High-Q×f value and temperature stable MgZrTa2O8 ceramics by Li heterovalent substitution
The Mg 1- x Li x ZrTa 2 O 8- x /2 ( x = 0–0.07) ceramics were fabricated to investigate the effects of Li + heterovalent substitution for Mg 2+ . 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 densification temperature from 1475 °C to 1400 °C. Notably, the Q × f exhibited an obvious increase by up to 74 % from 41,844 GHz at x = 0–72,782 GHz at x = 0.05. The Q × f 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 ε r decreased in term of ionic polarizability. The variations of resonant frequency temperature coefficient τ f were explained from the views of [TaO 6 ] oxygen octahedral distortion and bond energy. A near-zero τ f was obtained for x = 0.05 composition, accompanied by ε r = 11.97, Q×f = 72,782 GH at 1450 °C. Li substitution was effective and inexpensive for MgZrTa 2 O 8 ceramic to realize dielectric properties enhancement and densification temperature optimization simultaneously.
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