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反铁电晶体PbZrO3序参量和对称性的研究 总被引:2,自引:1,他引:1
在反铁电晶体锆酸铅(PbZrO3)顺电反铁电相变中,伴随有对称性的变化.前人工作中选择反极化参量(P)或子晶格的极化矢量(PA、PB)作为反铁电相的序参量,根据居里原理得出了反铁电晶体锆酸铅反铁电相对称性所属空间群为Pbam(D2h)或Pba2(C2v).但是通过对中子衍射实验结果分析,该晶体反铁电相对称性所属空间群不是Pbam(D2h)或Pba2(C2v),而是P2/m(C2i).本文选取轴矢量R作为反铁电相的序参量,对锆酸铅晶体应用居里原理,恰能得到正确的对称性P2/m(C2i). 相似文献
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利用助溶剂法,已经生长出15mm×25mm×60mm的大尺寸NdP5O14(NPP)晶体.用高分辨X射线衍射术对自发应变及铁弹畴结构进行了研究.对几个不同的反射,可在其摇摆曲线上观测到由基体畴和铁弹畴之间的取向差导致的反射峰的分离.通过反射峰分离的特点,可以确定铁弹畴结构.NPP晶体中大多数铁弹畴为a型畴,b型畴只出现在严重形变的区域. 基于NdP5O14晶体畴结构,我们分别计算了802,402和204反射的峰分离量.实验测量结果符合计算结果.另外,通过测量基体畴和铁弹畴的800反射的峰分离量我们确定了NdP5O14的自发应变是0.0082.通过结构和对称性分析,我们对这种晶体的畴结构进行了详细讨论. 相似文献
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在二元体系RbTiOPO4-CsTiPO5中通过助熔剂法生长出不同Cs+掺杂浓度的Cs+:RbTiOPO4晶体,X射线粉末衍射确定所获晶体的物相为斜方晶系Pna21型,研究了晶体的铁电相变及离子电导等物理性质,发现该类晶体具有典型的铁电体二次相变特征. 相似文献
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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. 相似文献
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原位氮化法制备TiN纳米粉体 总被引:3,自引:0,他引:3
用溶胶凝胶法合成的纳米TiO2粉体作为原料,将该粉体在氨气中进行原位氮化制备了TiN纳米粉体.用XRD,TEM,化学分析等手段对合成的TiN纳米粉体的物相组成、形貌、成分进行了分析.实验分析表明:在1000℃和1100℃下分别氮化5h,可以制备粒径大约为40nm和80nm的TiN粉体,其TiN的含量分别为95.40;和98.37;;而在1000℃条件下氮化时间减少到2h时,TiN的含量仅为58.36;.氮化温度和氮化时间是合成纳米TiN的重要因素,提高合成温度和延长氮化时间均可形成纯度较高的TiN纳米粉体,但延长氮化时间更有利于获得粒径小的氮化钛粉体. 相似文献
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A novel homologous series of ethylene derivatives of thermotropic liquid crystals has been synthesized. The methoxy to octyloxy derivatives are nematogenic, the decyloxy to tetradecyloxy derivatives are smectogenic, in addition to nematogenic, and the hexadecyloxy homologue is smectogenic only. All the members of the series are enantiotropically mesogenic. Thermotropic behavior was determined by an optical polarizing microscope equipped with a heating stage and Differential Scanning Calorimetry (DSC) study. Analytical and spectral data confirm the molecular structures of homologues (infrared, nuclear magnetic resonance, mass spectra, X-ray, and DSC data). Textures of the nematic phase are threaded or Schlieren and that of smectic phase are focal conic fan-shaped of smectic A or C. Transition curves of the phase diagram behave in a normal manner except one or two deviations from the normal trend. The mesophase range (Sm+N) varies from 3°C to 44°C. The average thermal stability for smectic is 93°C and that for nematic 117.4°C. The LC behavior of the novel series is compared with a structurally similar known series. 相似文献
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P.J. Lezzi 《Journal of Non》2011,357(10):2086-2092
The enthalpy of mixing of mixed alkali (Na2O and K2O) silicate glasses containing various concentrations of alumina was determined using an ion-exchange equilibrium method. For glasses with a constant alkali concentration, the enthalpy of mixing was found to become less negative with alumina addition. Consistent with our previous results on the enthalpy of mixing of alumina-free mixed alkali silicate glasses, the magnitude of enthalpy of mixing exhibited a good correlation with the molar volume mismatch of the corresponding two single alkali glasses as well as with the extent of conductivity mixed alkali effect, e.g. excess activation energy of conductivity, ΔE. The reduction of the magnitude of the enthalpy of mixing with alumina addition can be attributed to the reduction of non-bridging oxygen and ionic field strength. Combining the present results with results obtained earlier, the magnitude of the enthalpy of mixing for all mixed alkali (Na2O and K2O) silicate glasses with and without alumina was expressed by a simple function of a modified Tobolsky parameter, which takes into account the alkali concentration and the difference in cation-to-effective anion distances. The enthalpy of mixing data of the mixed alkali glasses was then compared with reported experimental data on the conductivity of mixed alkali aluminosilicate glasses. What appears to be conflicting experimental data can be understood in terms of the magnitude of the enthalpy of mixing and we can conclude that the mixed alkali effect is closely correlated with the negative enthalpy of mixing. 相似文献
