Theory of ferroelectric phase transition in SrTiO 3 induced by isotope replacement
Theory of ferroelectric phase transition in SrTiO 3 induced by isotope replacement
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同位素置换诱导SrTiO 3 铁电相变理论
DOI：
10.1103/physrevb.69.024103
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发表时间：
2003
影响因子：
3.7
通讯作者：
S. Miyashita
中科院分区：
文献类型：
--
作者：
Y. Yamada;N. Todoroki;S. Miyashita
发展了描述氧同位素置换引起的介电反常和铁电相变的理论。该模型对表面上相互矛盾的宏观介电测量结果和中子散射微观晶格动力学测量结果给出了一致的解释。这一本质特征被描述为一个三态量子有序-无序系统，该系统除了表征团簇的基态外，还表征了简并的激发态。通过激发态之间的隧穿频率考虑了同位素替代的影响。用平均场近似(MFA)分析了样品的介电性质，在整个同位素浓度范围内与实验结果定性一致。用量子蒙特卡罗方法研究了温度-隧穿频率坐标下的相图，验证了MFA分析的定性有效性。
A theory to describe the dielectric anomalies and the ferroelectric phase transition induced by oxygen isotope replacement in ${\mathrm{SrTiO}}_{3}$ is developed. The proposed model gives consistent explanation between apparently contradictory experimental results on macroscopic dielectric measurements and microscopic lattice dynamical measurements by neutron-scattering studies. The essential feature is described by a three-state quantum order-disorder system characterizing the degenerated excited states in addition to the ground state of ${\mathrm{TiO}}_{6}$ cluster. The effect of isotope replacement is taken into account through the tunneling frequency between the excited states. The dielectric properties are analyzed by the mean-field approximation (MFA), which gives qualitative agreements with the experimental results throughout full range of the isotope concentration. The phase diagram in the temperature-tunneling frequency coordinate is studied by a quantum Monte Carlo method to confirm the qualitative validity of the MFA analysis.