Designing Polar and Magnetic Oxides: Zn2FeTaO6 - in Search of Multiferroics

Polar oxides are technically of great interest but difficult to prepare. Our recent discoveries predicted that polar oxides can be synthesized in the corundum-derivative A2BB′O6 family with unusually small cations at the A-site and a d0 electron configuration ion at B′-site. When magnetic transition-metal ions are incorporated more interesting polar magnetic oxides can form. In this work we experimentally verified this prediction and prepared LiNbO3 (LN)-type polar magnetic Zn2FeTaO6 via high pressure and temperature synthesis. The crystal structure analysis indicates highly distorted ZnO6 and (Fe/Ta)­O6 octahedra, and an estimated spontaneous polarization (PS) of ∼50 μC/cm2 along the c-axis was obtained from point charge model calculations. Zn2Fe3+Ta5+O6 has a lower magnetic transition temperature (TN ∼ 22 K) than the Mn2FeTaO6 analogue but is less conductive. The dielectric and polarization measurements indicate a potentially switchable component.极性氧化物（polar oxides）在技术领域具有重要研究价值，但制备难度极高。我们此前的研究发现，可在刚玉衍生型A₂BB′O₆家族中合成极性氧化物，该家族的A位需搭载异常偏小的阳离子，B′位则需为具有d⁰电子构型的离子。当引入磁性过渡金属离子时，可形成更具研究价值的极性磁性氧化物。本研究通过高温高压合成工艺，实验验证了上述预测，并成功制备出LiNbO3（LN）型极性磁性Zn₂FeTaO6。晶体结构分析结果显示，其ZnO6与(Fe/Ta)O6八面体存在高度畸变；通过点电荷模型（point charge model）计算，得到沿c轴方向的自发极化（spontaneous polarization, PS）约为50 μC/cm²。Zn₂Fe³⁺Ta⁵⁺O6的磁转变温度（magnetic transition temperature, TN≈22 K）低于Mn₂FeTaO6同构类似物，但导电性更低。介电与极化测试结果表明，其极化组分具备可切换的潜在特性。