Control of the Electromagnetic Properties of the Polycrystalline Garnet Y3Fe3.75Al1.25O12

Abstract

The relationship of the composition to the dielectric loss tanδ and dielectric constant ε′ of the polycrystalline garnet Y₃Al_1.25Fe_xO₁₂ has been quantitatively determined. Single‐phase dense garnet which has a tanδx between 3.73 and 3.78. A high yield process, based on these data, to synthesize polycrystalline garnet with dielectric loss 3Fe_5−xAl_xO₁₂ can be changed by a short heat treatment. The effect of the heat treatment of the 25°C 4πM_s increases as the aluminum content of the garnet increases. Heat treatment can change the 4πM_s of Y₃Fe_3.75Al_1.25O₁₂ by as much as 40%. In the heat‐treatment range 1000° to 1250°C the data obtained by quenching small samples of Y₃Fe_3.75Al_1.25O₁₂ after a half‐hour equilibration at temperature are thermodynamically reversible and reflect changes in the Al³⁺ and Fe³⁺ ion distribution between tetrahedral and octahedral sites. Heat treatment from 1250° to 1500°C causes tanδ at 25°C to increase continuously from 0.0001 to 0.001. The lattice defects formed by heat treatment above 1250°C decrease the activation energy required to cause a change in the aluminum and iron ion distribution between tetrahedral and octahedral sites.