Pressure Derivative B0 Research Articles

FP-LAPW calculations of the structural, and optoelectronic properties of vanadium silicide compound for optoelectronic applications

Optoelectronic devices play an essential part in our daily lives by seamlessly integrating optics and electronics, leading to technologies such as smartphones, solar cells, and optical communication. In this study, the structural and optoelectronic characteristics of the hexagonal vanadium silicide are determined using the density functional theory (DFT). The structural parameters such as the zero-pressure bulk modulus B0, its pressure derivative B0′; equilibrium energy, and the volume of the primitive cell at equilibrium V0 are compared with experiment results. The metallic character of VSi2 is confirmed by calculating the density of states and band structure. Moreover, the optical properties like the dielectric function, reflectivity, energy loss function, refractive index, absorption coefficient, and optical conductivity are studied deeply, using the Drude model, within the energy interval from 0 to 14 eV and they are compared with experiment results of a polycrystalline and single crystal. However, the phonon dispersion spectrum shows the presence of imaginary modes, which indicates instability in the structure of vanadium silicide. The results indicate that the VSi2 material has the potential to be used in many applications, including mirrors, glass coatings, optoelectronic devices, optical networks, electronics, optical communications, and waveguide components.

Structural changes in hexagonal WO3 under high pressure

The high pressure of hexagonal-tungsten oxide (h-WO3) has been studied in diamond anvil cell up to 50 GPa at room temperature by angle-dispersive X-ray powder diffraction (AD-XRD). Cell refinement, FWHM and area of peaks and microstructure were analyzed. Results show that below 10 GPa, lattice strains follow linear trend, with bulk modulus B0 = 42(2) GPa, and its pressure derivative B0' = 13(2), and the crystalline grain sizes rapidly decrease in this range. In the range of 10–36 GPa, the lattice strains deviate linear trend, with decreasing amount of crystalline regions, and r.m.s. microstrain dominates this range. After 36 GPa, the lattice strain show a little increase, implying the crystalline-amorphous transformation occurs.

The effect of high pressure on the structure and stability of sodium formate: Probed by in situ synchrotron X-ray diffraction technique

The structural stability and equation of state (EoS) of sodium formate (NaHCOO) up to ∼6 GPa have been investigated using in-situ synchrotron X-ray diffraction technique, at room temperature. The results indicate that sodium formate remained the monoclinic structure at high pressures and exhibited anisotropic compressibility, the b- and c-axes are more compressible than a-axis. The experimental pressure-volume data are fitted well with the third-order Birch-Murnaghan EoS, yielding a bulk modulus of B0 = 26.0(1) GPa with its first pressure derivative B0' = 4.5(7). The present results can provide some insight for better understanding of the structural stability of alkali and alkaline earth metal formates under high pressure.

Boron monosulfide: Equation of state and pressure-induced phase transition

Quasi-hydrostatic compression of rhombohedral boron monosulfide (r-BS) has been studied up to 50 GPa at room temperature using diamond-anvil cells and angle-dispersive synchrotron X-ray diffraction. A fit of the experimental P–V data to the Vinet equation of state yields the bulk modulus B0 of 42.2(1.4) GPa and its first pressure derivative B0′ of 7.6(2) that are in excellent agreement with our ab initio calculations. Formation of a new high-pressure phase of boron monosulfide (hp-BS) has been observed above 35 GPa. According to ab initio evolutionary crystal structure predictions combined with Rietveld refinement of high-pressure X-ray diffraction data, the structure of hp-BS has trigonal symmetry and belongs to the space group P-3m1. As it follows from the electron density of state calculations, the phase transformation is accompanied by an insulator-metal transition.

