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
L. A. Shuvalov
Shubnikov L. V. Institute of Crystallografy, RAS Leninskij prospect., 59, Moscow 117333, Russia
(Received February 24, 1999 )
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.