Low Loss Dielectrics in the Ca(B′_1/2Nb_1/2)O₃ [B′=Lanthanides, Y] System

Abstract

The Ca(B′1/2Nb1/2)O3 [B′=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb, and In] complex perovskites have been prepared by conventional solid‐state ceramic route. The structure and microstructure of the ceramics have been characterized by X‐ray diffraction and scanning electron microscopy methods. The ceramics have dielectric constant (ɛr) in the range 23–32, normalized Q‐factor (Qu×f) 11 000–38 000 GHz and temperature coefficient of resonant frequency (τf) −43–5.2 ppm/°C. The microwave dielectric properties of Ca(B′1/2Nb1/2)O3 ceramics are found to depend on the ionic radii of B′‐site elements and tolerance factor (t). The substitution of Ba2+ and Sr2+ for Ca2+ resulted a phase transition in Ca(B′1/2Nb1/2)O3 ceramics. The (Ca0.05Ba0.95) (Y1/2Nb1/2)O3 has τf close to zero (1.2 ppm/°C) with ɛr=35 and Qu×f=48 500 GHz and is proposed as a useful material for base station applications. Dielectric properties of the Ca(B′1/2Nb1/2)O3 ceramics were tailored by the addition of TiO2 and CaTiO3.

Structure evolution and adjustment of τf in (Ba, Sr)HfO3 and (Sr, Ca)HfO3 microwave dielectric ceramics

“…The relationship between tolerance factor and phase transition can also be applied in other perovskite systems. 21 Different τ f can be observed frequently for the complex perovskites with the same t value. Park et al 22 indicated that this difference could be understood by bond valence sum (BVS) in microwave dielectric ceramics with perovskite structure.…”

“…further ascertained that for Ba‐ and Sr‐based complex perovskites, the first phase transition occurs around t = 0.985, and the other phase transition occurs around t = 0.965. The relationship between tolerance factor and phase transition can also be applied in other perovskite systems 21 . Different τ f can be observed frequently for the complex perovskites with the same t value.…”

Structural Transitions and Microwave Dielectric Properties of Ba2−2xSr2xSmSbO6 Double Perovskites

“…Although several types of dielectric materials have been investigated to meet the requirements of microwave applications, those with perovskite or related structure are one of the most researched types for their extreme structural and compositional flexibility, such as simple perovskites ABO 3 , 1:2 ordered complex perovskites A 3 B′B″ 2 O 9 , and B‐site cation‐deficient hexagonal perovskites A n B n −1 O 3 n . In recent years, double perovskites with a general formula A 2 (B′B″)O 6 used as microwave dielectric materials have also attracted much attention …”

Microwave Dielectric Properties of Ba2Ca1−xSrxWO6Double Perovskites

“…However, to obtain a high degree of ordering, prolonging high‐temperature sintering and soaking time or introducing small amounts of dopants is often necessary, which is not suitable for practical applications. Moreover, microwave dielectric properties of some 1:1 ordered perovskites with a general formula A 2 (B′B″)O 6 (A=Ba, Sr, Ca; B′=lanthanides and Y, B″=Nb, Ta) were also investigated 15–17 . It is concluded that ionic ordering driving force is favored by larger differences in charges and ionic radii between the two B‐site ions.…”