Calorimetric investigation of equilibrium and thermal relaxation properties of the switchable Prussian Blue analog Na_0.32Co[ Fe(CN)₆] _0.74 3.4 H₂O

¹  Instituto de Ciencia de Materiales de Aragón (CSIC-Universidad de Zaragoza) - Pedro Cerbuna 12, 50009 Zaragoza, Spain
²  Groupe d'Etudes de la Matière Condensée (ex-LMOV), CNRS-Université de Versailles - 45 Avenue des Etats Unis, F-78035 Versailles Cedex, France
³  Department of Chemistry, School of Science, The University of Tokyo - 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan

Corresponding author: mcastro@unizar.es

Received: 2 May 2007
Accepted: 8 June 2007

Abstract

Calorimetric measurements have been performed on the Prussian Blue analog Na_0.32Co[ Fe(CN)₆] _0.74 3.4 H₂O. The thermal relaxation of the metastable state obtained by thermal quenching of the high temperature phase gives rise to an exothermic peak (at the “thermal relaxation temperature”, T_TR) which appears at higher temperature and with a larger width as the temperature scan rate increases. Values for the enthalpy and entropy changes upon the charge transfer-induced spin transition (CTIST) have been subsequently determined. The equilibrium and thermal relaxation data have been quantitatively analyzed through a mean-field cooperative dynamic model that also provides a quantitative description of the trapping process. The changes in enthalpy and “apparent” entropy during the thermal relaxation process are investigated and the evaluation of the activation energy by the Kissinger's plot is also discussed.