Dielectric and Birefringent Properties of [(CH$\text{}_{3}$)$\text{}_{2}$NH$\text{}_{2}$]$\text{}_{5}$Cd$\text{}_{2}$CuCl$\text{}_{11}$ Solid Solutions in the Region of Their Phase Transitions

On the basis of the optical and dielectric investigations of [(CH$\text{}_{3}$)$\text{}_{2}$NH$\text{}_{2}$]$\text{}_{5}$Cd$\text{}_{2}$CuCl$\text{}_{11}$ solid solutions the existence of phase transitions at T$\text{}_{1}$=175 K and T$\text{}_{2}$=117.5 K was confirmed. Both phase transitions were found to be shifted toward lower temperatures with respect to the corresponding transitions in the "host" [(CH$\text{}_{3}$)$\text{}_{2}$NH$\text{}_{2}$]$\text{}_{5}$Cd$\text{}_{3}$Cl$\text{}_{11}$ crystals. It was found that the proton conductivity in [(CH$\text{}_{3}$)$\text{}_{2}$NH$\text{}_{2}$ ]$\text{}_{5}$Cd$\text{}_{2}$CuCl$\text{}_{11}$ crystals is realized through the Grotthus mechanism. The investigations of the birefringent properties confirmed existence of the structural changes at T$\text{}_{0}$=320 K connected with the complex co-operative effect involving weakening of the hydrogen bonds and modification of the Jahn-Teller distortion with temperature.