Fizika Nizkikh Temperatur: Volume 25, Number 8-9 (August 1999), p. 861-867    ( to contents , go back )

Raman scattering and phase transitions in mixed crystals of K1-x(NH4)xH2PO4

Yu. A. Popkov, A. V. Van`kevich, I. A. Taranova, E. M. Savchenko,

Kharkov State University, Svobody sq.4, 310077 Kharkov, Ukraine
E-mail: yury.a.popkov@univer.kharkov.ua

L. A. Shuvalov

Shubnikov L. V. Institute of Crystallografy, RAS Leninskij prospect., 59, Moscow 117333, Russia
pos Анотація:

(Received February 24, 1999 )

Abstract

The band spectrum characteristics of tetrahedron PO4 intrinsic vibration n2(A1) in mixed K1-xAxDP crystals with various ammonium concentration were investigated in the temperature range 4,2-300K. At the transition to ordered ferroelectric (x= 0,00; 0,02; 0,04; 0,08) or antiferroelectric (x = 0,74; 0,82) phases abrupt changes of frequency and half-width of the band studied were observed. The decrease of the band half-width during the ordering points to the involvement of excitations responsible for the appropriate states in the relaxation processes. The transition to the structural glass phase (x= 0,22; 0,32; 0,53) is not accompanied by sharp changes of the band parameters but the band half-width at low temperatures is smaller than that expected for completely disordered paraelectric phase.

PACS:
77.80.Bh - Phase transitions and Curie point
78.30.-j - Infrared and Raman spectra (for vibrational states in crystals and disordered systems, see 63.20.-e and 63.50.+x respectively)
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