Abstract :
The dielectric permittivities (ε11 and ε33), elastic compliance (S66) and piezoelectric constant (d36) for the K0.25(NH4)0.75H2PO4 single crystal were studied near antiferroelectric phase transition temperature (TN). It was found that diffused maximums in both the ε11(T) and the ε33(T) dependences as well as in the d36(T) dependences are observed above TN, while narrowed peak in S66(T) curve is located below TN. Analysis of experimental results speaks in favor of two-stage AFE→PE phase transition in the crystal under study. Below TN the drastic decreasing of electromechanical coupling factor (k36) is found.