A new Ca3MgSi2O8 compound and some of its thermodynamic properties

A new calcium magnesium orthosilicate with the composition Ca3MgSi2O8 was synthesized by a solid-state reaction process at 1.2GPa and 1373K for 7 days. We refined the crystallographic structure of this new compound using single-crystal X-ray data, and obtained some of its thermodynamic properties by performing some first-principles simulations. Our single-crystal X-ray analysis has shown that this new compound is monoclinic with the space group C2/c, and its unit-cell parameters are a = 9.344(4) Å, b = 5.3308(3) Å, c = 13.290(6) Å, α = 90°, β = 92.072(7)°, γ = 90°, and V = 658.7(6) Å3. The compressibility of this new compound was studied with the CASTEP code using density functional theory and planewave pseudopotential technique, which led to an isothermal bulk modulus B0 of 99(2)GPa with a pressure derivative B0′ of 3.5(5). The phonon dispersions and vibrational density of the states (VDoS) of this new compound were calculated by using density functional perturbation theory. Subsequently, the VDoS was combined with a quasi-harmonic approximation to compute the isobaric heat capacity (Cp) and standard vibrational entropy (S2980), yielding Cp = 3.927(2) × 102 – 1.159(6) × 103T−0.5 – 1.054(4) × 107T−2 + 1.362(8) × 109T−3Jmol−1 K−1 for the T range of 298–1000K and S2980 = 270.5(60)Jmol−1K−1.

Thermoelastic equation of state of boron subphosphide B12P2

Compressibility of boron subphosphide B12P2 has been studied under quasi-hydrostatic conditions up to 26 GPa and 2600 K using laser-heated diamond anvil cell and angle-dispersive synchrotron X-ray diffraction. 300-K data fit yields the values of bulk modulus B0 = 192(11) GPa and its first pressure derivative B0' = 5.5(12). At ambient pressure the thermal expansion is quasi-linear up to 1300 K with average volume expansion coefficient {\alpha} = 17.4(1) 10-6 K-1. The whole set of experimental p-V-T data is well described by the Anderson-Gr\"uneisen model with {\delta}T = 6.

First-principles study of structural, mechanical, and thermodynamic properties of cubic Y2O3 under high pressure

The structural, mechanical, and thermodynamic properties of cubic Y2O3 crystals at different hydrostatic pressures and temperatures are systematically investigated based on density functional theory within the generalized gradient approximation. The calculated ground state properties, such as equilibrium lattice parameter a0, the bulk modulus B0, and its pressure derivative B0′ are in favorable agreement with the experimental and available theoretical values. The pressure dependence of a/a0 and V/V0 are also investigated. Furthermore, the elastic constants Cij, bulk modulus B, shear modulus G, Young's modulus E, the ductile or brittle (B/G), Vickers hardness Hv, isotropic wave velocities and sound velocities are calculated in detail in a pressure range from 0 to 14GPa. It was found that the Debye temperature decreases monotonically with an increase in pressure, the calculated elastic anisotropic factors indicate that Y2O3 has low anisotropy at zero pressure, and that its elastic anisotropy increases as the pressure increases. Finally, the thermodynamic properties of Y2O3, such as the dependence of the heat capacities CV and CP, the thermal expansion coefficient α, the isothermal bulk modulus, and the Grüneisen parameter γ on temperature and pressure, are discussed from 0 to 2000K and from 0 to 14GPa, respectively, applying the non-empirical Debye model in the quasi-harmonic approximation.

High Pressure Structural Investigation of Benzoic Acid: Raman Spectroscopy and X-ray Diffraction

The structural stability of benzoic acid (C6H5COOH, BA), a hydrogen-bonded molecular crystal, has been investigated by Raman spectroscopy and angle-dispersive X-ray diffraction (ADXRD) up to ∼18 GPa at room temperature. Under ambient conditions, benzoic acid molecules are arranged in two sets of parallel planes and held together by hydrogen bonding and van der Waals interactions. Small changes (e.g., emergence of new peaks, splitting of original peaks) can be observed in the Raman spectra at high pressures. However, no obvious changes can be observed in the X-ray diffraction measurements, which rules out any symmetry/structure changes within this pressure range. The pressure dependence of lattice parameters is presented, which shows monotonously decrease without any anomalies. The experimental isothermal pressure–volume data are well fitted by the third-order Birch–Murnaghan equation of state, yielding bulk modulus B0 = 41.7(6) GPa and a first pressure derivative B0′ = 4.5(4). Axial compressibility shows ...

