Heat capacities of PbBi12O19(s) and ϕ-Pb5Bi8O17(s)

Heat capacities of PbBi12O19(s) and ϕ-Pb5Bi8O17(s) were measured by differential scanning calorimetry in the temperature range 280-820 K and 280-660 K, respectively. PbBi12O19(s) and ϕ-Pb5Bi8O17(s) showed order-disorder transitions whose onset temperatures are 520 K and 700 K, respectively. The measured heat capacities of PbBi12O19(s) and ϕ-Pb5Bi8O17(s) as a function of temperature are expressed as:Cp(JK−1mol−1)=791.68+112.18×10−3T−13.58×106T−2(280−820K)Cp<ϕ-Pb5Bi8O17>(JK−1mol−1)=700.02+161.58×10−3T−12.85×106T−2(280−660K)Enthalpy increments, entropies and Gibbs energy functions were derived from the measured heat capacity data.