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1.
Structural and thermodynamic properties of wurtzite-type aluminium nitride from first-principles calculations
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The lattice parameter, bulk modulus and its pressure derivative of
the wurtzite-type aluminium nitride (w-AlN) are investigated by using
the Cambridge Serial Total Energy Package (CASTEP) program in the
framework of Density Functional Theory (DFT). The calculated results
are in good agreement
with the available experimental data and other theoretical results.
Through the quasi-harmonic Debye model, the dependences of the
normalized lattice parameters $a/a_{0}$ and $ c/c_{0}$, axial ratio
$c/a$, normalized primitive-cell volume $V/V_{0}$, Debye
temperature ${\it\Theta} _{\rm D} $ and heat capacity $C_{\rm V}$ on
pressure $P $ and temperature $ T$ are obtained. It is found that the
interlayer covalent interactions (Al-N bonds) are more (even a
little) sensitive to temperature and pressure than intralayer ones
(N--N bonds), which gives rise to a little lattice anisotropy in the
w-AlN. 相似文献
2.
First-principles investigations on elastic and thermodynamic properties of zinc-blende structure BeS
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In this paper the elastic and thermodynamic properties of the cubic
zinc-blende structure BeS at different pressures and temperatures
are investigated by using \textit{ab initio} plane-wave
pseudopotential density functional theory method within the
generalized gradient approximation (GGA). The calculated results are
in excellent agreement with the available experimental data and
other theoretical results. It is found that the zinc-blende
structure BeS should be unstable above 60GPa. The thermodynamic
properties of the zinc-blende structure BeS are predicted by using
the quasi-harmonic Debye model. The pressure-volume-temperature
($P-V-T$) relationship, the variations of the thermal expansion
coefficient $\alpha$ and the heat capacity $C_{V}$ with pressure $P$
and temperature $T$, as well as the Gr\"{u}neisen
parameter-pressure-temperature ($\gamma -P-T$) relationship are
obtained systematically in the ranges of 0--90GPa and 0--2000K. 相似文献
3.
First-principles calculations of structural and thermodynamic properties of BeB2 compound 总被引:1,自引:0,他引:1
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The lattice parameter bulk modulus and pressure derivative of BeB2 are calculated by using the Cambridge Serial Total Energy Package (CASTEP) program in the frame of density function theory. The calculated results agree well with the average experimental data and other theoretical results. Through the quasi-harmonic Debye model, the dependences of the normalized lattice parameters a/ao, c/c0 and the normalized primitive cell volume V/Vo on pressure P, the variation of the thermal expansion coefficient ~ with pressure P and temperature T, as well as the dependences of the heat capacity Cv on pressure P and temperature T are obtained systematically. 相似文献
4.
The electronic and optical properties of the cubic zinc-blende (ZB)
structured filled tetrahedral semiconductor α-LiZnN
under pressure are investigated by using \textit{ab initio} plane
wave pseudopotential density functional theory method within the
generalized gradient approximation (GGA). The electronic band
structure and the density of state under pressure are systematically
described. The basic optical constants, including the reflection and
absorption spectra, the energy-loss function, the complex refractive
index and the dielectric function, are calculated and analysed at
different external pressures. Our results suggested that the ZB
α-LiZnN is transparent in the partially
ultra-violet to the visible light region, and it seems that the
transparency is hardly affected by the pressure. 相似文献
5.
