CRYSTALLOCHEMICAL, MAGNETIC AND ELECTRICAL-PROPERTIES OF THE K2NIF4 TYPE DILUTED SOLID-SOLUTION Y0.9CA1.1CRYAL1-YO4-DELTA (Y-LESS-THAN-OR-EQUAL-TO-0.10) - EVIDENCE FOR A PARTIAL CR3-]CR4+ OXIDATION()

The K2NiF4 type diluted solid solutio Y0.9Ca1.1Al1-yCryO4-delta (y les s than or equal to 10.10) has been prepared by solid state reaction at 1430 degrees C in air and studied to obtain evidence for the oxygen n on-stoichiometry phenomena, depending on the partial Y3+ --> Ca2+ repl acement and to some extent of Cr3+ --> Cr4+ oxidation. The structural characterization by X-ray diffraction for the composition y = 0 points to the simultaneous existence of an oxygen deficiency and supplementa ry oxygen which is located in the rock-salt layer of the perovskite-ro ck-salt intergrowth structure, as in La2NiO4.18. The effective magneti c moment which is calculated from the measured magnetic susceptibility for six compositions shows a systematic decrease over the whole tempe rature range 80-300 K, as a result of the decrease of the Y3+/Ca2+ rat io. The partial occurrence of Cr4+ oxidized species is considered for the modelling of the temperature dependence of mu(eff):the amount of C r4+ is found to be in the range 55-60% of the total chromium amount, a s deduced from the calculation of the distribution of the monomer and dimer Cr species in the perovskite layer, The electrical conductivity measured in the range 1100-1400 degrees C for T and 10(-13)-10(5) Pa f or p(O2) indicates a significant increase of the anionic contribution, due firstly to the decease of the Y3+/Ca2+ ratio and secondly to the increase of Cr content y in the oxygen defective solid solution; such an effect agrees well with the favourable role of the oxygen defects, namely both vacancies and interstitial positions. Finally, the overall crystallochemical, magnetic and electrical data are consistent with a partial Cr3+ --> Cr4+ oxidation which is coupled to the partial Y3+ - -> Ca2+ replacement: this creates oxygen non-stoichiometry phenomena v ery similar to those observed for the isotypic nickelates and cuprates .