前驱物合成条件对锰锌铁氧体结构和性能的影响

采用共沉淀-热处理工艺合成了尖晶石型锰锌铁氧体粉末,利用正交试验优化了制备工艺。利用X射线衍射仪(XRD)扫描电子显微镜(SEM)和振动样品磁强计(VSM)对粉体的显微结构和静磁性能进行了研究。结果表明:热处理温度为1350℃、保温时间为3.5 h、进料比为1.5时,若前驱物的pH值为6,制备的样品的主晶相为锰锌铁氧体;若前驱物的pH值为7 9,则形成单相尖晶石型锰锌铁氧体,样品的饱和磁化强度先增大后减小,矫顽力逐渐增大。pH值为7时,配方为Fe∶Mn∶Zn=68.4816∶17.1368∶14.381,进料比为1.5,滴加时间为40 min,反应温度为50℃,不加表面活性剂时得到的样品具有较高的饱和磁化强度。     

LaCo取代M型钡铁氧体致密化及磁性能研究

用固相法制备M型钡铁氧体Ba1-xLaxFe12-x Cox O19(x=0～0.45),研究了取代量和烧结温度对材料致密化及磁性能的影响.结果表明,烧结样品的密度随烧结温度的升高而逐渐增大,并趋于稳定;在相同的烧结温度下,烧结样品的密度随取代量的增加而减小.在1050℃烧结时,饱和磁化强度Ms随取代量的增加而减小,磁晶各向异性场Ha随取代量的增加先增加后减小,Ha在取代量x=0.3时取得极大值630 kA/m.     

Bi_2O_3对MnCoNiO基NTC热敏半导体陶瓷显微结构和电性能影响

采用Bi2O3作烧结助剂,研究了Bi2O3含量,烧结温度对MnCoNiO基NTC热敏半导体陶瓷显微结构与电性能。结果表明:添加0.25 wt%~1.5 wt%Bi2O3可以显著促进烧结,烧结温度可降低至1000℃。随着Bi2O3含量的增加,陶瓷样品的粒径先减小,后增大,含有1.0wt%Bi2O3的样品晶粒最大,伴随着显微结构的变化,材料的电阻率和材料常数(B)先减小,后增大;烧结温度对上述材料体系的电性能有着较大的影响,其影响主要来自于烧结温度对晶粒大小和体系内部阳离子分布的改变。     

ZnO掺杂对0.7CaTiO3-0.3NdAlO3微波介质陶瓷低温烧结及介电性能的影响

采用固相法制备0.7CaTiO3-0.3NdAlO3微波介质陶瓷,研究添加不同含量纳米ZnO对其烧结特性和微波介电性能的影响.结果表明,掺入ZnO烧结温度降低了100℃,随着ZnO掺量增加,样品介电常数εr和谐振频率温度系数τf减小,品质因数(Q×f)先增大后减小.掺入1.5wt;的ZnO在1350℃烧结4h时性能最佳:εr=36.50,Q×f=23785 GHz,τf=-2.47×10-6/℃.     

B2O3对YCaZrVIG铁氧体微结构及性能的影响

采用传统固相法制备添加B2O3的YCaZrVIG铁氧体,研究了B2O3添加量对其烧结温度、微结构和磁性能的影响。结果表明,添加的B2O3对材料的物相没有影响,所有样品均为单相石榴石结构。添加B2O3显著降低了YCaZrVIG铁氧体的烧结温度,且使颗粒尺寸逐渐减小。添加1.8wt%B2O3的样品,烧结温度约为1200℃,且体积密度最大。进一步提高B2O3添加量至3.0wt%,烧结温度又略有提高,且晶粒尺寸变得不均匀。随着B2O3添加量的增加,4πMs和Br先显著增大后减小,而Hc则减小后急剧增大。适当提高烧结温度,有利于Hc的减小。B2O3添加量为1.8wt%、1290℃烧结保温4 h制得的YCaZrVIG铁氧体综合性能较佳:Db=4.80 g.cm-3,4πMs=1670 Gs,Br=682 Gs,Hc=0.86 Oe。     

