Prediction Of Novel CuO Structures And Their Electronic Properties

Among the transition metal oxides?TMOs?,copper oxides have attracted extensive attention due to its rich physical and prospective applications.The copper and oxygen atoms can form compounds by various ratios,such as Cu₂O,Cu₄O₃ and CuO,in which the copper atoms can carry different charge.Although people have carried out a lot of research for three-dimensional copper oxide materials,there are still some unresolved problems,such as the contradictory of the theoretical and experimental results about the magnetic of CuO structure.Theoretically,all CuO materials are known to be antiferromagnetic or paramagnetic.However,there are many reports about ferromagnetic CuO.Recently the two-dimensional materials extend to copper oxide structures.Some two-dimensional copper oxide structures have been proposed and some corresponding experimental studies have been conducted.These thin films exhibit properties completely different from those of bulk materials.The origin of ferromagnetism in three-dimensional CuO and the electronic properties of a special two-dimensional Cu₃O₂ film are reseached in this paper.Divided into five chapters.The first chapter briefly introduces the current development of copper oxide materials,electronic,superconductivity and magnetic properties of Kagome materials and electronic properties of half-metal materials.In the second chapter,we briefly introduce the first-principles calculation theory and the correction PBE+U method based on Hubbard.The third chapter,we propose a new zinc-blende CuO?ZB-CuO?allotrope.It is not only a ferromagnetic material but also a perfect half metal.Its spin-up bands cross over the Fermi level,while a gap of approximate 1.5 eV appears in the spin-down bands.The origination of the half metallicity is explained by crystal-field-theory and Stoner criterion.In addition,we calculate the superconductivity of this new CuO structure,showing a critical temperature Tc=4.6 K.Finally,we compare the X-ray diffraction patterns of the experimental samples and the ZB-CuO.The fourth chapter,we first study nine types of d orbital frustrations in a model of Kagome lattice.Each type of d orbitals generates a group of three states,one singlet and one doublet,which is somewhat similar to the p orbitals.Then we propose a new Cu₃O₂ monolayer similar to that reported in experimental,and study electron properties of the monolayer structure.In this structure,some types of d orbitals and corresponding frustration states are found.Each group of d orbitals generates a set of Kagome band.We think that spontaneous ferromagnetism of monolayer Cu₃O₂ is a result of collaboration of flat-band physics and strong exchange interactions of Cu atoms.At the same time,the monolayer structure is an intrinsic superconductor with a high critical temperature T_c=10.5 K.In addition,we also simulated the growth of SiC?111?substrates,laying the foundation for future experimental synthesis.The fifth chapter,we summarize the content of this paper and look forward to the future work.