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1.
Ceramic KBiScNbO6 compound was synthesized for the first time. X‐ray diffraction analysis revealed that at room temperature the samples consist of a mixture of the perovskite and pyrochlore phases. The dominant phase is the perovskite one. This phase can be described as distorted pseudocubic Pm3m structure with unit‐cell parameter ac = 4.069 Å. Rhombohedral distortion leading the polar R3m phase is assumed to be one of possible structural distortions. Dielectric measurements of the compound under study demonstrated anomalies associated with relaxor ferroelectric behavior (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
The structural, electronic and optical properties of double perovskite oxides Ba2(InNb)O6 and Ba2(InTa)O6 are investigated by full-potential linearized augmented plane wave method based on density functional theory under generalized gradient approximation. The real and imaginary parts of the dielectric function and the optical constant (refractive index) are calculated. The calculated spectra are compared with the experimental results and are found to be in reasonable agreement. The interband contributions to the optical properties of these perovskite oxides have been analyzed. 相似文献
3.
M.G. Brik 《Journal of Physics and Chemistry of Solids》2012,73(2):252-256
The structural, electronic, optical and elastic properties of the cubic double perovskite Ba2MgWO6 were calculated using the ab initio plane wave method and compared with the available experimental data. The pressure effects were modeled by optimizing the crystal lattice structure and calculating the band gap at elevated hydrostatic pressures. The calculated values of the relative change of a unit cell volume with pressure are in excellent agreement with the recent experimental measurements [S. Meenakshi et al, J. Phys. Chem. Solids 72 (2011) 609]. The pressure coefficients of the lattice constant and the WO, MgO, BaO bonds variations were all evaluated. Elastic anisotropic properties were analyzed by calculating all independent components of the elastic constants tensor; the greatest and the smallest values of the Young's moduli were determined. 相似文献
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基于密度泛函理论框架下的第一性原理,采用考虑在位库仑作用的广义梯度近似(GGA+U)下的投影缀加波(PAW)方法,研究了具有双钙钛矿结构的Sr2FeWO6和SrKFeWO6材料的晶体结构、电子结构以及磁性性质.结构优化表明,K空穴掺杂稳定了FeO6及WO6八面体结构,Fe-O-W键角更加接近180°,有利于Fe-O-W-O-Fe超交换作用;对电子结构分析发现掺杂元素本身对总态密度贡献很小,空穴(p
关键词:
电子结构
磁性
6')" href="#">SrKFeWO6
双钙钛矿 相似文献
6.
The dielectric and conductive characteristics of La2NiMnO6 double perovskite ceramics were investigated together with the crystal structure. La2NiMnO6 ceramics crystallized in the monoclinic P21/n structure in which the Ni2+ and Mn4+ ions ordered periodically. Relaxor-like dielectric behavior combined with a giant dielectric constant step was observed in the present ceramics, and these unique dielectric characteristics should be attributed to the charge ordering of Ni2+ and Mn4+. The dielectric relaxation was well fitted by the modified Debye equation and Arrhenius law with the activation energy of 0.17 eV. The dc conductivity of La2NiMnO6 could be well fitted using a variable-range hopping mechanism instead of a band conduction mechanism. 相似文献
7.
Barón-González AJ Frontera C García-Mu?oz JL Rivas-Murias B Blasco J 《J Phys Condens Matter》2011,23(49):496003
The origin of dielectric anomalies and magnetodielectric response of La(2)MnCoO(6) has been investigated by means of ultra-high resolution synchrotron x-ray powder diffraction, neutron powder diffraction, resistivity, magnetization and dielectric measurements. The study has been performed on two different bulk samples presenting different degrees of Mn/Co order: 95 and 74%. Beside the well-known influence on magnetic properties, our results show that the main effect of disorder lies on the electrical resistivity. Bond distances clearly show Mn(4+)/Co(2+) valence states in the well-ordered sample, while for the disordered one this picture still holds. AC resistivity data show dielectric anomalies and a small magnetodielectric effect, but impedance complex plane analyses prove that these phenomena appear at the frequency-temperature region where extrinsic effects dominate the dielectric response. 相似文献
8.
