MEASUREMENT OF NONLINEAR DIELECTRIC-CONSTANT IN RB1-X(NH4)(X)H2PO4 MIXED-CRYSTALS

Temperature dependences of the third-order nonlinear dielectric consta nt in the mixed crystals of Rb1-x(NH4)(x)H2PO4 with x = 0.25; 0.3, 0.4 , 0.5, 0.6 and 0.7 were measured in the temperature range between 4 an d 50 K. It was observed that the nonlinear dielectric constant in thes e crystals increases near the glass transition point and it is strongl y dispersive at low frequencies. It was found that the third-order non linear dielectric constant is proportional to the imaginary part of th e linear dielectric constant when measured under changing temperature at a fixed frequency.