K and Rb substitution effects in Na layer of Na0.75CoO2 oxide are reported. K substitution caused elongation of lattice parameter c, while Rb substituted sample did not have such effect. Transport properties measured showed that all samples are metallic. Rb substitution eliminates characteristic transition point from ÃÂT curves at room temperature. High temperature electrical resistivity measurements revealed, that Rb substitution significantly reduced sodium cation migration in the samples.