Influence of Bi Substitution on the Microstructure and Dielectric Properties of Gd3Fe5O12 Ceramics

The exponential growth in microwave communications in recent years demands innovations and high yield microwave materials. Rare earth iron garnets are well known for their remarkable performance in microwave devices owing to their superior features. In this work we investigate the microstructure and dielectric properties of Bismuth substituted Gd3Fe5O12 ceramics prepared by the conventional solid state reaction route. The variation of lattice parameter, microstructure, permittivity, quality factor and temperature coefficient of resonant frequency (τf) of Gadolinium Iron Garnet (GIG) with several concentrations of bismuth was investigated. The Bi3+ ion is effectively incorporated into Gadolinium Iron Garnet, due to which the sintering temperature is considerably reduced, and the densification is improved significantly. Moreover, with increase in Bi concentration, the dielectric constant of GIG also increases, while the quality factor is slightly reduced, which is correlated with the higher ionic polarizability of bismuth. At an appreciably low sintering temperature of 1050°C, Gd2BiFe5O12 possess a porosity corrected relative permittivity value of 27.3 ± 0.2, unloaded quality factor (Qu × f) of 2990 ± 60 GHz (f = 7.3 GHz) and temperature coefficient of resonant frequency + 60 ± 1 ppm/°C.