Impedance spectroscopy, B-site cation ordering and structure–property relations of (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 ceramics for 5G dielectric waveguide filters

Abstract

Dense (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 ceramics were synthesized via solid-state reaction. The crystal structure and microwave dielectric properties of the ceramics were systematically investigated. Rietveld refinement revealed that when x ≤ 0.2, the ceramics had a rhombohedral structure with an R-3c space group. When x ≥ 0.5, the ceramics had an orthorhombic structure with a Pbnm space group. Selected area electron diffraction and Raman spectroscopy analyses proved that the microwave dielectric ceramics had a B-site order, which accounted for the great improvement in microwave dielectric properties. The content of oxygen vacancies was identified through X-ray photoelectron spectroscopy, and the change rule of Q × f was closely related to oxygen vacancy content. The perturbation of A-site cations had an important influence on dielectric constant. Specifically, with the increase in Ti4+ content, the perturbation effect of the A-site cations was enhanced and dielectric constant increased. When x = 0.65, the temperature coefficient of resonant frequency of the (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 microwave dielectric ceramics was near zero. The optimal microwave dielectric properties of 0.35LaAl0.9(Mg0.5Ti0.5)0.1O3–0.65CaTiO3 were εr= 44.6, Q × f = 32,057 GHz, and τf= +2 ppm/°C.