HIGH-TEMPERATURE ENTHALPY AND HEAT-CAPACITY OF ERMNO3

The heat capacity of ErMnO3 was measured by differential scanning calorimetry (DSC) from 300 K to about 850 K. The heat capacity value at 298 K was determined to be 103.7 J mol(-1) K-1. In order to obtain thermodynamic data at higher temperatures, the enthalpy change of ErMnO3, H-T(0)-H-298(0), was measured in the temperature range 673-1373 K by the drop method. The accuracy of the enthalpy measurement was checked by comparing the measured enthalpy changes of Er2O3 and Mn2O3 with literature values. The relative error was +/- 2% for both compounds. However, for the heat capacity calculated from the enthalpy change, the maximum deviation of the heat capacity from the references was +/- 3 %. The equation for the heat capacity of ErMnO3 derived by combining the two methods (DSC and drop methods) was C-p = 111.9 + 26.4 x 10(-3) T-1.33 x 10(6) T-2 from 298 to 1373 K. The standard Gibbs free energy of formation for ErMnO3, -1362.7 kJ mol(-1) at 298 K, was also calculated using the above data.