X-RAY STUDY OF PHASE-TRANSITIONS IN PBIN1 2NB1/2O3/

Ordered (S=0.8) and disordered (S=0) crystals of PbIn1/2Nb1/2O3 (PIN) were investigated by X-ray diffraction measurement in the temperature range of 20K to 580K, The (h/4 k/4 0) superlattice reflection for the ordered antiferromagnetic sample and the (h h h) fundamental reflectio n for the disordered ferroelectric sample were measured for evaluation of the temperature dependence of their order parameters, The (h/2 k/2 0) (alpha-spots) and the (h/2 0 O) (beta-spots) superlattice reflecti ons were also observed. The temperature dependence of the integrated i ntensity of the alpha-spot was compared with that of the (k/4 k/4 0) r eflection in both samples. Their reflections shelved the same temperat ure dependence. The origin of the alpha-spots is due to the antiferrom agnetic distortion, The temperature dependence of the integrated inten sity of the alpha-spot al the ordered sample was different from that o f the disordered sample. The differences were explained hy a size effe ct of the clusters.