MIXED FERROELECTRIC PHASE TRANSITIONS IN CRYSTALS LITHIUM TANTALATE AND LITHIUM NIOBATE

摘要

＜正＞ Ⅰ.INTRODUCTIONLithium tantalate LiTaO3 and lithium niobate LiNbO3 are ferroelectric materials ofABO3 structure with oxygen octahedrons.Their ferroelectric properties are similar to those ofthe perovskites,although neither of them belongs to perovskite structure.The Curie point inLiNbO3 is at 1480 K and in LiTaO3 is sample-dependent,a temperature range of 50 K from880 to 930 K in LiTaO3 is measured by the measurements of pyroeloctric effects,refractiveindexes and dielectric constants.Such a sample dependence of the transition is foundto be related to the growth conditions,internal components and internal stress in the crys-tals.