Synthesis and microwave dielectric properties of (Ce1−yDyy)(Nb1−xTax)TiO6 ceramics

The effects of the Ta substitution for Nb and the Dy substitution for Ce on the microwave dielectric properties and crystal structure of (Ce1−yDyy)(Nb1−xTax)TiO6 ceramics were investigated in this study. In the case of the Ta substitution for Nb in the CeNbTiO6 ceramic, a single phase of aeschynite-type structure was obtained over the whole composition range. On the other hand, the XRPD patterns of (Ce1−yDyy)(Nb0.5Ta0.5)TiO6 ceramics with the composition y ranging from 0 to 0.625 show a single phase which corresponds to the aeschynite-type structure, whereas those of the samples at the composition higher than y = 0.85 exhibit the euxenite-type structure. In the composition range of 0.65–0.85, the phase transition took place; the aeschynite and euxenite phases coexisted. The dielectric constant of (Ce1−yDyy)(Nb0.5Ta0.5)TiO6 ceramics decreased from 44.5 to 15.9, while the quality factor increased from 13,398 to 31,753 GHz with the Dy substitution for Ce. The temperature coefficient of resonant frequency of the ceramics varied from 79.8 to −42.9 ppm/°C; a near zero temperature coefficient of resonant frequency results in the composition of y = 0.75 with a dielectric constant of 30.9 and Qf value of 23,708 GHz. These variations in the microwave dielectric properties of (Ce1−yDyy)(Nb0.5Ta0.5)TiO6 ceramics are attributed to the phase transition of ceramics from aeschynite-type structure to euxenite-type structure.