Expansion of the Hexagonal Phase-Forming Region of Lu_1–<i>x</i>Sc_<i>x</i>FeO₃ by Containerless Processing

Abstract

Hexagonal Lu_1–<i>x</i>Sc_<i>x</i>FeO₃ (0 ≤ <i>x</i> ≤ 0.8) was directly solidified from an undercooled melt by containerless processing with an aerodynamic levitation furnace. The hexagonal phase-forming region was considerably extended compared to that of the conventional solid-state reaction (<i>x</i> ∼ 0.5). Synchrotron X-ray diffraction measurements revealed that the crystal structure of the hexagonal phase was isomorphous to hexagonal ferroelectric RMnO₃ (R = a rare earth ion) with a polar space group of <i>P</i>6₃<i>cm</i>. As <i>x</i> increased, the <i>a</i>-axis lattice constant decreased linearly, strengthening the antiferromagnetic interaction between the Fe³⁺ ions on the <i>a–b</i> plane. Accordingly, the weak ferromagnetic transition temperature increased from 150 K for <i>x</i> = 0 to 175 K for <i>x</i> = 0.7. These transition temperatures were much higher than those of hexagonal Lu_1–<i>x</i>Sc_<i>x</i>MnO₃. The results indicate that hexagonal Lu_1–<i>x</i>Sc_<i>x</i>FeO₃ is a suitable alternative magnetic dielectric for use at higher temperatures