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We have investigated the structural and magnetic properties of a novel type of hexaferrite with composition of [Ba.sub.3][M.sub.2][Fe.sub.23[O.sub.41] (where M = Co and Mn) (Z hexaferrite) with tunable permeability. The material is promising for very high frequency (VHF) control when used in a voltage-controlled oscillator (VCO) as a tunable inductor. We substituted Mn for Co in the composition [Ba.sub.3][Co.sub.2-x][Mn.sub.x][Fe.sub.23][O.sub.41] from x = 0.0 to 1.2 to improve the inductance tunability and quality factor of the inductor material. Mn substitution had significant influence on the grain size of the sintered hexaferrites, and the coercivity was greatly reduced. The initial permeability and quality factor increased with increasing substitution of Mn for Co until x reached 0.5, an effect attributed to the decrease of the magnetocrystalline anisotropy constant of the hexaferrite and increase of average grain size. The tunability of the samples also increased with increasing Mn substitution, reaching a maximum at x = 0.5, and then decreased with further substitution. This behavior is similar to that of the initial permeability and coercivity, and can be explained by the same mechanism. Index Terms--Magnetic properties, nonlinear magnetic properties, tunability, Z-type hexaferrite.

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]

In the present work, a series of scheelite-related ( Li0.5 Ln0.5) MoO4 ( Ln = Nd, Er, Gd, Y, Yb, Sm, and Ce) ceramics were prepared by using the solid-state reaction method. Except for the ( Li0.5 Yb0.5) MoO4, the other compositions were found to have a scheelite structure. Among all the compositions, the ( Li0.5 Sm0.5) MoO4, ( Li0.5 Nd0.5) MoO4, and ( Li0.5 Ce0.5) MoO4 ceramics were found to possess low sintering temperatures below melting point of aluminum (660°C) and be chemically compatible with Al. The relation between microwave dielectric properties and structure was analyzed by using the Shannon additive rule and bond-valence theory. This series of microwave dielectric ceramics might be candidate for low temperature co-fired ceramics technology. [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: 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]

In this work, the (Na 0.5 Bi 0.5 )(Mo 1-x W x )O 4 (x = 0.0, 0.5 and 1.0) ceramics were prepared via solid state reaction method. All the samples can be well densified at sintering temperature about ~720 °C. Dense and homogeneous microstructure with grain size lying between 2~8 μm can be observed from scanning electron microscopy (SEM). Microwave dielectric permittivity of the (Na 0.5 Bi 0.5 )(Mo 0.5 W 0.5 )O 4 ceramic was found to be temperature-independent in a wide range between 25~120 °C with a temperature coefficient of frequency (TCF) ~-6 ppm/°C, a permittivity ~28.9, and Qf values 12,000~14,000 GHz. Crystal structure was refined using Rietveld method and lattice parameters are a = b = 5.281 (5) Å and c = 11.550 (6) Å with a space group I 4 1 /a (88). The (Na 0.5 Bi 0.5 )(Mo 1-x W x )O 4 ceramics might be good candidate for low temperature co-fired ceramics (LTCC) technology.