New Quasi Low-Dimensional 4d and 5d Transition Metal Oxides with Correlated Electronic Properties - Synthesis and Characterizations

Abstract : Polar oxides are of much interest due to their symmetry-dependent properties including ferroelectricity/multiferroics, magnetoelectricity, piezoelectricity, pyroelectricity, and second-order harmonic generation (SHG) effect, which are all important for technological applications.[1] However, polar crystal design and synthesis is challenging, because multiple effects, such as steric or dipole-dipole interactions, typically combine to form non-polar structures, and the number of known polar, especially magnetoelectric materials, is still extremely few.[2] Therefore, as one of the focus of this program, we embarked on high pressure (HP) and high temperature (HT) synthesis to find new interesting and potentially useful polar materials. As will be shown here, we have been exceedingly successful, and opened a new path to design new polar and potentially multifunctional useful materials with corundum-type structure of general formula A2BBO6. In addition,HP and HT were also used to prepare new metastable double perovskites and quadruple perovskites with unusual structures and properties. In addition, ambient pressure and more conventional solid state methods to synthesize new phases with 3d, 4d and 5d transition metals and exotic correlated electronic properties was used in parallel with the HP/HT projects. As the results enumerated below show, a large number of new materials were synthesized; their physical properties were characterized indetail with a multitude of state-of-the-art techniques, and coupled experiment and theory lead to deeper understanding of the observed properties, as well as guiding synthesis of new phases.