A Structural and Magnetic Study of the Series of Double Perovskites Ca₂Fe_1+xW_1–xO₆

Abstract

The synthesis of the Ca 2 Fe 1+x W 1-x O 6 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 Xray and neutron diffraction together with magnetic measurements, is reported. . 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 P2 1 /n, with a ≈ b ≈ √2a 0 and c ≈ 2a 0 , although they show different levels of long-range ordering between the two different cations placed at the B positions of the A 2 BЈBЈЈO 6 perovskite structure. The driving force for this BЈ/ BЈЈ ordering is the charge difference between both kinds of cations, whereby the earlier members of the series, which contain a large proportion of Fe 2+ , are fully ordered whereas

Optical-active phonons in A3Fe2B″O9 (A=Ca, Sr; B″=Te, W) double perovskites

“…[17][18][19][20][21] There has been an increasing interest in the study of A 3 Fe 2 BЉO 9 ͑A = Ca, Sr; BЉ = Te, W͒ double perovskites, which exhibit exciting ferromagnetic properties at room temperature. [2][3][4][5][6][7] The Sr 3 Fe 2 WO 9 ͑SFWO͒ and Ca 3 Fe 2 WO 9 ͑CFWO͒ compounds have been investigated by neutron powder diffraction by Ivanov et al, 2,3 who determined that SFWO crystallizes at 300 K in a tetragonal structure belonging to the space group I4 / m, while CFWO crystallizes in a monoclinic structure belonging to the space group P2 1 / n. Identical results have been obtained for CFWO by Retuerto et al 22 These compounds exhibit a partially ordered double perovskite structures, in which the Fe and W cations are orderly distributed at the BЈ-and BЉ-symmetry sites of the perovskite lattice. For SFWO ͑CFWO͒, the occupation of the 2a-site is 0.79Fe͑1͒ 4 observed a minor cationic ordering with formula Sr 2 ͓Fe 0.72 Te 0.28 ͔ 2a ͓Fe 0.61 Te 0.39 ͔ 2b O 6 .…”