Improved temperature coefficient of resistivity in La0.67Ca0.25-xSr0.08AgxMnO3 (0.06 ≤ x ≤ 0.12) polycrystalline ceramics via Ag doping

Oxides with perovskite structures have received extensive research attention due to their fascinating physical properties. In this study, polycrystalline ceramics of La_0.67Ca_0.25-xSr_0.08Ag_xMnO₃ (LCSAMO, x = 0.06, 0.08, 0.10, and 0.12) were obtained by changing the previous sol-gel preparation process parameters. The results show that LCSAMO ceramics are orthogonal perovskite structures with a space group of Pnma. With increasing x, the grain size, lattice constants, Mn-O bond length (d_Mn-O), and Mn-O-Mn bond Angle (θ_Mn-O-Mn) are slightly affected. When x = 0.08, the average grain size achieved a maximum value of 8.84 µm, which enhanced the intergranular connectivity. The Mn⁴⁺/(Mn³⁺+Mn⁴⁺) ratio was the maximum value of 30.26% when x = 0.08, where the double exchange (DE) mechanism was the strongest among the four samples and optimized the electrical transport properties. Ag doping induces distortion in MnO₆ octahedron. The electrical transport properties of the ceramics were improved by the combined effect of the distortion and DE mechanism. The temperature coefficient of resistivity (TCR) achieved the maximum value of 24.07% K⁻¹ at 284.91 K. The results of this work provide a theoretical basis for Ag doping at the A-site and thus obtaining lanthanide perovskite manganese oxide with high TCR.