Phase, microstructural characterization and microwave dielectric properties of SrLa4Ti5-xSnxO17 (x = 0-3) ceramics

The phase, microstructure and microwave dielectric properties of SrLa4Ti5-xSnxO17 (0≤x≤3) were investigated in an attempt to tune their temperature co-efficient of resonant frequency (τf) to zero. The compositions sintered to single phase SrLa4Ti5O17 ceramics at x = 0, and SrLa4Ti4-xSnxO17 along with a small amount of La2Ti2O7 at x = 1. The major phase observed at x = 2 was La2Ti2O7 but along with SrLa4Ti4SnO17 and SrLa4Ti4O15. At x = 3, the major phases observed were La2Sn2O7 and Sr2La3Ti3SnO15. The observed variation in the chemical composition of the grains combined with the morphological change from rod-shaped grains to cubical and irregular-shaped grains with increase in Sn content appeared in agreement with the phase constitution of samples identified by X-ray diffraction. τf decreased from 117 to 9.5 ppm/degree C with increase in x from 0 to 3 but at the cost of εr and Qufo which decreased from ∼61 to 23 and 9969 to 2084GHz respectively due to the formation of secondary phases.