Liqin Yang

Composite varistors based on epoxy resin/La0.8Sr0.2MnO3

Polymer/perovskite manganese oxide (epoxy resin/La0.8Sr0.2MnO3) composites are prepared using bonded method. There is no reaction between La0.8Sr0.2MnO3 and the polymer. The nonlinear current–voltage property is significantly affected by the content of polymer. The resistivity and nonlinear coefficient increase with the increase of polymer content. The resistivity of the composites is 5–9 orders of magnitude higher than that of the sintering ceramics. The nonlinear electrical behavior is an intrinsic property. Compared with conventional sintered ceramic varistors, the polymer/manganese oxide composite varistors have greater nonlinear coefficient above 45.

Electrical and magnetic transport properties of Co-doped Bi2Se3 topological insulator crystals

Transition metal doped topological insulators (TI) CoxBi2-xSe3 were prepared and the phase structure, electrical and magnetic transport properties, Hall mobility and Hall resistivity were studied. The lattice constant c decreased with the increasing Co concentration. All samples exhibited weak metallic resistivity. With increasing Co concentration, the value of ρxx increased, reaching a maximum at x = 0.02, and then decreased. The resistivity data could be fitted by different formulas below and above 30 K in all samples result from different mechanism corresponding to different temperature regions. The magnetoresistance (MR) of Bi2Se3 TI showed a change dependence of concentration. The MR was enhanced by small quantity of Co doping, attaining a maximum value in Bi1.98Co0.02Se3 crystal; but MR was suppressed in high-doped sample (x > 0.02). Those results were ascribed to the rivalry between the phonon scattering effect and the magnetic ordering in single crystals caused by Co ions. For low-doped samples doped, the contribution of phonon scattering was much higher than that of magnetic ordering, leading to larger MR value. However, in samples doped with higher Co concentrations, the magnetic ordering effect became dominant and caused the MR decreases. The MR increased with decreasing temperature and increasing magnetic field. The Hall mobility data indicated that incorporating Co in Bi2Se3 single crystal can reduce native defect of Bi2Se3.

ELECTRICAL TRANSPORT AND LOW-FIELD MAGNETORESISTANCE IN La0.8Sr0.2MnO3/Zn COMPOSITES

La0.8Sr0.2MnO3 (LSMO)/Zn composites were prepared by bonded method. The phase structure, electrical transport and low-field magnetoresistance (LFMR) characteristics have been investigated. The binder segregated mostly at the grain boundaries. The bonded composites exhibited enhanced LFMR, which was attributed to the enhanced intergrain spin-polarized tunneling behavior.