MnO2掺杂对BiFeO3-PbTiO3-Bi(Zn1/2Ti1/2)O3-PbZrO3陶瓷组织与性能的影响

采用固相烧结法制备MnO2掺杂的BiFeO3-PbTiO3-Bi(Zn1/2Ti1/2)O3-PbZrO3 (BF-PT-BZT-PZ)压电陶瓷,研究了不同MnO2掺杂量对材料结构及压电介电性能的影响.实验结果表明,适量的MnO2掺杂,不仅能使晶粒长大,提高晶界强度,而且可以改善材料的介电压电性能.当MnO2掺杂量为0.1 mol;时,880℃(5 h)烧结的陶瓷样品性能参数为:d33 =97 pC/N,kp=0.29,kI=0.37,εr=390,tanδ ～0.02.     

Nb2O5掺杂对Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3陶瓷组织与性能的影响

采用固相烧结法制备Nb2O5掺杂的Pb(Mg1/3Nb2/3) O3-PbZrO3-PbTiO3+ 0.5mol; ZnO(PMN-PZT)压电陶瓷,研究了不同Nb2O5掺杂量对材料结构及压电介电性能的影响.实验结果表明,随着Nb2O5掺杂量的增加(0～1 mol;),PMN-PZT陶瓷的晶界强度提高,断裂模式由沿晶断裂逐渐转变为穿晶断裂,而且陶瓷的压电介电性能升高.当Nb2O5掺杂量为1mol;时,1250℃烧结的陶瓷样品性能参数为:d33=430 pC/N,Qm=60,kp=0.52,kt=0.38,εr=3620,tanδ=0.017.     

Na/Bi配比对0.94(Bi0.5+xNa0.5-x)TiO3-0.06BaTiO3压电陶瓷组织结构与性能的影响

采用传统固相烧结方法制备出0.94(Ri0.5+xNa0.5-x)TiO3-0.06BaTiO3(BNBT6)二元系无铅压电陶瓷(x分别为0,0.08;,0.12;,0.16;,0.24;和0.50;摩尔分数),系统地研究了不同Na/Bi配比对BNT基陶瓷材料物相结构、显微组织和压电、介电性能的影响.结果表明:添加不同的Na/Bi,所制备的BNBT6压电陶瓷组织分布均匀、致密度高,存在三方-四方共存的准同型相界结构,且不同的Na/Bi配比不影响陶瓷的相结构,但其烧结性能及电性能与Na/Bi配比密切相关,当x=0.16;时,BNBT6陶瓷样品的性能最佳,相对密度达到97;,在1 kHz的测试频率下,BNBT6陶瓷样品的压电常数d33为138 PC/N、介电常数εr为1486、介电损耗tanδ为2.1;、机械品质因数Qm为217.     

钇掺杂铌酸锶陶瓷的微观结构与电性能研究

采用固相法制备了Nb2Sr2-xYxO7陶瓷.研究了掺Y对陶瓷的晶体结构、表面形貌、铁电、介电和压电性能的影响.研究结果表明:钇掺杂Sr2 Nb2 O7陶瓷,Y3+取代了A位Sr2+,形成Nb2 Sr2-xYxO7固溶体,并提高了铌酸锶陶瓷铁电、介电和压电性能.在x=0.05时,Nb2 Sr2-xYxO7陶瓷的铁电性能达到最大(剩余极化强度Pr=0.254μC/cm2);在x=0.1时,Nb2Sr2-xYxO7陶瓷的介电性能达到最大(相对介电常数εr=90,介电损耗tarδ≤0.01).     

