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Abstract <p>Optimization of the compositions of nonstoichiometric fluorite phases Na<sub>0.5–<i>x</i></sub><i>R</i><sub>0.5+<i>x</i></sub>F<sub>2+2<i>x</i></sub> and Na<sub>0.5−<i>x</i></sub>(<i>R</i>,<i>R</i>′)<sub>0.5+<i>x</i></sub>F<sub>2+2<i>x</i></sub> (<i>R</i>, <i>R</i>′ are rare-earth elements Tb−Lu, Y; 0.08 ≤ <i>x</i> ≤ 0.13) on ionic conductivity and thermal stability was performed based on temperature measurements of the electrical conductivity of single crystals in dependence of the ionic radii of rare-earth cations (<i>R</i>) and the content of <i>R</i>F<sub>3</sub> trifluorides (<i>x</i>) and a comparative analysis of the phase diagrams of condensed NaF–<i>R</i>F<sub>3</sub> systems. It has been shown that the ionic conductivity (at 500 K) of 15 out of 27 studied compositions of Na<sub>0.5−<i>x</i></sub><i>R</i><sub>0.5+<i>x</i></sub>F<sub>2+2<i>x</i></sub> and Na<sub>0.5−<i>x</i></sub>(<i>R</i>,<i>R</i>′)<sub>0.5+<i>x</i></sub>F<sub>2+2<i>x</i></sub> solid solutions exceeds the conventional limit of 10<sup>−5</sup> S/cm, below which the use of solid electrolytes in electrochemical devices is considered undesirable because of insufficient electrical conductivity. The fluorite phase Na<sub>0.5–<i>x</i></sub>Lu<sub>0.5+<i>x</i></sub>F<sub>2+2<i>x</i></sub> has the highest thermal stability, and its composition Na<sub>0.4</sub>Lu<sub>0.6</sub>F<sub>2.2</sub> has the maximum fluorine-ion conductivity, equal to 1.4 × 10<sup>−4</sup> S/cm.</p>

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Optimization of Compositions of Solid Electrolytes Na0.5–xR0.5+xF2+2x on Ionic Conductivity and Thermal Stability

  • 期刊论文

  • 发表日期：

    2026年2月1日

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  • N. I. Sorokin

摘要

Abstract

Optimization of the compositions of nonstoichiometric fluorite phases Na0.5–xR0.5+xF2+2x and Na0.5−x(R,R′)0.5+xF2+2x (R, R′ are rare-earth elements Tb−Lu, Y; 0.08 ≤ x ≤ 0.13) on ionic conductivity and thermal stability was performed based on temperature measurements of the electrical conductivity of single crystals in dependence of the ionic radii of rare-earth cations (R) and the content of RF3 trifluorides (x) and a comparative analysis of the phase diagrams of condensed NaF–RF3 systems. It has been shown that the ionic conductivity (at 500 K) of 15 out of 27 studied compositions of Na0.5−xR0.5+xF2+2x and Na0.5−x(R,R′)0.5+xF2+2x solid solutions exceeds the conventional limit of 10−5 S/cm, below which the use of solid electrolytes in electrochemical devices is considered undesirable because of insufficient electrical conductivity. The fluorite phase Na0.5–xLu0.5+xF2+2x has the highest thermal stability, and its composition Na0.4Lu0.6F2.2 has the maximum fluorine-ion conductivity, equal to 1.4 × 10−4 S/cm.