High-Qxf value and temperature stable MgZrTa2O8 ceramics by Li heterovalent substitution

The Mg1-xLixZrTa2O8-x/2 (x = 0-0.07) ceramics were fabricated to investigate the effects of Li+ heterovalent substitution for Mg2+. The site occupancy and existence of the Li+ were examined based on Vienna Ab-initio Simulation Package (VASP) and X-ray photoelectron spectroscopy (XPS), respectively. Single phase solid solution with wolframite structure was identified in the whole region. Li+ substitution reduced the den-sification temperature from 1475 degrees C to 1400 degrees C. Notably, the Qxf exhibited an obvious increase by up to 74 % from 41,844 GHz at x = 0-72,782 GHz at x = 0.05. The Qxf for x < 0.01 was largely dependent on the intrinsic loss originating from packing fraction, while as 0.01 <= x <= 0.05, it was dominated by extrinsic factors, especially the oxygen vacancy concentration. The corresponding dielectric constant er decreased in term of ionic polarizability. The variations of resonant frequency temperature coefficient Tf were explained from the views of [TaO6] oxygen octahedral distortion and bond energy. A near-zero Tf was obtained for x = 0.05 composition, accompanied by er = 11.97, Qxf= 72,782 GH at 1450 degrees C. Li substitution was effective and in-expensive for MgZrTa2O8 ceramic to realize dielectric properties enhancement and densification tem-perature optimization simultaneously.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

The effects of Li+ heterovalent substitution for Mg2+ in Mg1-xLixZrTa2O8-x/2 (x = 0-0.07) ceramics were investigated. The site occupancy and existence of Li+ were examined using VASP and XPS. Single phase solid solution with wolframite structure was identified. Li+ substitution reduced the densification temperature and significantly increased the Qxf. The dielectric constant er decreased due to ionic polarizability. The variations in resonant frequency temperature coefficient Tf were explained by oxygen octahedral distortion and bond energy. Li substitution was effective and inexpensive for enhancing dielectric properties and optimizing densification temperature in MgZrTa2O8 ceramics.