共查询到20条相似文献,搜索用时 93 毫秒
1.
Jianzhe Wu Dongbin Hou C.E. Whiteley Yanzhang Ma 《Journal of Physics and Chemistry of Solids》2011,72(2):144-146
The high pressure properties of icosahedral boron arsenide (B12As2) were studied by in situ X-ray diffraction measurements at pressures up to 25.5 GPa at room temperature. B12As2 retains its rhombohedral structure; no phase transition was observed in the pressure range. The bulk modulus was determined to be 216 GPa with the pressure derivative 2.2. Anisotropy was observed in the compressibility of B12As2—c-axis was 16.2% more compressible than a-axis. The boron icosahedron plays a dominant role in the compressibility of boron-rich compounds. 相似文献
2.
Y. Yu Q.Q. Liu C.Q. Jin Y.C. Li X.D. Li J. Liu 《Physica C: Superconductivity and its Applications》2009,469(14):843-845
The high-pressure angle-dispersive X-ray diffraction experiments on the NdBa2Cu3O6+δ superconductor were performed from ambient to above 30 GPa at room temperature. The structure analysis based on the Rietveld refinement methods shows the different pressure dependence for the bond length between the basal-plane copper of the pyramids to the apical oxygen (denoted Cu(2)–O(1)) and bond length between basal-plane copper to plane oxygen (denoted Cu(2)–O(2,3)). The ambient bulk modulus B0 is derived as 127 GPa. A possible correlation between Cu(2)–O(1) and Tc was discussed. 相似文献
3.
4.
Xinting Li Xinyu Zhang Jiaqian Qin Suhong Zhang Jinliang Ning Ran Jing Mingzhen Ma Riping Liu 《Journal of Physics and Chemistry of Solids》2014
The structural stability and mechanical properties of WC in WC-, MoC- and NaCl-type structures under high pressure are investigated systematically by first-principles calculations. The calculated equilibrium lattice constants at zero pressure agree well with available experimental and theoretical results. The formation enthalpy indicates that the most stable WC is in WC-type, then MoC-type finally NaCl-type. By the elastic stability criteria, it is predicted that the three structures are all mechanically stable. The elastic constants Cij, bulk modulus B, shear modulus G, Young?s modulus E and Poisson?s ratio ν of the three structures are studied in the pressure range from 0 to 100 GPa. Furthermore, by analyzing the B/G ratio, the brittle/ductile behavior under high pressure is assessed. Moreover, the elastic anisotropy of the three structures up to 100 GPa is also discussed in detail. 相似文献
5.
6.
High pressure phases of boron hydrides B4H10, B4H8 and B4H6 and their stability against dissociation into H and smaller B–H units are reported. Structure predictions based on particle swarm optimization reveal that all the boron hydrides studied show a tendency to separate into smaller structural units at low pressure. Under high pressure, the three-dimensional network in all the stoichiometries selected seems to be the most favourable arrangement. A study of the dissociation of B4H10 reflects an affinity to dissociate into B4H8 and H2 in all the studied pressure range. Nevertheless, B4H8 does not seem to segregate in the studied pressure range and B4H6 may dissociate at 150 GPa. 相似文献
7.
Analyzing the crystalline structure of α- and β-rhombohedral boron as an approximant structure of a quasicrystal, atomic structures of two unit cells (prolate and oblate rhombohedra) of icosahedral quasicrystal are constructed. According to molecular orbital calculation, a neutral B 12 H 12 icosahedral cluster is distorted to a cubic or rhombohedral type by the Jahn–Teller effect. The distortion of B 12 in the β-rhombohedral boron and K2B12H12 has the same sign as the lowest energy distortion in the calculation. Among the α-rhombohedral type structures, the distortion of B12 is correlated with the rhombohedral axis angle, and the angle is the closest to the icosahedral angle for B6O and the distortion is the smallest for B–C. A meta-stable phase has been found on the way towards crystallization of amorphous B–C films. 相似文献
8.
Fe1.087Te exhibits three phases in the pressure range from ambient to 16.6?GPa and becomes amorphous at higher pressures. All three phases have tetragonal symmetry. The low pressure T-phase is stable in the pressure range 0≤P<4.1?GPa and is found to be relatively soft having zero pressure bulk modulus B 0=36(1)?GPa. The intermediate cT-phase is less compressible with B 0=88(5)?GPa and stable in the pressure range 4.1≤P<10?GPa while a more compressible phase was observed between 10 and 16.6?GPa. 相似文献
9.
J.-E.?J?rgensen T. C.?Hansen 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(4):411-415
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. 相似文献
10.
Quasi-hydrostatic compression of aluminum carbide, Al4C3 has been studied to 6 GPa at room temperature using energy-dispersive X-ray powder diffraction with synchrotron radiation. A fit of the experimental p-V data to the Birch equation of state yields the values of the bulk modulus, B0, of 130(5) GPa and the first pressure derivative of the bulk modulus, B′0, of 4.6(9). The compression is found to be anisotropic, with the a-axis being more compressible than the c-axis. 相似文献
11.
