Calibration of the Setaram high-temperature calorimeter for determination of heat capacity of phases in the Sr-Cu-O system

A high-temperature Setaram calorimeter was calibrated to measure the heat c apacities of Sr-Cu-O phases. The indicated temperature was calibrated throu gh the solidification points of pure metals (ITS-90). Powdered CuO having s imilar emissivity and heat conductivity to the measured materials was used as a standard for caloric calibration. Two different methods of measurement were examined. Working in continuous scanning mode, the 'classical' three- step method of heat flow rate calibration was used, while for the discontin uous method the respective peak areas were calibrated. The sensitivity cali bration curve for the discontinuous method was evaluated from two successiv e runs carried out on the reference material. The calibrated calorimeter wa s used for determination of temperature dependences (473-1133 K) of heat ca pacity of the SrCuO2 Sr2CuO3 and Sr14Cu24O41 phases. Obtained C-p,m(0), dat a measured by the step-by-step procedure were evaluated by two different me thods. In the first method, the mean value of C-p,m(0), was obtained by div iding the enthalpy change attributed to a given change of temperature by a corresponding Delta T. The second method consisted of summing the individua l enthalpy contributions and subsequent differentiation of the resulting te mperature dependence of enthalpy. Both these approaches yielded comparable results with relative standard deviations of 2-3% from the standard polynom ial fit C-p,m(0) = a + bT + cT(-2). The temperature dependences of heat cap acity of measured phases were compared with the low-temperature data taken from the literature as well as with the estimated curves. Our results exhib it a systematic shift to lower C-p,m(0) values. (C) 2000 Elsevier Science B .V. All rights reserved.