氢键铁电体相变的格林函数理论(Ⅱ)

GREEN'S FUNCTION THEORY OF PHASE TRANSITION IN HYDROGEN-BOND FERROELECTRICS (Ⅱ)

在文献[1]的基础上,计算了包括四体相互作用项的氢键铁电系统自由能,给出了确定铁电一级相变时序参数跃变和居里温度的表示式。通过对自由能在相变温度附近行为的详细分析,表明了微观理论结果与朗道热力学理论完全一致,并给出了朗道自由能表示式中各系数与微观相互作用参数之间的关系,使各系数的物理意义更加明确。再通过与PbHPO_4,PbDPO_4和H_2C_4O_4等晶体的实验结果比较,进一步证明本文理论能成功地处理氢键铁电体的一级相变和二级相变问题。

Based on our paper (I), we calculate the free energy of the hydrogen-bond ferroelectrics system with four-body interactions, and propose the conditions to determine the Curie temperature and the discontinuity of the first order phase transition. The detailed analysis of free energy around the transition temperature indicates that the results of our microscopic model coincide with the predictions of Landau's theory. And the relations between the coefficients in Landau free energy and the microscopic interaction constants are obtained, that makes the physical meaning of these coefficients more clear. By comparing with the experimental data of PbHPO4, PbDPO4 and H2C_4O4 crystals, we confirm that our theory can successfully explain the first order ferroelectric phase transition as well as the second order transition.