PHASE-TRANSITIONS IN ORDERED AND DISORDERED LEAD INDIUM NIOBATE PBIN12NB1/2O3 STUDIED BY X-RAY-DIFFRACTION/

Ordered and disordered PbIn1/2Nb1/2O3 (PIN) crystals were investigated over the temperature range of 20 - 580 K by means of X-ray diffractio n. The temperature dependence of the integrated intensities of the (h h h) reflection for the disordered sample and the (h/4 k/4 0) reflecti on for the ordered sample were measured in order to know their order-p arameters. In both samples, the temperature dependence of the integrat ed intensity of the (h/2 k/2 0) reflection (alpha-spot) was compared w ith that of the (h/4 k/4 0) reflection. The integrated intensities of the two reflections showed the same temperature dependence. This resul t led to the suggestion of a new model of superlattice-structure for P IN with inequivalent displacements delta(1) and delta(2) for the Pb2cations.