(Bi,La)4Ti3O12-Sr(Bi,La)4Ti4O15共生结构铁电材料性能研究

采用固相烧结工艺，制备了不同La掺杂量(x=0.00，0.25，0.50，0.75，1.00，1.25和1.50) 的(Bi, La)₄Ti₃O₁₂-Sr(Bi, La)₄Ti4O₁₅ (SrBi_8-xLa_xT i₇O₂₇)共生结构铁电陶瓷样品.用x射线衍射对其进行微结构分析 ，并测量铁 关键词： 4Ti₃O₁₂-SrBi₄Ti₄O₁₅')" href="#">Bi₄Ti₃O₁₂-SrBi₄Ti_{4O15 La掺杂 铁电性能 居里温度 弛豫铁电}     

高性能的钛掺杂O3相O3-Na1-xCr1-xTixO2(x=0, 0.03, 0.05)用于钠离子电池正极材料的研究

本文通过凝胶热聚合路线合成了层状的O3相正极材料Na_1-xCr_1-xTi_xO₂(x=0, 0.03, 0.05),采用X射线衍射、扫描电子显微镜来分析其晶体结构和微观形貌. 研究发现,适量的钛掺杂有助于形成更均匀的颗粒并且会改变样品的颜色. 作为钠离子电池正极材料,Na//Na_0.97Cr_0.97Ti_0.03O₂具有非常高的库伦效率(首次高于96%),并且在2.0-3.6 V的电化学窗口下,用0.2 C的倍率循环100次,只有4%的容量衰减;在32 C倍率下有110 mAh/g的比容量.     

Enhanced ferroelectric, magnetic and magnetoelectric properties of Bi1−xCaxFe1−xTixO3 solid solutions

We report on the enhanced electromechanical, magnetic and magnetoelectric properties of Bi_1−xCa_xFe_1−xTi_xO₃ solid solutions. The crystal structure of the x≈0.25 compounds are close to the rhombohedral-orthorhombic phase boundary, and the solid solutions are characterized by increased electromechanical properties due to the polarization extension near the polar-nonpolar border. The homogenous weakly ferromagnetic state is established at x>0.15 doping. The chemical doping shifts the magnetic transition close to room temperature, thus enlarging the magnetic susceptibility of the compounds. The solid solutions at the morphotropic phase boundary exhibit a nearly twofold increase in piezoelectric response, whereas the magnetoelectric coupling shows five times enhancement in comparison with the parent bismuth ferrite.     

Temperature impedance spectroscopy of (1 − x)Na1/2Bi1/2TiO3-xLaMg1/2Ti1/2O3 solid solutions

The dielectric properties of (1 ? x)Na_1/2Bi_1/2TiO₃-xLaMg_1/2Ti_1/2O₃ solid solutions (0 ≤ x ≤ 0.4) were studied over the temperature range 650–1030 K by measuring the impedance spectra over the frequency range 25–10⁶ Hz. The Curie temperature T _C was determined as a function of the composition of the solid solutions. It is shown that T _C decreases linearly with increasing x. The temperature dependences of the dc component (σ_dc) and the polarization component (σ′_ac) of the real part of the conductivity are found. The activation energy for the conductivity σ_dc is shown to increase abruptly as the temperature increases above approximately 770 K for all solid solution compositions. Over the temperature range corresponding approximately to the region of existence of the tetragonal phase of Na_1/2Bi_1/2TiO₃, the polarization component σ′_ac of the solid solutions, as well as that of the pure compound, is anomalously high at low frequencies, which can be due to structural inhomogeneities.     

Electronic band structure, optical absorption, and photocatalytic activity of iron-doped anatase

Quasi-one-dimensional solid solutions of the composition Ti_{1 ? x} Fe _x O_{2 ? x/2} (0.005 ≤ x ≤ 0.050) with the anatase-type structure and extended aggregates have been prepared by the precursor method. The absorption spectra of the solid solutions have been investigated in the ultraviolet and visible regions, and the photocatalytic activity in the oxidation reaction of hydroquinone in water has been estimated. It has been found that the synthesized solid solutions serve as photocatalysts only under ultraviolet irradiation, and their photoactivity increases with an increase in the dopant concentration. The first-principles calculations of the electronic band structure and optical absorption in iron-doped anatase and rutile have been performed using the pseudopotential method LSDA + U (with the VASP software package). The on-site exchange-correlation parameters have been calibrated in the calculations of the electronic band structure of hematite α-Fe₂O₃ and ilmenite FeTiO₃. It has been shown that, despite the appearance of impurity states within the band gap of anatase and rutile, doping with iron does not cause substantial absorption in the visible region, which correlates with the increase in photocatalytic activity only under ultraviolet irradiation. The most probable cause of the experimentally observed absorption in the visible region is the presence of finely dispersed hematite impurities in the obtained samples.     

