The effects on structural and paramagnetic to ferromagnetic transitions by isovalent chemical substitution of smaller Ca2+ into the bigger Ba2+ sites in La-0.6(Ba0.4-xCax)MnO3 (0 less than or equal to x less than or equal to 0.4) are investigated. With increasing x, a change from the rhombohedral cell (space group: R-3c) to an orthorhombic cell (space group: Pbnm) is observed. For x greater than or equal to 0.3, the structural transformation leads to an increase in the Mn-O(1) bond length along the c-axis which corresponds to the Jahn-Teller distortion of the distorted MnO6 octahedra in the orthorhombic cell. This effect gives rise to a decrease in T-C (the temperature of the paramagnetic to ferromagnetic transition) with increasing Ca content. (C) 2002 Elsevier Science B.V. All rights reserved.