Elastic, magnetic and electronic properties of iridium phosphide Ir2P.

Cubic (space group: Fmm) iridium phosphide, Ir2P, has been synthesized at high pressure and high temperature. Angle-dispersive synchrotron X-ray diffraction measurements on Ir2P powder using a diamond-anvil cell at room temperature and high pressures (up to 40.6 GPa) yielded a bulk modulus of B0 = 306(6) GPa and its pressure derivative B0′ = 6.4(5). Such a high bulk modulus attributed to the short and strongly covalent Ir-P bonds as revealed by first – principles calculations and three-dimensionally distributed [IrP4] tetrahedron network. Indentation testing on a well–sintered polycrystalline sample yielded the hardness of 11.8(4) GPa. Relatively low shear modulus of ~64 GPa from theoretical calculations suggests a complicated overall bonding in Ir2P with metallic, ionic, and covalent characteristics. In addition, a spin glass behavior is indicated by magnetic susceptibility measurements.

Ab-initio DFT FP-LAPW GGA and LDA TB-mBJ and SO theoretical study of structural and elastic properties of Zinc-Blende crystal phase GaAs1−xBix alloys

We present an ab-initio theoretical study of structural and elastic properties of GaAs1−xBix alloys in the Zinc-Blende (ZB) phase. We use a recent version of Wien2k package code based on Density Functional Theory (DFT) Full Potential and Linearized Augmented Plane Waves (FP-LAPW) method including recent Tran-Blaha modified Becke–Johnson correction of the exchange potential (TB-mBJ) and the spin–orbit interaction (SO). The calculations are performed within the Local Density Approximation (LDA) as well as the Generalized Gradient Approximation (GGA). We study first the structural properties of GaAs1−xBix alloys by solving Murnaghan equation of state. Our results show that the ZB phase is the lowest equilibrium crystal structure of GaAs1−xBix in the whole alloy composition range, in agreement with previous theoretical predictions. The variations versus Bi contents of the ZB GaAs1−xBix lattice constant a0, bulk modulus B0 and its pressure derivative B0′ are also found very close to other theoretical and experimental data, but with much smaller bowing effects indicating a better resolution thanks to TB-mBJ correction. The variations of B0 versus the reverse equilibrium volume of the unit cell (1/V0) are found to be described by the simple linear empirical expression B0 = −0.21068 + 0.16695/V0 which is close to the theoretical prediction for III-V semiconductors with, however, somewhat lower linear coefficients values, suggesting a more metallic behavior. In a second part of this work, we use Birch–Murnaghan approach to study the elastic properties of GaAs1-xBix alloys. The elastic stiffness coefficients, C11, C12 and C44, and their variations versus alloy composition were determined for ZB GaAs1−xBix alloy. Their values in GaAs and GaBi binary compounds are found in very good agreement with available experimental and/or theoretical data. Their variations in GaAs1−xBix alloy show a monotonic decrease with increasing Bi contents, indicating a softening behavior as is typically the case for metallic alloys. The values of the bulk modulus derived with the help of C11, C12 and C44 elastic stiffness coefficients are found very close to B0 values derived directly from Murnaghan equation of state, indicating the good accuracy of Cij coefficients deduced from Birch–Murnaghan procedure.

