Dielectric properties of Pb(Mg1/4Zn1/4Nb1/2)O11/4

Polycrystalline samples of Pb(Mg_1/4Zn_1/4Nb_1/2)O_11/4 have been synthesized by high temperature columbite precursor solid state reaction technique. Using X-ray diffraction (XRD) technique, compound formation in single phase cubic structure was observed and XRD analysis provided preliminary structural data. Detailed studies of dielectric properties of the compound reveal that this compound has high dielectric constant and diffuse phase transition in a wide range of temperatures around the Curie temperature. The charge deficiency of the compound presumably gets compensated in the high temperature columbite precursor process of sample preparation which is supported by single phasic form of the material.     

The investigations of phases with general formula M2FeV3O11, where M=Mg,Co, Ni,Zn by IR and Mössbauer spectroscopy

Phases of general formula M₂FeV₃O₁₁, where M=Mg, Co, Ni and Zn as well as the orthorhombic modification of FeNb₁₁O₂₉, have been investigated by the help of IR and Mössbauer spectroscopy. It was found that the isostructural compounds Co₂FeV₃O₁₁, Mg₂FeV₃O₁₁, Zn₂FeV₃O₁₁, as well as Ni₂FeV₃O₁₁ with a different structure have one single and almost identical chemical environment for iron(III). The large Mössbauer quadrupole splitting measured suggests that iron(III) is located in a highly distorted octahedron. The IR spectra of three isostructural M₂FeV₃O₁₁ compounds are similar but differ from that of Ni₂FeV₃O₁₁. The Mössbauer spectrum of orthorhombic FeNb₁₁O₂₉ has been fitted with two doublets, their hyperfine parameters indicating iron in distorted octahedral environment.     

Dielectric and photoelectric properties of Pb(Mg1/3Ta2/3O3 crystals

The temperature dependence of the dielectric constant ɛ and the spectral dependence of the photoconductivity of Pb(Mg_1/3Ta_2/3)O₃ crystals are investigated. The width of the band gap (3.4 eV) is determined. It is found that above the temperature of the maximum of the dielectric constant, its reciprocal 1/ɛ varies with temperature first quadratically and then according to a linear law, as is characteristic of ferroelectrics with a smeared phase transition. The smearing parameter of the transition estimated from the experimental data is close to the value calculated assuming the absence of long-range order in the arrangement of the Mg and Ta ions. Fiz. Tverd. Tela (St. Petersburg) 40, 109–110 (January 1998)     

Dielectric and impedance properties of Bi(Zn2/3V1/3)O3 electronic material

A polycrystalline vanadium doped lead free dielectric material of Bi(Zn_2/3V_1/3)O₃ (BZV) has been prepared using a standard high-temperature solid state reaction technique. Its temperature and frequency dependent capacitive, conductive and resistive characteristics are outlined though experimental investigation. The formation of single phase compound of BZV material with orthorhombic crystal symmetry is identified through X-ray diffraction data analysis, and the homogeneous distribution of grains are realized through scanning electron micrograph. The acquaintance of frequency–temperature dependent electrical parameters with the obtained micrograph provides the experimental evidence of contributions of grain as well as grain boundary in its capacitive and resistive characteristics. The negative temperature coefficient of resistance behaviour of the material is revealed from impedance characteristic, and non-Debye type relaxation has been realized from the Nyquist plot. The charge carriers of this electronic compound have both long & short range order that has been validated from the complex modulus and impedance analysis. The prepared electronic material substantiate some important dielectric features which props up the material as promising component for electronic devices.     

