An introduction to computational crystallography:the relationship between aluminum-based spinel structures and their morphologies

Computing technology is developing very fast and has permeated among many fields of sci-ence and technology, giving rise to many interdisciplinary subjects. Crystallography, originating from the activity of mining and smelting, has now become a comprehensive subject concerning crystal growth mechanism, chemical composition, structural morphology and physical properties and its research scope is widened by introducing many new achievements from basic sciences such as physics, chemistry, and math…     

Formation mechanism of barium titanate nanocrystalis under hydrothermal conditions

Growth units and the crystallization habit of BaTiO3 nanocrystals have been investigated. It has been proposed that the growth units of BaTiO3 were surface hydroxylated Ti(OH)62- octahedra. The relationship between crystal morphology and the variation of the current intensity in the solution has been obtained through the measurement of the OH in the solution and the hydrothermal experiment with superimposed direct electric field. Based on the computation of the stability energy of the growth units, the relationship between the crystallized morphology of crystallites and the most favorable growth units under different conditions has been derived. It has been found that there is structure similarity between anatase (TiO2) and BaTiO3 from the crystal chemistry viewpoint, so they are soluble in each other, which can serve as a reasonable explanation for the abnormal phenomenon of the retention of cubic substable phase at room temperature.     

预烧对水热BaTiO3介电性能的影响

水热ＢａＴｉＯ３粉料可在１２４０℃进行烧结，但由于粉料含有一定量的表面吸附水和结构水及ＯＨ等缺陷烧结体中气孔较多，介电性能也不理想，粉料在经９００℃，２ｈ的预烧处理后，可去除其中的水及ＯＨ等缺陷，示差扫描量热分析表明，粉料中四方相ＢａＴｉＯ３含量从１５％增加到２８％，并使其烧结体中气孔率降低，介电性能也得到改善。     

水热法制备的BaTiO3微晶粒的特性

本文报道了对水热法制备的ＢａＴｉＯ３纳米微粒性质和缺陷研究的结果．水热法制备的ＢａＴｉＯ３纳米微粒形貌和线度可通过改变前驱物形式和反应条件加以适度调控．在一定的条件下，水热法得到的是在常温下能稳定存在的立方相ＢａＴｉＯ３晶粒．这种“反常”结晶学特性是由于晶粒里含有一定量的Ｏ－Ｈ缺陷和钡离子空位缺陷所造成的．选择适宜的反应条件（如提高反应前驱物钡钛摩尔比等）或采用一定的处理手段（如热处理等），减少或消除这类缺陷，即可消除此“反常”结晶学特性．     

水热条件下钛酸钡粉体晶粒形成机理

以圩采用加直流电场水热法制备的ＢａＴｉＯ３粉体体系，测定了反应过程中外直流电场电流和反应反溶液中残 ＯＨＪ一。水热反应初期，电流随着反应温度的升高而增大，反应继续进行，电流达到极大值，然后急剧减小。反应温度越高，反应时间越长，反应后溶液里残留的ＯＨ量越少。结合粉体物相和晶粒形貌的表征，对水热条件下ＢａＴｉＯ３晶粒的形成机量进行了探讨。在反应初期，随着温度的升高驱物逐渐溶解，体系中导电离子数不断增多     

Solvothermal preparations of α-alumina and boehmite crystallites and investigations on the formation of their morphologies

Ｃｏｒｕｎｄｕｍ(αＡｌ2Ｏ3)ｉｓａｎｉｍｐｏｒｔａｎｔｈｉｇｈｔｅｍｐｅｒａｔｕｒｅｓｔｒｕｃｔｕｒａｌｃｅｒａｍｉｃｍａｔｅｒｉａｌ.Ｉｎｏｒｄｅｒｔｏｉｍｐｒｏｖｅｔｈｅｃｅｒａｍｉｃｐｒｏｐｅｒｔｉｅｓｏｆｔｈｅｍａｔｅｒｉａｌｓ,ｉｔｉｓｅｓｓｅｎｔｉａｌｆｏｒｕｓｔｏｐｒｅｐａｒｅｈｉｇｈｑｕａｌｉｔｙｓｕｐｅｒｆｉｎｅｐｏｗｄｅｒｓ(ｃｒｙｓｔａｌｌｉｔｅｓ).Ｈｙｄｒｏｔｈｅｒｍａｌｍｅｔｈｏｄｍａｙｂｅｕｓｅｄｔｏｐｒｅｐａｒｅｍａｎｙｋｉｎｄｓｏｆｓｕｐｅｒｆｉｎｅｐｏｗｄｅｒｓ(ｃ…     

超快大功率SiC光导开关的研究

选用钒掺杂浓度为0.2at％的高质量6H-SiC晶体, 电阻率为7.0×10⁸Ω·cm, 研制出超快大功率SiC光导开关. 在脉冲宽度为20ns的光源激发下, 分别测试了在不同的偏置电压和光能条件下开关的电脉冲输出特性. 结果表明: 1mm电极间隙的SiC开关器件的性能优越, 耐偏压高, 光导电脉冲的上升时间快(6.8ns), 脉宽<20ns, 稳定性好. 负载为40Ω的电阻上输出线性电脉冲电压随开关的偏置电压和光强增大而增大, 在2.5kV的偏置电压, 最大瞬时电流约为57.5A, 瞬时功率高达132kW.     

纳米二氧化钛粉体的多晶型制备及形成机理

本文分别以四氯化钛、硫酸钛和钛酸丁酯为前驱物,研究了水热条件下二氧化钛微晶粉体的结晶晶型、晶粒形貌和晶粒度.采用XRD和TEM等分析手段分别对产物的晶相和晶粒形貌进行表征.实验结果表明:对于200℃水热反应,以四氯化钛为前驱物,通过加入氢氧化钠调节反应介质酸碱度,当溶液pH值小于1时,有利于形成金红石型粉体;当溶液pH值大于3并小于7时,有利于形成锐钛矿型粉体;当溶液ph值大于7时,有利于形成板钛矿型粉体.以硫酸钛为前驱物,通过控制胶体制备工艺及反应温度,制备得到锐钛矿型和板钛矿型粉体.金红石型粉体呈长条柱状,锐钛矿呈菱形或双锥状,板钛矿呈板块状.经过较为系统的实验研究,获得了金红石、锐钛矿、板钛矿三种晶相的粉体,并可通过控制前驱物的种类及酸碱度和水热反应条件随意地制备出以上三种晶相中的单晶相粉体.从结晶学出发,解释了二氧化钛纳米粉体的结晶形貌,并从晶体生长过程及生长机理的角度讨论了二氧化钛同质变体的形成机理.