Preparation-dependent properties of Ca(Cu, Mn)(7)O-12 CMR materialsстатья
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Аннотация:Both magnetic ordering temperatures and lattice constants were observed to be a function of preparation temperature for single-phase CaCuMn6O12 CMR ceramics of the same cation, oxygen composition and crystal structure. It was found for the first time that higher preparation temperatures T-prep result in a linear increase of a cubic cell parameter a, Delta a/Delta T-prep similar to 4 x 10(-5) angstrom/degrees C, and in a sharp decrease of magnetic ordering temperatures T-crit, by about Delta T-crit/Delta T-prep similar to 3/5, for quenched samples. High resolution NPD experiments have shown the presence of antisite defects resulting in partial occupation of octahedral (8c) sites by Cu2+ at higher preparation temperatures as never assumed for an ideal structure. The data obtained give a new insight to the problem of functional properties reproducibility suggesting stronger requirements for the production control of CMR materials. (c) 2006 Elsevier Ltd. All rights reserved.