Preparation and crystallographic properties of Sr7-x(Ca/Ba)(x)Mn4O15

Polycrystalline samples of the new phases Sr(7-x)A(x)Mn(4)O(15) (A = Ca, Ba ; 0 less than or equal to x less than or equal to 1) and Sr7-2xCaxBaxMn4O15 (0 less than or equal to x less than or equal to 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 wit h 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 c omplicated behavior. The cell volume is linear dependent on the average ion ic radius of the A-cation, for all compounds. Ca enters the structure on th e small Sr(1) site, whereas Ba occupies the larger Sr(3) and Sr(4) sites. T he results show that the structure of Sr7Mn4O15 is flexible with respect to the average size of the A-cation. (C) 2001 Elsevier Science Ltd. All right s reserved.