Andrzej Katrusiak 《高压研究》2013,33(3):155-167
Abstract 2-Methyl-1, 3-cyclopentanedione (C6H8O2-enol form) crystals have been studied at high pressures to 3.01(5) GPa by single crystal X-ray diffraction. The pressure dependence of the unit-cell dimensions is strongly anisotropic and non-linear, the largest relative changes are observed for & perpendicular to the planes comprising the planar chains of the hydrogen-bonded molecules. The crystal structure has been determined at 1.50, 2.40 and 3.01 GPa. The structure is very stable, the main structural change with pressure is the compression of intermolecular distances including the O … O hydrogen bond—but the position of the molecule in the unit cell remains unchanged. Some systematic changes of the bond lengths (in the limit of statistical significance) can be noted. The structure has been compared with the structures of 1,3-cyclopentanedione and 1,3-cyclohexanedione (enol forms), both undergoing pressure induced phase transitions. The exceptional stability of the 2-methyl- 1,3-cyclopentanedione crystal can be explained on the basis of its structure: energetically favourable orientation of the dipole moments of the molecules of close neighbouring chains. The R-factor/number of unique reflections for the structure determinations at 1.50, 2.40 and 3.01 GPa are 0.103/153,0.093/142 and 0.097/139, respectively. Over 3.01 GPa the unit cell is compressed to less than 84% of its ambient-pressure volume. The root-mean-square displacements of the atoms decreased on average by the factor of 0.75 at 1.50 GPa and 0.74 at 2.40 and 3.01 GPa. 相似文献
12.
The tight-binding linear muffin tin orbital (TB-LMTO) method within the local density approximation is used to calculate structural, electronic and magnetic properties of GdN under pressure. Both nonmagnetic (NM) and magnetic calculations are performed. The structural and magnetic stabilities are determined from the total energy calculations. The magnetic to ferromagnetic (FM) transition is not calculated. Magnetically, GdN is stable in the FM state, while its ambient structure is found to be stable in the NaCl-type (B1) structure. We predict NaCl-type to CsCl-type structure phase transition in GdN at a pressure of 30.4 GPa. In a complete spin of FM GdN the electronic band picture of one spin shows metallic, while the other spin shows its semiconducting behavior, resulting in half-metallic behavior at both ambient and high pressures. We have, therefore, calculated electronic band structures, equilibrium lattice constants, cohesive energies, bulk moduli and magnetic moments for GdN in the B1 and B2 phases. The magnetic moment, equilibrium lattice parameter and bulk modulus is calculated to be 6.99 μB, 4.935 Å and 192.13 GPa, respectively, which are in good agreement with the experimental results. 相似文献
13.
在室温下测量了GdoBr:Eu的常压和高压荧光谱,光谱范围在13 000~21 500 cm-1之间,压力至12 GPa。由光谱数据得到了Eu3+晶场能级随压力的变化曲线。7F0~5能级随压力的变化规律比较复杂,而5D0~2各能均随压力的升高几乎线性地降低。在基态谱项7F的49个状态上进行了晶场拟合计算,所得常压下的5个非零晶场参数分别为:B02=-1 124.0 cm-1,B04=-969.6 cm-1,B44=827.9 cm-1,B06=889.6 cm-1,B46=377.0 cm-1。高压下的计算结果表明,B04、B06这两个晶场参数随压力的增加而增大,B46随压力的增加而减小,而B02、B44随压力的变化有些起伏。晶场强度在8 GPa以下随压力增加而减小,其后开始变强。 相似文献
14.
Yong-Kai WeiJing-Xin Yu Zhi-Guo LiYan Cheng Guang-Fu Ji 《Physica B: Condensed Matter》2011,406(23):4476-4482
The elastic and thermodynamic properties of CsCl-type structure CaB6 under high pressure are investigated by first-principles calculations based on plane-wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The calculated lattice parameters of CaB6 under zero pressure and zero temperature are in good agreement with the existing experimental data and other theoretical data. The pressure dependences of the elastic constants, bulk modulus B (GPa), and its pressure derivative B′, shear modulus G, Young's modulus E, elastic Debye temperature ΘB, Zener's anisotropy parameter A, Poisson ratios σ, and Kleinmann parameter ζ are also presented. An analysis for the calculated elastic constants has been made to reveal the mechanical stability of CaB6 up to 100 GPa. The thermodynamic properties of the CsCl-type structure CaB6 are predicted using the quasi-harmonic Debye model. The pressure-volume-temperature (P-V-T) relationship, the variations of the heat capacity CV, Debye temperature ΘD, and the thermal expansion α with pressure P and temperature T, as well as the Grüneisen parameters γ are obtained systematically in the ranges of 0-100 GPa and 0-2000 K. 相似文献
15.
