DETERMINATION OF STOICHIOMETRY IN LANTHANUM STRONTIUM MANGANATES(III)(IV) BY WET CHEMICAL METHODS

Wet chemical analyses and powder diffractometry were used to characterize lanthanum strontium manganates(III)(IV) with a composition La1-xSrxMnO3+delta (0.00 less-than-or-equal-to x less-than-or-equal-to 0.50). Two series prepared by different thermal treatments were investigated. In series I the materials were calcined in air. These materials were hexagonal. In series II the materials were prepared from series I materials by calcination in a nitrogen atmosphere. Series II materials with 0.00 less-than-or-equal-to x < 0.20 were orthorhombic. For x greater-than-or-equal-to 0.20, series II materials were hexagonal. For series I delta decreases with increasing x until x = 0.30, where it becomes almost zero (and remains 0 for x > 0.30). For series I the molar ratio Mn(IV)/Mn(IV) + Mn(III) is a nearly constant 0.3 in the range 0.00 less-than-or-equal-to x less-than-or-equal-to 0.20. For series II delta is near zero in the whole range. For these materials the ratio Mn(IV)/Mn(IV) + Mn(III) increases with x. The changes of unit cell volumes with x is shown to be consistent with the found composition of the materials. The observed and calculated densities of the materials are consistent with cation vacancies. Full descriptions of procedures for syntheses and analyses are reported. (C) 1994 Academic Press, Inc.