Compressibility and structural stability of spinel-type MnIn2O4

Spinel-type MnIn2O4 materials are synthesized at 500°C from an In3+–Mn3+ co-precipitate; the synthesis is based on the in situ reduction of Mn3+ to Mn2+ during calcination. The structure refinement of the powder X-ray diffraction data reveals that the degree of inversion i of the (Mn1-i2+Ini3+)[Mni2+In2-i3+]O4 spinel synthesized in the air and N2 is small (i=0.08) and increases to 0.30 for the spinel synthesized in Ar. The distribution of Mn cations over tetrahedral and octahedral sites is confirmed by X-ray absorption near-edge spectroscopy. As shown by the high-temperature in situ X-ray diffractometry, MnIn2O4 spinel is stable against oxidation in the air up to 550°C. The in situ X-ray diffraction experiments in a diamond anvil cell reveal that MnIn2O4 is stable up to 22GPa at room temperature. The bulk modulus B0 and its first pressure derivative B0' determined by the third-order Birch–Murnaghan equation of state are 139.8(4)GPa and 5.4(5), respectively.

Structural Transition of MnNb2O6 under Quasi-Hydrostatic Pressure

High-pressure Raman scattering and X-ray diffraction studies on manganese niobate (MnNb2O6) have been carried out in a diamond anvil cell at room temperature up to 41 GPa. A pressure-induced phase transition was observed at 12 GPa accompanied by the softening of two internal vibration modes ν10(B2g) and ν8(Ag). Disappearing of most Raman vibration peaks under high pressure reveals that the NbO6 octahedra distort heavily through the transition; this is evidenced by the X-ray diffraction results, but the octahedral units still exist, as the internal Nb–O strengthening vibration is observable even at the highest pressure in this study. The equation of state for MnNb2O6 in low pressure phase I was obtained with third-order Birch–Murnaghan method, yielding a zero-pressure bulk modulus B0 and its pressure derivative B0′ of 154.4 ± 3.5 GPa and 4.1, respectively. The volume dependencies of the optical lattice mode frequencies and their respective Gruneisen parameters were extracted; it is suggested that the insta...

Thermoelastic equation of state of boron suboxide B6O up to 6 GPa and 2700 K: Simplified Anderson-Grüneisen model and thermodynamic consistency

p-V-T equation of state of superhard boron suboxide B6O has been measured up to 6 GPa and 2700 K using multianvil technique and synchrotron X-ray diffraction. To fit the experimental data, the theoretical p-V-T equation of state has been derived in approximation of the constant value of the Anderson-Gr\"uneisen parameter {\delta}T. The model includes bulk modulus B0 =181 GPa and its first pressure derivative B0' = 6 at 300 K; two parameters describing thermal expansion at 0.1 MPa, i.e. a = 1.4x10-5 K-1 and b = 5x10-9 K-2, as well as {\delta}T = 6. The good agreement between fitted and experimental isobars has been achieved to the absolute volume changes up to 5% as compared to volume at standard conditions, V0. The fitted thermal expansion at 0.1 MPa is well consistent with the experimental data, as well as with ambient-pressure heat capacity cp, bulk modulus B0 and {\delta}T describing its evolution with volume and temperature. The fitted value of Gr\"uneisen parameter {\gamma} = 0.85 is in agreement with previous empiric estimations for B6O and experimental values for other boron-rich solids.

First-principles study of the structural, electronic and optical properties of tetragonal LiIO3

The structural parameters, electronic structure, chemical bonding, and optical properties of tetragonal LiIO3 have been studied using the ab initio pseudopotential density functional method within the generalized gradient approximation. The structural parameters of tetragonal LiIO3 agree well with the experimental data. Results are given for bulk modulus B and its pressure derivative B0′. The energy band structure, density of states, and Mulliken charge population are obtained, which indicates that tetragonal LiIO3 has an indirect band gap of 2.65eV at A–Γ, in the absence of the scissors operation. Furthermore, in order to clarify the mechanism of optical transitions of tetragonal LiIO3, the complex dielectric function ε(ω), refractive index n(ω), extinction coefficient κ(ω), absorption efficient α(ω), reflectivity R(ω) and energy loss function L(ω) are also calculated.

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.