A new transition metal diphosphide α-MoP2 synthesized by a high-temperature and high-pressure technique
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Xiaolei Liu 《中国物理 B》2023,32(1):18102-018102
Monoclinic $\alpha $-MoP$_{2}$, with the OsGe$_{2}$-type structure (space group $C2/m$, $Z = 4$) and lattice parameters $a = 8.7248(11) $ Å, $b = 3.2322(4) $ Å, $c = 7.4724(9) $ Å, and $\beta =119.263^\circ $, was synthesized under a pressure of 4 GPa at a temperature between 1100 ${^\circ}$C and 1200 ${^\circ}$C. The structure of $\alpha $-MoP$_{2}$ and its relationship to other transition metal diphosphides are discussed. Surprisingly, the ambient pressure phase orthorhombic $\beta $-MoP$_{2}$ (space group Cmc2$_{1}$) is denser in structure than $\alpha $-MoP$_{2}$. Room-temperature high-pressure x-ray diffraction studies exclude the possibility of phase transition from $\beta $-MoP$_{2}$ to $\alpha $-MoP$_{2}$, suggesting that $\alpha $-MoP$_{2}$ is a stable phase at ambient conditions; this is also supported by the total energy and phonon calculations. 相似文献
6.
Structural, thermodynamic and electronic properties of zinc-blende AlN from first-principles calculations
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Structural, thermodynamic and electronic properties of zinc-blende
AlN under pressure are investigated by first-principles calculations
based on the plane-wave basis set. Through the analysis of enthalpy
variation of AlN in the zinc-blende (ZB) and the rock-salt (RS)
structures with pressure, we find the phase transition of AlN from
ZB to RS structure occurs at 6.7 GPa. By using the quasi-harmonic
Debye model, we obtain the heat capacity CV, Debye temperature
ΘD, Grüneisen parameter γ and thermal
expansion coefficient α. The electronic properties including
fundamental energy gaps and hydrostatic deformation potentials are
investigated and the dependence of energy gaps on pressure is
analysed. 相似文献
7.
LIU Zhong-Li CHENG Yan TAN Ni-Na GOU Qing-Quan 《理论物理通讯》2006,46(3):573-576
The thermodynamic properties of LiBC are investigated by using the full-potential linearlzed muffin-tin orbital method (FP-LMTO) within the frame of density functional theory (DFT) and using the quasi-harmonic Debye model. The dependencies of the normalized lattice parameters a/a0 and c/c0, the ratio (c/a)/2, the normalized primitive volume V/V0 on pressure and temperature are successfully obtained. It is found that the interlayer covalent interactions (Li-B bonds or Li-C bonds) are more sensitive to temperature and pressure than intralayer ones (B-C bonds), as gives rise to the extreme lattice anisotropy in the bulk hop LiBC. 相似文献
8.
The thermodynamic properties of LiBC are investigated by using the full-potential linearized muffin-tin orbital method (FP-LMTO) within the frame of density functional theory (DFT) and using the quasi-harmonic Debye model. The dependencies of the normalized lattice parameters a/a0 and c/c0, the ratio (c/a)/2, the normalized primitive volume V/V0 on pressure and temperature are successfully obtained. It is found that the interlayer covalent interactions (Li-B bonds or Li-C bonds) are more sensitive to temperature and pressure than intralayer ones (B-C bonds), as gives rise to the extreme lattice anisotropy in the bulk hcp LiBC. 相似文献
9.
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 B′0 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. 相似文献
10.
First-principles calculations of structure and high pressure phase transition in gallium nitride
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The phase transitions of semiconductor GaN from the Wurtzite (WZ)
structure and the zinc-blende (ZB) structure to the rocksalt (RS)
structure are investigated by using the first-principles plane-wave
pseudopotential density functional method combined with the
ultrasoft pseudopotential scheme in the generalized gradient
approximation (GGA) correction. It is found that the phase
transitions from the WZ structure and the ZB structure to the RS
structure occur at pressures of 46.1 GPa and 45.2 GPa, respectively.
The lattice parameters, bulk moduli and their pressure derivatives of
these structures of GaN are
also calculated. Our results are consistent with available
experimental and other
theoretical results. The dependence of the normalized formula-unit volume
$V/V_{0 }$ on pressure $P$ is also successfully obtained. 相似文献
11.
