Enthalpy increments of Ba2Te3O8(s) and Ba3Te2O9(s) compounds

The enthalpy increments of the compounds Ba2Te3O8(s) and Ba3Te2O9(s) were measured in the temperature range 298–965 K, using a high temperature Calvet calorimeter. The values were least square fitted in the following temperature dependent polynomial equations:ΔH298.15 KT (J/mol) Ba2Te3O8(s)=−77,233+234.87T+0.08108T2 (298.15–862.8 K),ΔH298.15 KT (J/mol) Ba2Te3O8(s)=21,533−209.39T+0.46007T2 (862.8–965 K),ΔH298.15 KT (J/mol) Ba3Te2O9(s)=−116,177+338.96T+0.00741T2+4,310,572T.The temperature differentials of the above equations gave the heat capacity equations for the respective compounds, which were compared with Neumann–Kopp's estimated heat capacities. As heat capacity of TeO3 was not available in literature, it was estimated from that of TeO2. Using the Gibbs energy of formation data of Ba3Te2O9(s), reported in literature, ΔfH298.15 K°ΔfH298.15 K°, and S298.15 K°S298.15 K° of the compound were calculated as −2258 kJ/mol and 822 J/(mol K), respectively.