An indirectly coupled open-ended resonator applied to characterize dielectric properties of MgTiO3–CaTiO3 powders

Abstract

The effect of CaTiO3 addition on the complex permittivity of MgTiO3 powder was characterized with an open-ended coaxial cavity resonator in the range of 2.12–3.66 GHz. Permittivities and loss tangents of (1 − x)MgTiO3-xCaTiO3 composite powders with x of 0, 2, 5, and 10 mol. % were measured and compared to theoretical values. Inclusion permittivities and dielectric loss tangents were determined by using Bruggeman symmetric and Looyenga mixing rules and a general mixing model. Additions of CaTiO3 resulted in a clear increase in inclusion permittivities from 13.4 up to 14.9 and in loss tangents from 7.1 × 10−3 up to 8.5 × 10−3. Comparison with the theoretical loss tangent values and quantitative determination of CaTiO3 molar ratios by using measured loss tangents and a general mixing model gave a good correlation. The characterization method was proved to be capable of detecting dielectric changes of MgTiO3–CaTiO3 composite powder and of quantifying the amount of additional substances. This information can be exploited, for example, in the analysis and quality control of different composite powders.

Determining the Quality Factor of Dielectric Ceramic Mixtures with Dielectric Constants in the Microwave Frequency Range

“…The quality factor of the binary phase composite can be estimated by 4,8,28 where Q represents the quality factor of the mixture system, and Q 1 and Q 2 are the quality factors of the two ceramics, respectively. From the definition of Q (it will be given in equation (8) in the next section) at the microwave frequency range, the quality factor of the mixture is related to both the dielectric constant and the resonant frequency 1,5,6,25,26,29 .…”

Microwave dielectric properties of (1‐x)Ba3.75Nd9.5Cr0.25Nb0.25Ti17.5O54–xNdAlO3 ceramics

“…One of the most effective and widely used methods for obtaining a zero temperature coefficient is to combine two phases with τ f of opposite signs viawhere x denotes volume molar ratios and and have opposite signs . Most of the reported τ f results fit well with Equation while the variation of the dielectric constant and quality factor always depends on whether the solid solution is formed or not .…”

“…Besides the dielectric constant, quality factor is another important property parameter of ceramics. The quality factor of the mixed ceramic is usually related to the dielectric losses ( tan δ) of individual phases, tan δ ~ 1/ Q , which can be added linearly:where Q mix is the quality factor of the mixed ceramic, while Q 1 and Q 2 are the quality factors of two original ceramics . Figure displays the measured quality factor ( Q ) of (1‐ x )BNCNTO– x NAO ceramics.…”

“…It has been always confirmed that the Equation is precise enough to predict the τ f variation without considering the phase state, for example, multiphase or solid solution, when two ceramics are mixing. Therefore, it is taken to calculate the τ f value in the whole x range, where τ f is the temperature coefficients of the mixture, τ f1 =49 ppm/°C and =−33 ppm/°C are temperature coefficients of two starting materials . Figure shows both measured and calculated temperature coefficient of resonant frequency values τ f .…”

“…Microwave dielectric ceramics play an increasingly important role in a wide range of microwave frequency devices. For example, resonators made from these ceramics need high dielectric constants (ε r ), high quality factors ( Q ), and near‐zero temperature coefficients (τ f ) at the resonant frequencies . The size of devices made from ceramics is proportional to ε r −1/2 , so a higher dielectric constant will decrease the device footprint .…”