Pressure Derivative B0 Research Articles

High-pressure neutron diffraction study of BaFe2As2

The crystal structure of BaFe2As2 was studied by high-pressure neutron powder diffraction in the pressure range from ambient to 6.5 GPa as well as in the temperature range from 12 K to 293 K at 4.4 GPa and no pressure or temperature induced phase changes were observed. The compression mechanism of BaFe2As2 was found to be anisotropic as the a- and c-axes are reduced by 2.49 and 3.66%, respectively at 6.5 GPa. Within the FeAs layers the Fe-As and Fe-Fe bonds decrease by 2.49 and 3.66%, respectively. The Ba-As distance decreases by 3.70% while the As-As inter-atomic distance along the c-axis exhibits a complex pressure dependence. The bulk modulus B 0 and its pressure derivative B 0' were determined to be B 0 = 59(2) GPa and B 0' = 6.1(7) at ambient temperature.

Pressure-induced phase transition in cubic Lu2O3

The phase transition in cubic Lu2O3 has been investigated by angle dispersive x-ray diffraction and Raman scattering in a diamond anvil cell up to 46.8 GPa and 40.2 GPa, respectively. The diffraction data indicated that a phase transition from the cubic to a monoclinic structure started at 12.7 GPa and completed at 18.2 GPa. This high pressure monoclinic phase is stable up to at least 46.8 GPa and can be quenched to ambient conditions. This irreversible cubic to monoclinic structural transformation has also been confirmed by Raman scattering measurements. A third-order Birch–Murnaghan fit based on the observed pressure-volume data yields a zero pressure bulk modulus of B0=214(6) GPa, its pressure derivative B0′=9(1) for the low-pressure cubic phase; and B0=218(13) GPa, B0′=2.3(3) for the high pressure monoclinic phase, respectively. The mode Grüneisen parameters of different Raman modes for both cubic and monoclinic phases have also been determined.

First-Principles Calculations of Thermodynamic Properties of Superhard Orthorhombic $\beta-BC_2N$

We investigate the thermodynamic properties of the potential superhard or- thorhombic structure boron-carbonitride b-BC2N by using ab initio plane-wave pseu- dopotential density functional theory method within both local density approxima- tion (LDA) and generalized gradient approximation (GGA). The lattice parameters (a, b and c), equilibrium volume V, bulk modulus B0 and its pressure derivative B0' have been calculated, and compared with those of diamond and cubic boron nitride (c-BN). The obtained results are in excellent agreement with the available experimental data and other theoretical results. Through the quasi-harmonic Debye model, we also in- vestigate the thermodynamic properties of b-BC2N. The variation of the thermal ex- pansion a, the heat capacity CV and the Gr ¨ uneisen parameter g with pressure P and temperature T, as well as the pressure-normalized volume (P-Vn) and the pressure- bulk modulus (P-B) relationship of b-BC2N are obtained systematically.

Dynamic Disorder of Bi82+ Clusters in the Plastic Phase (Bi8)3Bi[InI4]9

AbstractBlack, air‐insensitive crystals of the bismuth‐rich tetraiodido‐indate(III) (Bi8)3Bi[InI4]9 have been prepared from melts of the contributing elements. X‐ray diffraction on a single crystal at 293 K and 220 K revealed a cubic structure with [InI4]– tetrahedra, isolated Bi3+ ions and rotationally disordered Bi82+ square antiprisms ace group Fmc; a = 20.162(2) Å at T = 293(1)]. The principal arrangement of the complex ions corresponds to the AuCu3 type. The small bulk modulus B0 = 12(1) GPa and its large pressure derivative B0′ = 11(1) as well as the low Debye temperature θD = 52 K are in accordance with a plastic behavior. Cooling below 148(1) K induces the first order transition into an orderedphase with 0.43 % higher density but much larger unit cell and lower crystallographic point group. The transition enthalpy ΔH ≈ 3.8 kJ·mol–1 and transition entropy ΔS ≈ 3 R were determined from specific heat data. A similar reversible phase transition into a lower symmetric structure is observed at a pressure of approximately 5 GPa. (Bi8)3Bi[InI4]9 is a diamagnetic semiconductor.

