Structural Features of Mg-Containing Solid Solutions Based on Y₂FeTaO₇

The existence regions of the Y_2–xMg_xFeTaO_7–δ (x = 0–0.15), Y_2–xMg_xFe_1–x/2Ta_1+x/2O_7–δ (x = 0–0.15), Y₂Fe_1–xMg_xTaO_7–δ (x = 0–0.3), and Y₂Fe_1–3/2xMg_xTa_1+x/2O_7–δ (x = 0–0.3) solid solutions were estimated. It was found that, regardless of the composition, the entry of Mg²⁺ into the crystal lattice of Y₂FeTaO₇ causes a similar distortion of the structure (space group R \(\bar {3}\) → space group P3₁21). Based on XANES and Mössbauer spectroscopy data, it was suggested that Mg²⁺ ions occupied the eight-coordinated sites in the crystal lattice of solid solutions, displacing iron ions, while vacant yttrium sites in Y_2–xMg_xFeTaO_7–δ and Y_2–xMg_xFe_1–x/2Ta_1+x/2O_7–δ are occupied by tantalum ions. The XANES method confirmed the existence of Fe⁴⁺ ions in the Y₂FeTaO₇ solid solutions along with Fe³⁺. The simultaneous presence of the Ta⁴⁺ and Ta⁵⁺ ions ensures the electroneutrality of there crystal lattices. Herewith, the entry of Mg²⁺ does not lead to an increase in the Fe⁴⁺ concentration.