The as-compacted green pellets at 1

The as-compacted green pellets at 180°C yielded a high relative density of ~ 90% and the ceramics that were post-sintered over a broad temperature range (800°C–950°C) possessed highly dense microstructure with a relative density of ~ 96%. The average grain size varied from 100 to 1200 nm for the samples sintered at 800°C–950°C. Furthermore, the quality (Q × f) values of the obtained specimens exhibited a strong positive dependency on the grain size, which increased from 17790 to 47960 GHz for grain sizes ranging between 100 and 1200 nm, while the dielectric permittivity (εr) and temperature coefficient of the resonant frequency (τf) values did not undergo any significant changes over this range of grain size.