Hard mode Raman spectroscopy and renormalization phenomena in diluted lead phosphate, (Pb_1−xM_x)₃(PO₄)₂

Renormalization phenomena in the palmierite-type compound lead phosphate are a consequence of order parameter coupling with defect induced conjugated fields. The influence of the lead dilution by barium and strontium on the improper ferroelastic transformation, the plateau effect and the ferroelastic domain pattern is studied. The critical behaviour of the diluted three states Potts system with the order parameter components {Q_1..3} was determined by Raman spectroscopy, optical birefringence and X-ray diffraction.