A combined sol–gel and spark plasma sintering route to produce highly dense and fine-grained La_0.65Ca_0.20Na_0.15MnO₃ ceramics for magnetocaloric applications

Sol–gel chemistry and spark plasma sintering were coupled to produce fine-grained and dense La_0.65Ca_0.20Na_0.15MnO₃ ceramics and their magnetic properties were explored in order to evaluate their efficiency for domestic magnetocaloric applications. The obtained manganites crystallize in the rhombohedral symmetry (R-3c). They present grain size in the sub-micrometer range. Their density and their average grain size increase when the sintering temperature increases from 600 to 800 °C. This entails an increase of the Curie temperature (T _C) and of the maximum of the magnetic entropy change, even if these values remain smaller than those measured on their bulk counterparts prepared by a conventional solid state route. However, the magnetic transition occurs on a broad temperature range, resulting in a relative cooling power reaching about 265 J Kg⁻¹ for an applied magnetic field of 5 T. This value is very close to that previously measured on bulk La_0.65Ca_0.20Na_0.15MnO₃ ceramics and represents about 64% of that measured on the standard Gd. The ceramics produced here by a low-energy and time-consuming method can thus be considered as technically and economically valuable for the desired applications. (papers)