High-pressure synthesis and in-situ high pressure x-ray diffraction study of cadmium tetraphosphide

Pure-phase polycrystalline cadmium tetraphosphide (CdP4) has been successfully synthesized under high pressures in a large volume cubic press, and the pressure–temperature (P-T) formation boundary of CdP4 from the Cd–P binary system has been determined. The equation of state of monoclinic CdP4 has also been evaluated by synchrotron-radiation angle-dispersive X-ray diffraction (ADXRD) under quasihydrostatic compression up to 26.4 GPa in a diamond-anvil cell. The ADXRD data yield a bulk modulus B0 = 94 ± 9 GPa with a pressure derivative B0′ = 8.0. The experimental data are discussed and compared to the results of first-principles calculations.

Effect of nanostructuration on compressibility of cubic BN

Compressibility of high-purity nanostructured cBN has been studied under quasi-hydrostatic conditions at 300 K up to 35 GPa using diamond anvil cell and angle-dispersive synchrotron X-ray powder diffraction. A data fit to the Vinet equation of state yields the values of the bulk modulus B0 of 375(4) GPa with its first pressure derivative B0' of 2.3(3). The nanometer grain size (\sim20 nm) results in decrease of the bulk modulus by ~9%.

High pressure studies on uranium and thorium silicide compounds: Experiment and theory

The actinide silicides ThSi, USi and USi2 have been studied under high pressure using both theory and experiment. High pressure synchrotron X-ray diffraction experiments were performed on polycrystalline samples in diamond anvil cells at room temperature and for pressures up to 54, 52 and 26GPa, for ThSi, USi and USi2, respectively. At ambient conditions, the uranium silicides crystallize in tetragonal structures (space groups: I4/mmm for USi and I41/amd for USi2), while ThSi adopts an orthorhombic structure (space group: Pbnm) (including an anharmonic analysis of the silicon). These structures are found to be stable with no structural transitions observed up to the highest pressures achieved. The zero-pressure bulk modulus B0 and its pressure derivative B0′ at ambient pressure are obtained from the measured P–V relations. The experiments are accompanied by first principles calculations using the full-potential linear muffin-tin orbital method within the generalized gradient approximation for exchange–correlation effects. Experimental results are well reproduced by the calculated equation of state and ground state properties.

Structure and nuclear density distribution in the cheralite—CaTh(PO4)2: studies of its behaviour under high pressure (36 GPa)

The crystal structure of the cheralite—CaTh(PO4)2—has been revisited by neutron diffraction and its behaviour under high pressure investigated by X-ray diffraction up to 36 GPa. The neutron diffraction data at ambient pressure gave a more accurate determination of the Ca/Th cation position than previous XRD data, taking advantage that the neutron scattering lengths of calcium and thorium are of same order of magnitude. The nuclear density distribution was also determined using the maximum entropy method (MEM) confirming that the two cations are not located at the same position in the unit cell but are slightly displaced from one another along a specific direction in order to minimize the electrostatic repulsion with the surrounding phosphorus atoms. At high pressure, the compound did not show any phase transition or amorphization. From the evolution of the unit-cell volume as a function of the pressure, the zero-pressure bulk modulus B0 and its pressure derivative B0 ′ have been determined by fitting the experimental compressibility curve to the Birch–Murnaghan equation of state. The results are B0 = 140(2) GPa and B 0 ′ = 4.4(4) GPa.

Structural and Elastic Properties of AlAs under Pressure from First-Principles Calculations

A first-principles plane wave method with the ultrasoft pseudopotential scheme in the frame of the density functional theory (DFT) is performed to calculate the structural and lattice parameters, the bulk modulus B0 and its pressure derivative B0' of the zinc-blende AlAs, rocksalt AlAs and NiAs-AlAs. The elastic parameters of the zinc-blende AlAs, rocksalt AlAs and NiAs- AlAs were calculated. We also calculate the phase transition pressures between different phases. Our results are satisfactory. Our results are consistent with other results.