Characterization of nonstoichiometric nickel manganite spinels NixMn3−x□3δ/4O4+δ by temperature programmed reduction |
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Authors: | Christel Laberty Jerzy Pielaszek Pierre Alphonse and Abel Rousset |
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Institution: | a Laboratoire de Chimie des Matériaux Inorganiques, 118 route de Narbonne, 31062 Toulouse Cedex, France b Instytut Chemii Fizycznej PAN, Kasprzaka 44/52, 01-224 Warszawa, Poland |
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Abstract: | Cation deficient spinels NixMn3?x□3δ/4O4+δ (0≤x≤1) have been prepared by thermal decomposition of mixed oxalates Nix/3Mn(3?x)/3(C2O4)·nH2O in air at 623 K. They have been characterised by temperature programmed reduction (TPR) under H2, the reaction being followed by gravimetric and powder X-ray diffraction measurements. It has been shown that TPR proceeds in several steps. The first steps correspond to the loss of nonstoichiometric oxygen leading to the formation of a stoichiometric oxide. During the following stages the manganese cations are reduced, causing the spinel structure to be destroyed, and the formation of solid solution of NiO in a cubic MnO. Subsequently, Ni2+ cations undergo a reduction to metallic nickel, and, finally, a mixture of nonstoichiometric MnO1?δ and metallic nickel is formed. These oxides contain a high level of vacancies which vary with the nickel content with a maximum of δ≈1 near x=0.6. This nonstoichiometry is ascribed both to the presence of Ni3+ and excess of Mn4+. |
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Keywords: | Manganese oxide Nickel manganite Spinel nonstoichiometry TPR XRD |
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