Li_(0.025)Na_(0.975)NbO_3晶体的低温热学性质

LOW TEMPERATURE THERMAL PROPERTIES OF Li_(0.025)Na_(0.975)NbO_3 CRYSTAL

在320K 至120K 的温度范围内,研究了 Li_(0.025)Na_(0.975)NbO_3晶体的热学性质。焓的时间变化率和比热在降温过程中于180K 左右发生突变,在升温过程中于257K 左右发生突变,这暗示着晶体中发生了一级相变。根据升温时的测量结果,得出转变热为ΔQ=213.5268±(17)J/mol,相应的熵变为ΔS=0.7787J/mol.该相变的热滞约为70K,与介电及热电测量所得结果基本一致。

The thermal properties of Li_(0.025)Na_(0.075)NbO_3 crystal have been inve- stigated in the temperature range from 320K to 120K.The time deriva tive of enthalpy and the specific heat change anomalously at about 188K on cooling and about 257K on heating,implying a first order phase transition.The heat of transition ΔQ=213.5268(±17)J/mol and the corresponding change in enthalpy ΔS=0.7787J/mol.The thermal hysteresis of the transition is about 70K,in agreement with that obtained from the dielectric and pyroe- lectric measurements.