Synthesis, structure and magnetic entropy change of polycrystalline La1-xKxMnO3+delta

The use of a sol-gel synthetic method allows the preparation, at temperatur es as low as 873 K, of single-phase perovskites in the potassium-doped lant hanide manganites La1-xKxMnO3+delta. Samples prepared at 1273 K remain sing le phase and are constituted by submicrometer homogeneous particles, withou t deviation from nominal stoichiometries upon heating. These materials exhi bit paramagnetic-to-ferromagnetic phase transitions at 230, 283, 338, and 3 44 K for x = 0.075, 0.10, 0.165, and 0.20, respectively, By measuring the s ample magnetization as a function of held and temperature we have determine d the magnetic entropy change associated with these transitions. It is sugg ested by the results that these materials can be utilized as suitable magne tic refrigerants with very large temperature span. (C) 1999 Elsevier Scienc e B.V. All rights reserved.