Both real and imaginary parts of the dielectric constants are measured in the pellet samples of $K_{1-x}(NH_4)_xPO_4[(KDP)_{1-x}(ADP)_x or KADP-x]$ over the whole range of x between x=0 and x=1 at the temperatures from room temperature to 15K. Proton glass behaviour is observed in the range of 0.28＜x＜0.64, while ferroelectric and antiferroelectric phase transitions are observed for x＜0.22 and x＞0.70 respectively. Phase coexistences are observed for x of the phase boundary layer in the pressed samples of KADP-x. Pyroelectric current measurement is applied to obtain the field-cooled polarization $P_FC$ and zero field-cooled polarization $P_ZFC$ of KADP-x pellet samples. Remanent polarization $P_R$ is observed in both ferroelectric and proton glass regimes of x, but not observed in the antiferroelectric regime. Nonergodicity, phase coexistence, and diffuse phase transition characteristics seem to be well identified by the pyroelectric measurements of $P_FC$, $P_ZFC$, and $P_R$, $P_FC$, $P_ZFC$, $P_R$, and thermo-remanent polarization $P_TRP$ are also measured to study the nonergodicity effects of the glass phase in $Rb_0.68(NH_4)_0.32AsO_4$ mixed crystal. Stretched-exponential relaxation, Almeida-Thouless like instability lines, etc of the spin glass systems are observed in the proton glass system of dielectric RADA-0.32 crystal. Temperature and frequency dependence of the dielectric loss are analyzed by Vogel-Fulcher scaling to obtain the distribution function f(E) of the energy barrier parameter E, the attempted frequency $υ_0$, and the static freezing temperature of the Vogel-Fulcher law $T_0$ for DRADP-0.37 crystal. The temperature and frequency which are obtained from the maximum value of the imaginary part of the dielectric constants are well fitted by the phenomenolocical Vogel-Fulcher law $υ_c = υ_0 exp(-E/(T - T_0)$.
