RAMAN INTENSITY STUDY OF SCALING PROPERTIES OF NA-TRANSITIONS(, K+, AG+, AND PB2+ DOPED NH4NO3 CRYSTALS DURING PHASE)

It is observed that, for molecular crystals, during phase transitions the Raman intensities of the vibrational modes obey the power law \T-T -c\(beta). The exponent beta contains much critical information and is mode dependent. The scaling properties of the doped materials are imb edded in beta which is found to be very sensitive to very small degree s of doping. One of the eminent phenomena is the so-called crossover p oint where beta of the totally symmetric nu(1) mode equals the nonsymm etric nu(4) mode of the nitrate ion. The scaling is expressed through the scaled coordinate d/M-1/2 where d is the averaged interdoped-catio nic distance and M is the mass of the cation. beta of the nu(1) mode b ehaves as (d/M-1/2)(gamma) with exponent gamma rather independent of t he transitions and the kinds of doping. Resonant modes due to doped ca tions are employed to explain the origin of the scaling. (C) 1998 Amer ican Institute of Physics.