Equilibria among point defects in GdF3–doped CaF2

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Abstract
EPR and dielectric relaxation measurements, reported earlier, have been combined to produce estimates of the mole fraction (n′) of pairs formed of substitutional Gd3+ ions and F− interstitials as a function of total GdF3 mole fraction (M) and temperature at which the crystals are annealed prior to rapid cooling. Over the range of M from 1×10−4 to 27×10−4, n′ rises to a saturation value when M increases to about 10−3. At constant M, n′ goes through a maximum at anneal temperatures from about 1073 to 1273 K. The rate of the annealing reaction increases with M and with decreasing sample size, and the density increases with increasing M faster than the interstitial model predicts. A qualitative model of the annealing process is suggested, in which F− interstitials react with an atmospheric constituent (probably HF) to form an immobile complex that provides remote charge compensation for the cubic Gd3+ ions. The remaining free F− interstitials are trapped by Gd3+ ions during quenching to form the pairs.
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