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Abstract: K0.5(Nd1−xBix)0.5MoO4 (0.2 ≤ x ≤ 0.7) ceramics were prepared via the solid‐state reaction method. All ceramics densified below 720°C with a uniform microstructure. As x increased from 0.2 to 0.7, relative permittivity (ɛr) increased from 13.6 to 26.2 commensurate with an increase in temperature coefficient of resonant frequency (TCF) from – 31 ppm/°C to + 60 ppm/°C and a decrease in Qf value (Q = quality factor; f = resonant frequency) from 23 400 to 8620 GHz. Optimum TCF was obtained for x = 0.3 (−15 ppm/°C) and 0.4 (+4 ppm/°C) sintered at 660 and 620°C with ɛr ~15.4, Qf ~19 650 GHz, and ɛr ~17.3, Qf ~13 050 GHz, respectively. Ceramics in this novel solid solution are a candidate for ultra low temperature co‐fired ceramic (ULTCC) technology. [ABSTRACT FROM AUTHOR]

Ag2 MoO4 ceramic was prepared by using the solid-state reaction method, which could be sintered at 450°C for 2 h, having a relative permittivity of 8.08, a Qf value of 17 000 GHz, and a temperature coefficient of resonance frequency about −133 ppm/°C. Ag2 MoO4 ceramic was chemically compatible with silver but reacted seriously with aluminum to form ( Ag0.5 Al0.5) MoO4 during the sintering. The fitting of infrared spectra and the Shannon's additive rule were employed to study intrinsic dielectric behaviors of the ceramics at microwave region. Ionic displacive polarization and the electronic polarization contributed almost equally to the dielectric permittivity of the ceramic at microwave region. The Ag2 MoO4 ceramics could be a good candidate for ultra-low temperature co-fired microwave devices. [ABSTRACT FROM AUTHOR]

In the present work, ( Bi1− x Fe x) VO4 ( x ≤ 0.40) ceramics were prepared using the solid-state reaction method. All the ceramics could be well densified at sintering temperatures below 800°C. X-ray diffraction ( XRD) results showed that monoclinic solid solution was formed within x ≤ 0.08. When x ≥ 0.10, both monoclinic scheelite and FeVO4 phases were detected. The ( Bi0.92 Fe0.08) VO4 sample sintered at 720°C for 2 h had a permittivity of 57.5 and a Qf value of 15 000 GHz. The IR reflectivity was fitted to study the intrinsic dielectric properties, showing that the majority of the dielectric contribution for this system at microwave region was attributed to the absorptions of structural phonon oscillation in infrared region. [ABSTRACT FROM AUTHOR]

Abstract A scheelite structured [Ca 0.25 (Nd 1-x Bi x) 0.5 ]MoO 4 (0.2 ≤ x ≤ 0.8) ceramics were prepared via solid state reaction method. All the ceramics can be well densified below 780 °C. As x value increased from 0.2 to 0.8, microwave dielectric permittivity increased from 14.0 to 27.8, Qf (Q = quality factor = 1/dielectric loss; f = resonant frequency) value decreased from 42,000 GHz to 19,000 GHz, and TCF shifted from −50 ppm/oC to +18 ppm/oC. The best microwave dielectric properties with permittivity between 23.54 and 23.56, Qf value between 24,000 GHz–21,000 GHz and TCF value ∼ −8 ppm/oC in wide temperature range 25 °C–130 °C were obtained in x = 0.6 ceramic. This work showed that Bi played an important role to modify the TCF from negative to positive value in scheelite materials and this result further accelerate the application of scheelite materials in low temperature co-fired ceramics (LTCC) technology. Highlights • Defect type scheelite [Ca 0.25 (Nd 1-x Bi x) 0.5 ]MoO 4 ceramics were formed. • Near zero TCF was obtained with a ɛ r 23.54 and Qf value 24,000 GHz. • Low sintering temperature ∼ 780° were achieved. [ABSTRACT FROM AUTHOR]

(Bi 1−x Ln x ) 2 MoO 6 (Ln=Nd and La) ceramics were prepared by conventional solid state reaction method. Solid solutions crystallizing in a monoclinic structure with a space group P 21/ c were obtained in the (Bi 1−x La x ) 2 MoO 6 (x≤0.3) ceramics. For the (Bi 1−x Nd x ) 2 MoO 6 ceramics, tetragonal Nd 2 MoO 6 phase with a space group I4 1 /acd was detected when x value reached 0.2 besides the Bi 2 MoO 6 solid solution. Temperature stability and quality factor Qf value at microwave frequencies were improved by appropriate substitution for Bi 3+ by Nd 3+ and/or La 3+ in Bi 2 MoO 6 system. When x=0.2, for both (Bi 1−x Nd x ) 2 MoO 6 and (Bi 1−x La x ) 2 MoO 6 ceramics, Qf values reached maximum about 30,200 GHz and 32,900 GHz, respectively. TCF value shifted towards zero with substitution of Bi 3+ by Nd 3+ and/or La 3+ . When x=0.3, TCF values of (Bi 1−x Nd x ) 2 MoO 6 and (Bi 1−x La x ) 2 MoO 6 ceramics were −70 and −85 ppm/°C, respectively. Relation between crystal structure, microstructure and microwave dielectric properties were discussed. [ABSTRACT FROM AUTHOR]

Abstract: ZnTa2O6 microwave dielectric ceramics have been prepared using ZnTa2O6 nano-powders synthesized by sol–gel processing in this study. The crystal structure and microstructure of the ZnTa2O6 powders and ceramics were characterized by XRD and SEM techniques. ZnTa2O6 ceramics can be densified at a lower sintering temperature of 1200°C. Microwave dielectric properties show that both of Q × f and ɛ r values are lower than those of ceramics prepared by solid state route, and the τ f values do not show different from that of solid state route. ZnTa2O6 ceramics sintered at 1200°C exhibit good microwave dielectric properties: Q × f =50,600GHz, ɛ r =35.12 and τ f =9.69ppm/°C. [Copyright &y& Elsevier]