Selective Metal Exsolution in BaFe2鈥?i>yMy(PO4)2 (M = Co2+, Ni2+) Solid Solutions
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- 作者：Ignacio Blazquez Alcover ; Sylvie Daviero-Minaud ; R茅nald David ; Dmitry Filimonov ; Marielle Huv茅 ; J. Paul Attfield ; Houria Kabbour ; Olivier Mentr茅
- 刊名：Inorganic Chemistry
- 出版年：2015
- 出版时间：September 8, 2015
- 年：2015
- 卷：54
- 期：17
- 页码：8733-8743
- 全文大小：695K
- ISSN：1520-510X
文摘
The 2D-Ising ferromagnetic phase BaFe2+2(PO4)2 shows exsolution of up to one-third of its iron content (giving BaFe3+1.33(PO4)2) under mild oxidation conditions, leading to nanosized Fe2O3 exsolved clusters. Here we have prepared BaFe2鈥?i>yMy(PO4)2 (M = Co2+, Ni2+; y = 0, 0.5, 1, 1.5) solid solutions to investigate the feasibility and selectivity of metal exsolution in these mixed metallic systems. For all the compounds, after 600 掳C thermal treatment in air, a complete oxidation of Fe2+ to Fe3+ leaves stable M2+ ions, as verified by 57Fe M枚ssbauer spectroscopy, TGA, TEM, microprobe, and XANES. The size of the nanometric 伪-Fe2O3 clusters coating the main phase strongly depends on the yM metal concentration. For M-rich phases the iron diffusion is hampered so that a significant fraction of superparamagnetic 伪-Fe2O3 particles (100% for BaFe0.5鈥?i>xCo1.5(PO4)2) was detected even at 78 K. Although Ni2+ and Co2+ ions tend to block Fe diffusion, the crystal structure of BaFe0.67Co1(PO4)2 demonstrates a fully ordered rearrangement of Fe3+ and Co2+ ions after Fe exsolution. The magnetic behaviors of the Fe-depleted materials are mostly dominated by antiferromagnetic exchange, while Co2+-rich compounds show metamagnetic transitions reminiscent of the BaCo2(PO4)2 soft helicoidal magnet.