Preparation and crystallographic properties of Sr7−x(Ca/Ba)xMn4O15

Polycrystalline samples of the new phases Sr7−xAxMn4O15 (A = Ca, Ba; 0 ≤ x ≤ 1) and Sr7−2xCaxBaxMn4O15 (0 ≤ x ≤ 1) have been characterized by X-ray powder diffraction. Apart from changes in the cell parameters, no significant alterations of the crystal structure are found upon doping with Ca and/or Ba. The application of chemical pressure causes an anisotropic change of the unit cell with the a (Ca) and b (Ba) axes showing the largest changes. The compounds with double-doping Sr7−2xCaxBaxMn4O15 show a more complicated behavior. The cell volume is linear dependent on the average ionic radius of the A-cation, for all compounds. Ca enters the structure on the small Sr(1) site, whereas Ba occupies the larger Sr(3) and Sr(4) sites. The results show that the structure of Sr7Mn4O15 is flexible with respect to the average size of the A-cation.