RENORMALIZATION PHENOMENA IN BA-DILUTED FERROELASTIC LEAD PHOSPHATE, (PB1-XBAX)(3)(PO4)(2)

In the improper ferroelastic palmierite-type lead phosphate order para meter coupling with a defect induced conjugate held leads to the renor malization of the two different critical temperatures of three order p arameter components {Q(3)} and {Q(1)Q(2)}. The influence of the lead d ilution by barium on the ferroelastic domain pattern, the critical tem perature of the ferroelastic transformation R(3) over barm$-C2/c and t he development of the intermediate regime in (Pb1-xBax)(3)(P0(4))2 is studied using optical birefringence measurements, Raman and infrared s pectroscopy. At the ferroelastic transition temperature T-c the orient ational contribution of the three-states Potts model becomes critical. T-c is reduced from 453 K (x = 0) to zero K at x similar or equal to 0.12. Modifications of the shape of zigzag needle domains as well as t he angle between the monoclinic binary axis and the W walls along [031 ] with temperature and increasing Ba-content are reported. Above the f erroelastic transition point the component Q(3), which corresponds to the displacive part in the Gibbs free energy, leads to dynamic short-r ange monoclinic deformation in the trigonal matrix. The temperature wh ere Q(3) shows critical behaviour is renormalized to 720 K (x = 0.12) as compared with 563 K in pure lead phosphate. For x>0.13 no monoclini c precursor clusters were found.