Thermal Expansion of (CH3\text{}_{3}NH3\text{}_{3})5\text{}_{5}Bi2\text{}_{2}X11\text{}_{11} (X=Cl, Br) Crystals in the Temperature Range from 80 to 300 K

Thermal expansion studies on (CH$\text{}_{3}$NH$\text{}_{3}$)$\text{}_{5}$Bi$\text{}_{2}$Cl$\text{}_{11}$ and (CH$\text{}_{3}$NH$\text{}_{3}$)$\text{}_{5}$Bi$\text{}_{2}$Br$\text{}_{11}$ in the temperature range 80-350 K are reported. The dilatometric measurements revealed a considerable similarity with respect to the anisotropy of dilatations of both isomorphous crystals. A diffused thermal anomaly was found around 170 K in (CH$\text{}_{3}$NH$\text{}_{3}$)$\text{}_{5}$Bi$\text{}_{2}$Cl$\text{}_{11}$ crystal