Dielectric, elastic and electromechanical nonlinearity of relaxor and "nearly" relaxor KDP-ADP mixed crystals

Temperature dependences of linear and nonlinear dielectric,elastic and electromechanical responses in K_(1-x)(NH_(4))_(x)H_(2)PO_(4)(x≈0.19 and 0.24)single crystals have been studied within temperature range 10–300 K.It was found near linear relations between dielectric permittivity(ε_(33)),elastic compliance(S_(6))and piezoelectric constant(d_(36)).Different behavior of elastic and dielectric nonlinear responses was revealed in the crystals undergoing ferroelectric phase transitions and transition to relaxor state.Obtained temperature dependences of nonlinear permittivity and elastic compliance are discussed in the framework of Random Field model.