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<p>In this study, La<sub>1.8</sub>Ho<sub>0.2</sub>Sn<sub>2</sub>O<sub>7</sub> ceramic was synthesized via the solid-state reaction method, with the confirmation of a single-phase pyrochlore structure by X-ray diffraction (XRD). Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) revealed that Ho<sup>3+</sup> substitution for La<sup>3+</sup> at the A-site in La<sub>2</sub>Sn<sub>2</sub>O<sub>7</sub> led to the contraction of AO<sub>8</sub> polyhedra, which in turn induced the distortion of SnO<sub>6</sub> octahedra, resulting in a long-range ordered but locally disordered microstructure. Substituting La<sup>3+</sup> with smaller Ho<sup>3+</sup> ions lowers the cation radius ratio (r<sub>A</sub>/r<sub>Sn</sub>) and thus decreases the oxygen vacancy formation energy. Furthermore, lattice distortion elongates and weakens the Sn–O bonds, providing an additional driving force for the formation of oxygen vacancies. X-ray photoelectron spectroscopy (XPS) and electrical performance demonstrated a significant increase in oxygen vacancies concentration after Ho<sup>3+</sup> doping, thereby greatly enhancing the conductivity and reducing the B value of the ceramic. Consequently, it exhibited typical negative temperature coefficient (NTC) behavior in the wide temperature range of 200 – 1200&#xa0;℃, with a highly linear relationship (R<sup>2</sup> &gt; 0.999) between lnρ and 1000/T. Notably, after ageing for 500&#xa0;h at 1000&#xa0;℃, the resistance drift rate of La<sub>1.8</sub>Ho<sub>0.2</sub>Sn<sub>2</sub>O<sub>7</sub> remained low at 1.58%, demonstrating excellent high-temperature structural and electrical stability. These features make La<sub>1.8</sub>Ho<sub>0.2</sub>Sn<sub>2</sub>O<sub>7</sub> a highly promising candidate for high-temperature NTC thermistor applications with a wide temperature range.</p>

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Ho3+-doped La2Sn2O7 ceramic for high-temperature negative temperature coefficient thermistor with a wide temperature range

  • 期刊论文

  • 发表日期：

    2026年5月6日

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  • Zhuangzhuang Lu,
  • Zhiming Sheng,
  • Xiaohui Li,
  • Bo Gao,
  • Aimin Chang

摘要

In this study, La1.8Ho0.2Sn2O7 ceramic was synthesized via the solid-state reaction method, with the confirmation of a single-phase pyrochlore structure by X-ray diffraction (XRD). Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) revealed that Ho3+ substitution for La3+ at the A-site in La2Sn2O7 led to the contraction of AO8 polyhedra, which in turn induced the distortion of SnO6 octahedra, resulting in a long-range ordered but locally disordered microstructure. Substituting La3+ with smaller Ho3+ ions lowers the cation radius ratio (rA/rSn) and thus decreases the oxygen vacancy formation energy. Furthermore, lattice distortion elongates and weakens the Sn–O bonds, providing an additional driving force for the formation of oxygen vacancies. X-ray photoelectron spectroscopy (XPS) and electrical performance demonstrated a significant increase in oxygen vacancies concentration after Ho3+ doping, thereby greatly enhancing the conductivity and reducing the B value of the ceramic. Consequently, it exhibited typical negative temperature coefficient (NTC) behavior in the wide temperature range of 200 – 1200 ℃, with a highly linear relationship (R2 > 0.999) between lnρ and 1000/T. Notably, after ageing for 500 h at 1000 ℃, the resistance drift rate of La1.8Ho0.2Sn2O7 remained low at 1.58%, demonstrating excellent high-temperature structural and electrical stability. These features make La1.8Ho0.2Sn2O7 a highly promising candidate for high-temperature NTC thermistor applications with a wide temperature range.