The magnetic effect and the magnetocaloric effect in La_2NiMnO_6(LNMO) double perovskite are studied using the Monte Carlo simulations.The magnetizations,specific heat values,and magnetic entropies are obtained for different exchange interactions and external magnetic fields.The adiabatic temperature is obtained.The transition temperature is deduced.The relative cooling power is established with a fixed value of exchange interaction.According to the master curve behaviors for the temperature dependence of △S_m~(max) predicted for different maximum fields,in this work it is confirmed that the paramagnetic-ferromagnetic phase transition observed for our sample is of a second order.The near room-temperature interaction and the superexchange interaction between Ni and Mn are shown to be due to the ferromagnetism of LNMO. 相似文献
9.
N. M. Olekhnovich A. N. Salak A. V. Pushkarev Yu. V. Radyush N. P. Vyshatko D. D. Khalyavin V. M. Ferreira 《Physics of the Solid State》2009,51(3):582-588
Physics of the Solid State - The dielectric properties of metastable high-pressure perovskite ceramics Bi(Mg1/2Ti1/2)O3 were studied by impedance spectroscopy at frequencies of 25 Hz-1 MHz at... 相似文献
10.
WANG Xin-qiang CHEN Yong 《原子与分子物理学报》2004,21(Z1):211-212
The structural and electronic properties of (CdSe)n(1≤n≤5) clusters are calculated using density functional theory within the pseudopotential and generalized gradient approximations. The calculated binding energies and highest occupied molecular orbital lowest unoccupied molecular orbital gaps are compared with those obtained within local density approximation. 相似文献
11.
《中国物理 B》2019,(9)
We study the magnetic properties of the double perovskite ruthenate compound Sr_2YRuO_6 using Monte Carlo simulations(MCS).We elaborate the ground state phase diagrams for all possible and stable configurations.The magnetizations and the susceptibilities as a function of temperature for the studied system are also reported.The effects of the exchange coupling interactions and the crystal field are examined and discussed.On the other hand, since the compound Sr_2YRuO_6 exhibits an antiferromagnetic behavior, we find its Néel temperature, T_N≈ 31 K, which is in good agreement with the experimental results in the literature.To complete this study, the hysteresis loops and the coercive field as a function of the external magnetic field are also obtained for fixed values of the physical parameters. 相似文献
12.
The structural, electronic and magnetic properties of the double perovskite Pb2FeMoO6 have been studied by using the first-principle projector augmented wave (PAW) potential within the generalized gradient approximation (GGA) as well as taking into account the on-site Coulomb repulsive interaction (GGA+U). Similar to Sr2FeMoO6 and Pb2FeReO6, the optimized crystal structure of Pb2FeMoO6 is a body-centered tetragonal (BCT) with the lattice constants a=b=5.60 Å and c=7.94 Å. The two axial TM?O distances are slightly larger than the four equatorial TM?O distances, which shows that the Jahn–Teller structural distortion exists in FeO6 and MoO6 octahedra. The half-metallic ferromagnetic nature implies a potential application of this new compound in spintronics devices. The Fe3+ and Mo5+ ions are in the states (3d5, S=5/2) and (4d1, S=1/2) with magnetic moments 3.87 and ?0.38μB respectively and thus there exists an antiferromagnetic coupling via oxygen between them. 相似文献
13.