掺杂半导体β-FeSi2电子结构及几何结构第一性原理研究

采用基于第一性原理的密度泛函理论全势线性缀加平面波法，使用广义梯度近似处理交换相关势能，首先计算了β-FeSi₂的电子结构及其各元素各亚层电子的能态密度，β-FeSi₂的电子能态密度主要由Fe的d层电子和Si的p层电子的能态密度确定；其次通过计算不同掺杂系统的总能量确定了掺杂原子在β-FeSi₂中的置换位置，在β-FeSi₂中，Co置换Fe_Ⅱ位置的Fe原子，Al置换Si_Ⅰ位置的Si原子，这种择位置换与现有的计算结果完全一致；最后计算了Fe_1-xCo_xSi₂和Fe(Si_1-xAl_x)₂的电子结构，对它们的电子结构特征进行了分析，并探讨了电子结构对其热电性能(塞贝克系数、电传输及热传输性能)的影响. 关键词： 第一性原理 电子结构 热电性能 2')" href="#">FeSi₂     

Microstructure and thermoelectric properties of Zn1−xAlxO ceramics fabricated by spark plasma sintering

Al-doped ZnO powders were synthesized via solid reaction between Zn(OH)₂ and Al(OH)₃ and consolidated by spark plasma sintering (SPS) to fabricate fine-grained Zn_1−xAl_xO ceramics as a thermoelectric material. X-ray diffraction and spectrophotometer experiments revealed that Al doping into ZnO is enhanced by the present process, and consequently the SPS-processed Zn_1−xAl_xO samples show significantly improved electrical conductivity as compared with those prepared via mixing ZnO and Al₂O₃ oxide powders. Because of the combined effect of Al doping and grain refinement, the present Zn_1−xAl_xO ceramics show much lower thermal conductivity, which also results in an enhanced dimensionless figure of merit (ZT), than un-doped ZnO oxides prepared also by SPS.     

Effect of co-dopant on the formation and properties of anatase-type titania solid solutions doped with niobium

The effect of co-dopant M (M=gallium (Ga), aluminum (Al), and scandium (Sc)) on the formation, crystallite growth, optical band gap, photocatalytic activity, and phase stability of anatase-type titanium dioxide solid solutions (Ti_1−2XNb_XM_XO₂) containing the same amount of dopant niobium (Nb) that were directly formed as nanoparticles under mild hydrothermal conditions at 180 °C for 5 h was investigated. The composition range X of the anatase-type solid solutions (Ti_1−2XNb_XM_XO₂) depended on the co-dopant M, i.e., X=0.15-0.20 for M=Ga and Al, and X=0.33 for M=Sc. A remarkable increase in the lattice parameter c₀ was detected in the solid solutions co-doped with M=Sc. The increase in the amount of co-dopant M=Ga and Al enhanced the crystallite growth of the anatase-type solid solutions under the hydrothermal conditions. The photocatalytic activity of the solid solutions (Ti_0.80Nb_0.10M_0.10O₂) co-doped with M=Sc, Ga, and Al increased in that order. The co-dopant M=Ga promoted the anatase-to-rutile phase transformation of the solid solutions at lower temperature.     

Magnetic properties of fcc (Co95Fe5)1-xAlx ribbons

Rapidly quenched (Co₉₅Fe₅)_1-xAl_x ribbons are investigated by X‐ray diffraction, magnetization, and Mössbauer effect measurements. A single fcc phase is obtained for all ribbons x ? 10 at.%. The lattice constant increases linearly with x and is discussed in connection with magnetic moment. The influence of Al substitution on both magnetization and Fe‐atom hyperfine field (H) is studied. At 296 K, the magnetization decreases linearly while H drops nonlinearly as x increases. Al substitution leads to substantial differences in iron hyperfine fields in bcc and fcc systems. Fe moment is perturbed differently by Al substitution in fcc (Co₉₅Fe₅)_1-xAl_x and bcc Fe–Al systems.     

