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The effect of Bi-substitution on the dielectric properties of yttrium iron garnet (YIG) was studied in this paper. The Bi-substituted YIG (YIG:Bi) polycrystalline samples, having composition of Y3-xBixFe5O12, were prepared by the solid-state reaction method. x varied from 0 to 1.2. The phase formation and microstructure were performed by X-ray diffraction and scanning electron microscopy, respectively. Ions valency was identified by X-ray photoelectron spectroscopy. The impedance analyzers are used to measure the frequency dependence and the temperature dependence of relative dielectric constant (#x03B5;r) and loss tangent (tan δ). The experimental results show that the Bi-substitution lowers the phase formation and sintering temperature. Electronic carrier concentration drops dramatically due to limitation of ferric valency variation. Hence, #x03B5;r and tan δ decrease with addition of Bi. Dispersion characteristic indicates non-Debye-type dispersion. A maximum of #x03B5;r appears as the temperature rises. [Copyright &y& Elsevier]

A tunable isotropic negative effective permeability is experimentally demonstrated in a three-dimensional (3D) dielectric composite consisting of dielectric ceramic cube arrays by temperature changing. It shows that a strong subwavelength magnetic resonance can be excited in dielectric cubes corresponding to the first Mie resonance mode and can be continuously and reversibly adjusted from 13.65 to 19.28 GHz with the temperature changing from -15 to 35 °C. Accordingly, negative permeability can be performed in the frequency range of about 6 GHz by adjusting the temperature. It provides a convenient route to design adaptive metamaterials and 3D invisible cloak. [ABSTRACT FROM AUTHOR]