预烧温度对(Ba0.85Ca0.15)(Ti0.9Hf0.1)O3压电陶瓷电性能的影响

采用固相法分别在1100~1250 ℃的预烧温度下制备了(Ba0.85Ca0.15)(Ti0.9Hf0.1)O3(BCHT)无铅压电陶瓷,通过对所制备陶微观结构和电性能的测试,发现:所有样品均具有纯的钙钛矿结构;随预烧温度的增加,室温下样品逐渐由四方相向三方相转变,预烧温度在1150~1250 ℃时两相共存;样品的压电常数d33、剩余极化强度Pr均随预烧温度的升高呈现先减小后增加的趋势,相对介电常数εr、弥散系数γ呈现先增加后减小的趋势,而矫顽场Ec则逐渐降低.样品的综合性能在预烧温度1250 ℃处达到最佳值: d33=525 pC/N,Pr=10.2 μC/cm2,Ec=1.30 kV/cm,εr=17699,γ=1.65,表明该材料具有良好的应用前景.     

Zn含量对NiCuZn旋磁铁氧体的显微结构、磁性能和介电性能的影响

采用氧化物陶瓷工艺制备了Ni0.6533-xCu0.1005 Zn0.2613+xFe1.9899O4(x=0,0.0402,0.0804,0.1206)微波铁氧体,研究了不同Zn含量对NiCuZn铁氧体的显微结构、磁性能和介电性能的影响.结果表明:ZnO具有明显的助熔作用,NiCuZn铁氧体的平均晶粒尺寸与饱和磁化强度随着Zn含量的增多逐渐增大,而矫顽力和居里温度则逐渐减小.样品的剩余磁感应强度随着温度的升高而不断降低,且Zn含量越多,其下降速率越大.当x=0.0804时,室温下NiCuZn铁氧体具有最高的剩余磁感应强度356 mT,且其温度稳定性也较好.此外,x在0～0.1206范围内,铁氧体的电阻率、介电常数和介电损耗角正切变化不大.     

热处理对纳米钡铁氧体磁性的优化研究

对水热法制备的BaFe12 O19纳米颗粒进行了不同温度的热处理,研究热处理温度对纳米钡铁氧体微结构和磁性能的影响.结果表明,随着热处理温度的提升,铁氧体样品粒径逐渐增大,结晶性能趋于完善;水热合成的钡铁氧体纳米颗粒室温测得的矫顽力为92.21Oe,饱和磁化强度为8.87 emu/g,呈现为半硬磁特性;同时,样品的磁性能与热处理温度有密切关系,在800℃处理的纳米钡铁氧体室温饱和磁化强度Ms增加到52.97 emu/g,矫顽力Hc增加到5.052 kOe,居里温度大小为712.2 K,样品转变为硬磁体,转变温度区间定为500 ～ 700℃.     

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.     

Mn掺杂对YBiCaZrVIG铁氧体微结构及性能的影响

用固相反应法在空气气氛中制备了Y2.1 Bi0.2Ca0.7 Zr0.3 V0.2Mnx Fe4.42-xO12(x=0,0.02,0.04,0.06,0.08)铁氧体,研究了Mn掺量和烧结温度对YBiCaZrVMnIG铁氧体烧结性能、微观结构和电磁性能的影响.研究发现,所有样品均形成单一的石榴石相.Mn的掺入使晶胞参数增加,并促进了YBiCaZrVIG铁氧体的致密化.Fe离子的数量、微观结构的变化以及晶格中离子空位的增多造成了介电损耗先显著降低后略有增加趋势.而介电损耗随着烧结温度的升高和材料的致密化先急剧下降,后由于烧结温度过高使部分Fe3+还原成Fe2+而略有增加.Mn掺量对YBiCaZrVMnIG铁氧体介电常数影响不大,但是随着烧结温度和样品致密度的提高,介电常数呈增大趋势.而饱和磁化强度4πMs随着Mn掺量的增加先呈缓慢降低趋势,后又逐渐增加,但随烧结温度的升高呈相反的变化趋势.因此,在YBiCaZrVIG铁氧体中掺杂适量的Mn 能够促进烧结,提高材料的电磁性能.综上,Mn掺量为x=0.04(Y2.1Bi0.2Ca0.7Zr0.3V0.2Mn0.04Fe4.38O12)、烧结温度为1260℃的铁氧体综合性能最佳:RD＞ 98;,εr=15.7,tanδe =2.1×10-4,4πMs=1629 Gs.     

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...     

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.     

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.     

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...     

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.     

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.     

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.