Compositional modulation in ZnGa2O4 via Zn2+/Ge4+ co-doping to simultaneously lower sintering temperature and improve microwave dielectric properties

Ying Xiong,Chunchun Li,Laijun Liu,Zhengfeng Wang,Hongyuan Xie,Zhenggang Rao

doi:10.1007/s40145-021-0511-0

Abstract

AB2O4-type spinels with low relative permittivity (εr) and high quality factor (Q × f) are crucial to high-speed signal propagation systems. In this work, Zn2+/Ge4+ co-doping to substitute Ga3+ in ZnGa2O4 was designed to lower the sintering temperature and adjust the thermal stability of resonance frequency simultaneously. Zn1+xGa2−2xGexO4 (0.1 ⩽ x ⩽ 0.5) ceramics were synthesised by the conventional solid-state method. Zn2+/Ge4+ co-substitution induced minimal variation in the macroscopical spinel structure, which effectively lowered the sintering temperature from 1385 to 1250 °C. All compositions crystallized in a normal spinel structure and exhibited dense microstructures and excellent microwave dielectric properties. The compositional dependent quality factor was related to the microstructural variation, being confirmed by Raman features. A composition with x = 0.3 shows the best dielectric properties with εr ≈ 10.09, Q × f ≈ 112,700 THz, and τf ≈ −75.6 ppm/°C. The negative τf value was further adjusted to be near-zero through the formation of composite ceramics with TiO2.

Highlights

Microwave dielectric ceramics can meet the evergrowing requirements of wireless communication as primary functional materials for dielectric resonators and filters
Given that the ZnGa2O4 is a normal spinel while MgGa2O4 is a partial inverse spinel, the difference in dielectric properties between the two materials may be due to structural differences in the cation distribution in tetrahedra and octahedra sites
Keeping in view the above challenges, spinel ZnGa2O4 was selected as the parent material and Zn2+/Ge4+ co-substitution for Ga3+ was proposed to form solid solution of Zn1+xGa2−2xGexO4 with an aim to study the correlation among cation occupation, crystal structure, and microwave dielectric properties

Summary

Introduction

Microwave dielectric ceramics can meet the evergrowing requirements of wireless communication as primary functional materials for dielectric resonators and filters. The last few decades have witnessed intensive development and commercialization of microwave dielectric ceramics and a lot of candidates with good dielectric performances (high relative permittivity r, high quality factor Q × f, tunable temperature coefficient of resonance frequency τf) have been explored [4,5,6].

Results

Conclusion