Yanyu Liu

Room-temperature ferromagnetism and optical properties in Mg-doped TiO2: A density functional theory investigation

The magnetic and optical properties of Mg-doped anatase TiO2 have been theoretically investigated using the LDA+U method. The total induced moments are about 2 μB, which mainly localize on the nearest apical oxygen atoms. Moreover, the hole-induced interactions indicate that the magnetic moments prefer to the ferromagnetic coupling with the antiferromagnetic state lying 1160 meV higher in energy. This implies that the ferromagnetic state can be stable against thermal fluctuations up to room temperature. Additionally, the Mg doping is able to enhance the absorption efficiency of solar spectrum, especially in the near-infrared light region, which origins from the isolated O 2p states above the valence-band maximum rather than the effect of band-gap narrowing.

Electronic structure and optical properties of Ta-doped and (Ta, N)-codoped SrTiO3 from hybrid functional calculations

A systematic study has been carried out to research the effect of Ta monodoping and (Ta, N)-codoping on the electronic structure and optical properties of SrTiO3. The results indicate that the incorporation of N into the SrTiO3 lattice is in favor of the substitution of Ta at a Ti site, which is the most favorable structure with respect to both the energetic stability and high photocatalytic activity. Furthermore, the carrier recombination centers induced by Ta monodoping are passivated in the (Ta, N)-codoped SrTiO3 system with Ta at a Ti site. Simultaneous incorporation of N and Ta results in a band gap decreasing about 0.7 eV due to the appearance of the new states hybridized by N-p states with the O-p states above the valence band. The band alignment verifies that the (Ta, N)-codoped SrTiO3 simultaneously meets the criteria of band-edge energetic positions and band gap for the overall water splitting under visible light.

Unexpected ferromagnetism in n-type polycrystalline K-doped ZnO films prepared by RF-magnetron sputtering

The room temperature ferromagnetism in highly c-axis orientated K-doped ZnO polycrystalline films prepared by RF-magnetron sputtering were systematically investigated in this work. The decrease of n-type carriers and the enhanced acceptor-related photoluminescence with the K doping imply the formation of K substitution and Zn vacancy defects. It can be speculated that the room-temperature ferromagnetism observed in K-doped ZnO polycrystalline films is related with the hole. Since the saturation magnetization was positively dependent on the amount of hole defects based on the PL spectra analysis. The ferromagnetism coupling and the room temperature ferromagnetism obtained in K-doped ZnO polycrystalline films thus is originated from p–p coupling of the surrounding O atoms of the K substitution and Zn vacancy defects. The co-existing of both the n-type conductivity and the ferromagnetism induced by localized holes, which is much different from the previous report for epitaxial samples, give new insight into the behavior of d0 ferromagnetism in oxides.