Strain engineering has emerged as a powerful tool to create new states of known materials with excellent performance. Here, we show a general and practically realizable method via interphase strain to obtain a new super tetragonality providing giant polarization. This method is illustrated for the case of PbTiO3, where we report a c/a ratio of up to 1.238 in epitaxial composite thin films, compared to that of 1.065 in bulk PbTiO3. These thin films of super-tetragonal structure possess an unprecedented giant remanent polarization, 236.3 μC/cm 2 , which is almost twice the value of all known ferroelectrics. The tetragonal phase is stable up to 725 °C as compared to the bulk's transition temperature of 490 °C. The present interphase strain approach could provide a new avenue to enhance the physical properties of materials with respect to their multiferroic, photonic, superconductor, and energy-harvesting behavior.
Hydrogen-related defects play crucial roles in determining physical properties of their host oxides. In this work, we report our systematic experimental and theoretical (based on density functional theory) studies of the defect states formed in hydrogenated-rutile TiO2 in gaseous H2 and atomic H. In gas-hydrogenated TiO2, the incorporated hydrogen tends to occupy the oxygen vacancy site and negatively charged. The incorporated hydrogen takes the interstitial position in atom-hydrogenated TiO2, forming a weak O-H bond with the closest oxygen ion, and becomes positive. Both states of hydrogen affect the electronic structure of TiO2 mainly through changes of Ti 3d and O 2p states instead of the direct contributions of hydrogen. The resulted electronic structures of the hydrogenated TiO2 are manifested in modifications of the electrical and optical properties that will be useful for the design of new materials capable for green energy economy.
The ferroelectric doped BiFeO3thin films exhibit large resistive switching (with ON/OFF ratios ∼104) and stably switchable photovoltaic response with good retention properties, providing multiple selections for non-destructive ferroelectric memory diveces.
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