Mechanochemical synthesis of nonstoichiometric fluorite Ca1−x LaxF2+x nanocrystals from CaF2 and LaF3 single crystals

The nonstoichiometric Ca 1− x La x F 2+ x phase ( x ≥ 0.1) is obtained by mechanochemical synthesis from CaF 2 and LaF 3 single crystals. This phase is the first representative of fluorite fluorides obtained by mechanochemical synthesis in the M F m - R F n systems ( m < n ≤ 4). The average grain size ranges within 10–30 nm. The temperature dependence of ionic conductivity of the mechanochemically synthesized phase pressurized at 600 MPa (at its high-temperature portion at temperatures exceeding 200–250°C) coincides with the conductivity of the single crystals of the same composition (Ca 0.8 La 0.2 F 2.2 ). The activation energy of ionic conductivity (0.95 eV) corresponds to migration of interstitial fluoride ions in the crystal bulk. Mechanochemical synthesis of a multicomponent fluoride material with nanometer grains opens a new chapter in the chemistry of inorganic fluorides. A decrease of the sintering temperature of the powders with nanometer grains is very important for preparing dense fluoride ceramics of complicated compositions and other polycrystalline forms of fluoride materials.