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On the influence of structural features of DNA on the possibility of metabolic transfer of electrons
A. D. Suprun 《Molecular Crystals and Liquid Crystals》2020,701(1):28-39
AbstractA fragment of a DNA molecule is considered as one of the channels of metabolic electron transfer. The heterogeneity of the complementary chains is effectively taken into account. This made it possible to find the speed of the electron injected into the DNA conduction band and the current density that it creates. Estimates of electron mobility in nucleic acid chains are made. They were an order of magnitude smaller than that of typical semiconductors. For the specific conductivity of nucleic acid chains, estimates provide a conductivity of one to two orders of magnitude lower than in graphite. 相似文献
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研究了在复合电铸过程中,当其它工艺参数一定时,复合电铸层的沉积速率及其厚度随时间的变化趋势, 以及复合电铸层表面微观形貌随电沉积时间的变化趋势.测定了复合电铸层的组织成分,并就纳米颗粒在复合电铸层表面和横截面上分布的均匀性进行了评价.结果表明,复合电铸层表面平整,组织均匀致密,其组成主要是镍和所复合的纳米颗粒,纳米颗粒较为均匀地分散在复合电铸层中. 相似文献
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N. G. Kakazey L. A. Klockov I. I. Timofeeva T. V. Sreckovic B. A. Marinkovic M. M. Ristic 《Crystal Research and Technology》1999,34(7):859-866
Zinc-oxide powder was tribophysically activated in a high-energy vibro mill in a continual regime in air for 3, 30 and 300 minutes with the purpose of modifying the powders physico-chemical properties. By analyzing of data obtained by X-ray powder diffraction, electron diffraction and transmission electron microscopy, the values of distances between corresponding crystallographic planes, average domain sizes of coherent scattering, i.e. crystallites, width of diffraction lines due to the existence of microstrains, and microstrain values, minimal dislocation densities, dislocation density due to microstrain and real dislocation density, and also average distances between dislocations were determined. The dependence of these values on the activation time was established, which enabled analysis of the evolution of the defect structure of zinc-oxide powders during tribophysical activation by grinding in the described regime. 相似文献
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Yu. G. Terent'yeva V. M. Yashchuk O. M. Snitserova M. Yu. Losytsky 《Molecular Crystals and Liquid Crystals》2017,642(1):81-88
This article presents the results of spectral investigations of white blood human cells including absorption, fluorescence and phosphorescence (using low-temperature measurements). For this research, the main optical centres were identified and local distribution of emitting and absorbing centres into white blood human cells was determined. In addition, the spectra of normal and pathological (B-cell chronic lymphocytic leukemia, B-CLL) cells were compared. 相似文献
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为制备适用于干压成型的氧化铝造粒粉,研究了PEG聚合度对氧化铝造粒粉微观形貌、流动性和松装密度的影响.结果表明PEG的聚合度对氧化铝浆料粘度影响显著,PEG2000-6000是较为理想的粘结剂选择,造粒粉的流动性与环境温度及湿度相关.采用正交实验设计,以造粒粉的流动性和松装密度为评价指标,对PEG聚合度、粘结剂添加量和固含量进行了优选,其影响顺序为PEG聚合度>固含量>粘结剂添加量.以优选参数PEG6000、添加量为4wt;、固含量为80wt;,制备了性能优良的氧化铝喷雾造粒粉. 相似文献