《Journal of magnetism and magnetic materials》2001,237(2):124-134
The nuclear and magnetic structure and the magnetic properties of the polycrystalline double perovskite Sr2MnWO6 have been studied. Rietveld analysis of neutron powder diffraction (NPD) data at T=295 K shows that the sample is tetragonal (space group P42/n, a=8.0119(4) Å, c=8.0141(8) Å). Some additional magnetic diffraction peaks were found in the NPD pattern at 10 K, which can be accounted for by antiferromagnetic ordering of spins at the Mn sites. The magnetic unit cell is doubled in all three unit axes directions (a=b=15.9984(8) Å, c=16.012(2) Å) and the manganese moments are coupled antiferromagnetically along the unit cell axes. The total magnetic moment of Mn2+ is found to be 2.27(7) μB. The antiferromagnetic behaviour was confirmed from magnetisation measurements. The transition from a paramagnetic to an antiferromagnetic state takes place at 13.0±0.1 K. 相似文献
14.
A fully orthorhombic boron nitride (BN) polymorph with an orthorhombic symmetry (Ima2-BN, space group: Ima2) was investigated by first-principles calculations. The Ima2-BN under 30 GPa is both mechanically and dynamically stable via elastic constants and phonon spectra. The anisotropic and electronic properties of Ima2-BN under different pressure are investigated in this work. The anisotropic properties calculations show that the Young's modulus of Ima2-BN in (001) plane exhibits the greatest anisotropy under ambient pressure, while in (111) plane it is the greatest when P > 20 GPa, while the (010) plane has always exhibited the minimal anisotropy whether under ambient pressure or high pressure. Ima2-BN is an indirect wider band gap semiconductor material under ambient pressure, and the band gap of Ima2-BN decreases with the increasing pressure. The minimum thermal conductivities κmin of Ima2-BN is 1.85 W/(cmK), it is slightly higher than of B4N4-I and c-BN. 相似文献
15.
Q. Zhang G.H. Rao Y.G. Xiao G.Y. Liu Y. Zhang J.K. Liang 《Applied Physics A: Materials Science & Processing》2006,84(4):459-463
Hole-doped double perovskite compounds (Sr,Na)2FeMoO6 with the Na content of x=0,0.02,0.03,0.07 and 0.17 have been synthesized by sol–gel method. Effects of hole doping on the crystal structure and magnetic properties of Sr2FeMoO6 have been investigated by means of X-ray powder diffraction (XRD) and magnetic measurements. The XRD pattern indicates that all the samples are of single phase and belong to the space group I4/m. Due to the smaller ionic radius of Na+ than that of Sr2+ ions, the lattice constants and unit cell volume of the compound decrease slightly with x. The degree of cation ordering in the Na-doped Sr2FeMoO6 compounds shows a non-monotonic variation with the doping level, increasing from x=0 to x=0.03 and decreasing slightly with further increase of the doping. In contrast to the composition dependence of the degree of ordering, the Curie temperature of the compound decreases at low doping level and increases at high doping level. The saturation magnetization of the compound increases with x for x<0.17. Similar to the electron-doped Sr2FeMoO6, provided that the doped hole enters selectively the spin-down band, the variation of the saturation magnetization can be explained in light of the ferrimagnetic model (FIM). PACS 61.72.Ww; 75.50.-y; 75.30.Cr; 75.50.Gg 相似文献
16.
C. Etz D. Stoeffler 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(4):429-434
We investigate the electronic structure of bulk
Sr2CoMoO6-δ double perovskites using the
ab initio Full Potential Linearized Augmented Plane Wave
method in order to study their magnetic properties
within the GGA and GGA+U methods. We discuss the relative stability of ferromagnetic (FM) and antiferromagnetic (AFM) orders
(i) without and with
taking into account the observed tilting of the oxygen octahedra
and (ii) by introducing oxygen vacancies. We show that a very good agreement with experimental results — AFM order for δ=
0 and FM order for δ= 1/2 — is obtained only when the tilting of the oxygen tetrahedra
is taking into account and when the GGA+U method is used. 相似文献
17.
