Optical phonons and ferroelectric phase transition in the LaBGeO5 crystalстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:Infrared (IR) reflectivity and submillimeter transmission measurements of ferroelectric and paraelectric LaBGeO5 single crystals were carried out in the temperature range of 300 to 870 K. From the classical oscillator fit to the spectra, the complex dielectric function in the range of 4 to 3000 cm(-1) was calculated. In addition, room temperature polarized Raman spectra were recorded and evaluated which, together with the known high temperature Raman data, enabled us to identify and classify all of the 46 transverse optical modes predicted by the factor-group analysis and their longitudinal optical analogues. The order-disorder type of the ferroelectric transition at T-c approximate to 800 K was confirmed by revealing a microwave critical relaxation near and above T-c. However, this relaxation vanished below approximate to 700 K and an anomalous IR phonon mode was detected which softens partially from 87 cm(-1) at 300 K down to approximate to 60 cm(-)1 near T-c, where it becomes nearly overdamped and coupled to the relaxation. This represents a novel partial displacive feature which is revealed when the structure below the order-disorder transition becomes ordered.