文摘
We show here that the exsolution of Fe2+ ions out of two-dimensional (2D) honeycomb layers of BaFe2(PO4)2 into iron-deficient BaFe2鈥?i>x(PO4)2 phases and nanometric 伪-Fe2O3 (typically 50 nm diameter at the grain surface) is efficient and reversible until x = 2/3 in mild oxidizing/reducing conditions. It corresponds to the renewable conversion of 12 wt % of the initial mass into iron oxide. After analyzing single crystal X-ray diffraction data of intermediate members x = 2/7, x = 1/3, x = 1/2 and the ultimate Fe-depleted x = 2/3 term, we observed a systematic full ordering between Fe ions and vacancies (VFe) that denote unprecedented easy in-plane metal diffusion driven by the Fe2+/Fe3+ redox. Besides the discovery of a diversity of original depleted triangular 鈭?/sub>{Fe2/3+2鈥?i>xO6} topologies, we propose a unified model correlating the x Fe-removal and the experimental Fe/VFe ordering into periodic one-dimensional motifs paving the layers, gaining insights into predictive crystal chemistry of complex low dimensional oxides. Increasing the x values led to a progressive change of the materials from 2D ferromagnets (Fe2+) to 2D ferrimagnets (Fe2/3+) to antiferromagnets for x = 2/3 (Fe3+).