Chunhong Mu

Room temperature magnetic and dielectric properties of cobalt doped CaCu3Ti4O12 ceramics

CaCu3Ti4−xCoxO12 (x = 0, 0.2, 0.4) ceramics were prepared by a conventional solid state reaction, and the effects of cobalt doping on the room temperature magnetic and dielectric properties were investigated. Both X-ray diffraction and energy dispersive X-ray spectroscopy confirmed the presence of Cu and Co rich phase at grain boundaries of Co-doped ceramics. Scanning electron microscopy micrographs of Co-doped samples showed a striking change from regular polyhedral particle type in pure CaCu3Ti4O12 (CCTO) to sheet-like grains with certain growth orientation. Undoped CaCu3Ti4O12 is well known for its colossal dielectric constant in a broad temperature and frequency range. The dielectric constant value was slightly changed by 5 at. % and 10 at. % Co doping, whereas the second relaxation process was clearly separated in low frequency region at room temperature. A multirelaxation mechanism was proposed to be the origin of the colossal dielectric constant. In addition, the permeability spectra measurements i...

Electrospun Cu2ZnSnS4 microfibers with strong (112) preferred orientation: fabrication and characterization

In this study, Cu2ZnSnS4 (CZTS) microfibers were fabricated using a non-vacuum method of electrospinning following vulcanization process. CZTS fibers were obtained via the vulcanization of the electrospun precursor fibers at 500 °C (CZTS-500), 550 °C (CZTS-550), and 600 °C (CZTS-600), in sulfur ambient conditions. Samples were characterized by scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), XRD mapping scan, Raman spectrum and UV-vis absorption. Polycrystalline CZTS fibers with kesterite crystallization were formed in CZTS-500, whereas higher temperature vulcanization in CZTS-550 led to a strong preferential crystallization along CZTS [112] crystal direction around fiber surface, which is definitely confirmed by XRD mapping scan. More interestingly, the band gap value (Eg), which was 1.48 eV for CZTS-500, reduced to 1.43 eV for CZTS-550. Eg reduction may be related to lattice distortion induced by stress or strain around fiber surface, and can be beneficial for broadening optical absorption range thus increasing the efficiency of CZTS-based solar cells.

ELECTRICAL AND MAGNETIC PROPERTIES OF LOW-TEMPERATURE SINTERED xTiO2+(1-x)Ni0.2Cu0.2Zn0.62O(Fe2O3)0.98 CERAMICS

For the purpose of multi-layer chip electromagnetic interference (EMI) filters, a series of xTiO2 + (1 - x)Ni0.2Cu0.2Zn0.62O(Fe2O3)0.98 (NiCuZn ferrite) (0 ≤ x ≤ 60 wt.%) composite ceramics were primarily prepared by a solid-state reaction method. With addition of 3 wt.% Bi2O3, all the ceramics can be sintered at 900°C. The effects of composition x on the sintering behaviors, phase compositions and electromagnetic properties of TiO2+NiCuZn ferrite ceramics were investigated. The X-ray diffraction (XRD) results showed that the ceramics were composed of NiCuZn, Fe3Ti3O10 and TiO2 phases. Scanning electron micrographs showed that 10 wt.% TiO2 to 90 wt.% Ni0.2Cu0.2Zn0.62O(Fe2O3)0.98 ceramics had small grain size and high density. With an increase of TiO2 content x, the value of er decreased and the component with 10 wt.% TiO2 had maximum relative dielectric constant. The permeability and the saturation magnetization decreased gradually with increasing TiO2 content, and the permeability curve exhibited excellent stability of frequency. The composite materials with 10 wt.% TiO2 showed typical magnetic hysteresis of the magnetic materials. For the specimens with 10 wt.% TiO2 to 90 wt.% Ni0.2Cu0.2Zn0.62O(Fe2O3)0.98, the good dielectric (er = 50) and magnetic properties (μ = 30, tanδ|10 MHz = 0.13) have been obtained at 900°C.