Electronic structures and optical properties of cuprous oxide and hydroxide
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Electronic structures and optical properties of cuprous oxide and hydroxide Yunguo Li, Cláudio M. Lousada and Pavel A. Korzhavyi Division of Materials technology Department of Materials and Engineering, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden ABSTRACT The broad range of applications of copper, including areas such as electronics, fuel cells, and spent nuclear fuel disposal, require accurate description of the physical and chemical properties of copper compounds. Within some of these applications, cuprous hydroxide is a compound whose relevance has been recently discovered. Its existence in the solid-state form was recently reported. Experimental determination of its physical-chemical properties is challenging due to its instability and poop crystallinity. Within the framework of density functional theory calculations (DFT), we investigated the nature of bonding, electronic spectra, and optical properties of the cuprous oxide and cuprous hydroxide. It is found that the hybrid functional PBE0 can accurately describe the electronic structure and optical properties of these two copper(I) compounds. The calculated properties of cuprous oxide are in good agreement with the experimental data and other theoretical results. The structure of cuprous hydroxide can be deduced from that of cuprous oxide by substituting half Cu+ in Cu2O lattice with protons. Compared to Cu2O, the presence of hydrogen in CuOH has little effect on the ionic nature of Cu–O bonding, but lowers the energy levels of the occupied states. Thus, CuOH is calculated to have a wider indirect band gap of 2.73 eV compared with the Cu2O band gap of 2.17 eV. INTRODUCTION Copper has been used for thousands of years for a variety of purposes most often as pure metal [1,2]. At present, it is the most suitable candidate material for the longtime storage of highlevel radioactive spent nuclear waste in a deep underground repository [3,4]. Such application requires accurate knowledge of the behavior of copper under deep geological conditions. Among the copper compounds containing oxygen and hydrogen, the monovalent copper (cuprous) compounds [5,6] are less stable than the divalent compounds (in terms of formation energy), but are still very important in corrosion processes or in applications such as transparent electronics. Cuprous oxide Cu2O has been extensively studied and is well known for its prototypical ptype conducting behavior [7-11]. The cuprite crystal structure of Cu2O contains two sublattices: one Cu+ face-centered cubic and one O2 body-centered cubic. The conducting behavior has been attributed to the existence of Cu vacancies, VCu [11-14]. It has been reported that the Cu vacancies are the energetically favored sites for the incorporation of hydrogen impurities [9], which implies a relation between Cu2O and cuprous hydroxide CuOH. A crystalline form of cuprous hydroxide was recently studied with theoretical and experimental techniques [5,6]. Its atomic structure resembles that of Cu2O but with half of the Cu+ replaced by protons.
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