稀土掺杂Pb(Mg1/3Nb2/3)O3-PbTiO3压电陶瓷的烧结特性研究

在传统的固相反应制备工艺中,固相反应的烧结温度直接影响着陶瓷的物相结构、陶瓷致密度以及介电性能等.本文采用固相反应法制备x; Sm3掺杂PMN-PT压电陶瓷,通过控制不同的烧结温度,制备了一系列Sm-PMNPT陶瓷样品.利用X射线衍射仪、介电温谱以及准静态d33测量仪对陶瓷结构、介电性能、压电系数等性能进行表征.研究结果表明:烧结温度在1250℃,x=1.875mol;～2.5mol;,陶瓷样品的钙钛矿含量最大,压电系数最高可达1254 pC/N,kp=0.58,相对介电常数高达30000左右,密度达到8.48 g/cm3.     

Sb掺杂对0.96(K0.49Na0.51)(Nb0.97-xTa0.03Sbx)O3-0.04Bi0.5(Na0.8K0.2)0.5ZrO3无铅压电陶瓷结构与电性能的影响研究

采用固相法制备了0.96(K0.49 Na0.51)(Nb0.97-xTa0.03Sbx) O3-0.04Bi0.5(Na0.8K0.2)0.5ZrO3(0.96KNNTSx-0.04BNKZ,x=0,0.01,0.02,0.03,0.04)无铅压电陶瓷,研究了Sb掺杂量对0.96KNNTSx-0.04BNKZ陶瓷相结构、微观结构和电性能的影响规律.X射线衍射(X-ray Diffraction,XRD)分析结果表明:0.96KNNTSx-0.04BNKZ陶瓷具有纯钙钛矿结构,随着Sb掺杂量x的增加,陶瓷由正交-四方两相共存逐渐转变为四方相,在x≤0.01时,陶瓷为正交-四方两相共存的多型相转变(Polymorphic Phase Transition,PPT)结构,而当x≥0.02时,陶瓷则转变为四方相结构.在PPT向四方相转变的组成边界x=0.02处,陶瓷具有优异的电性能:压电常数d33=345 pC/N,机电耦合系数kp=39.2;,机械品质因数Qm=51,介电常数ε33T/ε0=1520,介电损耗tanδ =2.7;,剩余极化强度Pr=15.4 μC/cm2,矫顽场Ec =1.09kV/mm,居里温度Tc=275℃.     

(1-x)(K0.49Na0.51)(Nb0.97Ta0.03)O3-xBi0.5Na0.5ZrO3无铅压电陶瓷的结构与电性能研究

采用固相法制备了(1-x)(K0.49Na0.51)(Nb0.97 Ta0.03) O3-xBi0.5 Na0.5 ZrO3(KNNT-BNZ,x=0,0.01,0.02,0.03,0.04,0.05)无铅压电陶瓷,研究了Bi0.5 Na0.5ZrO3 (BNZ)的掺杂量对KNNT-BNZ陶瓷相结构、微观结构和电性能的影响.结果表明:KNNT-BNZ陶瓷具有纯的钙钛矿结构,随着BNZ掺杂量x的增加,陶瓷从正交相转变为四方相,并在0.03≤x≤0.04出现正交-四方两相共存的多型相转变区域.在该多型相转变区域靠近四方相的边界x =0.04处,陶瓷具有优异的电性能:压电常数d33 =317 pC/N,机电耦合系数kP=36.4;,机械品质因数Qm=68,介电常数ε3T/ε0=1225,介电损耗tanδ =3.1;,剩余极化强度Pr=20.5 μC/cm2,矫顽场Ec=1.16 kV/mm,居里温度Tc=310℃.     

SnO2掺杂对(Ba0.85Ca0.15)(Ti0.9Zr0.1-xSnx)O3无铅压电陶瓷介电弛豫与电性能的影响

采用固相烧结法制备了(Ba0.85Ca0.15)(Ti09Zr0.1-xSnx) O3(BCZTS)无铅压电陶瓷.研究了不同含量SnO2(x=0,0.02,0.04,0.06,0.08)对BCZT无铅压电陶瓷相结构、压电性能、介电性能和铁电性能的影响,并利用XRD、SEM、准静态d33测试仪等表征样品.结果表明,所有样品均为单一钙钛矿结构.当掺杂x=0.02时,(Ba0.ss Ca0.1s)(Ti0.9 Zr0.1-xSnx) O3无铅压电陶瓷材料的综合性能优异:d33 =553 pC/N,kp=49;,εr～ 7474(l kHz),tanδ～1.5; (lkHz),Pr=6.06 μC/cm2,Ec=2 kV/cm,利用Curie-Weiss定律对该实验结果进行拟合,发现x=0.02的样品的介电弛豫特征更为明显.     

