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<p>Accurate data regarding the phase transition of SrFeO<sub>3-<i>δ</i></sub> are crucial for optimizing its performance as an oxide ion and hole-mixed conductor in energy and gas separation applications. However, reported transition temperatures are inconsistent owing to difficulties in the preparation of SrFeO<sub>3-<i>δ</i></sub> specimens with homogenous oxygen content. To address this issue, the present study systematically investigates the phase evolution of SrFeO<sub>3-<i>δ</i></sub> across varying temperatures and oxygen contents. Using thermogravimetry–differential thermal analysis and differential scanning calorimetry with samples of controlled oxygen contents, the phase transition behavior of SrFeO<sub>3-<i>δ</i></sub> was evaluated with high accuracy concerning temperature and oxygen content. The validity of the clarified phase transition behavior was confirmed through high-temperature X-ray diffraction. For specimens with 2.87 &lt; 3-<i>δ</i>, composed of a mixture of tetragonal SrFeO<sub>2.87</sub> and cubic SrFeO<sub>3.00</sub> originating from the miscibility gap, the tetragonal-to-cubic phase transition temperature slightly decreased from approximately 300&#xa0;°C, accompanied by broadening of the transition range with increasing oxygen content, specifically with increasing cubic phase composition. For the specimens with 2.76 &lt; 3-<i>δ</i> &lt; 2.87, composed of a mixture of tetragonal SrFeO<sub>2.87</sub> and orthorhombic SrFeO<sub>2.76</sub> originating from the miscibility gap at room temperature, the tetragonal-to-cubic phase transition temperatures remained constant at ~ 300&#xa0;ºC regardless of 3-<i>δ</i>. By contrast, orthorhombic-to-cubic phase transition temperatures decreased from ~ 420&#xa0;°C accompanied by broadening of the transition range with increasing oxygen content, corresponding to a higher proportion of cubic phase transformed from the tetragonal phase. Anomalies in thermal expansion and conductivity confirmed phase transitions, resolving inconsistencies and providing crucial insights into SrFeO<sub>3-<i>δ</i></sub> transformations.</p>

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Structural phase transitions and their impact on thermal expansion and electrical conductivity in SrFeO3-δ with various oxygen contents

  • 期刊论文

  • 发表日期：

    2025年12月15日

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  • Taizo Yoshino,
  • Kosuke Shido,
  • Takayuki Sugimoto,
  • Takuya Hashimoto

摘要

Accurate data regarding the phase transition of SrFeO3-δ are crucial for optimizing its performance as an oxide ion and hole-mixed conductor in energy and gas separation applications. However, reported transition temperatures are inconsistent owing to difficulties in the preparation of SrFeO3-δ specimens with homogenous oxygen content. To address this issue, the present study systematically investigates the phase evolution of SrFeO3-δ across varying temperatures and oxygen contents. Using thermogravimetry–differential thermal analysis and differential scanning calorimetry with samples of controlled oxygen contents, the phase transition behavior of SrFeO3-δ was evaluated with high accuracy concerning temperature and oxygen content. The validity of the clarified phase transition behavior was confirmed through high-temperature X-ray diffraction. For specimens with 2.87 < 3-δ, composed of a mixture of tetragonal SrFeO2.87 and cubic SrFeO3.00 originating from the miscibility gap, the tetragonal-to-cubic phase transition temperature slightly decreased from approximately 300 °C, accompanied by broadening of the transition range with increasing oxygen content, specifically with increasing cubic phase composition. For the specimens with 2.76 < 3-δ < 2.87, composed of a mixture of tetragonal SrFeO2.87 and orthorhombic SrFeO2.76 originating from the miscibility gap at room temperature, the tetragonal-to-cubic phase transition temperatures remained constant at ~ 300 ºC regardless of 3-δ. By contrast, orthorhombic-to-cubic phase transition temperatures decreased from ~ 420 °C accompanied by broadening of the transition range with increasing oxygen content, corresponding to a higher proportion of cubic phase transformed from the tetragonal phase. Anomalies in thermal expansion and conductivity confirmed phase transitions, resolving inconsistencies and providing crucial insights into SrFeO3-δ transformations.