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Nanocrystallization of LaF 3 in a glass of composition 55SiO 2 -20Al 2 O 3 -15Na 2 O-10LaF 3 (mol%) has been achieved by heat treatment above the glass transition temperature. A maximum crystal size of 14 nm has been attained, with the crystalline fraction and crystal size dependent on the time and temperature of thermal treatment. The effect of lanthanum fluoride crystallization is noticeable from the microstructural and compositional changes in the glass matrix, which have been studied using several techniques, including viscosity, dilatometry, X-ray diffraction, and quantitative Rietveld refinement, transmission electron microscopy, and differential scanning calorimetry. The crystallization mechanism is shown to occur via regions of La-and Si-phase separation in the glass, from which the fluoride crystals develop during heat treatment. The interface between the glass matrix and the crystals in the demixed ranges is enriched in network formers, mainly SiO 2 , creating a viscous barrier, which inhibits further crystal growth and limits the crystal size to the nanometric range.

Atomic-scale studies using advanced simulation techniques have investigated the energetics of defects, oxygen migration, and dopant incorporation in the proton-conducting SrCeO3 system. The interatomic potential model first reproduces the observed distorted perovskite structure of SrCeO3. Substitution with trivalent dopants (M) on the A site in SrCe(Yb)O3 - δ (via Vo •• consumption) is compared with substitution on the B site (via Vo •• creation); the results support the premise that the absence of ionic conductivity at low doping levels is associated with dopant partitioning over both A and B sites. Dopant-vacancy association is predicted to occur in SrCe0.9M0.1O2.95 for a wide range of M cations. Formation of (M‘Ce−OHo •) clusters is also calculated to be favorable in accordance with reported proton-trapping effects. The lowest M‘Ce−OHo • binding energies and the largest M−H distances are found for the most common dopants for proton conductivity in the SrCeO3 system, namely, Y and Yb. The pathway for oxygen migration is proposed as a curved trajectory with an asymmetric energy distribution. The lowest energy redox process is calculated to be oxidation with the formation of holes in accordance with the observation of p-type conductivity at increasing oxygen partial pressures (pO2).

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