Heat Capacity Measurement of Nonstoichiometric BaSm2Mn2O7 Phase at High Temperature.

概要

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New method for the measurement of heat capacity at high temperature was developed with DSC by using the special heating patterns where the temperature region in each cycle overlaps with that in the previos or next cycle, and a procedure of multiple regression analysis was used for calculation of the heat capacity. Accuracy of this method was checked by measuring heat capacities of standard α-Al2O3 and Mn2O3 from room temperature to 850K and comparing those with the corresponding values from the references. The accuracy was within ±2.5% in relative error.Using this method, heat capacities of nonstoichiometric compound (BaSm2Mn2)1-xO7 (x=0.000 and 0.031), whose thermodynamic data are very poor, were measured, and a (λ-type) heat capacity anomaly caused by the phase transition was observed for the stoichiometric composition. The transition temperature and the enthalpy change accompanied by the phase transition were 520K and 1.65kJ·mol-1, respectively. The difference of the heat capacity between the stoichiometric and nonstoichiometric phase at 840K was about 8J·mol-1·K-1, while difference of heat capacity predicted by Dulong-Petit's law from their chemical formula is 4J·mol-1·K-1. Thus it was considered that the values of heat capacity tends to decrease slightly with increasing nonstoichiometry.
日本熱測定学会の論文