A-site and B-site charge orderings of perovskite PbCoO$_{\mathrm{3}}$

Metal ions with half-integer valence tend to split into two integer valence ions and these get spatially ordered as typically observed in La$_{\mathrm{0.5}}$Ca$_{\mathrm{0.5}}$Mn$^{\mathrm{3.5+}}$O$_{\mathrm{3}}$ [1]. Perovskite PbCoO$_{\mathrm{3}}$ synthesized at 12 GPa was found to have an unusual average charge distribution of Pb$^{\mathrm{3.5+}}$Co$^{\mathrm{2.5+}}$O$_{\mathrm{3}}$ with half-integer valences in both of A and B sites. Comprehensive studies using electron diffraction (ED), synchrotron X-ray diffraction (SXRD), neutron powder diffraction (NPD) and measurements of magnetic and electrical properties provide evidence of lead ion and cobalt ion charge ordering leading to Pb$^{\mathrm{2+}}$Pb$^{\mathrm{4+}}_{\mathrm{3}}$Co$^{\mathrm{2+}}_{\mathrm{2}}$Co$^{\mathrm{3+}}_{\mathrm{2}}$O$_{\mathrm{12}}$ quadruple perovskite structure. Here we show that half-integer valence states in both the A and B sites can be stabilized by tuning the energy levels of Pb 6$s$ and transition metal 3$d$ orbitals. [1] P. G. Radaelli et al., Phys. Rev. B \textbf{55}, 3015--3023 (1997).