New stable ternary alkaline-earth metal Pb(II) oxides: Ca/Sr/BaPb2O3 and BaPbO2

Abstract

The different but related chemical behaviors of Pb(II) oxides compared to Sn(II) oxides, and the existence of known alkali/alkali-earth metal Sn(II) ternary phases, suggest that there should be additional ternary Pb(II) oxide phases. Here, we report structure searches on the ternary alkaline-earth metal Pb(II) oxides leading to four new phases. These are two ternary Pb(II) oxides, ${\mathrm{SrPb}}_{2}{\mathrm{O}}_{3}$ and ${\mathrm{BaPb}}_{2}{\mathrm{O}}_{3}$, which have larger chemical potential stability ranges compared with the corresponding Sn(II) oxides, and additionally two other ternary Pb(II) oxides, ${\mathrm{CaPb}}_{2}{\mathrm{O}}_{3}$ and ${\mathrm{BaPbO}}_{2}$, for which there are no corresponding Sn(II) oxides. Those Pb(II) oxides are stabilized by Pb-rich conditions. These structures follow the Zintl behavior and consist of basic structural motifs of ${({\mathrm{PbO}}_{3})}^{4\ensuremath{-}}$ anionic units separated and stabilized by the alkaline-earth metal ions. They show wide band gaps ranging from 2.86 to 3.12 eV, and two compounds $({\mathrm{CaPb}}_{2}{\mathrm{O}}_{3}$ and ${\mathrm{SrPb}}_{2}{\mathrm{O}}_{3})$ show rather light hole effective masses (around $2{m}_{0})$. The valence band maxima of these compounds have a Pb-$6s$/O-$2p$ antibonding character, which may lead to $p$-type defect (or doping) tolerant behavior. This suggests alkaline-earth metal Pb(II) oxides may be potential $p$-type transparent conducting oxides.