CRYSTAL-STRUCTURES OF LI4ZRF8 AND LI3ZR4F19 AND REINVESTIGATION OF THE LIF-ZRF4 PHASE-DIAGRAM

The crystal structure of Li4ZrF8 has been refined from X-ray powder da ta using the Rietveld profile analysis. This compound is isostructural with Li4UF8 and crystallizes in the orthorhomic system (space group P nma, no. 62) with cell parameters a = 9.581(1) Angstrom, b = 9.611(1) Angstrom, c = 5.663(1) Angstrom, Z = 4. The crystal structure of Li3Zr 4F19 has been solved from single-crystal X-ray diffraction data and re fined to a conventional R = 0.028 (R(w) = 0.032) for 4078 unique refle ctions with I > 3 sigma(I). This fluoride crystallizes in the triclini c system (<P(1)over bar> space group no. 2) with unit cell dimensions a = 5.418(2) Angstrom, b = 10.822(2) Angstrom, c = 12.708(2) Angstrom, alpha = 107.7 degrees(1), beta = 92.0 degrees(1), gamma = 103.4 degre es(1). The 3D structure is built of corner- and edge-shared pentagonal bipyramids [ZrF7]. This three-dimensional framework delimits channels parallel to the a direction, with an S-like shape, within which lie t he Li+ ions in octahedral coordination. These (LiF6)(5-)octahedra are linked by corners or edges in hexameric units. Since a controversial s tatement about the LiF-ZrF4 system exists in the literature, these pub lished inconsistencies prompt a reinvestigation of the system. In the light of our structural studies a revised phase diagram of this system is presented. (C) 1995 Academic Press, Inc.