Na3Zr2-xInxSi2-xP1+xO12系统的组成、结构和离子电导的关系

用固相反应、X射线衍射、金相显微镜观察、测定比热和复平面阻抗谱的方法研究了Na₃Zr_2-xIn_xSi_2-xP_1+xO₁₂系统。在此系统中存在两种固溶体:单斜固溶体(0≤x<0.8)和三方固溶体(0.8≤x≤1.8)。即从x=0.8的组成开始,NASICON型Na₃Zr_2-xIn_xSi_2-x 关键词：     

Control of the properties of Pb(TixZr1-x )O3 solid solutions by external disturbances

The influence of x-ray irradiation to absorbed radiation doses D = (0.5?12) × 10⁸ rad on the properties of ferroelectric ceramic Pb(Ti_xZr_1?x )O₃ solid solutions with compositions close to the morphotropic phase boundary was studied. The effects of x-ray radiation on the electrical conductivity of ferroelectric ceramics are shown to differ with x ranging from 0.42 to 0.60. Using empirical equations and numerical techniques, quantitative relations are established between the composition, absorbed radiation dose, and electrical conductivity for Pb(Ti_xZr_1?x )O₃.     

Evolution from relaxor-like dielectric to ferroelectric in Ba[(Fe0.5Nb0.5)1−xTix]O3 solid solutions

Ba[(Fe_0.5Nb_0.5)_1−xTi_x]O₃ (x=0.2,0.4,0.6,0.8,0.85,0.9 and 0.95) solid solutions were synthesized by a standard solid-state reaction technique. X-ray diffraction at room temperature and dielectric characteristics over a broad temperature and frequency range were evaluated systematically. The structure of Ba[(Fe_0.5Nb_0.5)_1−xTi_x]O₃ solid solutions changed from cubic to tetragonal with increasing x. A Debye-like dielectric relaxation following the Arrhenius law similar to that in Ba(Fe_0.5Nb_0.5)O₃ was observed at lower temperature in the composition range 0.2≤x≤0.8, while the relaxor ferroelectric, diffused ferroelectric and normal ferroelectric behavior were observed for x=0.85,0.9 and 0.95, respectively. The process of the evolution of relaxor-like dielectric to ferroelectric suggested the changing from dilute polar micro-domains to polar micro-domains, polar micro/macro-domains and then polar macro-domains in the present ceramics.     

Magnetic interaction in Mg, Ti, Nb doped manganites

An effect of Mn substitution with Me=Mg²⁺, Ti⁴⁺, Nb⁵⁺ in manganites has been investigated by preparing La_0.7Sr_0.3(Mn_1-xMe_x)O₃ and La_1-xSr_x(Mn_{1 - x/2}Nb_x/2)O₃ series. It was established that substitution of manganese with magnesium up to x = 0.16 leads to a collapse of a long-range ferromagnetic order whereas La_0.7Sr_0.3(Mn ^{3 +} _0.85Nb ^{5 +} _0.15)O₃ is ferromagnet with T _C = 123 K and exhibits a large magnetoresistance below Curie point despite an absence of four-valent manganese. Hypothetical magnetic phase diagrams are constructed for La_0.7Sr_0.3(Mn_1-xMe_x)O₃ and La_1-xSr_x(Mn_{1 - x/2}Nb_x/2)O₃. Our results show that Mn³⁺-O-Mn³⁺ exchange interaction is ferromagnetic in the orbitally disordered manganites as well as an increase of Mn⁴⁺ content above 50% from a total amount of manganese ions leads to formation of a spin glass state due to a competition between antiferromagnetic Mn⁴⁺-O-Mn⁴⁺ and ferromagnetic Mn³⁺-O-Mn⁴⁺(Mn³⁺) superexchange interactions. Received 24 January 2002 Published online 9 July 2002     

Al高掺杂浓度对ZnO禁带和吸收光谱影响的第一性原理研究

采用密度泛函理论框架下的第一性原理平面波超软赝势方法, 建立了未掺杂与不同浓度的Al原子取代Zn原子的两种Zn_1-xAl_xO超胞模型,分别对模型进行了几何结构优化、态密度分布和能带分布的计算. 结果表明: ZnO高掺杂Al的条件下, 掺杂的Al原子浓度越大,间隙带越窄, 蓝移越弱. 计算结果和实验结果相一致.     

Crystal structure,dielectric and piezoelectric properties of Ta/W codoped Bi3TiNbO9 Aurivillius phase ceramics

Aurivillius phase Bi₃Ti_1−xTa_xNb_1−xW_xO₁₂ high temperature piezoceramics were prepared by a conventional solid state reaction method. The crystal structure, dielectric, electrical conduction and piezoelectric properties were systematically studied. Pure or modified Bi₃TiNbO₉ ceramics revealed the presence of only two-layered Aurivillius phase, indicating that Ta/W doping entered into the B-site of pseudo-perovskite structure and formed solid solutions. The Curie temperature had a strong reliance on the structural distortion. Furthermore, Ta/W dopants act as a donor doping, decrease the number of oxygen vacancies and facilitate the domain wall motion. As a result, Ta/W modifications significantly increase the DC resistivity and piezoelectric properties. Bi₃Ti_0.98Ta_0.02Nb_0.98W_0.02O₁₂ ceramics possess the optimum d₃₃ value (∼12.5 pC/N) together with a high T_C point (∼893 °C). Moreover, the resonance–antiresonance spectra demonstrate that the Ta/W-BTN ceramics are indeed piezoelectric in nature at 600 °C. The d₃₃ value of BTTNW-2 ceramic remains ∼12.2 pC/N after annealing at 700 °C. These factors suggest that the BTTNW-based ceramic is a promising candidate for ultra-high temperature sensor applications.     

