Prediction of ternary alkaline-earth metal Sn(II) and Pb(II) chlorides with potential applications as p-type transparent conductors

Non-metallic Sn(II) and Pb(II) compounds, particularly those with p-type properties, are essential functional materials due to their notable electronic arrangement and chemical characteristics. The presence of additional Sn(II) and Pb(II) chlorides is suggested by the existence of known Sn(II) and Pb(II) compounds. By utilizing first-principles calculations and swarm intelligence structure search techniques, we have predicted the existence of up to seven new ternary alkaline-earth metal chlorides: ABCl₄ (where A = Sr and B = Sn or Pb) and AB₂Cl₆ (where A = Mg, Ca, or Ba and B = Sn, or A = Ca or Sr and B = Pb). These seven chlorides are in the divalent state. The interaction between Sn-5s (or Pb-6s) and Cl-3p in these compounds creates an anti-bonding effect in the upper valence bands, which enhances defect tolerance and promotes high p-type conductivity. These stable chlorides exhibit notable electronic properties, including wide band gaps ranging from 3.91 to 4.94 eV, broad hole effective masses ranging from 0.93 to 5.62 m₀, and high valence band alignments ranging from 6.83 to 8.38 eV under vacuum. Specifically, Ca/BaSn₂Cl₆ and CaPb₂Cl₆ have the potential to be used as p-type transparent conductors due to their favorable properties, including a lower hole effective mass (0.93 m₀ for CaPb₂Cl₆) and higher ionization potentials (6.83/7.05 eV for Ba/CaSn₂Cl₆). Furthermore, the predicted CaPb₂Cl₆ crystal exhibits an attenuated negative linear compressibility and negative zero-linear-compressibility of the c-axis in different pressure ranges due to the wine-rack structure. This report highlights potential applications for alkaline-earth metal Sn(II) and Pb(II) chlorides, including their use as transparent conductors, particularly the p-type.