Lattice dynamics of strontium titanate: anharmonic interactions and structural phase transitions

作者：Ann Bruce, Roger Arthur Cowley · 发表于：Journal of Physics C Solid State Physics · 年份：1973 · DOI：10.1088/0022-3719/6/15/006 · 被引用次数：69 · 研究领域：High-pressure geophysics and materials、Ferroelectric and Piezoelectric Materials、Solid-state spectroscopy and crystallography

An anharmonic model of strontium titanate has been developed which gives reasonable agreement with the temperature-dependent frequency and linewidth of both the zone-centre and zone-corner soft modes. The model is based upon harmonic models derived from the results of neutron inelastic scattering experiments, and extended to include anharmonic interactions of short range. The anharmonic parameters were determined by constraining the model to fit anharmonic properties, for which particularly simple expressions can be derived. Other anharmonic effects were then computed and found to give reasonable agreement with experiment. The main conclusions drawn from the work are: firstly, it is possible to explain the temperature dependence of the zone-corner soft mode with an anharmonic model that is consistent with other properties; secondly, it is found that the soft-mode self-energy below the transition is different in the thermodynamic and collisionless regimes by an amount that is about 10% of the square of the mode frequency. This result questions the validity of using the conventional phenomenological models to correlate low-frequency (thermodynamic) properties with high-frequency (dynamic) properties such as the results of Raman or neutron scattering.