A transmission electron microscope and group theoretical study of the new Bi-based high-Tcsuperconductors and some closely related Aurivillius phases

Novel layered Bi3MoMTO9 (MT = Mn, Fe, Co and Ni) thin films with tunable multifunctionalities

Bi3MoMTO9 (BMoMTO; MT, transition metals of Mn, Fe, Co and Ni) thin films with a layered supercell structure have been deposited on LaAlO3 (001) substrates by pulsed laser deposition. Microstructural analysis suggests that pillar-like domains with higher transition metal concentration (e.g., Mn, Fe, Co and Ni) are embedded in the Mo-rich matrix with layered supercell structures. The layered supercell structure of the BMoMTO thin films accounts for the anisotropic multifunctionalities such as the magnetic easy axis along the in-plane direction, and the anisotropic optical properties. Ferroelectricity and ferromagnetism have been demonstrated in the thin films at room temperature, which confirms the multiferroic nature of the system. By varying the transition metal MT in the film, the band gaps of the BMoMTO films can be effectively tuned from 2.44 eV to 2.82 eV, while the out-of-plane dielectric constant of the thin films also varies. The newly discovered layered nanocomposite systems present their potential in ferroelectrics, multiferroics and non-linear optics.

Statistical estimation of atomic positions from exit wave reconstruction with a precision in the picometer range

The local structure of Bi4W2/3Mn1/3O8Cl is determined using quantitative transmission electron microscopy. The electron exit wave, which is closely related to the projected crystal potential, is reconstructed and used as a starting point for statistical parameter estimation. This method allows us to refine all atomic positions on a local scale, including those of the light atoms, with a precision in the picometer range. Using this method one is no longer restricted to the information limit of the electron microscope. Our results are in good agreement with x-ray powder diffraction data demonstrating the reliability of the method. Moreover, it will be shown that local effects can be interpreted using this approach.