Abstract
In this work, La0.67Ca0.23K0.1MnO3:Agx (x = 0.1, 0.2, 0.3, 0.4, 0.5) polycrystalline ceramic samples were prepared by sol-gel method, and their structural and electrical properties were systematically investigated. X-ray diffraction (XRD) analysis showed that crystal structures of all samples were rhombohedral. Surface morphology was investigated by scanning electron microscopy (SEM), which indicated that the number of pores increased with the increase in Ag content. Elemental mapping image showed that Ag was uniformly distributed over the entire sample on macro-scale, which could create conduction channels and improve the connectivity of grains. Therefore, the resistivity decreased sharply with the increase in Ag content. Standard four-probe method was used to measure temperature dependence of resistivity (ρ-T). Insulator-metal transition temperature (TP) shifted to higher temperature when the value of x was below 0.3. Temperature coefficient of resistivity (TCR%) decreased as Ag content increased. Fitted curves for resistivity of LCKMO:Agx composites at low temperature range (T <TP) indicated that grain boundary effects, electron-electron scattering and electron-magnon scattering mechanisms were involved. High-temperature (T >TP) resistivity data were explained using small-polaron hopping (SPH) and variable-range hopping (VRH) models. Resistivity data over the entire temperature range (100–300K) could be fitted by percolation model.
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