Abstract: Single-phase polycrystalline samples of La_0.5Ca_0.5-xBa_xMnO₃ (0.1≤ x≤0.5) were fabricated
by the solid state reaction method. With increasing the content of Ba doping, the structural transition occurs from cubic to orthorhombic.
The measurement of resistance as a function of temperature under zero field shows that the samples of lower doping behave a semiconducting
behavior in the whole studied temperature range, and a transition from semiconducting to metallic states appears in the samples x≥0.14. The
transition moves toward the high temperature region with increasing the doping content. The role of Ba doping on the Ca sites was discussed on
the basis of analyzing the experimental data.

Key words: CMR, double-exchange interaction, charge-ordering, average A-site ions radius