First-principle calculations of the structure and elastic properties of GaAs under pressure

A first-principles plane-wave method with the ultrasoft pseudopotential scheme in the framework of density functional theory is performed to calculate the lattice parameters, the bulk modulus B0 and its pressure derivative B0' of the zinc-blende GaAs (ZB–GaAs), rocksalt GaAs (RS–GaAs), CsCl–GaAs, NiAs–GaAs, and wurtzite GaAs (WZ–GaAs). We also calculate the phase transition pressures between different phases, Debye temperatures, and the anisotropies. Our results are consistent with other theoretical results.

Anisotropic Lattice Compression and Possible Valence Change in Kondo Compound CeAu2Si2

Lattice constants and crystal structure of tetragonal Kondo compound CeAu2Si2 have been investigated at high pressure in order to examine pressure-induced change of crystal structure and gradual valence change of Ce atom. It is found that the lattice constants a and c decrease with increasing pressure without any discontinuity up to 13 GPa at room temperature. The bulk modulus B0 and its pressure derivative B0' were obtained to be 112 GPa and 3.2. These values are comparable with other Kondo compounds. From the ρ(T) curve at high pressure which does not change so much under high pressure, it is suggested that the valence of Ce changes sluggishly with pressure and the Kondo state of CeAu2Si2 is very stable at high pressure.

First-principles calculations for elastic properties of rutile TiO2 under pressure

This paper studies the equilibrium structure parameters and the dependences of the elastic properties on pressure for rutile TiO2 by using the Cambridge Serial Total Energy Package (CASTEP) program in the frame of density functional theory. The obtained equilibrium structure parameters, bulk modulus B0 and its pressure derivative B0 are in good agreement with experiments and the theoretical results. The six independent elastic constants of rutile TiO2 under pressure are theoretically investigated for the first time. It is found that, as pressure increases, the elastic constants C11, C33, C66, C12 and C13 increase, the variation of elastic constant C44 is not obvious and the anisotropy will weaken.

Elastic moduli and hardness of c-Zr2.86(N0.88O0.12)4 having Th3P4-type structure

The equation of state of the recently discovered oxygen-bearing cubic zirconium (IV) nitride, c-Zr2.86(N0.88O0.12)4, was measured at room temperature in a diamond anvil cell using x-ray powder diffraction combined with synchrotron radiation. From these studies the bulk modulus B0=219(13)GPa and its first pressure derivative B0′=4.4(1.0) [or B0=223(5)GPa, for B0′ fixed at 4] were obtained. Applying nanoindentation techniques the reduced modulus Er≈220GPa and hardness H≈18GPa were measured for porous c-Zr2.86(N0.88O0.12)4. The shear modulus of c-Zr2.86(N0.88O0.12)4 was estimated to be at least G0=96(13)GPa using the experimental data of B0 and Er, exclusively.

Structural and Thermodynamic Properties of Gallium Arsenide withHexagonal Wurtzite Structure from First-Principles Analysis

A first-principles plane wave method with the ultrasoft pseudopotentialscheme in the frame of the generalized gradient approximation (GGA) isperformed to calculate the lattice parameters, the bulk modulus B0and its pressure derivative B0′ of the hexagonal wurtzite GaAs(w-GaAs) by the Cambridge serial total energy package (CASTEP). Ourcalculations show that the most stable structure of the w-GaAscorresponds to the axial ratio c/a = 1.651 and the internal parameteru = 0.374, consistent with other theoretical results. Also, thethermodynamic properties of the w-GaAs are investigated from thequasi-harmonic Debye model. The dependences of the normalized latticeparameters a/a0, c/c0, the axial ratio c/a, the normalizedvolume V/V0, the heat capacity Cv and the thermal expansionα on pressure P and temperature T are also obtainedsuccessfully.

