Mixture behavior and microwave dielectric properties of (1 − x)CaWO4–xTiO2

doi:10.1016/j.jeurceramsoc.2006.11.035

Journal of the European Ceramic Society

Volume 27, Issues 8–9, 2007, Pages 3087-3091

https://doi.org/10.1016/j.jeurceramsoc.2006.11.035 Get rights and content

Abstract

The microwave dielectric characteristics and mixture behavior of (1 − x)CaWO₄–xTiO₂ ceramics prepared with conventional solid-state route were studied using a network analyzer and X-ray power diffraction, respectively. The CaWO₄ compound had good properties (low permittivity and high quality factor) for microwave applications, but it had a high negative temperature coefficient of resonant frequency (τ_f = −53). Hence, in order to tune the dielectric properties, (1 − x)CaWO₄–xTiO₂ were prepared for different values of x. X-ray powder diffraction and SEM analysis revealed that CaWO₄ and TiO₂ coexisted as a mixture. The mixture formation and dielectric properties could be explained by mixture rule. In particular, at x = 2.6, good microwave dielectric properties were obtained: Qf = 27,000, ɛ_r = 17.48, and τ_f = ∼0 ppm/°C.

Introduction

According to the development of high-frequency communication technology, microwave dielectric materials with stable temperature coefficient of resonant frequency (near zero) and lower dielectric loss (higher quality factor value) have been required. Searching for microwave dielectric materials with both stable temperature coefficient of resonant frequency and higher quality factor is constantly needed in ceramic material research.¹ In our previous study, compounds with the general formula AWO₄ (A = Mg, Mn, Zn, Ca, Sr, Ba) are found promising materials for microwave substrate application.² These materials exhibit good microwave properties, high quality factor and low permittivity but with a high negative temperature coefficient resonant frequency around −50 ppm/°C. The most popular method of achieving stable temperature coefficient of resonant frequency is mixing materials, which have opposite value.³ In this way mixed materials form solid solution or mixture and show stable temperature coefficient of resonant frequency. The present investigation revealed that the τ_f of CaWO₄ can be adjusted to zero with TiO₂ addition.

Section snippets

Experimental

The used starting materials were CaCO₃ (high purity chemicals, 99.99%), WO₃ (high purity chemicals, 99.9%) and TiO₂ (high purity chemicals, 99.9%). The CaWO₄ powders were prepared using conventional mixed oxide method by calcining at 800 °C for 2 h. CaWO₄ and TiO₂ powders were mixed for varying composition according to the formula (1 − x)CaWO₄–xTiO₂ (x = 0.0, 0.1, 0.15, 0.2, 0.24, 0.25, 0.26, 0.3, 0.4, 0.5, 0.7, 0.9 and 1.0) and were ball-milled with ZrO₂ balls for 24 h using ethanol. After drying

Result and discussion

Fig. 1 represents the X-ray diffraction (XRD) patterns for x = 0, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9 and 1 in (1 − x)CaWO₄–xTiO₂. With increasing TiO₂ content, the intensity of the reflections of CaWO₄ phase decreased and those of TiO₂ phase increased without peak shift. The XRD pattern data indicates that CaWO₄ and TiO₂ behave as mixture and not a solid solution and no second phase was found. Therefore, the dielectric properties of (1 − x)CaWO₄–xTiO₂ are proportional to their variation of the molar

Conclusion

The mixture behavior and microwave dielectric properties of CaWO₄ with TiO₂ system were investigated. The dielectric constant was increased with the molar addition of TiO₂ into CaWO₄ to form mixtures based on (1 − x)CaWO₄–xTiO₂. The analysis of the crystal structure by XRD indicated that no additional second phase was formed and (1 − x)CaWO₄–xTiO₂ exist as mixture in the entire range. The densities of mixture were over 97% of theoretical density and effects of porosity on dielectric properties

Acknowledgements

This research was supported by a grant from the Center for Advances Materials Processing (CAMP) of the 21st Century Frontier R&D Program funded by the Ministry of Commerce Industry and Energy (MOCIE), Republic of Korea.

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View full text

Mixture behavior and microwave dielectric properties of (1 − x)CaWO4–xTiO2

Abstract

Introduction

Section snippets

Experimental

Result and discussion

Conclusion

Acknowledgements

J. Eur. Ceram. Soc.

J. Eur. Ceram. Soc.

Temperature stable low loss ceramic dielectrics in (1 − x)ZnAl2O4–xTiO2 system for microwave substrate applications

Eur. Phys. J. B

Validation of a novel dielectric constant simulation model and the determination of its physical parameters

Microelectron. J.

Mixture behavior and microwave dielectric properties of (1 − x)CaWO₄–xTiO₂

Temperature stable low loss ceramic dielectrics in (1 − x)ZnAl₂O₄–xTiO₂ system for microwave substrate applications