Anomalous microwave dielectric behaviour induced by the orthorhombic-tetragonal phase transition in CaLaGaO4 ceramics. Issue 4 (April 2022)

• Record Type: Journal Article
• Authors: Fang, Weishuang; Chen, Junqi; Yang, Yang; Ao, Laiyuan; Tang, Ying; Li, Jie; Fang, Liang
• Is Part Of: Journal of the European Ceramic Society. Volume 42:Issue 4(2022)
• Page Start: 1474
• Page End: 1479
• Publication Date: 2022-04
• Subjects: K2NiF4-structure -- Phase transition -- Microwave dielectric properties -- P-V-L theory; Ceramic materials -- Periodicals; Composite materials -- Periodicals; Matériaux céramiques -- Périodiques; Composites -- Périodiques; Ceramic materials; Composite materials; Periodicals; Electronic journals; 666.05
• DOI: 10.1016/j.jeurceramsoc.2021.12.010
• Languages: English
• ISSNs: 0955-2219

Abstract

Highlights: Novel microwave dielectric ceramics CaLaGaO4 with orthorhombic (sintered below 1260 °C) and tetragonal (sintered at 1280 °C–1300 °C) structure were synthesized by conventional solid-state method. Microwave dielectric properties of o-CaLaGaO4 ceramic sintered at 1240 °C were εr =11.23, Q × f = 63, 900 GHz, and τ f = –56.6 ppm/°C. Phase transformation leads to a significantly increased εr (19.5) in t-CaLaGaO4, and a near-zero τf (+2.3 ppm/°C). Abstract: In this work, orthorhombic (o-) and tetragonal (t-) phase CaLaGaO4 ceramics were synthesized using a conventional solid-state method. Phase evolution and crystal structure were investigated via XRD and TEM, and o-CaLaGaO4 phase with Pna21 space group can be obtained at a low temperature (<1260 °C). With the increase in sintering temperature, o-CaLaGaO4 and t-CaLaGaO4 phases ( I4/mmm ) coexisted when sintered in the range of 1280 °C – 1300 °C. The microwave dielectric properties of the o-CaLaGaO4 ceramic sintered at 1240 °C were εr = 11.2, Q × f = 63, 900 GHz, and τf = −56.6 ppm/℃. By contrast, the phase transformation in the CaLaGaO4 ceramic led to a significantly increased εr (19.5) in t-CaLaGaO4 and a near-zero τf (+2.3 ppm/℃). The theoretical permittivity ( εth ) was calculated on the basis of the Clausius–Mossotti equation and P-V-L theory. Results indicate that in the low-symmetry-structure o-CaLaGaO4 ceramics, εth can be estimated accurately by the latter.