Phase evolution and microwave dielectric properties of A 5 M 5 O 17 -type ceramics

Abstract

A number of A 5 M 5 O 17 (A = Na, Ca, Sr, La, Nd, Sm, Gd, Dy, Yb; B = Ti, Nb, Ta) type compounds were prepared by a solid-state sintering route and characterized in terms of structure, microstructure and microwave dielectric properties. The compatibility of rare earths with mixed niobate/tantalate and titanate phases was investigated. The larger ionic radii mismatch resulted in the formation of pyrochlore and/or mixed phases while in other cases, pure A 5 M 5 O 17 phase was formed. The samples exhibited relative permittivity in the range of 35 to 82, quality factor (Q × f o ) = 897 GHz to 11946 GHz and temperature coefficient of resonance frequency (τ f ) = -120 ppm/°C to 318 ppm/°C.