increased there is enhanced overlapping between the wave functions of the neighbouring atoms. As a result the widths of the valence and empty conduction bands increase. These changes lead to the narrowing and indirect closing of band gaps in AlN (metallization). In AlN, the metallization (at V/Vo=0.756 and PM = 1 Mbar) occurs through indirect closing of the band gap between valence band maximum at  point and conduction band minimum at X point. It is also confirmed that the metallization and structural phase transition do not occur simultaneously in this compound.

Structural properties of Alumnum nitride compound

Structural properties of Alumnum nitride in wurtzite, zinc-blende and rock-salt phases have been investigated by Full Potential-Linearized Augmented Plane Waves method based on Density Functional Theory within Local Density Approximation and seven Generalized Gradient schemes. It is found that, Alumnum nitride in wurtzite phase is the stable ground state structure and makes a transition to rock-salt phase at a low transition pressure (11.54 GPa). According to present total energy calculations, zinc-blende phase of Alumnum nitride also makes a transition to rock-salt phase, at a low transition pressure (10.17 GPa). Generalized Gradient functionals of Perdew-Wang-Engel-Vosko and Perdew-Burke-Ernzerhof are found to be more successful than other approximations considered in this work for providing the closest values of the structural features, such as, lattice constants, bulk moduli, first order pressure derivatives of bulk moduli and cohesive energies of Alumnum nitride three phases to available experimental ones. Although Generalized Gradient approaches of Perdew-Wang-Engel-Vosko, Perdew-Burke-Ernzerhof, Becke-Perdew-Wang and Perdew-Burke-Ernzerhof (revised) are found to be accurate schemes for elastic constants of rock-salt AlN, only Perdew-Wang-Engel-Vosko and Perdew-Burke-Ernzerhof functionals are observed to be more successful than the other schemes for supplying accurately both \(C_{11}\) and \(C_{12}\) of zinc-blende Alumnum nitride structure. Perdew-Wang-Engel-Vosko functional is observed to be superior to Perdew-Burke-Ernzerhof for elastic constants of wurtzite Alumnum nitride structure. Elastic constants of wurtzite Alumnum nitride obtained by self Perdew-Wang-Engel-Vosko approach and Martin’s transformation calculations in which elastic constants of zinc-blende Alumnum nitride are calculated with Perdew-Wang-Engel-Vosko scheme, are very close to the experimental ones. Hence, functional of Perdew-Wang-Engel-Vosko is decided to be the most accurate approximation among Local Density Approximation and other Generalized Gradient schemes considered in this work for all structural properties of Alumnum nitride three phases.

First principles calculations on structural, elastic, acoustic and optical properties of fluorite phase TiO2 under pressure

The electronic, elastic, acoustic and optical properties of fluorite phase TiO 2 are calculated by using the first principles method. Different exchange-correlation functionals are used with the ultrasoft plane wave pseudopotential method under pressure from 0 GPa to 90 GPa. The calculated values of the lattice constant, cell volume, bandgap, bulk modulus and the pressure derivative of bulk modulus are in agreement with the prior published results. The calculated elastic parameters show that the fluorite structure is mechanically stable, the ratio of bulk to shear modulus [Formula: see text] indicates that it is brittle, and pressure derivative of the bulk modulus shows that it is not a super hard material, but a hard material. The longitudinal and transverse acoustic velocities in the direction [100], [110] and [111] are computed by using prior determined data. Besides, the optical properties are also studied under the aforementioned range of pressure, and the results show more photolytic activity over the other phases.

Pressure-induced volume anomaly and structural phase transition in nanocrystalline SnO2

High-pressure behavior of tetragonal rutile structured, nanocrystalline SnO2, with an average grain size of 5 nm is investigated by in situ synchrotron based angle dispersive powder X-ray diffraction technique up to 34 GPa at ambient temperature. Results indicate that the tetragonal structure remains stable up to 18 GPa. Beyond 18 GPa a first order phase transformation to a cubic phase with large volume discontinuity is observed. Co-existence of both ambient and high pressure phases is observed till the highest pressure investigated. On pressure release, the high pressure daughter phase is retained. The bulk modulus for ambient rutile phase and high pressure daughter phase is 217 (±10) and 202 (±5) GPa respectively with the value of pressure derivative of bulk modulus fixed at 4. The observed phase transition sequence in nanomaterial is different from the bulk compound. It is concluded that the anomaly in the pressure-volume data in present studies and electrical transport data seen near 3 GPa in previous [38] work is of electronic in nature since material is structurally stable in this pressure region.

