Abstract: The complex oxide compounds Ln_0.67Sr_0.33MnO₃(Ln=La, Pr?, Nd, Sm) were synthesized through co-precipitation route. Compared with the
traditional ceramic sintering method, the temperature at which the compounds were formed were reduced by about 450℃. The X-ray powder diffraction patterns indicated that the structure of the compounds belongs to cubic perovskite-type phase and their crystal
unit parameters vary with the radius of rare earth ions regularly. The resistivity of samples was measured by a standard four-probe method. The results show that the radius of rare
earth ion is crucial to the ability of electric conduction of the compounds. The double exchange theory can only explain our experimental results partially. The autors deduced that the
electrons of 4f state of rare earth ions may play a role in electric conduction.

Key words: co-precipitation, perovskite-type phase, ion radius, electric conduction