RAMAN-SPECTROSCOPIC STUDY OF ORDER-DISORDER IN LEAD MAGNESIUM NIOBATE

Precision Raman spectra have been measured on lead magnesium niobate (PMN)-lead titanate (PT) solid solution at various temperatures. The multiband Raman spectra are inconsistent with Pm3m symmetry but can be accommodated within a model of ordered nanodomains of rhombohedral symmetry. Raman band widths are large and nearly independent of temperature indicating a static structural disorder rather than a dynamic dipolar disorder. Abrupt changes in wave number and widths of certain bending modes at 200 K are interpreted as evidence for a reversible phase transition at this temperature. All of the spectroscopic properties are largely independent of the titanium concentration in the PMN-PT solid solutions.