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This paper presents the extraction of microwave properties of low-temperature cured inorganic composite materials based on barium titanate (BaTiO3). These composite materials exhibit attractive features such that when the volume fraction of the filler contents varied, its electrical properties of high permittivity and moderately low loss tangent can be manipulated to suit different areas of applications. For the extraction of the permittivity and the loss tangent, three different ink particles were developed and printed on the top of interdigital-shaped microwave capacitor. The properties of the inks were extracted from measured results through computer simulations. The obtained results were verified with several types of interdigital capacitor structures of different fingers and linewidths. The effect of the thickness of the ink layer materials on the top of the capacitor structures was likewise investigated. The results show relative permittivity ( $\varepsilon _{r}$ ) values of 30, 25, and 27 for composite layers printed using inks with Pr. A shape at 67.4 wt% (percentage by weight), Pr. B shape at 66.3 wt%, and Pr. C shape at 67.1 wt% of BaTiO3, respectively, at 2 GHz. Corresponding loss tangents (tan $\delta $ ) were 0.065, 0.040, and 0.025. The dielectric properties of the composite materials are influenced by the thickness variation of the ink layers on the capacitor structures. This novel capacitor composite materials would be a promising candidate for printed application in mobile telecommunication operations, especially in the frequency range of 0.5–3 GHz.

Composite dielectrics comprising the crystal phases of Co-doped magnesium titanates MgTiO3 and Mg2TiO4, and CaTiO3 were examined with regard to their phase composition and its effect on the microwave dielectric properties. In the case of MgTiO3-based composites an increase in the Co concentration results in increasing amount of an additional phase MgTi2O5, which significantly deteriorates the product Q × f. In contrast, the materials based on the spinel Mg2TiO4 never contain MgTi2O5, and consequently demonstrate excellent Q × f magnitude which is as high as 100,000 GHz at low Co doping. At higher Co concentration, however, an additional phase MgTiO3 appears in these materials that is accompanied by a slight reduction of the Q × f magnitude. A slight addition (5 wt.%) of the glass-forming zinc borate into the Mg2TiO4-based composite allows a noticeable reduction of its sintering temperature by 150–200 °C without a significant degradation of its dielectric properties.

A study of K x Ba 1− x Ga 2− x Ge 2+ x O 8 ceramics revealed that these solid solutions undergo a monoclinic-to-monoclinic P 2 1 / a ⇔ C 2/ m phase transition. The temperature of this phase transition decreases with an increase in x , in a similar way to the sintering temperature, which decreases from 1100 °C ( x = 0) to 970 °C ( x = 1). The temperature of the P 2 1 / a ⇔ C 2/ m phase transition is below the sintering temperatures of K x Ba 1− x Ga 2− x Ge 2+ x O 8 (0.67 ≤ x ≤ 1) solid solutions, whereas the compositions at lower x ( x = 0.4 and 0) remain in the P 2 1 / a modification over a wide temperature range above the sintering temperature. Compared to the C 2/ m modification of K x Ba 1− x Ga 2− x Ge 2+ x O 8 (0.67 ≤ x ≤ 1), with a permittivity of 6.2–6.9, the P 2 1 / a modifications exhibit permittivities of 5.9–7.0 and three-to-eight times higher Q × f values of ∼100,000 GHz (at ∼12 GHz). The temperature coefficient of the resonant frequency is ∼−25 ppm/K, regardless of the composition.

