Tailoring the microwave dielectric properties of GdTiNb1−xTaxO6 and Sm1−x YxTiTaO6 ceramics

Microwave dielectric ceramics based on GdTiNb1−xTaxO6 and Sm1−xYxTiTaO6 have been prepared by conventional solid state method. The GdTiTaO6 and SmTiTaO6 have aeschenite structure with positive τf and GdTiNbO6 and YTiTaO6 have euxenite structure with negative τf. The τf of the ceramics has been tuned by preparing solid solution phases between the aeschynites and euxenites for a possible zero τf material. It is observed that GdTiNb1−xTaxO6 undergoes a phase transition from aeschynite to euxenite when x=0.75 and in Sm1−xYxTiTaO6 for x=0.73. The microwave dielectric properties change abruptly near the transition region. The τf value approaches zero near the phase transition region while the samples have poor sinterability and poor quality factor. The unloaded quality factor, dielectric constant and the sign of τf of the solid solution phases are found to depend on the average ionic radius of the rare earth ion in RE1−xRE′xTiTaO6. The boundary of the euxenite-aeschynite phase transition occurs at an average (RE) ionic radius of 0.915 Å in Sm1−x YxTiTaO6 solid solution phases.