石墨/Li（Ni1/3Co1/3Mn1/3）O2电池充放电过程中电极材料的XRD研究

利用XRD系统地研究了石墨/Li（Ni_1/3Co_1/3Mn_1/3）O₂ 18650型锂离子电池充放电过程中正负极活性材料的晶体结构和微结构的变化.已观测到,由于Li原子的脱嵌,使得LiMO₂点阵参数a缩小,c增大,微应变增大,衍射强度比I₁₀₄/I₁₀₁和I₀₁₂/I₁₀₁降低;此外,由于Li原子的嵌入,2H-石墨的点阵参数a和c,以及微应变ε和堆垛无序度P都增加.同时,讨论了活性材料Li（Ni_1/3Co_1/3Mn_1/3）O₂和石墨在电池充放电过程中的嵌脱锂的物理机理.在充电时,正极Li（Ni_1/3Co_1/3Mn_1/3）O₂中处于（000）位的Li原子优先脱离晶体点阵,继后才是位于（2/3 1/3 1/3）和（1/3 2/3 2/3）位的Li原子离开点阵.锂嵌入石墨,优先进入碳原子六方网格面间的间隙位置,当负极的堆垛无序度达到一定值后,3R相逐渐析出.当电池满充或过充时,在六方石墨中形成LiC₁₂和LiC₆相.放电时,与上述过程相反,但并非是完全可逆的. 关键词： 锂离子电池 微结构 X射线衍射 嵌脱锂物理机理     

Magnetic and transport properties of some U3T3X4-compounds (T = Co, Ni, Cu and X = Sb, Sn)

We have prepared and studied a new series of isostructural U₃T₃X₄-compounds with T = Co, Ni, Cu for X = Sb and T = Ni for X = Sn. Ferromagnetism is found for U₃Co₃Sb₄ and U₃Cu₃Sb₄ below 10 and 88 K, respectively. In contrast, no magnetic order was observed down to 1.7 K for the semiconductor U₃Ni₃Sb₄ and the “moderately” heavy-fermion system U₃Ni₃Sb₄.     

The superconducting properties of YBa2(Cu1−xMx)3O7 for M=Zn and Ni

Transverse and zero-field μSR measurements were made on YBa₂(Cu_1−xNi_x)₃O_7−y withx=0.1 and 0.2, and YBa₂(Cu_1−x Zn _x )₃O_7−y withx=0.03, 0.06, 0.1, and 0.16, wherey≈0.1. Since doping may lead to magnetic ordering this was searched for with both zero and transverse field μSR, but no evidence was found over the temperature range studied: 10–100 K. However, depolarization rates as functions of temperature were obtained, and the low temperature values of these are σ=3.2 μs⁻¹.1.6μs⁻¹, and 1 μs⁻¹ forx=0.01, and 0.2 Ni, respectively, and σ=0.8 μs⁻¹, 0.75 μs⁻¹, 0.65 μs⁻¹, and 0.4 μs⁻¹ forx=0.03, 0.06, 0.1, and 0.16 Zn, respectively. Estimates for the effect of decreasing electron concentration for Zn are made, but these alone do not account for the drop in σ. Estimates for the effect of scattering on λ and hence σ are made. The reduction in σ for Ni dopant is in surprisingly good agreement with these estimates. For Zn the order of magnitude is correct, but the relative lack of further change in σ after the effect of the first 0.03 addition seems to imply a saturation of the effect of scattering.     

Effect of Hydrostatic Pressure on the Dielectric Response of Pb(Mg1/3Nb2/3)O3 Relaxor

The effect of hydrostatic pressure on the dielectric response of Pb(Mg_1/3Nb_2/3)O₃ relaxor single crystal was studied. An increase in the dispersion of the dielectric anomaly, characteristic of the relaxors, was observed: pressure-induced downward shift of the temperature T _m of permittivity maximum at 1 kHz amounts to dT _m /dp = ? 3.8 K/100 MPa, whereas that measured at 1 MHz equals ? 3.3 K/100 MPa. Analysis of the dielectric response of the highly polarizable Pb(Mg_1/3Nb_2/3)O₃ shows that hydrostatic pressure results in a decrease of the correlation radius r _c of polar nanodomains, as well as their activation energy.     

