Three oxidation states and atomic-scale p–n junctions in manganese perovskite oxide from hydrothermal systems

Abstract

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, La_0.66Ca_0.29K_0.05MnO₃, 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⁺ ${\left( {{\text{t}}^{{\text{3}}}_{{{\text{2g}}}} {\text{e}}^{1}_{{\text{g}}} } \right)}$ and Mn⁵⁺ ${\left( {{\text{t}}^{{\text{2}}}_{{{\text{2g}}}} {\text{e}}^{{\text{0}}}_{{\text{g}}} } \right)}$ in octahedral symmetry serve as a donor and an acceptor, respectively, corresponding to the localized Mn⁴⁺ ${\left( {{\text{t}}^{{\text{3}}}_{{{\text{2g}}}} {\text{e}}^{{\text{0}}}_{{\text{g}}} } \right)}$.