Phase transitions in delafossite CuLaO2 at high pressures

Structural stability of a transparent conducting oxide CuLaO2 at high pressures is investigated using in-situ Raman spectroscopy, electrical resistance, and x-ray diffraction techniques. The present Raman investigations indicate a sequence of structural phase transitions at 1.8 GPa and 7 GPa. The compound remains in the first high pressure phase when pressure is released. Electrical resistance measurements carried out at high pressures confirm the second phase transition. These observations are further supported by powder x-ray diffraction at high pressures which also showed that a-axis is more compressible than c-axis in this compound. Fitting the pressure dependence of unit cell volume to 3rd order Birch-Murnaghan equation of state, zero pressure bulk modulus of CuLaO2 is determined to be 154(25) GPa. The vibrational properties in the ambient delafossite phase of CuLaO2 are investigated using ab-initio calculations of phonon frequencies to complement the Raman spectroscopic measurements. Temperature dependence of the Raman modes of CuLaO2 is investigated to estimate the anharmonicity of Raman modes.

Pressure effect on elastic, lattice dynamic and superconducting behaviour of yttrium sulfide: A first principle study

First principles calculations have been carried out to analyze structural, elastic, and dynamic stability of yttrium sulphide (YS) under hydrostatic compression. The comparison of enthalpies of rocksalt type (B1) and CsCl type cubic (B2) structures determined as a function of compression suggests the B1 → B2 transition at ∼49 GPa (the same transition occurs at ∼48 GPa at 300 K). Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state. The single crystal elastic constants derived from the energy strain method agree well with the experimental values. The activation barrier between B1 and B2 phases calculated at transition point is ∼17/mRy/f.u. Our lattice dynamic calculations show that at ambient condition, the B1 phase is lattice dynamically stable, and frequencies of phonon modes in different high symmetry directions of Brillouin zone agrees well with experimental values. The B2 phase also is dynamical stable at ambient condition as well as at ∼49 GPa, supporting our static lattice calculation. The effect of temperature on volume and bulk modulus of the YS in B1 phase has also been examined. The superconducting temperature of ∼2.78 K determine at zero pressure agrees well with experimental data. The effect of pressure is found to suppress the superconducting nature of this material.

Theoretical Investigations of Structural Phase Transitions and Magnetic, Electronic and Thermal Properties of DyNi: Under High Pressures and Temperatures

Present work is influenced by the requirement of investigation of rare earth intermetallics due to the nonavailability of theoretical details and least information from experimental results. An attempt has been made to analyse the structural, electronic, magnetic and thermal properties of DyNi using full potential linear augmented plane wave method based on density functional theory. DyNi differs from other members of lanthanides nickelates as in ground state it crystallizes in FeB phase rather than orthorhombic CrB structure. The equilibrium lattice constant, bulk modulus, and pressure derivative of bulk modulus are presented in four polymorphs (FeB, CrB, CsCl and NaCl) of DyNi. At equilibrium the cell volume of DyNi for FeB structure has been calculated as 1098.16 Bohr3 which is comparable well with the experimental value 1074.75 Bohr3. The electronic band structure has been presented for FeB phase. The results for thermal properties, namely, thermal expansion coefficient, Gruneisen parameter, specific heat and Debye temperature at higher pressure and temperatures have been reported. The magnetic moments at equilibrium lattice constants have also been tabulated as the rare earth ions associated with large magnetic moments increase their utility in industrial field for the fabrication of electronic devices due to their magnetocaloric effect used in magnetic refrigeration.

High-pressure structural studies of Li x La1/3NbO3 (x = 1/6, 1/3, 1/2, 2/3)

The high-pressure behavior of LixLa1/3NbO3 (x = 1/6, 1/3, 1/2, 2/3) perovskites where Li cations were substituted for the existing vacancies was studied using synchrotron X-ray diffraction. It was shown that all these materials undergo irreversible pressure-induced amorphization around 14.5 GPa regardless of the Li concentration. The Li-inserted materials were found to exhibit a standard pressure response (bulk modulus pressure derivative B0′ ~4) when in the crystalline phase, whereas La1/3NbO3 shows a linear volume contraction versus pressure, i.e., B0′ ~(−1). These results suggest that the structural collapse is not a consequence of cation disorder resulting from the Nb atoms (B-site) migrating to the A-site vacancies. The observed pressure response can be understood by increased occupancy of the A-sites opposing the tilting of the NbO6 octahedra. The pressure evolution of the Nb oxidation state is discussed.