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

Wet chemical analyses and powder diffractometry were used to character ize lanthanum strontium manganates(III)(IV) with a composition La1-xSr xMnO3+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 mat erials by calcination in a nitrogen atmosphere. Series II materials wi th 0.00 less-than-or-equal-to x < 0.20 were orthorhombic. For x greate r-than-or-equal-to 0.20, series II materials were hexagonal. For serie s 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 rati o Mn(IV)/Mn(IV) + Mn(III) is a nearly constant 0.3 in the range 0.00 l ess-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 w ith x is shown to be consistent with the found composition of the mate rials. The observed and calculated densities of the materials are cons istent with cation vacancies. Full descriptions of procedures for synt heses and analyses are reported. (C) 1994 Academic Press, Inc.