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0.7CaTi1-x(Mg1/3Nb2/3)xO3–0.3SmAlO3 (0 ≤ x ≤ 0.04) ceramics were prepared by solid-state reaction method. The effects of (Mg1/3Nb2/3)4+ substitution on crystal structure, microstructure, and microwave dielectric properties of the ceramics were investigated. The orthorhombic perovskite structure remains unchanged, but the dielectric properties are affected significantly by replacing Ti4+ with (Mg1/3Nb2/3)4+. The dielectric constant (εr) exhibits a slight decrease from 44.9 to 43.9, and the temperature coefficient of resonance frequency (τf) exhibits a transition from + 4.1 to ‒1.4 ppm/°C with the increase of x. An appropriate amount of (Mg1/3Nb2/3)4+ substitution can promote sintering and, thus, reduce dielectric loss. The ceramic with x = 0.02 sintered at 1390 °C shows excellent microwave dielectric properties: εr = 44.1, Q × f = 45 600 GHz, and τf = + 0.8 ppm/°C. [ABSTRACT FROM AUTHOR]

Multiferroic materials with sizeable magnetization and electric polarization simultaneously at room temperature hold the promise for the realization of low-dissipation multifunctional devices. Here, we demonstrate room temperature multiferroicity in a single-phase Mg0.3Co0.7Fe2O4 spinel ferrite thin films. X-ray diffraction (XRD) patterns along with Raman spectroscopy elucidate spinel structure with Fd 3 ¯ m space group for Mg0.3Co0.7Fe2O4 thin film. The existence of Fe3+, Co2+, and Mg2+ in the Mg0.3Co0.7Fe2O4 films was confirmed by using X-ray photoelectron spectroscopy (XPS). The local magnetic properties were probed by conducting the (magnetic force microscopy) MFM measurements and grain-like magnetic domain structures have been observed. The irreversible behavior of temperature-dependent field cooled (FC) and zero field cooled (ZFC) magnetization curves suggests that the Neel temperature and blocking temperature are higher than 380 K. Mg0.3Co0.7Fe2O4 thin film exhibits typical ferroelectric hysteresis and ferromagnetic hysteresis with saturation polarization of 1.7 µC cm–2 and saturation polarization 148 emu cm–3, which suggest the multiferroicity of the spinel thin film. Piezoresponse response measurements suggest a piezoelectric displacement of 30 Å. The peculiar multiferroicity in the spinel films likely originates from cation ordering and local frustration induced by the inclusion of Mg2+ in the sublattices of the spinel structure. The activation energy of 0.467 eV is calculated which suggests that the polar on hopping could be responsible for the conduction characteristics in the present films. The finding of multiferroicity of Mg0.3Co0.7Fe2O4 thin film may lead to the advancement of multiferroic material for new information storage technology and magnetoelectric sensors. [ABSTRACT FROM AUTHOR]

Barium dititanate (BaTi2O5, BT2) materials have potential excellent electrical properties, but regarded as metastable phase, limiting their research and actual application. In this work, high-densified and stable Ba0.995−xEr0.005Tbx(Ti0.94Zr0.06)2O5 (BE(TZ)2-xTb) ceramics doped with varying terbium contents (x) were prepared by a solid-state reaction at 1180 °C with as-synthesized nanoparticles. A series of measurements was conducted to investigate structural information and electrical properties. A pure BT2 phase without decomposition was obtained, and terbium was impregnated into the Ba ion position in the structure. Adding a small amount of x (< 0.9 mol%) increased the dielectricity and resistance of the ceramics because of the eliminated oxygen vacancies as determined through defect chemistry mechanism analysis. However, the Curie temperature and electrical properties deteriorated as the large composition fluctuation under excessive x. Terbium could influence on the degree of ferroelectric relaxor of the ceramics. Relatively high activation energy (1.32–1.63 eV) was calculated by the Arrhenius formula, indicating that the ceramics featured a high insulating character. [ABSTRACT FROM AUTHOR]

In the present work, the Li2Mg3Ti0.95(Mg1/3Nb2/3)0.05O6 (LMT(MN)) samples with LiF additions (1–5 wt%) were prepared using the solid state method. The effects of LiF additives on sintering behavior, phase compositions and microwave dielectric properties of LMT(MN) samples were explored. According to XRD analysis, the LMT(MN) cubic solid solution was formed in ceramic sample in the whole composition range. LiF obviously lowered the optimum sintering temperature of LMT(MN) ceramic from 1550 to 1000 °C, indicating that LiF additive was beneficial to the improvement of the sintering characteristic of the matrix. The variations of the LiF additives and sintering temperatures were important factors to affect the microwave dielectric properties of sintered samples. High performances of microwave dielectric properties were achieved in LMT(MN)-3 wt% LiF ceramic sintered at 1000 °C with a dielectric constant (εr) of 14.95, a high quality factor (Qf) of 117,630 GHz and a temperature coefficient of resonant frequency (τf) of -11.22 ppm/°C. [ABSTRACT FROM AUTHOR]

Microwave dielectric ceramics based on monoclinic-structure ZnZrNbO were prepared by an aqueous sol-gel process. Highly reactive nanosized ZnZrNbO powders with particle sizes of 10-30 nm were successfully obtained at 600 °C as precursors. And the evolution of phase formation was investigated by means of DTA-TG and XRD analysis. Both selected area electronic diffraction patterns and high-resolution crystal lattice image were characterized for the evaluation of crystallinity by mean of transmission electron microscopy. Sintering characteristics and microwave dielectric properties of ZnZrNbO ceramics were studied depending on sintering temperatures ranging from 1100 to 1250 °C. The dielectric properties were strongly dependent on the compositions, the densifications and the microstructures of the specimens. With the increase of sintering temperature, density, ε and Q· f values increased and saturated at 1200 °C with excellent microwave properties: ɛ of 27.38, Q· f value of 66,700 GHz, and τ value of −38.4 ppm/°C. The correlations of microstructure and dielectric properties for ZnZrNbO ceramics were also investigated. [ABSTRACT FROM AUTHOR]