摘要
设计了一套模拟实验，以获得关于晶体形态和界面非稳定性的差异的可靠数据，如高温溶液生长的骸晶和枝蔓晶．这些实验是在高温实时观察装置（ＨＩＴＩＳＯＴ）内进行的．高温溶液晶体生长实验是在环形铂金丝炉圈内进行的．炉圈直径为２ｍｍ．铂金丝既起加热又起支撑熔体的作用．选用ＫＮｂＯ３和Ｌｉ２Ｂ４Ｏ７的混合物进行晶体生长实验．在只存在扩散机制的快速生长过程中，会形成不同的晶体不完整性，如晶面凹坑、骸晶和枝蔓晶．采用淬火实验以分辨不同的ＫＮｂｏＯ３晶体形态，并用扫描电镜研究Ｌｉ２Ｂ４Ｏ７溶体中ＫＮｂＯ３晶体生长的形貌．在一般情况下，当晶体在气液界面附近液相区成核时，会产生晶体界面非稳定性．导致晶体形状不稳定的溶液层的厚度为６０μｍ．通过扫描电镜观察，发现晶体在这一溶液层中由多面体晶变为枝蔓晶．骸晶和枝蔓晶的各向异性反映了ＫＮｂＯ３的立方特性，也反映了界面非稳定性是沿［１１０］晶棱扩大的，［１１０］晶棱方向的分支证实了晶体生长形状的各向异性·形成界面非稳定性的临界尺寸为１０μｍ．与此相反，中持稳定的晶面形状是通过６０μｍ厚度以下的溶液内的晶体生长来实现的．晶体生长过程是由高温实时观察装置进行实时观察和记录的，并能观察到晶体固液?
Model experiments were designed in order to obtain more reliable data on the diversity of some crystal forms and polyhedral instability-skeletal and dendritic growth in high temperature solution growth.These experiments were performed by High Temperature in Situ Observation Technique. Most of our investigations on high temperature solution growth were performed in a loop-shaped Pt wire heater, having a diameter about 2mm. The Pt wire (φ ~0.2mm) was used to heat and suspend the solution. A mixture of KNbO3 (20wt%) and Li2B4O7 was chosen for growth. Rapid growth, and hence diffusion mechanism limitations can result in various imperfections; such as the formation of cavities in the facets, skeletal and dendritic patterns. Quenching experiments were designed to distinguish some KNbO3 crystal forms, and the morphology of KNbO3 crystals grown in Li2B4O7 solution was studied with a scanning electron microscope. In all cases, when the crystal is nucleated near air/solution interface, it looses its polyhedral stability. The thickness of this shape destabilizing solution layer is about 60μm. The morphologies of crystals observed by a scanning electron microscope, vary in the layer from polyhedrons to dendrites. Anisotropic aspects of skeletal and dendritic structures reflect the cubic nature of KNbO3 as well as the fact that. instabilities amplify and propagate along the four (110) crystal edges. The side branches in the four (110) directions provide convincing evidence for the growth shape anisotropy. The value of the critical size for loss of polyhedral stability is about 10pm. In contrast, the stable shape of the faceted crystal is generally retained with adequate reproducibility for all crystals grown in the solution beneath the shape-destabilizing layer. The polyhedral crystal growth processes were in-situ observed and recorded by HITISOT. The thermoconcentrational driven convection (i.e.microconvection) around the solid-liquid interface of the polyhedral crystal was also visualized.
出处
《无机材料学报》
SCIE
EI
CAS
CSCD
北大核心
2000年第5期769-776,共8页
Journal of Inorganic Materials
基金
国家科学技术委员会攀登资助!(95-预-34)
国家自然科学基金!(59832080)
关键词
高温
氧化物
界面非稳定性
晶体生长
high-temperature oxide
polyhedral instability
KNbO3
high-temperature in situ observation device
scanning electron microscope
