Abstract
La1−x Ca x MnO3 (x ranges from 0.28 to 0.34) ceramics with Ag addition were synthesized by sol–gel method using methanol as solvent. The EDS elemental mapping shows that Ag element was detected dominantly on the sample surface. The sample of x = 0.28 has almost no pore and bigger grain size, which indicated that it has better crystallization and high density. Temperature dependence of resistivity shows that the samples for all Ca content exhibit sharp metal–insulator transition, and the corresponding metal–insulator temperature shift toward higher temperature with increasing Ca content. The temperature coefficient of resistance value for x = 0.28 reaches its the highest value, 71.8%·K−1. This temperature coefficient of resistance value is even higher than the previously reported for LCMO films and single crystals, and it shows a very promising application for the infrared and bolometric detectors. The high magnetoresitance for x = 0.28 reaches up to 69.3% in magnetic field of 1 T near room temperature. It was concluded that it improved the properties of LCMO:Ag composites are attributed to its improved crystallization by Ag addition, homogeneity and Mn4+/Mn3+ ratio. Different theoretical models are employed to analyze the resistance behaviors in different temperature regions, which give good agreements with experimental results.
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