Crystal structure and microwave dielectric properties of temperature stable (Co_xZn_1–x)TiNb₂O₈ ceramics

Abstract

Co x Zn 1-x )TiNb 2 O 8 (x = 0.2-0.8) microwave dielectric ceramics were synthesized via the conventional solid-state reaction route, and the correlation of microwave dielectric properties on the crystal structure was discussed. Crystal structures of ceramic samples were systematically investigated by X-ray powder diffraction. Moreover, composition-induced phase transitions were confirmed via the following sequence: for x ≤ 0.2, single-phase orthorhombic ixiolite (ZnTiNb 2 O 8 ) was formed, whereas for 0.3 ≤ x<0.8, ixiolite and rutile coexisted.When x ≥ 0.8, only single-phase rutile was detected. For the (Co x Zn 1-x )TiNb 2 O 8 ceramics, the microwave dielectric properties were changed with the crystal structural transitions: the dielectric constant (ε r ) and the temperature coefficient of resonant frequency (τ f ) increased upon increasing the Co 2+ , but the quality factor (Q) decreased. A near-zero τ f = +1.6 ppm/ • C was obtained in the Co 0.38 Zn 0.62 TiNb 2 O 8 ceramics with ε r = 40.7 and high Q × f = 16 790 GHz. These research outcomes are expected to have great significance for developing microwave dielectric ceramics in practical applications.

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“…The demand for miniaturization of microwave devices and equipment in recent years has led to the development of high dielectric constant (ε r ) ceramics, as the size of the components is reduced by a factor of ε r 1/2 for a given operating frequency. 1 High dielectric constant microwave dielectric ceramics, including perovskite, 2 scheelite, 3 and rutile 4 structures, have been extensively studied in recent years. In addition to the requirement for a high dielectric constant, other two key properties of the ceramics in the GHz frequency range are also highly concerned: a high quality factor (Q × f, Q is approximately equal to 1/tan δ) to improve selectivity and a near-zero temperature coefficient of resonance frequency (τ f ) to achieve temperature stability (most microwave devices applications require τ f ≤ ±10 ppm/ • C).…”