First principles study on lattice vibration and electrical properties of layered perovskite Sr_2M_2O_7(M=Nb,Ta)
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In this paper, we performed calculations to investigate the dielectric, piezoelectric properties, Born effective charge(BEC), and spontaneous polarization of Sr_2M_2O_7, the method used in our study was a well-known density functional theory based on first-principles. The optimized results were in good agreement with previous experiments and calculations,which indicates that our calculated method is reasonable. The research we have done suggested that greater piezoelectric components of Sr_2Nb_2O_7 were e_(31) and e_(33), and the contributions were derived from the A_1. By studying the Born effective charge, it could be seen that the valence of ions changed, and the O of Sr_2Nb_2O_7 were most obviously that caused by the covalent character of ions and the hybridization of O-2 p and Nb-4 d. The spontaneous polarization of Sr_2Nb_2O_7 in the [001]direction is 25 μC/cm~2, while for Sr_2Ta_2O_7, there was no spontaneous polarization in the paraelectric state. Finally, the effect of pressure on the piezoelectric properties were also investigated, the polarization of Sr_2Nb_2O_7 decreased linearly with the increase after pressure. All our preliminary results throw light on the nature of dielectric, piezoelectric properties,Born effective charge, and spontaneous polarization of Sr_2M_2O_7, it was helpful for experimental research, the development of new materials, and future applications. 相似文献
18.
Zhen-Long Lv Hong-Ling Cui Xiao-Hong Li Hui Wang Guang-Fu Ji 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(3):57
SrClF is an important optical crystal and has many technological applications. In this work, vibrational, dielectric and thermal properties of SrClF were investigated by density functional perturbation calculation. The calculated Born effective charges are close to their nominal ionic charges, revealing the ionic characteristic of SrClF. Group theory analysis indicates that there are two E u and A 2u infrared modes at the Brillouin zone center of SrClF. The LO-TO splitting of these infrared modes were calculated and discussed and their vibrational modes were sketched. Static dielectric constants were studied, which show that SrClF has a larger ionic dielectric contribution than its electrons. Its birefringence was calculated and the infrared reflectance spectra were simulated, which can be used to explain the experimental findings. Based on the computed phonon dispersion curves, the lattice heat capacity, the Grüneisen parameter and the thermal expansion coefficient as functions of temperature were predicted. 相似文献
19.
Radheshyam Rai 《Solid State Communications》2004,129(5):305-309
Polycrystalline samples of Pb0.9(La1−zBiz)0.1(Zr0.55Ti0.45)0.975O3 [referred as PLBZT] (z=0.0, 0.3, 0.5 and 0.7) have been synthesized by a high-temperature solid-state reaction technique. X-ray diffraction analysis suggests the formation of single-phase compounds with monoclinic structure. The dielectric studies of the compounds as a function of temperature (room temperature, RT to 350 °C) at frequency (1, 10 and 100 kHz) show that the compounds undergo a phase transition of diffuse type. Diffusivity (γ) study of phase transition of these compounds provided its value between 1 and 2, indicating the variation of degree of disordering in the system. Measurement of dc resistivity (ρ) as a function of temperature (RT to 350 °C) at a constant biasing field suggests the compounds have negative temperature coefficient of resistance. 相似文献
20.
二氧化钛(TiO2)作为一种性能优良的光催化剂已经受到越来越多的关注.本研究采用密度泛函理论的第一性原理和广义梯度近似+U方法,对锐钛矿结构TiO2晶体三种可能的(Nb,N)共掺杂TiO2的几何结构、形成能、能带结构、电子密度和光吸收系数进行了研究,并与单掺杂(Nb/N)体系进行了对比.对掺杂后体系的几何结构进行的计算表明杂质原子掺入后晶格发生了不同程度的畸变.此外,(Nb,N)共掺杂体系与纯TiO2相比,其禁带宽度和吸收边较小.同时,与N掺杂TiO2相比,N的2p态在共掺杂情形下变为完全占据,从而减少了电子空穴对的复合.而且共掺杂体系的形成能比N单掺杂体系低,因而更加稳定.因此,(Nb,N)共掺杂可以很好地提升锐钛矿型TiO2在可见光波段的光催化性能. 相似文献