Abstract

Structural studies on the samples of nominal compositions of the series, La_1.2(Sr_1 − xCa_x)_1.8Mn₂O₇ and Ca_3 − yLa_yMn₂O₇, have been carried out using neutron and X-ray diffraction techniques. These studies show that, unlike the case of the (La,Sr)₃Mn₂O₇ system, the samples belonging to the (La,Ca)₃Mn₂O₇ system form layered Sr₃Ti₂O₇-type structures in a very restricted composition range. Through a systematic study on the effect of substitution of La for Ca in the layered compound Ca₃Mn₂O₇, the solubility of La in Ca₃Mn₂O₇ has been determined. The results go against the literature reports, which claim that the samples of nominal compositions Ca_3 − yLa_yMn₂O₇ (1.0 ≤ y ≤ 2.3) form with layered Sr₃Ti₂O₇ structures. The usefulness of the neutron diffraction technique in unambiguous structural characterization of the layered compounds has also been discussed.