Yiyu Li

Electrical conductivity anomaly and X-ray photoelectron spectroscopy investigation of YCr1−xMnxO3 negative temperature coefficient ceramics

Electrical conductivity anomaly of perovskite-type YCr1−xMnxO3 negative temperature coefficient (NTC) ceramics produced by spark plasma sintering (SPS) has been investigated by using defect chemistry theory combination with X-ray photoelectron spectroscopy (XPS) analysis. From the results of the lnρ-1/T curves and the XPS analysis, it can be considered that YCr1−xMnxO3 ceramics exhibit the hopping conductivity. The major carriers in YCrO3 are holes, which are compensated by the oxygen vacancies produced due to the introduction of Mn ions. The Mn4+ ion contents increase monotonically in the range of 0.2 ≤ x ≤ 0.5. The resistivity increases at first and then decreases with increasing Mn contents, which has the same varying tendency with activation energy. The electrical conductivity anomaly appearing in these ceramics may be due to the variation of Cr4+ and Mn4+ ions concentration as Mn content changes.

Green Phosphorescence of Zinc Sulfide Optical Ceramics

In the present work, we report a novel luminescent characteristic of the ZnS ceramics. ZnS undoped nanopowders have been synthesized by a wet chemical precipitation method using Na2S as the source of sulfur. Spark plasma sintering (SPS) has been applied to the nanopowders to fabricate dense ZnS ceramics in the pure phase of zinc blende. Photoluminescence (PL) and fluorescence lifetime spectra have been utilized to characterize the luminescent properties of the ZnS ceramics, indicating that these materials exhibit green phosphorescence. In addition, elemental analysis has also been adopted to determine the elemental composition and valency of elements within the ceramic samples. It is concluded that the green phosphorescence results from the presence of elemental sulfur species and Na impurities.

Synthesis and characterization of calcium lanthanum sulfide via a wet chemistry route followed by thermal decomposition

Calcium lanthanum sulfide (CaLa2S4) has been extensively studied as a promising candidate for advanced infrared optical ceramics. In the present research, we report the successful synthesis of CaLa2S4 via a wet chemistry method followed by thermal decomposition. CaLa2S4 precursor material was first prepared by a facile ethanol-based wet chemical single-source precursor route. The precursor was then thermally decomposed in argon at high temperature to form CaLa2S4. The phase composition and morphology of the synthesized CaLa2S4 powder were confirmed and observed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. Surface area and pore size analyses showed that the CaLa2S4 powder had a high specific surface due to a combined effect of small particle size and the existence of mesopores. Optical characterization revealed that the synthesized CaLa2S4 powder exhibited quantum size confinement and near-band-edge photoluminescence.