Electrical Properties and High-Temperature Stability of High-Entropy Pyrochlore Ceramics (La0.2Nd0.2Sm0.2Gd0.2M0.2)2Sn2O7 (M = Eu, Dy, Ho, or Yb) for Negative Temperature Coefficient Thermistor Applications

Understanding electrical transport mechanisms and key thermal stability factors in high-temperature thermosensitive ceramics is essential for developing highly stable temperature sensors under extreme thermal conditions. This study develops the high-entropy pyrochlore stannates (La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 M 0.2 ) 2 Sn 2 O 7 (M = Eu, Dy, Ho, or Yb) via solid-state synthesis, demonstrating exceptional negative temperature coefficient (NTC) behavior across 300 – 1400 °C. Hall measurements and X-ray photoelectron spectroscopy (XPS) analyses reveal a dual redox mechanism for these ceramics: partial reduction of Sn 4+ to Sn 2+ at B-sites and rare-earth ions (Sm/Eu/Yb) to RE 2+ at A-sites, generating hole-dominated p-type conductivity. The materials exhibit outstanding thermal stability, with resistance drift below 1.96% after 500 hours at 1400 °C, attributed to the entropy-stabilized structure that effectively suppresses lattice disorder transformation. Aging studies further demonstrate that high oxygen vacancy concentrations lead to resistance drifts, as oxygen filling at elevated temperatures oxidizes RE 2+ to RE 3+ , reducing charge carriers and ultimately increasing resistivity. This study elucidates for the first time the hole-dominated conduction mechanism arising from dual-site cation valence changes (Sn/RE) and the regulation effect of oxygen vacancies on high-temperature stability, which provides an important theoretical basis and material design strategy for the development of the next-generation high-temperature NTC sensors with excellent stability.