Single-phase inhomogeneity in ceramic garnets

Abstract

Sintered ceramic garnets of composition (Y,Gd)3 (Fe,Al)5012 are of technological importance for the construction of microwave phase shifters. Mossbauer spectroscopy near Tc provides a unique monitor of the effect of ceramic processing variables, as well as sintering time at temperature, on chemical homogeneity. Near Tc we observe the coexistence of ferrimagnetic and paramagnetic phases, with the width of the coexistence region, ΔTc, varying sharply between samples. The ΔTc values are a quantitative measure of local chemical fluctuations, presumably in the Fe/Al ratio, which remain after the particular preparation. Roughly similar fluctuations are also inferred from x‐ray line broadening, but which much less precision. Concurrent with the decrease in ΔTc from 9°C to 3°C, the X‐band resonance line width decreases from 67 to 45 Oe. This change is more than twice the maximum estimated for the observed slight decrease in porosity, and illustrates the influence of single‐phase inhomogeneity on the microwave properties of substituted garnets.Sintered ceramic garnets of composition (Y,Gd)3 (Fe,Al)5012 are of technological importance for the construction of microwave phase shifters. Mossbauer spectroscopy near Tc provides a unique monitor of the effect of ceramic processing variables, as well as sintering time at temperature, on chemical homogeneity. Near Tc we observe the coexistence of ferrimagnetic and paramagnetic phases, with the width of the coexistence region, ΔTc, varying sharply between samples. The ΔTc values are a quantitative measure of local chemical fluctuations, presumably in the Fe/Al ratio, which remain after the particular preparation. Roughly similar fluctuations are also inferred from x‐ray line broadening, but which much less precision. Concurrent with the decrease in ΔTc from 9°C to 3°C, the X‐band resonance line width decreases from 67 to 45 Oe. This change is more than twice the maximum estimated for the observed slight decrease in porosity, and illustrates the influence of single‐phase inhomogeneity on the microwave pro...