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

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, SrPb2O3 and BaPb2O3, which have larger chemical potential stability ranges compared with the corresponding Sn(II) oxides, and additionally two other ternary Pb(II) oxides, CaPb2O3 and BaPbO2, 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 (PbO3)(4) (-)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 (CaPb2O3 and SrPb2O3) show rather light hole effective masses (around 2m(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.