HIGH-TEMPERATURE ENTHALPIES AND HEAT-CAPACITIES OF YBMNO3 AND YMNO3

Heat capacities of YbMnO3 and YMnO3 were measured by differential scan ning calorimetry (DSC) from room temperature to 850 K. Enthalpy change s of YbMnO3 and YMnO3 were measured by drop calorimeter in the tempera ture range 573 to 1373 K and heat capacity equations were also estimat ed. The heat capacity equations were determined by combining the data from both calorimeters and the equations derived for YbMnO3 from 298 K to 1373 K were Cp,m (J K-1 mol(-1)) = 125.3 + 11.5 x 10(-3).T - 1.78 x 10(6).T-2 and for YMnO3 Cp,m(J K-1 mol(-1)) = 120.8 + 15.8.10(-3).T - 2.41.10(6).T-2. The standard Gibbs free energy changes of formation for YbMnO3 and YMnO3 at 298 K were also calculated by using above data . The values were determined to be -1317.6 kJ mol(-1) and -1367.1 kJ m ol(-1), respectively. (C) 1998 Elsevier Science S.A.