Preparation, structural and microwave dielectric properties of CaLa4(ZrxTi1−x)4O15 ceramics
Introduction
With the great development in microwave low-power communication modules, such as WiFi, RFID, and ZigBee communication systems, microwave ceramics with excellent dielectric characteristics that can reduce the dimensions of the microwave devices or improve the power-consumption of the microwave low-power communication modules have become quite important. Candidate microwave ceramics for such microwave communication applications must have a high relative permittivity (εr > 30), high dielectric Q × f value (Q × f > 5000 GHz), and temperature coefficient of resonant frequency close to zero (τf ∼ 0 ppm/°C) [1], [2]. Several hexagonal-phase ceramics (M, La)nTin−1O3n (M = Ca, Sr, Ba; n = 5, 6), which belong to the cation-deficient perovskite AnBn−1O3n system, where the M and La ions occupy the A sites and Ti ions occupy the B sites, have been reported to have excellent microwave dielectric properties [3], [4]. Among these, the CaLa4Ti4O15 composition has also been widely applied in microwave communication components because it has high dielectric constant ( ∼ 41), high quality factor (Q × f ∼ 50,000 GHz), and small temperature coefficient of resonant frequency (τf ∼ −25 ppm/°C) [5].
Several studies have been carried out to improve the microwave dielectric properties, such as the partial replacement of B-site and selection of a compensator in the ceramic systems [6], [7]. Huang et al. reported that the Mg2(Ti0.95Sn0.05)O4 ceramics have the following values: εr = 16.67, Q × f = 2,75,000 GHz, and τf = −53.2 ppm/°C; and that its dielectric constant and quality factor can be improved with Sn4+ substitution [8]. In addition, Tseng et al. also reported that substitution with Zr effectively improved the microwave dielectric properties of MgTiO3 ceramics, which exhibited the values εr = 18.1, Q × f = 3,80,000 GHz, and τf = −50 ppm/°C [9]. As mentioned earlier, it is interesting to study the influence of microwave dielectric properties on the Zr4+ substitutions in the B-sites in the CaLa4Ti4O15 materials because of the ionic radii of Zr (0.72 nm) and Ti (0.605 nm) are similar. In this study, the CaLa4(ZrxTi1−x)4O15 (x = 0.01–0.1) ceramics were prepared by using conventional solid-state methods, and their microwave dielectric properties were investigated as a function of the Zr content. In addition, the correlation between the microstructure and microwave dielectric properties was also investigated.
Section snippets
Experimental procedure
The CaLa4(ZrxTi1−x)4O15 (x = 0.01–0.1) microwave dielectric ceramics systems were fabricated according to the stoichiometry and were synthesized by conventional solid-state methods from individual high-purity oxide powders (>99.9%) of CaCO3, La2O3, ZrO2, and TiO2. The powders were ball-mixed in distilled water for 12 h in a plastic bottle with agate balls. All wet mixtures were dried and calcined at 1250 °C for 4 h. The calcined powder with PVA as a binder was pressed into pellets with the
Results and discussions
Fig. 1, Fig. 2 show the XRD patterns of the CaLa4(ZrxTi1−x)4O15 (x = 0.01–0.1) ceramics system sintered at 1490–1570 °C for 4 h. All the diffraction peaks in the XRD patterns were similar and can be indexed with a hexagonal structure that belonged to the P m space group at various Zr contents and sintering temperatures [4]. In addition, the CaLa4Ti5O17 phase was also detected in the XRD patterns and the peak index of the secondary phase of CaLa4Ti5O17 increased with increasing Zr content and
Conclusion
In the present study, microwave dielectric properties and sintering behavior of Zr substituted for Ti to form CaLa4(ZrxTi1−x)4O15 (x = 0.01–0.1) solid solution ceramic system were investigated. The CaLa4Ti5O17 was detected as the secondary phases at various sintering temperatures and Zr contents. The dielectric constant and temperature coefficient of the resonant frequency of CaLa4(ZrxTi1−x)4O15 ceramics, ranging from 45.8 to 46 and from −11.3 to −9.5 ppm/°C, were slightly improved, when compared
Acknowledgment
This work was sponsored by the National Science Council of the Republic of China under Grant NSC 101-2622-E-239-004-CC3.
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