Sg. Ma et al., RAMAN INTENSITY STUDY OF SCALING PROPERTIES OF NA-TRANSITIONS(, K+, AG+, AND PB2+ DOPED NH4NO3 CRYSTALS DURING PHASE), The Journal of chemical physics, 108(18), 1998, pp. 7758-7762
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.