OPTICAL AND NONLINEAR-OPTICAL STUDIES OF THE RELAXOR PB(MG1 3NB2/3)O-3/

Temperature dependence of the birefringence of relaxer Pb(Mg1/3Nb2/3)O -3 was precisely measured under zero and non-zero electric field. Mark ed differences were observed among zero-field cooling, field heating, field cooling and zero-field heating processes. In the low temperature region, long-range order developed with quite long relaxation time wh ich depended strongly on temperature and applied electric field. The r hombohedral phase which grew in the cubic matrix with decreasing tempe rature was confirmed to be polar by the second harmonic generation exp eriment.