Microstructure characterization of polycrystalline yttrium iron garnets (YIGs) sintered from the calcined sol-gel powder

Abstract

We present the results of microstructural characterization of the polycrystalline yttrium iron garnet (YIG) during high temperature sintering. Three YIG samples, compacted from the calcined sol-gel powder, are annealed at 1400 degrees C for 350 min, 1050 min and 1750 min, respectively. During the annealing, the polycrystalline YIG coarsens via normal grain growth, developing self-similar steady-states in grain size distribution, grain texture, and grain boundary texture. However, the 1050-min and 1750-min samples feature x-ray peaks with narrower full width at half-maximum (FWHM), and smaller local misorientation than the 350-min one, signifying that the strain still decreases after annealing for 350 min at 1400 degrees C. EPMA analyses show that more uniform distribution of the elements is found in 1750-min sample than in 350-min sample. Notably, little segregation of metal ele-ments is observed on the grain boundary of the current YIG samples, as opposed to previously reported conventionally sintered YIGs using yttrium-oxide and iron-oxide powders, often featuring either second phases or segregation of Fe on YIG grain boundaries.