First-principles study of the difference in permittivity between Ba(Mg1 / 3Ta2 / 3)O3 and Ba(Mg1 / 3Nb2 / 3)O3

This paper discusses the difference in permittivity at infrared frequencies between Ba(Mg_1/3Ta_2/3)O₃ (BMT) and Ba(Mg_1/3Nb_2/3)O₃ (BMN) based on a first-principles calculation. The permittivity, far-infrared and Raman spectra are successfully computed. Analysis of these results shows that the smaller amplitude of O in the low frequency mode E_u² (BMT), which is caused by the larger polarizability of Ta⁵⁺, is the origin of the smaller permittivity of BMT.     

锂电池正极材料Li(Co,Ni)O2化合物的第一性原理研究

锂离子电池以其高能量存储密度和优良的循环性能而受到广泛关注, 尤其是其正极材料成为储能材料领域的研究热点.本文采用基于密度泛函理论的第一性原理方法对LiCoO2,LiNiO2和Li(Co0.5Ni0.5)O2化合物的晶体结构、电子结构、化学键合特性进行了研究. 结果表明：Li(Co0.5Ni0.5)O2化合物中主要是氧和过渡金属之间成键, 锂原子对晶体总态密度贡献很少. Ni/Co混合后将导致Li(Co0.5Ni0.5)O2中Co的3d轨道和O的2p轨道之间成键得以加强.     

On the shape of iron K absorption edges for monoferrites with a Me(Mg, Mn, Ni, Zn)Fe2O4 spinel structure

Calculations of the K-edge x-ray absorption near-edge structure (XANES) in a pure metal and in monoferrites of stoichiometric compositions MgFe₂O₄, MnFe₂O₄, NiFe₂O₄, and ZnFe₂O₄ are carried out using a FEFF8 program. It was confirmed that the Fe K-edge energy shift found experimentally occurs upon the transition from pure iron to monoferrites. It is demonstrated that this shift is identically directed for ferrites with a structure of normal (MnFe₂O₄, ZnFe₂O₄) and inverted (MgFe₂O₄, NiFe₂O₄) spinels, but numerical values of theoretical Fe K-edge shifts agree well with experimental data only for normal spinels.     

Dielectric and magnetic properties of(Zn,Co) co-doped SnO_2 nanoparticles

Polycrystalline samples of(Zn, Co) co-doped SnO2 nanoparticles were prepared using a co-precipitation method. The influence of(Zn, Co) co-doping on electrical, dielectric, and magnetic properties was studied. All of the(Zn, Co) co-doped SnO2 powder samples have the same tetragonal structure of SnO2. A decrease in the dielectric constant was observed with the increase of Co doping concentration. It was found that the dielectric constant and dielectric loss values decrease, while AC electrical conductivity increases with doping concentration and frequency. Magnetization measurements revealed that the Co doping SnO2 samples exhibits room temperature ferromagnetism. Our results illustrate that(Zn, Co) co-doped SnO2 nanoparticles have an excellent dielectric, magnetic properties, and high electrical conductivity than those reported previously, indicating that these(Zn, Co) co-doped SnO2 materials can be used in the field of the ultrahigh dielectric material, high frequency device, and spintronics.     

Spin dynamics investigated by EPR in the paramagnetic regime of La2/3Ca1/3Mn1−x Me x O3 (Me = Al, In) manganites

We report an electron paramagnetic resonance (EPR) investigation of the spin dynamics in the paramagnetic regime of the colossal magnetoresistive manganites La_2/3Ca_1/3Mn_1?x Me _x O₃ (Me=Al, In;x≤0.05). The temperature dependences of the EPR linewidth and integral intensity have been analyzed in terms of the bottleneck spin relaxation and small-polaron hopping models. The exchange coupling integral between Mn³⁺ and Mn⁴⁺ ions and the polaron activation energy decrease with increasing doping level. A discussion is given concerning the factors which could explain the observed changes.     

