Raman scattering and phase transitions in mixed crystals of K1-x (N H4)x H2 P O4

The band spectrum characteristics of tetrahedron P O4 intrinsic vibration v2(A1) in mixed K1-x Ax DP crystals with various ammonium concentration were investigated in the temperature range 4,2-300 K. At the transition to ordered ferroelectric (x = 0.00; 0,02; 0,04; 0,08) or antiferroelectric (x approx 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