Direct measurements of of grain boundary properties and mechanism of electroceramics.

用微操作仪测量了掺钛酸锶晶体中单晶界极窄区域的电学性质。用氙弧像浮区法制备了具有马赛克结构的半导体钛酸锶单晶界样品。在各晶界观察到了电压和电流的非线性关系。单晶界样品的击穿电压(Vb)和非线性系数(α)分别为0.5~3.5V和1~7。压敏特性与晶体的取向无关。在还原气氛中热处理后，压敏电阻特性消失。还原后的样品在高温下再次氧化，然后再次观察压敏特性。氧化或还原处理使晶界的伏安特性发生了可逆的变化。样品的击穿电压随氧化温度和时间的增加而增加，但非线性系数(α)几乎不变。在样品中，将SrTiO3FZ-单晶切割成两个相，氧化后在同一方向上机械接触，分离前观察到与晶界相同的电压-电流非线性关系。

The electrical properties in very narrow region of a single grain boundary in Ladoped SrTiO_3 crystals were measured by using the micromanipulatoR.The sample having one grain boundary was prepared from semi conductive SrTiO_3 crystals having mosaic structure prepared by xenon-arc image floating zone method. The nonlinear relation of voltage and current was observed in the every grain boundaries. Although there were no electrical effects from the neighbor grains in the single grain boundary sample, the break down voltage (Vb) and nonlinear coefficient (alpha) varied 0.5 to 3.5 V and 1 to 7 respectively. The varistor characteristic was independent from the directions of crystals. After heat treatment in reduced atmosphere, the varistor characteristics was disappears. The reduced samples were re-oxidized at high temperature, then teh varistor characteristics were observed again. The voltage-current characteristics of grain boundary were changed reversibly by oxidation or reduction of the sample. The break down voltage was increase with oxidation temperature and time, but nonlinear coefficient (alpha) was almost constant.In the sample, cut the SrTiO_3 FZ-single crystal into two pic es and oxidized them and then contacted them mechanically in same direction before separation, the nonlinear relation of voltage and current was observed same as the grain boundary in the FZ-crystals.