Calorimetric study of CaCu 3 Ti 4 O 12 , a ceramic with giant permittivity
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Loïc Marchin Centre Interuniversitaire de Recherche et d’Ingénierie des Matériaux (CIRIMAT/LCMIE), Université Paul Sabatier, Bât. 2R1, 31062 Toulouse Cedex 9, France
Yosuke Moriya,a) Hitoshi Kawaji, and Tooru Atake Materials and Structures Laboratory, Tokyo Institute of Technology, Midori-ku, Yokohama, 226-8503 Japan
Sophie Guillemet-Fritsch and Bernard Durand Centre Interuniversitaire de Recherche et d’Ingénierie des Matériaux (CIRIMAT/LCMIE), Université Paul Sabatier, Bât. 2R1, 31062 Toulouse Cedex 9, France
Alexandra Navrotskyb) Peter A. Rock Thermochemistry Laboratory and Nanomaterials in the Environment, Agriculture, and Technology-Organized Research Unit (NEAT ORU), University of California at Davis, Davis, California 95616 (Received 2 July 2007; accepted 23 October 2007)
We conducted an investigation into the thermodynamic properties of two stoichiometric CaCu3Ti4O12 (CCTO) samples prepared by solid-state reaction and soft chemistry methods to probe the stability of the material relative to simpler oxide constituents (e.g., CaO, CuO, and TiO2) over a wide temperature range. Thermodynamic functions (i.e., heat capacity, formation enthalpies, entropies, and Gibbs free energies) have been measured from near absolute zero to 1100 K using calorimetric methods, including drop solution, low-temperature adiabatic relaxation, and differential scanning calorimetry. In addition, the thermodynamic characteristics of the magnetic-phase transition from the antiferromagnetic to the paramagnetic state are reported. It has been shown that CCTO is very stable relative to constituent oxides and calcium titanate at room temperature and higher, independent of the synthesis route. The enthalpic factor is dominant in the thermodynamics of CCTO, with the entropic factor having almost no effect on the stability of the compound relative to other oxide assemblages. The recommended values for the standard molar enthalpy of formation from constituent oxides and from elements at 298.15 K are −122.1 ± 4.5 and −4155.7 ± 5.2 kJ/mol−1, respectively. The mean of the third law entropy at 298.15 K is 368.4 ± 0.1 J/mol−1/K−1. Based on the thermodynamic data reported, the study confirms the possibility of CCTO decomposition in a reducing atmosphere or CO2 under conditions recently observed in experiments. I. INTRODUCTION
ATiO3 titanate perovskites (where A = Ca, Sr, Ba, and Pb) have been long known for unique electric properties, making them useful as components in electronic devices.
a)
Present address: Neutron Science Laboratory, Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581 Japan. b) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0201 1522 J. Mater. Res., Vol. 23, No. 6, Jun 2008 http://journals.cambridge.org Downloaded: 26 Oct 2015
The recent discovery by Subramanian et al.1 of an apparently high permittivity of 1.2 × 103 at 1 kHz in calcium copper titanate CaCu3Ti4O12 (CCTO) has attracted much attention to this material from the vie
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