Mechanochemical Synthesis of Nonstoichiometric Fluorite Ca1-x Lax F2+x Nanocrystals from CaF2 and LaF3 Single Crystals

The nonstoichiometric Ca1-x LaxF2+x phase (x ≥ 0.1) is obtained by mechanochemical synthesis from CaF2 and LaF3 single crystals. This phase is the first representative of fluorite fluorides obtained by mechanochemical synthesis in the MFm-RFn 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 deg. C) coincides with the conductivity of the single crystals of the same composition (Ca0.8La0.2F2.2). 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