Concentration dependences of the properties of multicomponent PZT-based piezoelectric ceramics in the morphotropic transition range

The following three ternary PZT-based systems are studied in detail: 0.98Pb(Ti_xZr_1−x )O₃-0.02Pb(Nb_1/2Bi_1/2)O₃, 0.98(Pb_0.9727Sr_0.0273)(Ti_xZr_1−x )O₃-0.02Pb(Nb_1/2Bi_1/2)O₃ + 1 wt% PbO, and 0.98(Pb_0.9727Sr_0.0273)(Ti_xZr_1−x )O₃-0.02Pb(Nb_1/2Bi_1/2)O₃ + 2 wt % PbGeO₃, where 0.45 ≤ x ≤ 0.49 and the concentration step is Δx = 0.025. A number of concepts are formulated regarding the phase diagrams of PZT-type systems near the morphotropic transition. A scheme for real tetragonal-rhombohedral transformation is given. The maxima of the electrophysical characteristics of the solid solutions from the morphotropic range are shown to be caused mainly by an appearing intermediate phase. Analysis of the insulating, piezoelectric, and mechanical properties of the samples demonstrates that there is a group of solid solutions that are promising materials for high-temperature piezoelectric devices operating in the medium-frequency band.     

The theory of morphotropic phase transition in PbZr<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ti<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript>

The concept of the mechanism of formation of morphotropic boundaries in T?x phase diagrams of solid solutions of complex oxides with the perovskite structure has been formulated. This concept is illustrated by calculation of the conditions for existence of morphotropic phase transition in a quasy-binary solid solution of the PbZr_{1 ? x} Ti _x O₃ and (1 ? x)PbMg_1/3Nb_2/3O₃ + xPbTiO₃ compositions.     

Ab initio study on elastic and thermodynamical properties of Ti<Subscript>1-x</Subscript>Zr<Subscript>x</Subscript>C

Elastic and Thermodynamical properties of Ti_1-xZr_xC have been investigated using LAPW + lo within the density-functional theory with the generalized gradient approximation. We have studied the stability of the alloy Ti_1-xZr_xC as a function of Zr composition in rocksalt (B1) structure by calculating the elastic constants C₁₁, C₁₂ and C₄₄ using the tetragonal and trigonal distortions. Mechanical properties such as Poisson ratio, bulk, shear and Young’s modulii of Ti_1-xZr_xC are calculated. The Debye temperature and hardness are also computed for the first time to our knowledge for Ti_1-xZr_xC in various compositions.     

(Nd1－xGdx)3Fe27.31Ti1.69化合物的结构和磁性

通过X射线衍射和磁性测量等手段研究了(Nd_1-xGd_x)₃Fe_27.31Ti_1.69(0≤x≤0.6)化合物的结构和磁性.X射线衍射测量结果表明Gd替代后并未改变Nd₃(Fe,Ti)₂₉化合物的晶体结构，但引起了晶胞体积收缩.随着Gd含量的增加，化合物的居里温度T_C和室温磁晶各向异性场B_a单调增加，而自旋重取向 关键词： 1-xGd_x)₃Fe_27.31Ti_1.69化合物')" href="#">(Nd_1-xGd_x)₃Fe_27.31Ti_1.69化合物 磁晶各向异性 自旋重取向 磁相图     

Solid solutions on the base of bismuth vanadate: Preparation, structure, phase transitions, dielectric and transport properties

Ceramic solid solutions (Bi_1-yLa_y)₄(V_1-xMe_x)₂O_11-y with x, y < 0.2, Me-Zr, Ga, Fe, Cu, have been prepared by the solid state reaction method. Crystal structure parameters, phase transitions, dielectric and transport properties of ceramic samples have been studied. Concentration and temperature stability regions of monoclinic α-, orthorhombic β- and tetragonal γ- or γ’- polymorph modifications have been determined.Annealing of samples, containing large amount of Cu and/or La dopants, at 973 K in the reducing atmosphere resulted in their decomposition, though compositions containing low content of La, Ga or Zr dopants, remained pretty stable.