The ambient structural details and the results of room temperature high pressure angle dispersive X-ray diffraction and electrical resistance measurements on the quasi-one-dimensional sulfide, InV6S8, to a pressure of 25 GPa are reported. The material does not undergo a phase transition in this pressure range, though an anomaly in the c/a ratio has been observed around 10 Gpa. A fit of the Murnaghan equation of state to the V/V0 versus pressure data, with the value of the derivative of B0 with respect to pressure, B′0, fixed at 4 has yielded a value of the bulk modulus, B0, of 110 GPa. We also present data of the pressure dependence of the lattice constants, a and c, the ratio c/a, and the resistance at room temperature. 相似文献
16.
Pooja Soni Gitanjali Pagare Sankar P. Sanyal 《Journal of Physics and Chemistry of Solids》2011,72(6):810-816
The structural, elastic and thermal properties of four transition metal monocarbides ScC, YC (group III), VC and NbC (group V) have been investigated using full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA) both at ambient and high pressure. We predict a B1 to B2 structural phase transition at 127.8 and 80.4 GPa for ScC and YC along with the volume collapse percentage of 7.6 and 8.4%, respectively. No phase transition is observed in case of VC and NbC up to pressure 400 and 360 GPa, respectively. The ground state properties such as equilibrium lattice constant (a0), bulk modulus (B) and its pressure derivative (B′) are determined and compared with available data. We have computed the elastic moduli and Debye temperature and report their variation as a function of pressure. 相似文献
17.
Ravhi S. Kumar Sandeep Rekhi D. Prabhakaran M. Somayazulu Eunja Kim Jeremy D. Cook Timothy Stemmler A.T. Boothroyd Mark R. Chance Andrew L. Cornelius 《Solid State Communications》2009,149(39-40):1712-1716
The crystal structure of Na0.75CoO2 was studied at ambient and low temperatures down to 10 K at pressures up to 40 GPa using synchrotron x-rays and a diamond cell in angle dispersion geometry. A reduction in the c/a ratio was observed at both conditions with the application of pressure. An increase in Co–O bond lengths and a decrease in Na–O bond lengths were observed above 10 GPa. The results of the density functional calculations performed agree well with the pressure induced bond length changes. The anomalous change in the c/a ratio and bond lengths indicate a pressure induced isostructural phase transition above 10 GPa. Bulk modulus calculations show this compound is less compressible than its hydrated analogues. 相似文献
18.
Abstract The method of quenching in fusing state under high static pressure (MQFSHP) was applied for the first time to prepare the quasicrystal icosahedral phase of Al80Mn14Si6 alloy. The pressure was from 2.8GPa to 3.1GPa and the cooling rate during quenching was of about 100°C/s. Some sharp electron diffraction spots showing an arrangement with a five-fold symmetry axis and noncrystalline ring have been observed in electron diffraction experiment. The crystallization temperature of I phase obtained from high pressure(HP) is close to that of rapid cooling ribbon, but the cooling rate of the sample obtained is lower than that of rapid cooling ribbon. 相似文献
19.
Abstract Plutonium monoselenide was studied under high pressure up to 47 GPa, at room temperature, using a diamond anvil cell in an energy dispersive X-ray diffraction facility. At ambient pressure, PuSe has the NaC1-type (B1) structure. The compound has been found to undergo a second-order crystallographic phase transition at around 20 GPa. This phase can be described as a distorted B1 structure, with a rhombohedral symmetry. PuSe transforms to a new phase at around 35 GPa, which can be indexed in the cubic CsCl-type (B2). The volume collapse at this phase transition is 11%. When releasing pressure, we observed a strong hysteresis to the inverse transformation down to 5 GPa. From the pressure-volume relationship, the bulk modulus has been determined to B 0 = 98 GPa and its pressure derivative as B 0 = 2.6. These results are compared to those obtained with other actinide monmictides and monochalcogenides. 相似文献
20.
V. Srivastava M. Rajagopalan S. P. Sanyal 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):131-139
A first-principles tight-binding linear muffin tin orbital (TB-LMTO) method
within the local-density approximation is used to calculate the total
energy, lattice parameter, bulk modulus, magnetic moment, density of states
and energy band structures of half-metallic CrO2 at ambient as well as
at high pressure. The magnetic and structural stabilities are determined
from the total energy calculations. From the present study we predict a
magnetic transition from ferromagnetic (FM) state to a non-magnetic (NM)
state at 65 GPa, which is of second order in nature. We also observe from
our calculations that CrO2 is more stable in tetragonal phase
(rutile-type) at ambient conditions and undergoes a transition to an
orthorhombic structure (CaCl2-type) at 9.6 GPa, which is in good
agreement with the experimental results. We predict a second structural
phase transition from CaCl2- to fluorite-type structure at 89.6 GPa
with a volume collapse of 7.3%, which is yet to be confirmed
experimentally. Interestingly, CrO2 shows half metallicity under
ambient conditions. After the first structural phase transition from
tetragonal to orthorhombic, half metallicity has been retained in CrO2 and it vanishes at a pressure of 41.6 GPa. Ferromagnetism is quenched at a
pressure of 65 GPa. 相似文献