Investigation on phase structure, spectral characteristics, microstructure and microwave dielectric properties of Li2Zn[Ti1-x(Co1/3Nb2/3)x]3O8 (0.0? x? 0.4) ceramics

In this paper, a series of Li2Zn[Ti1-x(Co1/3Nb2/3)x]3O8 (0.0 <= x <= 0.4) ceramics were prepared via the conventional solid-state method. The influences of (Co1/3Nb2/3)4+ complex ions on the phase composition, spectral characteristics, microstructure, and microwave dielectric properties of Li2Zn[Ti1-x(Co1/3Nb2/3)x]3O8 ceramics were studied systematically. XRD analysis accompanied with Rietveld refinements showed that pure Li2ZnTi3O8 solid solution ceramics with the cubic spinel structure were obtained at x = 0.2-0.4. New Raman-active mode of about 858 cm-1 should be attributed to the vibrations of NbO6 due to the high bond energy of Nb-O bonds, exerting a certain impact on the structure and performance of Li2Zn[Ti1-x(Co1/3Nb2/3)x]3O8 ceramics. XPS results indicated that Nb5+ ion donor suppressed the deoxidation process and therefore resulted in the disappearance of Ti3+ ion and oxygen vacancy. The downward trend variation in the epsilon r value with the increase of (Co1/3Nb2/3)4+ content could be explained by the presence of "compressed" cations and "rattling" cations effect. In addition, the Q x f of the current ceramics was closely dependent on relative density, grain size, FWHM, and oxygen vacancy. Good combined microwave dielectric properties of epsilon r = 24.5, Q x f = 91,250 GHz, and tau f = -16.8 ppm/degrees C were achieved for the Li2Zn[Ti0.8(Co1/3Nb2/3)0.2]3O8 ceramic sintered at 1120 degrees C. High quality factor gives evidence that the Li2Zn[Ti0.8(Co1/3Nb2/3)0.2]3O8 ceramic is an appealing candidate for highly selective microwave devices.