Effects of Re3+ radius on phase composition and thermal sensitivity of Ba4.5Re9Ti18O54 ceramics

Tungsten-bronze materials are widely used in the fields of electro-optic, photorefractive, pyroelectric, millimeter-wave, and piezoelectric devices. In particular, tungsten-bronze Ba_4.5Sm₉Ti₁₈O₅₄ is believed to be useful for fabricating high-temperature thermistors owing to its semiconductor properties. However, inherent shortcomings such as poor linearity (electrical properties deviate from the Arrhenius equation) and high aging coefficients limit the practical applications of these materials. Incorporating rare-earth (Re) ions is an effective means of improving the electrical properties of thermistor materials. In this study, we explore the phase composition and thermosensitive properties of Ba_4.5Re₉Ti₁₈O₅₄ (Re = Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu) ceramics with tungsten–bronze structures. The results indicate that the tungsten–bronze phase (Ba_4.5Re₉Ti₁₈O₅₄) is generated when the radius of the Re³⁺ ion exceeds 1.04 Å and the tolerance factor surpasses 0.82. Conversely, a pyrochlore phase (Re₂Ti₂O₇) accompanied by a monoclinic impurity phase (BaTi₂O₅), is formed. Moreover, all Ba_4.5Re₉Ti₁₈O₅₄ ceramics with a tungsten-bronze structure exhibit exceptional linear electrical properties (R² ≥ 999.09‰) and high sensitivity coefficients (α_1000°C ≥ −0.79%/K). In particular, after aging at 1100°C for 600 h, both the aging coefficient and drift rate of material constant are as low as 5.76% and 1.79%, respectively. These results indicate that Ba_4.5Re₉Ti₁₈O₅₄ ceramics are promising for high-temperature and high-accuracy temperature measurements.