First-principles study on the effect of Hf content onmartensitic transformation temperatureof TiNiHf alloy 总被引:1,自引:0,他引:1
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In this paper a first-principles study of the electronic structure and stability of B2
TiDFT TiNiHf 电子结构 马氏体转化温度 平面波 DFT, TiNiHf, electronic structure, martensitic
transformation temperature Project supported by the National Natural Science Foundation of China
(Grant No 50471018). 3/3/2006 12:00:00 AM 6/7/2006 12:00:00 AM In this paper a first-principles study of the electronic structure and stability of B2 Ti1-xNiHfx (x = 0.2, 0.4, 0.6) and B19′ Ti1-xNiHfx(x = 0, 0.5) alloys is presented. The calculations are performed by the plane-wave pseudopotential method in the framework of the density functional theory with the generalized gradient approximation. This paper calculates the lattice parameters, density of states, charge density, and heats of formation. The results show that the electronic structure and stability of B2 Ti1-xNiHfx change gradually with Hf content. However, Hf content has little effect on the electronic structure and stability of B19′ Ti1-xNiHfx. The mechanism of the effect of Hf content on martensitic transformation temperature of TiNiHf alloys is studied from the electronic structure. 相似文献
12.
The electronic, optical and thermodynamic properties of ZnS in the zinc-blende (ZB) and wurtzite (WZ) structures are investigated by using the plane-wave pseudopotential density functional theory (DFT). The results obtained are consistent with other theoretical results and the available experimental data. When the pressures are above 20.5 and 27 GPa, the ZB-ZnS and the WZ-ZnS are converted into indirect gap semiconductors, respectively. The critical point structure of the frequency-dependent complex dielectric function is investigated and analysed to identify the optical transitions. Moreover, the values of heat capacity Cv and Debye temperature θ at different pressures and different temperatures are also obtained successfully. 相似文献
13.
We employ a first-principles plane wave method with the
relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter
(HGH) scheme in the frame of DFT to calculate
the equilibrium lattice parameters and the thermodynamic properties of
AlB2 compound with hcp structure. The obtained lattice parameters are in
good agreement with the available experimental data and those calculated by
others. Through the quasi-harmonic Debye model, obtained successfully are
the dependences of the
normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized
primitive cell volume V/V0 on pressure P, the variation of the thermal
expansion α with pressure P and temperature T, as well as the Debye
temperature \ThetaD and the heat capacity CV on pressure P and
temperature T. 相似文献
14.
A new compound with the stone cheinical composition as Li3AlB2O6 but with a different x-ray powder diffraction pattern as reported before was synthesized and studied experimentally by M. He, Chen X Let al (J. Solid State Chem. 163, 369 (2002)), but there lacks first principles study on the structure of it. Using conjugant gradient (CG) molecule dynamics (MD) simulation with a full relaxation of the atomic positions and of the shape and size of the cell, the structure of Li3AlB2O6 is studied from first principles. For the density functional, the local density approximation (LDA) and the generalized gradient approximation (GGA) forms are used respectively. Both the LDA and GGA results support the experimental structure of M. He et al. The result of MD simulation using GGA agrees with the experimental result much better. The energy bands are also studied, the band gap given by LDA and GGA are 5.65 eV, 5.34eV, respectively. 相似文献
15.
Elastic and thermodynamic properties of c-BN from first-principles calculations 总被引:1,自引:0,他引:1
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The elastic constants and thermodynamic properties of c-BN are
calculated using the first-principles plane wave method with the
relativistic analytic pseudopotential of the Hartwigen, Goedecker
and Hutter (HGH) type in the frame of local density approximation
and using the quasi-harmonic Debye model, separately. Moreover, the
dependences of the normalized volume V/V0 on pressure P, as
well as the bulk modulus B, the thermal expansion α, and the
heat capacity CV on pressure P and temperature T are also
successfully obtained. 相似文献
16.
We have investigated the structural and elastic properties
of MgB2 under high pressures using the full-potential linearized
muffin-tin orbital (FP-LMTO) scheme within the generalized gradient
approximation correction (GGA) in the frame of density functional
theory. The calculated pressure dependence of the normalized
volume is in excellent agreement with the experimental results.
