Raman scattering and phase transitions in mixed crystals K1-x(NH4)(x)H2PO4

Spectral parameters of the Raman scattering band corresponding to intrinsic vibration nu(2)(A(1)) of the PO4 tetrahedron in mixed crystals of K(1-x)A( x)DP with various ammonium concentrations are studied in the temperature ra nge 4.2-300 K. Abrupt changes in frequency and half-width of the band are o bserved during transitions to ordered ferroelectric (x=0.00, 0.02, 0.04, 0. 08) or antiferroelectric (x=0.74,0.82) phases. The decrease in the band hal f-width during ordering indicates the participation of excitations responsi ble for the corresponding states in relaxation processes. The transition to the structural glass phase (x=0.22, 0.32, 0.53) is not accompanied with sh arp changes in the band parameters, but the band half-width at low temperat ures is smaller than the expected value for totally disordered paraelectric phase. (C) 1999 American Institute of Physics.