Characterization and Microwave Dielectric Properties of M ²⁺ Nb ₂ O ₆ Ceramics

Abstract

This paper details the investigation of the quality factor ( Q ), dielectric permittivity (ɛ r ) and temperature coefficient of resonant frequency (τ f ) of the TE 01δ mode of the columbite binary niobate ceramics, with the formula MNb 2 O 6 where M= 2+ cation, in relation to their degree of sintering, microstructure and phase composition. The ceramics were made from a mixed oxide preparative route and fired over a range of temperatures from 800° to 1400°C, and most formed the columbite structure. A comprehensive study was made of the niobates containing the transition metal cations M=Mn 2+ , Co 2+ , Ni 2+ , Cu 2+ , and Zn 2+ , and the group II metal cations M=Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ . All columbite niobates were found to have ɛ r between 17 and 22 and negative τ f values between –45 and –76 ppm/°C, and ZnNb 2 O 6 , MgNb 2 O 6 , CaNb 2 O 6 , and CoNb 2 O 6 had high Q f values of 84 500, 79 600, 49 600, and 41 700 GHz, respectively. The Q f of MgNb 2 O 6 was found to rise to over 95 000 GHz when heated at 1300°C for 50 h.