Thermochimica Acta, Vol.347, No.1-2, 123-128, 2000
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 capacities of Sr-Cu-O phases. The indicated temperature was calibrated through the solidification points of pure metals (ITS-90). Powdered CuO having similar 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 discontinuous method the respective peak areas were calibrated. The sensitivity calibration curve for the discontinuous method was evaluated from two successive runs carried out on the reference material. The calibrated calorimeter was used for determination of temperature dependences (473-1133 K) of heat capacity of the SrCuO2 Sr2CuO3 and Sr14Cu24O41 phases. Obtained C-p,m(0), data measured by the step-by-step procedure were evaluated by two different methods. In the first method, the mean value of C-p,m(0), was obtained by dividing the enthalpy change attributed to a given change of temperature by a corresponding Delta T. The second method consisted of summing the individual enthalpy contributions and subsequent differentiation of the resulting temperature dependence of enthalpy. Both these approaches yielded comparable results with relative standard deviations of 2-3% from the standard polynomial fit C-p,m(0) = a + bT + cT(-2). The temperature dependences of heat capacity of measured phases were compared with the low-temperature data taken from the literature as well as with the estimated curves. Our results exhibit a systematic shift to lower C-p,m(0) values.