10.1021/acs.cgd.5b00525.s002 Ignacio Blazquez Alcover Ignacio Blazquez Alcover Rénald David Rénald David Sylvie Daviero-Minaud Sylvie Daviero-Minaud Dmitry Filimonov Dmitry Filimonov Marielle Huvé Marielle Huvé Pascal Roussel Pascal Roussel Houria Kabbour Houria Kabbour Olivier Mentré Olivier Mentré Reversible Exsolution of Nanometric Fe<sub>2</sub>O<sub>3</sub> Particles in BaFe<sub>2–<i>x</i></sub>(PO<sub>4</sub>)<sub>2</sub> (0 ≤ <i>x</i> ≤ 2/3): The Logic of Vacancy Ordering in Novel Metal-Depleted Two-Dimensional Lattices American Chemical Society 2015 members x Fe ions 2 D ferrimagnets Reversible Exsolution x values honeycomb layers 2 D ferromagnets Vacancy Ordering Nanometric Fe 2O Particles crystal chemistry 50 nm diameter iron oxide grain surface 2015-09-02 00:00:00 Dataset https://acs.figshare.com/articles/dataset/Reversible_Exsolution_of_Nanometric_Fe_sub_2_sub_O_sub_3_sub_Particles_in_BaFe_sub_2_i_x_i_sub_PO_sub_4_sub_sub_2_sub_0_i_x_i_2_3_The_Logic_of_Vacancy_Ordering_in_Novel_Metal_Depleted_Two_Dimensional_Lattices/2135875 We show here that the exsolution of Fe<sup>2+</sup> ions out of two-dimensional (2D) honeycomb layers of BaFe<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub> into iron-deficient BaFe<sub>2–<i>x</i></sub>­(PO<sub>4</sub>)<sub>2</sub> phases and nanometric α-Fe<sub>2</sub>O<sub>3</sub> (typically 50 nm diameter at the grain surface) is efficient and reversible until <i>x</i> = 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 <i>x</i> = 2/7, <i>x</i> = 1/3, <i>x</i> = 1/2 and the ultimate Fe-depleted <i>x</i> = 2/3 term, we observed a systematic full ordering between Fe ions and vacancies (V<sub>Fe</sub>) that denote unprecedented easy in-plane metal diffusion driven by the Fe<sup>2+</sup>/Fe<sup>3+</sup> redox. Besides the discovery of a diversity of original depleted triangular <sub>∞</sub>{Fe<sup>2/3+</sup><sub>2–<i>x</i></sub>O<sub>6</sub>} topologies, we propose a unified model correlating the <i>x</i> Fe-removal and the experimental Fe/V<sub>Fe</sub> ordering into periodic one-dimensional motifs paving the layers, gaining insights into predictive crystal chemistry of complex low dimensional oxides. Increasing the <i>x</i> values led to a progressive change of the materials from 2D ferromagnets (Fe<sup>2+</sup>) to 2D ferrimagnets (Fe<sup>2/3+</sup>) to antiferromagnets for <i>x</i> = 2/3 (Fe<sup>3+</sup>).