Large temperature coefficient of resistance at near room temperature in Sr-doped La0.72Ca0.28MnO3:Ag0.2 polycrystalline composites

A series of La0.72Ca0.28−xSrxMnO3:Ag0.2 (x = 0.00, 0.01, 0.03, 0.05, 0.07, and 0.10) composites was prepared by sol-gel method using methanol as solvent. Sample composition was analyzed by X-Ray diffraction, which revealed that all samples are pseudo-perovskite. Grain size and morphology were characterized by scanning electron microscopy. The results showed that all samples are of high density and large grain size in the range of 50-100 µm. All samples exhibited sharp metal-insulator (M-I) transitions, along with a drastic transition from paramagnetism to ferromagnetism. With increased Sr doping, radius of A-site ion increased, both Curie temperature TC and M-I transition temperature shift to higher temperature increases, and transition width turns widener which makes a decreased temperature coefficient of resistance (TCR). Larger ionic radius of Sr2+, which resulted in enhancement of double exchange, enlarges Mn-O-Mn bond angle, hence improves electrical and magnetic properties. It was found that TCR could reach 24.3% K−1 by Ag addition at near room temperature, which makes this composite promising potential applications in infrared detection and night vision.