Perovskite oxides have provided magical structural models for superconducting and colossal magnetoresistance, and the search for nano-scale and/or atomic-scale devices with particular property by specific preparations in the same systems has been extensively conducted. We present here the three oxidation states of manganese (Mn3+, Mn4+, Mn5+) in the perovskite oxide, La0.66Ca0.29K0.05MnO3, which most interestingly shows the rectifying effect as atomic-scale p-n junctions (namely FY-Junctions) of single crystals and films. The family of cubic perovskite oxides were synthesised by the so-called hydrothermal disproportionation reaction of MnO2 under the condition of strong alkali media. The new concept of the atomic-scale p-n junctions, based on the ideal rectification characteristic of the p-n junctions in the single crystal, basically originates from the structural linkages of [Mn3+-O-Mn4+-O-Mn5+], where Mn3+ (t(2g)(3)e(g)(1)) and Mn5+ (t(2g)(2)e(g)(0)) in octahedral symmetry serve as a donor and an acceptor, respectively, corresponding to the localized Mn4+ (t(2g)(3)e(g)(0)).