Structural and electronic properties of Cu₄O₃ (paramelaconite): the role of native impurities

Hybrid density functional theory has been used to study the phase stability and formation of native point defects in Cu₄O₃. This intermediate copper oxide compound, also known as paramelaconite, was observed to be difficult to synthesize due to stabilization issues between mixed-valence Cu¹⁺ and Cu²⁺ ions. The stability range of Cu₄O₃ was investigated and shown to be realized in an extremely narrow region of phase space, with Cu₂O and CuO forming readily as competing impurity phases. The origin of p-type conductivity is confirmed to arise from specific intrinsic copper vacancies occurring on the 1+ site. Away from the outlined stability region, the dominant charge carriers become oxygen interstitials, impairing the conductivity by creating deep acceptor states in the electronic band gap region and driving the formation of alternative phases. This study further demonstrates the inadequacy of native defects as a source of n-type conductivity and complements existing experimental findings.