Interatomic force constants studies of AMF3perovskite-type crystals (A = K,Rb; M = Mg,Ni, Co,Zn, Mn)

A simple model involving only three force constants allows us to evaluate the short range interactions in perovskite fluorides from the experimental values of the elastic constants and the lattice parameters of these compounds. The results indicate that the A-F bonds are quite central in character whereas the M-F bonds are axially symmetric; thus the short range A-F interactions are assumed to have the Born-Mayer form:ZZZZZBy studying the variations of the force constants with respect to the lattice parameter r, it is determined that ρ = 0·232 , λ = 2·8 × 10^?8 ergs for K⁺-F^?; ρ = 0·232 , λ = 4·1 × 10^?8 ergs for Rb⁺-F^?; λ₂, ρ₂ and ρ₂ are respectively 6·9 × 10^?10 ergs, 0·34 , 0·98for Co²⁺-F^? and 2·9 × 10^?10 ergs, 0·46 , 1·40for Mn²⁺-F^?. Taking into account both the short range repulsive potential and the long range electrostatic potential we can study the variations of the lattice energy as a function of r near the equilibrium position and deduce a theoretical value of the lattice distance. In spite of the simplicity of the model, the discrepancy between the experimental and the theoretical values is less than 10 per cent for all the compounds.     

Impedance spectroscopy of dielectric properties of perovskite ceramics Bi(Mg1/2Ti1/2)O3

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...     

Mössbauer study of Zn x Ni5/3−x Fe1Sb1/3O4 spinel ferrite

The antimony substituted nickel ferrite Zn_xNi_5/3–xFe₁Sb_1/3O₄ with different values ofx are prepared, checked by x-ray and studied with⁵⁷Fe Mössbauer spectroscopy over a wide temperature range. Characteristic spectra of paramagnetic, magnetic and electronic relaxation types for the different compositions have been observed. The interpretation of the spectra allows the cation distribution of the compounds to be deduced. The Mössbauer effect parameters at different temperatures are calculated and their dependence on the substitution of non-magnetic Zn⁺² for the magnetic nickel ions are discussed. The temperature dependence of the hyperfine magnetic fields and the respective Néel temperature points are obtained.     

Specific-heat anomaly caused by ferroelectric nanoregions in Pb(Mg(1/3)Nb(2/3))O3 and Pb(Mg(1/3)Ta(2/3))O3 relaxors

The specific heat of typical relaxors, Pb(Mg(1/3)Nb(2/3))O3 (PMN) and Pb(Mg(1/3)Ta(2/3))O3 (PMT), was measured by adiabatic and relaxation methods between 2 and 420 K. A broad anomaly was found in the specific heat curve over the wide temperature range between 150 and 500 K for PMN, and between 50 and 400 K for PMT, which provides evidence for the formation of ferroelectric nanoregions (FNR) in the paraelectric matrix. The entropy of the anomaly was estimated as 3.3 J K(-1) mol(-1) and 2.9 J K(-1) mol(-1) for PMN and PMT, respectively, which implies an order-disorder-type mechanism for the formation of FNR.     

赝能隙导致的YBa2(Cu1-xMx)3O7-δ(M=Co,Zn)薄膜的输运性质异常

报道了两类典型元素替代的超导Y123相体系-YBa2(Cu1-xCox)3O7-δ(x=0.01,0.02)和YBa2(Cu1-yZny)3O7-δ(y=0.005,0.010)薄膜的电阻率-温度特性(ρ(T))和Hall效应(RH (T)).研究表明,Co掺杂的Y123相体系十分类似于氧欠掺杂的情况,对Co掺杂的薄膜样品,由电阻率-温度特性定义的赝能隙打开的温度T*分别为193和225K.而Zn掺杂的样品没有观察到赝能隙打开对电阻率-温度特性的影响.由Hall效应的测量和Hall角(cotθH)定义了另一个特征温度T 0,介于Tc与T*之间,这一特征温度与核磁共振(NMR)给出的赝能隙打开温度相近,说明可能源于电子自旋自由度上的能隙打开.在室温到Tc范围内,电阻率-温度特性和Hall效应分别定义了两类不同的转变温度(T*和T 0),可能分别源于电子电荷和自旋通道上的赝能隙的打开,预示着电荷和自旋自由度分别进入某种基态.