Temperature Dependence of the ν₂Band of PO₄Tetrahedrons in Rb_1-x(NH₄)_xH₂PO₄Mixed Crystals

Abstract

The ν 2 band of PP 4 tetrahedrons in Rb 1- x (NH 4 ) x H 2 PO 4 mixed crystals has been measured in the temperature region from 30 K to room temperature by Raman spectroscopy. Peculiar temperature dependence in the frequency and shape of the ν 2 band of PO 4 tetrahedrons which reflects the structure change in the mixed crystals has been found. The temperature dependence is well understood if we assume the existence of ferroelectric and antiferroelectric clusters in the mixed crystals below the onset temperature of a structure change; PO 4 tetrahedrons themselves and the surrounding ions in the ferroelectric and antiferroelectric clusters are ordered into the ferroelectric and antiferroelectric configurations, respectively.