The layered manganate Sr4-xBaxMn3O10:: synthesis, structural and magnetic properties

The layered manganate Sr4Mn3O10 has been synthesized and a partial substitution of Ba for Sr, leading to the solid solution Sr4-xBaxMn3O10 with 0 less than or equal to x less than or equal to 2.50, has been shown. This phase, isotypic to Ba4TiPt2O10, crystallizes in the Cmca space group with a = 5.4766(1) Angstrom, b = 12.4659(2) Angstrom, c = 12.5282(2) Angstrom for x = 0. The structural analysis of this oxide shows close relationships with the 9 L-hexagonal BaMnO3 structure, both structures being built up from 'Mn3O12' trioctahedral units of face sharing octahedra, linked through their apices. The main difference between the two structures concerns the relative orientation of two successive Mn3O12 groups, leading to a layered structure for Sr4Mn3O10 and to a tridimensional framework for 9 L-BaMnO3. The detailed HREM study shows the existence of extended defects, mainly along (010), which correspond to shearing mechanisms and suggests the possible existence of other original members. These oxides show an antiferromagnetic transition at T-N = 210-215 K. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved.