A_xMn_(1-x)Fe_2O_4铁氧体(A=Zn,Ni)中阳离子的占位有序化行为研究

Study of the Site Occupancy Ordering Behaviors of Cations in the A_xMn_(1-x)Fe_2O_4 Ferrites(A=Zn,Ni)

基于尖晶石晶体结构信息,本文采用热力学三亚晶格模型,将材料热力学计算和第一性原理计算相结合,研究了Zn_xMn_(1-x) Fe_2O_4和Ni_xMn_(1-x)Fe_2O_4立方相中的Zn^(2+)、Ni^(2+)、Mn^(2+)以及Fe^(3+)在8a和16d亚晶格上的占位有序化行为。结果表明:在锰铁氧体中,室温下Mn^(2+)完全占据在8a亚晶格上,Fe^(3+)完全占据在16d亚晶格上,属于正尖晶石结构;随着热处理温度升高,在1 273 K达到热处理平衡时的占位构型为(Fe^(3+)0.09Mn^(2+)0.91)[Fe^(3+)1.91Mn^(2+)0.09]O_4,在热处理温度升至1 473 K时,达到热处理平衡时的占位构型为(Fe^(3+)0.11Mn^(2+)0.89)[Fe^(3+)1.89Mn^(2+)0.11]O_4,均与实验结果符合较好。在锌铁氧体中,室温下Zn^(2+)完全占据在8a亚晶格上,Fe^(3+)完全占据在16d亚晶格上,属于正尖晶石结构;在热处理温度较高时,Zn^(2+)和Fe^(3+)发生部分置换,符合实验结果。在镍铁氧体中,半数的Fe^(3+)在室温下占据在8a亚晶格上,Ni^(2+)与剩下另一半的Fe^(3+)共同占据在16d亚晶格上,仅在热处理温度较高的时候发生微弱变化,亦与已有的实验结果吻合。在此基础上,本文进一步通过热力学模型研究了立方相尖晶石结构的Zn_xMn_(1-x)Fe_2O_4、Ni_xMn_(1-x)Fe_2O_4复合体系中阳离子占位行为与热处理温度对占位的影响规律。

Based on the crystal structure of spinel, we applied the thermodynamic ternary sublattices model to investigate the site occupancy ordering behaviors of Zn^2＋, Ni^2＋, Mn^2＋and Fe^3＋on the 8a and 16 d sublattices in the ZnxMn1-xFe2O4 and NixMn1-xFe2O4 by combining thermodynamic calculations with first-principles calculations. Our results suggest that in the manganese ferrites, Mn^2＋occupies the 8a sublattice completely, and Fe^3＋occupies the16 d sublattice at room temperature, which belongs to a normal spinel. The site configuration is（Fe^3＋0.09Mn^2＋0.91）[Fe^3＋1.91Mn^2＋0.09]O4, when the ferrite is subjected to the heat treatment of 1 273 K. When the temperature increases to 1 473 K, the site configuration is（Fe^3＋0.11Mn^2＋0.89）[Fe^3＋1.89Mn^2＋0.11]O4, which agrees well with the available reliable experimental results. In the zinc ferrites, Zn^2＋occupies the 8a sublattice completely, and Fe^3＋completely occupies the 16 d sublattice at room temperature. It also belongs to normal spinel, and the cations trend to exchange the site occupancy each other at higher temperature. In the Ni ferrites, all Ni^2＋occupies the 16 d sublattice, and the Fe^3＋cations occupy both the 8a and the 16 d sublattices, which agrees with the experimental results. It belongs to an inverse spinel. Then, the relationship between the occupancy behaviors and the composition, as well as the heat treatment temperature in the ZnxMn1-xFe2O4 and NixMn1-xFe2O4 were established based on theoretically predictions.