NKLNx-KBT-BZ无铅压电陶瓷的电性能研究

采用传统固相烧结法制备0.92(Na0.51K0.49-xLix)NbO3-0.02K0.5Bi0.5TiO3-0.06BaZrO3(简写为NKLNx-KBT-BZ,x=0.00～0.05)系无铅压电陶瓷.用X射线衍射仪、扫描电子显微镜、精密阻抗分析仪及铁电性能测试仪等研究了Li+含量对该体系陶瓷的晶相、显微结构和电性能的影响.结果表明:在研究组成范围内,陶瓷均具有单一的钙钛矿结构,随着Li+含量的增加,晶体结构从菱方转变为四方结构,并且经过菱方-四方两相共存的准同型相界(MPB)组成区域0.01 ＜x ＜0.03.在MPB区域的四方相边界x=0.03处获得优异的电性能:d33=227 pC/N,kp=39.3;,Qm=69,εT33/ε0=1642,tanδ =2;,Pr=13.3μC/cm2,Ec=1.64 kV/mm.     

Y2O3掺杂对(Ba0.85Ca0.15)Zr0.1Ti0.896Sm0.004O3无铅压电陶瓷介电弛豫与电性能的影响

采用固相法制备了(Ba0.85Ca0.15)1-xYxZr0.1Ti0.896Sm0.004O3(BCZTS-Yx)无铅压电陶瓷.研究了Y2O3含量对BCZTS-Yx无铅压电陶瓷相结构、压电与介电性能的影响.结果表明:Y3+作为施主掺杂物占据A位.当0.004≤x≤0.006时,陶瓷存在三方相与四方相共存的准同型相界结构.当x=0.006时,陶瓷具有最佳的电性能,分别为d33=384 pC/N,kp=37.2;,εr～6775,tanδ ～ 2.04;.利用Curie-Weiss定律对该实验结果进行拟合,发现x为0.006的样品的介电弛豫特征更为明显.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.     

Investigation of the Mechanism of Influence of Stress Corrosion on the Development of Macroplastic Instabilities of Aluminum–Magnesium Alloy

Crystallography Reports - Macroscopic jumps of plastic deformation (few percent in amplitude) on creep curves of aluminum–magnesium alloy, caused by a local effect of concentrated solution of...     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

Mechanism of thermal expansion of structural modifications of zinc pyrovanadate

Crystal chemical characteristics of the α and β modifications of Zn₂V₂O₇ are calculated based on in situ high-temperature X-ray measurements. The expansion of the structure is found to be strongly anisotropic up to the negative volumetric thermal expansion of the α-Zn₂V₂O₇ unit cell in the temperature range of 300–600°С, α _V =–17.94 × 10^–6 1/K. The transformations of the “hard” and “soft” sublattices with an increase temperature and at the phase transition are considered in detail. It is shown that the negative volumetric thermal expansion of α-Zn₂V₂O₇ is due to the degeneracy of the zigzag-like shape of zinc–oxygen columns at constant distances between their vertices.     

A SAXS study of kinetics of aggregation of silica sols

SAXS in situ experiments on the evolution of TMOS solutions during hydrolysis and polycondensation lead to power laws with scaling exponents ≈ 2. It is suggested that this could be the result of the polydispersity of the samples and that only an apparent fractal dimension can be obtained in this way. Kinetic studies tend to indicate that agglomeration in the sol is the result of a diffusion-controlled process.