%0 Journal Article
%T THERMODYNAMIC BEHAVIOR OF Ca3Co3.93+xO9+¦Ä CERAMICS
%A O. JANKOVSKY
%A D. SEDMIDUBSKY
%A Z. SOFER
%A P. SIMEK
%J Ceramics-Silik¨¢ty
%D 2012
%I Academy of Sciences of the Czech Republic
%X Based on the results of differential thermal analysis, differential scanning calorimetry, thermogavimetric analysis, low temperature calorimetry and X-Ray powder diffraction of equilibrated samples as well as on the assessed thermodynamic data phase a section of the Ca¨CCo¨CO diagram for pO2 = 0.21 was calculated using the FactSage software. Among the involved phases the misfit cobaltite Ca3Co3.93+xO9+¦Ä is well known for its distinctive thermoelectric properties. As shown by our experiments and reproduced by the proposed thermodynamic model the Ca3Co3.93+xO9+¦Ä phase actually exhibits a narrow homogeneity range with respect to cation composition. The primary focus was put on the heat capacity of Ca3Co3.93O9+¦Ä collected in a broad temperature range and analyzed in terms of a combined Debye - Einstein model. This made it possible to separate two peaks detected at ~ 400 K and ~ 840 K and to evaluate the corresponding entropy and enthalpy changes. The second effect was interpreted as a spin transition from intermediate state to high state.
%K Misfit cobaltites
%K Thermoelectric materials
%K Heat capacity
%K Thermodynamic properties
%K Debye-Einstein model
%K Phase equlibria
%U http://www.ceramics-silikaty.cz/2012/pdf/2012_02_139.pdf