Abstract
AbstractThe synthesis of the Ca2Fe1+xW1–xO6 perovskite solid solution in the range x = 0.13–0.33 by a soft‐chemistry procedure followed by annealing at different temperatures under different reducing atmospheres, and its characterization by X‐ray and neutron diffraction together with magnetic measurements, is reported. The average Fe oxidation state in this series varies smoothly from Fe2.46+ in Ca2Fe1.13W0.87O6 to Fe3+ in Ca2Fe1.33W0.67O6. A detailed description of the crystal structure of four selected members of this series (x = 0.2, 0.23, 0.30, 0.33) is provided. All these compounds crystallize in the space group P21/n, with a ≈ b ≈ √2a0 and c ≈ 2a0, although they show different levels of long‐range ordering between the two different cations placed at the B positions of the A2B′B″O6 perovskite structure. The driving force for this B′/B″ ordering is the charge difference between both kinds of cations, whereby the earlier members of the series, which contain a large proportion of Fe2+, are fully ordered whereas a strong antisite disorder effect is observed for the later members. The evolution of this antisite disordering has a dramatic influence on the magnetic properties across the series. Thus, for x = 0.20, the ferrimagnetic Curie temperature is above 400 K, although the saturation magnetization is very low, since there is a poor coherence between the antiferromagnetic patches formed by Fe–O–Fe interactions between the B′ and B″ positions of the perovskite, whereas the x = 0.33 compound, which has a lower TC of 310 K, shows a considerable saturation magnetization and a surprisingly strong magnetic neutron scattering for such a structurally disordered sample. The observed scattering can be ascribed to the good coherence obtained via Fe–O–Fe superexchange interactions among the Fe‐rich, antiferromagnetically ordered patches that occur naturally thorughout the crystal. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
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