Deeper insights into dodecahedron distortion and microwave dielectric properties of Y3-xRxAl(Oct)2Al(Tet)3-xSixO12 (x = 0.1–0.5; R = Mg, Ca) garnet-type ceramics

Abstract

Y3-xRxAl(Oct)2Al(Tet)3-xSixO12 (x = 0.1–0.5; R = Mg, Ca) ceramics were prepared via solid-state reaction method. The effects of Mg2+ (∼0.89 Å) and Ca2+ (∼1.12 Å) substitution at the dodecahedral site for Y3+ (∼1.019 Å) on the microstructure, crystal structure and microwave dielectric properties of Y3-xRxAl(Oct)2Al(Tet)3-xSixO12 garnet ceramics were investigated and discussed using the P–V-L theory, Raman spectrum, bond valence theory, Terahertz time-domain spectroscopy and infrared reflectance spectrum. Different from normal garnet structure of ceramics, the dielectric constant is abnormally increased in Y3-xMgxAl(Oct)2Al(Tet)3-xSixO12 (x = 0.1–0.5) ceramics due to the increase of ion polarizability caused by the rattling effect. There is a dependence of bond energy, bond valence and dodecahedral distortion on τf value, which provides new possibility for tuning the temperature coefficient of garnet ceramics. There are strong effects of grain size distribution, average lattice energy, packing fraction, FWHM of Raman peak on their Q×f values of Y3-xRxAl(Oct)2Al(Tet)3-xSixO12 isostructural ceramics caused by the difference of Mg2+ and Ca2+ ionic radius. Above work provides deeper insights into the understanding of the microstructural characteristics and performance relationship of garnet-type microwave ceramics, and lays a foundation for future applications in the 5G/6G frequency bands.