扩镁铌酸锂表层的富MgO层特性

MgO-RICH LAYER CHARACTERISTICS IN THE MAGNESIUM DIFFUSED LITHIUM NIOBATE SURFACE LAYER

利用常规Ｘ射线衍射、掠入射Ｘ射线衍射和差热分析，对扩镁铌酸锂表层的富ＭｇＯ层特性进行了分析，提示出在富ＭｇＯ层具有一种未能确认的化合物和ＭｇＮｂ_２Ｏ_６的物相结构。ＭｇＮｂ_２Ｏ_６出现在富ＭｇＯ层的近表层，而未知化合物在次表层，且它们都具有明显的取向性。这些扩镁铌酸锂单晶的Ｃｕｒｉｅ温度先随扩散时间的增长而降低，但与扩散时间超过一定限度后又开始升高，并且出现另一个相变点，这可能是富ＭｇＯ层中未知化合物的相变点。利用阳离子空位理论模型较好地解释了Ｃｕｒｉｅ温度变化的异常现象。

MgO-rich layer characteristics in the magnesium diffused lithium niobate surface layer is investigated with the conventional X-ray diffraction,grazing-incidence X-ray diffraction and differential thermal analysis,It is found that the MgO-rich layer exhibits a crystal structure of an unknown compound and MgNb_2O_6.Their appearance indicates that MgNb_2O_6 is in the surface layer of MgO-rich layer, the unknown compound is in the subsurface layer and beneath the layer where MgNb_2O_6 exists,and these compounds have obviously preferred orientation.The Curie temperature of the magnesium diffused lithium niobate single crystal decreases with increase of diffusion time at first,but beyond a limit,the Curie temperature starts to increase again and another phase transition point appears at about 1186℃,which is probably the phase transition point of the unknown compound.These anomalous of the Curie temperature variation are well analyzed by the cation vacancy model.