Improvement of electrical transport properties of La0.7Ca0.16Sr0.08Ag0.06MnO3 polycrystalline ceramics via optimizing the sintering temperatures

In this work, the sol-gel method was utilized to synthesize La_0.7Ca_0.16Sr_0.08Ag_0.06MnO₃ (LCSAMO) polycrystalline ceramics at different sintering temperatures (T_s, with T_s = 1543, 1573, 1603, 1633, and 1673 K). Using X-ray diffraction and scanning electron microscopy, we observed that the ceramics exhibited higher densities and superior crystalline quality with elevated T_s. Simultaneously, the reduction in internal strain leads to distortions of MnO₆ octahedron, which subsequently affects the hopping and conductive properties of electrons. The increase of Mn³⁺/Mn⁴⁺ ratio inhibited the double-exchange mechanism, resulting in a shift of both the peak resistivity temperature (T_p) and temperature corresponding to TCR_max (T_k) to lower temperatures. Moreover, the electrical transport properties within the metal-insulator transition region were interpreted using the variable-range hopping (VRH), small-polaron hopping (SPH), and phenomenological percolation (PP) models. The increase in T_s effectively reduced the carrier effective mass and grain boundary scattering of LCSAMO ceramic samples, thus improving the electrical transport properties. Because of the loss of Ag due to volatilization, T_s was carried out in a lower temperature range of 1543–1673 K and a large TCR of 16.21 % K⁻¹ was obtained at 1633 K. Notably, the peak temperature coefficient of resistivity (TCR_max) increased from 6.89 % K⁻¹ (T_s = 1543 K, T_k = 301.13 K) to 16.21 % K⁻¹ (T_s = 1633 K, T_k = 287.59 K). The high room-temperature TCR of LCSAMO is expected to be used in advanced uncooled infrared bolometers, providing a basis for studying the influence of T_s on the electrical transport performance of ceramics.