SPECIFIC-HEAT AND PHASE-TRANSITION PHENOMENA IN (CH3NH3)5BI2CL11

Specific heat of (CH3NH3)5Bi2Cl11 was measured by adiabatic calorimetr y between 13 K and 325 K. A typical second-order type of anomaly was o bserved at 307.4 K. The enthalpy and entropy of transition were determ ined as 3.06 kJ mol-1 and 10.6 J K-1 mol-1, respectively. A broad hump in the curve of specific heat was found around 160 K. Its contributio n was estimated as the excess specific heat extending from about 100 K to 200 K over an assumed normal base line, which results in the value s of enthalpy and entropy as 1.57 kJ mol-1 and 9.85 J K-1 mol-1, respe ctively. The phase transition in the crystal was discussed in connecti on with such specific heat anomalies.