Structural and vibrational properties of solid nitromethane under high pressure by density functional theory

The structural, vibrational, and electronic properties of solid nitromethane under hydrostatic pressure of up to 20 GPa have been studied using density functional theory. The changes of cell volume, the lattice constants, and the molecular geometry of solid nitromethane under hydrostatic loading are examined, and the bulk modulus B0 and its pressure derivative B0' are fitted from the volume-pressure relation. Our theoretical results are compared with available experiments. The change of electron band gap of nitromethane under high pressure is also discussed. Based on the optimized crystal structures, the vibrational frequencies for the internal and lattice modes of the nitromethane crystal at ambient and high pressures are computed, and the pressure-induced frequency shifts of these modes are discussed.

Four-parameter equation of state of solids

A four-parameter equation of state (EOS), expressed in terms of the equilibrium volume V0, cohesion energy EC, isothermal bulk modulus B0, and its first pressure derivative B0′, is proposed and successfully applied to 40 selected metals. From the proposed EOS, the thermal expansions α, melting points TM, ultimate strengths PC, and critical volume VC of the selected metals are calculated and are in good agreement with the experimental observations. Besides, a strong correlation between PC∕B0 and (VC−V0)∕V0 is found to be (PC∕B0)∕[(VC−V0)∕V0]≈0.31.

Iron Silicides and Their Corresponding Oxides: A High‐Pressure Study of Fe5Si3.

AbstractFor Abstract see ChemInform Abstract in Full Text.

In situ high-pressure x-raydiffraction study of icosahedral Al-Cu-TM (TM = V, Cr, Mn)alloys

Icosahedral Al-Cu-TM (TM: transition metals = V, Cr, Mn)alloys were obtained by single-roller melt-spinning in a protectiveinert-gas atmosphere. The high-pressure properties up to 20 GPawere investigated by in situ energy-dispersive x-raydiffraction at a synchrotron source using a gas-membranediamond-anvil cell. No phase transitions could be observed. Thebulk modulus of the Al-Cu-TM quasicrystalline phases was found toincrease with the Hume-Rothery factor. Moreover, the bulk modulusof the quasicrystalline phase is imposed by the bulk modulus of thetransition metal element. The derived values for the first pressurederivative B0' indicate strong anharmonic contributions in thelattice potentials.

A high-pressure study of Th3P4and some U3X4compounds

Abstract The high-pressure crystal structures of Th3P4 and U3X4, where X = P, As and Sb, have been studied by means of synchrotron x-ray diffraction in the pressure range up to 50 GPa. The cubic phase of these compounds is retained in the whole pressure range. The bulk modulus B0 and its pressure derivative B0’ have been determined for each compound. A log-log plot of B0 versus unit-cell volume gives a straight line for the uranium pnictides, with a slope about -5/3.

Compression ratio and red shift of the R1 line for YAG : Cr

Abstract The linear compression ratio of high-purity YAG and the red shift of the R1 line for YAG : Cr were measured under pressure up to 24 GPa. The experimental results show that the Murnaghan equation is satisfactory for describing the state of YAG. The isothermal bulk modulus B0 and its pressure derivative B0’ were determined from the equation, which are B0 = 191. 7GPa and B0’ = 6.52. The quantitative relationship between the linear compression ratio and the red shift of the R1 line was also obtained.

Pressure-induced electronic instability in CeO

The volume behaviour of cerium monoxide CeO, obtained by synthesis under high pressure, has been determined as a function of pressure up to 25 GPa at room temperature in a diamond anvil cell. Cerium monoxide retains its cubic NaCl-type structure over the whole pressure range investigated but a rapid volume decrease of approximately 8% occurs between normal pressure and 3 GPa with a mean bulk modulus B0 approximately 30 GPa. Above 3 GPa, the volume variations are described by a Birch equation of state with a bulk modulus B0=171 GPa, a pressure derivative B0'=4.8 and an initial relative volume calculated at normal pressure of 0.937. The low bulk modulus at low pressures can be interpreted as resulting from a volume-dependent Kondo interaction.