Densification, microstructural evolution and dielectric properties of Ba6 − 3x(Sm1 − yNdy)8 + 2xTi18O54 microwave ceramics

Utilizing different rare-earth cations R3+ to the Ba6 − 3xR8 + 2xTi18O54 compounds is one of effective route to tailor the dielectric constant, quality factor and temperature coefficient of frequency. In this study, densification, microstructural evolution, and microwave dielectric properties of Ba6 − 3x(Sm1 − yNdy)8 + 2xTi18O54 compound, with x ranging from 0.3 to 0.7; and y from 0 to 1.00, were investigated. The ceramics with x = 0.7 [Ba3.9(Sm1 − yNdy)9.4Ti18O54] has a higher densification compared with others, due to the formation of vacancy, in the perovskite-like tetragonal cavity of the tungsten bronze-type framework structure. Differential thermal analysis and density results show that the densification of Ba6 − 3x(SmyNd1 − y)8 + 2xTi18O54 ceramics during sintering is primarily resulting from the solid state sintering process. The phase homogeneity for the Ba6 − 3x(Sm0.5Ndo.5)8 + 2xTi18O54 system is at least extended in the range of x between 0.3 and 0.7. Combining different rare-earth cations appears not alter the single phase range in tungsten bronze-type Ba6 − 3xR8 + 2xTi18O54 ceramics. The size of the columnar-grain in the microstructure increases with increasing the Nd/Sm ratio as well as the x value. Dielectric constant changes from 91.0 to 84.2 as the x increases from 0.3 to 0.7. Variation of the Nd/Sm ratio allows one to control the τf value to the nearly 0 ppm/°C.