Structural Phase Transition and Nonstoichiometry of Li2FeCl4—Neutron Diffraction Studies

✍ Scribed by H.D. Lutz; A. Pfitzner; J.K. Cockcroft

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 157 KB
• Volume: 107
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1993.1344

✦ Synopsis

Neutron powder diffraction studies have been performed on (\mathrm{Li}{2} \mathrm{FeCl}{4}) at 298,498 , and (698 \mathrm{~K}). The resulting powder profiles were fitted by the Rietveld method to final (R_{\mathrm{I}}=6.9,3.2), and (4.0 %), respectively. The orthorhombic room-temperature polymorph (RTM) (\mathrm{Li}{2} \mathrm{FeCl}{4} o C 14) crystallizes in the (\mathrm{SnMn}{2} \mathrm{~S}{4})-type (\mathrm{NaCl}) superstructure (space group (\mathrm{Cmmm}, Z=2, a=732.95(8), b=1034.2(1)), and (c=365.90(4) \mathrm{pm}) ), the high-temperature form (\mathrm{Li}{2} \mathrm{FeCl}{4} c F 56) in an inverse spinel structure (space group (\mathrm{Fd} \overline{3} m, Z=8, a=1043.64(1) \mathrm{pm}) at (498 \mathrm{~K}) ) with increasing Frenkel disorder of the lithium ions from the tetrahedral (8 a) lattice sites to the octahedral (16 c) interstitial sites with the increase in temperature. (\mathrm{Li}{2} \mathrm{FeCl}{4} \mathrm{RTM}{\text {possesses }} \mathrm{Li}^{+})ion deficiency as given by the formula (\mathrm{Li}{2-2} \times \mathrm{Fe}{1+x} \mathrm{Cl}{4}). Stoichiometric samples annealed at (373 \mathrm{~K}) are two-phase containing Suzuki-type (\mathrm{Li}{6} \mathrm{FeCl}{8}). 1993 Academic Press, Inc.