Mechanochemical synthesis of nonstoichiometric fluorite Ca1?xLaxF2+x nanocrystals from CaF2 and LaF3 single crystals

The nonstoichiometric Ca_1−x La_xF_2+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 MF_m-RF_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_0.8La_0.2F_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. __________ Translated from Kristallografiya, Vol. 50, No. 3, 2005, pp. 524–531. Original Russian Text Copyright ? 2005 by Sobolev, Sviridov, Fadeeva, Sul’yanov, Sorokin, Zhmurova, Herrero, Landa-Canovas, Rojas.