The K₂NiF₄ type diluted solid solutio Y_0.9Ca_1.1Al_1-yCr_yO _4-δ (y ≤ 0.10) has been prepared by solid state reaction at 1430°C in air and studied to obtain evidence for the oxygen non-stoichiometry phenomena, depending on the partial Y³⁺ → Ca²⁺ replacement 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 supplementary oxygen which is located in the rock-salt layer of the perovskite-rock-salt intergrowth structure, as in La₂NiO_4.18. The effective magnetic moment which is calculated from the measured magnetic susceptibility for six compositions shows a systematic decrease over the whole temperature range 80-300 K, as a result of the decrease of the Y³⁺/Ca²⁺ ratio. The partial occurrence of Cr⁴⁺ oxidized species is considered for the modelling of the temperature dependence of μ_eff: the amount of Cr⁴⁺ is found to be in the range 55-60% of the total chromium amount, as 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°C for T and 10^-13-10⁵ Pa for p_o2 indicates a significant increase of the anionic contribution, due firstly to the decrease 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 very similar to those observed for the isotypic nickelates and cuprates.