Enhancement of densification and microwave dielectric properties in LiF ceramics via a cold sintering and post-annealing process

Liu, Bing; Li, Lei; Song, Kai Xin; Mao, Min Min; Lu, Zhilun; Wang, Ge; Li, Linhao; Wang, Dawei; Zhou, Di; Feteira, Antonio; Reaney, Ian M.

Abstract

LiF is a low-firing fluoride with excellent microwave dielectric properties, however densification of LiF ceramics is challenging owing to their low surface free energy. In this study, a cold sintering process (150 °C, 250 MPa, 60 min) was employed to pre-densify LiF ceramics to 78 % relative density. Post-annealing treatments between 650 °C and 800 °C led to significant grain growth which was accompanied by an increase in relative density to 92 %. The microwave quality factor (Qf) increased with increasing annealing temperature to a maximum of 110,800 GHz at 800 °C, 1.5 times higher than the value obtained via conventional sintering (78,800 GHz), with relative permittivity εr = 8.2 and temperature coefficient of resonant frequency, τf =–135 ppm/°C. Such high values of Qf and its compatibility with Ag electrode suggest that cold sintered LiF has great potential as a component or additive in low temperature co-fired ceramic formulations.

• Journal Article Type: Article
• Acceptance Date: Sep 30, 2020
• Online Publication Date: Oct 4, 2020
• Publication Date: 2021-02
• Deposit Date: Oct 23, 2021
• Journal: Journal of the European Ceramic Society
• Print ISSN: 0955-2219
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 41
• Issue: 2
• Pages: 1726-1729
• DOI: https://doi.org/10.1016/j.jeurceramsoc.2020.09.073
• Keywords: LiF, Cold sintering, Microwave dielectric properties, Densification
• Public URL: http://researchrepository.napier.ac.uk/Output/2815759