At the same time the elastic constants and acoustic anisotropy
as a function of applied pressure are presented. Through the
quasi-harmonic Debye model, we also investigate the thermodynamic
properties of MgB2. 相似文献
17.
采用基于密度泛函理论的第一性原理平面波赝势方法研究ZrV2的晶体结构和弹性,利用准谐Debye模型计算在不同温度(T=0~1200 K)和不同压强(P=0~20 GPa)下ZrV2的热力学性质,包括弹性模量与压强,热熔与温度,以及热膨胀系数与温度和压力的关系.结果表明:计算的ZrV2晶格常数与实验值符合较好,晶体材料的弹性常数随着压力增加而增加;在一定温度下,相对体积、热熔随着压强的增加而减小,德拜温度、弹性模量随着压强的增加而增加,且高压下温度对ZrV2热膨胀系数的影响小于压强的影响. 相似文献
18.
Hai-Hua ChenZuo Li Yan Cheng Yan BiLing-Cang Cai 《Physica B: Condensed Matter》2011,406(17):3338-3341
The energy-volume curves of OsB have been obtained using the first-principles plane-wave ultrasoft-pseudopotential density functional theory (DFT) within the generalized gradient approximation (GGA) and local density approximation (LDA). Using the quasi-harmonic Debye model we first analyze the specific heat, the coefficients of thermal expansion as well as the thermodynamic Grüneisen parameter of OsB in a wide temperature range at high pressure. At temperature 300 K, the coefficients of thermal expansion αV by LDA and GGA calculations are 1.67×10−5 1/K and 2.01×10−5 1/K, respectively. The specific heat of OsB at constant pressure (volume) is also calculated. Meanwhile, we find that the Debye temperature of OsB increases monotonically with increasing pressure. The present study leads to a better understanding of how the OsB materials respond to pressure and temperature. 相似文献
19.
Both in local-density approximation (LDA) and in generalised-gradient approximation (GGA) the electronic structure of Aluminium is evaluated by use of the modified augmented plane wave (MAPW) self-consistent scheme. The LDA based on the exchange correlation functional by Vosko, Wilk and Nusair gives the equilibrium lattice constant in good accord with its experimental value. The hole sheet of the Fermi surface, h2, is well described by weakly distorted spheres with origin at
and
in the reciprocal lattice. Near and above the equilibrium lattice constant the electronic sheet, e3, is found to be quite similar to the model originally proposed by Ashcroft. However, even moderate compressions induce a drastic variation.Received: 17 November 2003, Published online: 2 April 2004PACS:
71.18. + y Fermi surface: calculations and measurements; effective mass, g factor - 71.20.-b Electron density of states and band structure of crystalline solids 相似文献
20.
Magnetism and giant magnetocaloric effect in rare-earth-based compounds R_3BWO_9(R = Gd,Dy, Ho)
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《中国物理 B》2021,30(7):77501-077501
The magnetism and magnetocaloric effect(MCE) of rare-earth-based tungstate compounds R_3 BWO_9(R=Gd,Dy,Ho) have been studied by magnetic susceptibility,isothermal magnetization,and specific heat measurements.No obvious long-range magnetic ordering can be found down to 2 K.The Curie-Weiss fitting and magnetic susceptibilities under different applied fields reveal the existence of weak short-range antiferromagnetic couplings at low temperature in these systems.The calculations of isothermal magnetization exhibit a giant MCE with the maximum changes of magnetic entropy being 54.80 J/kg-K at 2 K for Gd_3 BWO_9,28.5 J/kg-K at 6 K for Dy_3 BWO_9,and 29.76 J/kg-K at 4 K for Ho_3 BWO_9,respectively,under a field change of 0-7 T.Especially for Gd_3 BWO_9,the maximum value of magnetic entropy change(-ΔS_M~(max)) and adiabatic temperature change(-ΔT_(ad)~(max)) are 36.75 J/kg·K and 5.56 K for a low field change of 0-3 T,indicating a promising application for low temperature magnetic refrigeration. 相似文献