Structure and reaction with lithium of tetragonal pyrochlore-like compoundSm2Ti2O7

Single crystals of Sm2Ti2O7 have been grown by incongruent melting of powde r samples with a nominal composition of Sm0.5Li0.5TiO3 and their structure determined by means of single crystal X-ray diffraction. The structure is t etragonal (space group I4(l)/amd, a = b = 7.208(1) Angstrom, c = 10.198(2) Angstrom). This is the first pyrochlore-like compound with tetragonal symme try and a unit cell smaller than that of the cubic pyrochlore reported so f ar. The study of the reaction between lithium and the Sm2Ti2O7 by both chem ical (lithium vapour and n-Bu-Li reagent) and electrochemical methods has s hown that this structure can not lodge lithium; instead a decomposition occ urs when it is reduced. It is concluded that this material can not be used as the cathode of rechargeable batteries despite having an open structure w ith vacant tunnels and titanium cations in a high oxidation state. (C) 1999 Elsevier Science S.A. All rights reserved.