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Abstract <p>A comparative analysis of ion transport mechanisms in crystals was carried out for three phases formed in the CaF<sub>2</sub>–HoF<sub>3</sub> condensed system: a fluorite phase (the <i>F</i>-phase, CaF<sub>2</sub> and Ca<sub>1–<i>x</i></sub>Ho<sub><i>x</i></sub>F<sub>2+<i>x</i></sub> solid solution), a tysonite phase (the <i>T</i>-phase, Ho<sub>1–<i>y</i></sub>Ca<sub><i>y</i></sub>F<sub>3–<i>y</i></sub> solid solution), and a phase having the orthorhombic β-YF<sub>3</sub> structure (the <i>R</i>-phase, HoF<sub>3</sub>). The ionic conductivity σ<sub>dc</sub>(<i>T</i>) fundamental data gained in experiments on single-crystal samples was used to derive ionic conductivity versus composition and activation enthalpy of ion transfer versus composition dependences. A comparison of the properties of the components of the system under study shows that the conductivity of the HoF<sub>3</sub> <i>R</i>-phase (σ<sub>500 K</sub> = 5 × 10<sup>−6</sup> S/cm at 500 K) is five orders of magnitude that of the stoichiometric CaF<sub>2</sub> <i>F</i>-phase. In the region of the Ca<sub>1–<i>x</i></sub>Ho<sub><i>x</i></sub>F<sub>2 +</sub> <sub><i>x</i></sub> (0 &lt; <i>x</i> ≤ 0.35) nonstoichiometric <i>F</i>-phase, the interstitial mechanism of electrical conductivity occurs. The σ<sub>500 K</sub> increases as the HoF<sub>3</sub> concentration increases to reach 4 × 10<sup>−5</sup> S/cm at <i>x</i> = 0.35. The Ho<sub>1–<i>y</i></sub>Ca<sub><i>y</i></sub>F<sub>3–<i>y</i></sub> (<i>y</i> = 1 − <i>x</i>, <i>x</i> = 0.77) nonstoichiometric <i>T</i>-phase has σ<sub>500 K</sub> = 2 × 10<sup>−4</sup> S/cm, which is five and 40 times as high as the electrical conductivity of the Ca<sub>0.65</sub>Ho<sub>0.35</sub>F<sub>2.35</sub> <i>F</i>-phase and HoF<sub>3</sub> <i>R</i>-phase, respectively. The reasons for the rapid anionic transport in the nonstoichiometric <i>T</i>-phase are the ion vacancy electrical conductivity and extensive heterovalent isomorphism of cations.</p>

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Ionic Conductivity of the Three Solid Phases in the CaF2–HoF3 System: A Comparative Analysis

  • 期刊论文

  • 发表日期：

    2025年5月1日

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  • N. I. Sorokin

摘要

Abstract

A comparative analysis of ion transport mechanisms in crystals was carried out for three phases formed in the CaF2–HoF3 condensed system: a fluorite phase (the F-phase, CaF2 and Ca1–xHoxF2+x solid solution), a tysonite phase (the T-phase, Ho1–yCayF3–y solid solution), and a phase having the orthorhombic β-YF3 structure (the R-phase, HoF3). The ionic conductivity σdc(T) fundamental data gained in experiments on single-crystal samples was used to derive ionic conductivity versus composition and activation enthalpy of ion transfer versus composition dependences. A comparison of the properties of the components of the system under study shows that the conductivity of the HoF3 R-phase (σ500 K = 5 × 10−6 S/cm at 500 K) is five orders of magnitude that of the stoichiometric CaF2 F-phase. In the region of the Ca1–xHoxF2 + x (0 < x ≤ 0.35) nonstoichiometric F-phase, the interstitial mechanism of electrical conductivity occurs. The σ500 K increases as the HoF3 concentration increases to reach 4 × 10−5 S/cm at x = 0.35. The Ho1–yCayF3–y (y = 1 − x, x = 0.77) nonstoichiometric T-phase has σ500 K = 2 × 10−4 S/cm, which is five and 40 times as high as the electrical conductivity of the Ca0.65Ho0.35F2.35 F-phase and HoF3 R-phase, respectively. The reasons for the rapid anionic transport in the nonstoichiometric T-phase are the ion vacancy electrical conductivity and extensive heterovalent isomorphism of cations.