GLASS-LIKE PHASE-TRANSITIONS AND DIELECTRIC NONLINEARITY IN LEAD MAGNESIUM NIOBATE CRYSTALS

Temperature dependence of differential dielectric nonlinearities beta = partial derivative2epsilon/partial derivative E2 of lead-magnesium-niobate crystals (PMN) has been studied using small-signal dielectric permittivity epsilon data when a bias electric field E= is applied to the crystal. The nonergodicity of PMN is observed at temperatures 150-300 K. As a bias electric field E= is decreased (50 less-than-or-equal-to E= < 500 V/cm), the value beta is increased. At fields 500 less-than-or-equal-to E= < 1,000 V/cm beta practically does not depend on E=. Two minima observed in temperature dependence beta correspond to phase transitions into glass-like state in PMN.