Dense, single-phase Sr x Ba 1− x Al 2 Si 2 O 8 (0 ≤ x ≤ 1) and Ca y Ba 1− y Al 2 Si 2 O 8 (0 ≤ y ≤ 0.05) ceramics were synthesized and then structurally and dielectrically characterized. The substitution of Ba with Ca or Sr promotes the transformation of hexacelsian to monocelsian. The substitution with Ca led to a more-than-two-times-lower Q × f value at y = 0.05, whereas the Q × f value of the Sr 0.05 Ba 0.95 Al 2 Si 2 O 8 ( x = 0.05) was only 5% lower than the Q × f value of the BaAl 2 Si 2 O 8 , which exhibited Q × f values of 70,600 and 77,700 GHz when sintered at 1500 °C for 12 and 40 h, respectively. The improvement in the Q × f value with the prolongation of the heat-treatment time, which can be attributed to an increase in the Al:Si ordering, was also noticed for other Sr x Ba 1− x Al 2 Si 2 O 8 solid solutions. In contrast to the dielectric losses, the permittivity ( ɛ = 7.3 and 7.2 at 1 MHz and 10.5 GHz, respectively) did not change significantly with the composition and the sintering conditions.

Composite ceramics based on the spinel Mg2TiO4 were prepared by a conventional mixed-oxide route. To achieve the temperature stabilization of the dielectric constant, each of the composites was added with 7 mol% CaTiO3. The effect of the substitution of isovalent Co for Mg on the microstructure and the microwave dielectric properties of the composite ceramics was also investigated. A maximum Q×f value of around 150–160 THz was obtained for the undoped Mg2TiO4, whereas a reduced Q×f value was observed for an increase in the Co concentration in the system (1−x)Mg2TiO4−xCo2TiO4. Upon doping with 7 mol% CaTiO3, the Q×f value passed through a maximum with increasing Co concentration. Adding ZnO–B2O3 to the composite system based on Co-doped Mg2TiO4 resulted in a reduction of the sintering temperature by 150°–200°C without any significant degradation in the Q×f value.

Ceramics with a composition close to BaZn 2 Ti 4 O 11 were synthesized according to various substitutional mechanisms in order to verify an existence of a homogeneity range in the vicinity of this composition. Structural and microstructural investigations showed that the crystal structure of BaZn 2 Ti 4 O 11 was formed in the homogeneity range corresponding to the formula BaZn 2 − x Ti 4 O 11 − x (0 x 2 − x Ti 4 O 11 − x (0 x τ f = −30 ppm/K and high Q × f values, which increased from ∼68,000 GHz at x = 0 to ∼83,000 GHz at x = 0.05. Structurally, the deficiency of Zn in BaZn 2 − x Ti 4 O 11 − x (0 x 2 Ti 4 O 11 -based materials on the microwave dielectric properties was also investigated. A presence of small amounts of ZnO, BaTiO 3 , hollandite-type solid solutions (Ba x Zn x Ti 8 − x O 16 ) and BaTi 4 O 9 caused a decrease in Q × f values.

NaxCa1� xAl2� xSi21xO8 plagioclase solid solutions (0rxr1) were synthesized under sub-solidus conditions using a solid-state reaction technique. The plagioclase formation and the sintering temperature decreased with an increase in x from the anorthite (CaAl2Si2O8; x 5 0) to the albite (NaAlSi3O8; x 5 1). Microwave (MW) dielectric measurements revealed that

Albite and anorthite, the end-members of the plagioclase feldspar structural family (Na x Ca 1− x Al 2− x Si 2+ x O 8 ), were synthesized under sub-solidus conditions using the solid-state reaction technique. The structural investigations revealed that both the plagioclase-phase formation and sintering temperature decreased from the anorthite (CaAl 2 Si 2 O 8 ; x = 0), which started to form at 1000 °C and sintered at 1300 °C, to the albite (NaAlSi 3 O 8 ; x = 1), which started to form at 800 °C and sintered at 1000 °C. Dielectric measurements in the microwave (MW) frequency region revealed that a high temperature (1500 °C) and an extended heat-treatment time were needed to obtain low-loss anorthite ceramics (Qxf = 10 000–12 000 GHz). In contrast, the albite attained Qxf = 11 200 GHz at a lower temperature (1025 °C). A temperature coefficient of resonant frequency ( τ f ) close to zero (−5 ppm/°C) was another advantage of the albite over the anorthite, which exhibited τ f = −130 ppm/°C. The dielectric measurements also revealed that a slow cooling rate considerably improved the Qxf values of the anorthite and albite.