Layered perovskite Ca2.91Na0.09Ti2-xRhxO7 (x?=?0.00, 0.02, 0.04, 0.06) were synthesized by a conventional solid-state reaction. Room temperature ferroelectricity has been confirmed. The remanent polarization increases with an increase of Rh content, which is due to a larger oxygen octahedral distortion by Rh doping. The coercive field increases with Rh doping as the pinning effect of oxygen vacancies reduce the mobility of domain wall. Remanent polarization and coercive field are caused by different mechanisms, so it is possible to modulate them independently to meet the requirement of application in ferroelectric field. The concentration of oxygen vacancy increased with Rh doping, leading to the significant increase of leakage current density. The bandgap of samples doped with Rh drastically decrease and the visible light response of the sample was improved by Rh doping due to the formation of impurity energy levels within the band gap.
An experimental-numerical method for measuring dynamic crack propagating velocities under stress wave loading is established in this paper. The experiments of the three-point bend specimen are done on the improved Hopkinson bar. Deflection of loading point, dynamic load and instantaneous crack length are measured, then crack propagating velocities are calculated. Experiments on 40Cr steel show that the results given by this method have a good agreement with that obtained by the resistance fracture gage method. Therefore this method is feasible for measuring crack propagating velocities under high loading rate and will have wide application. 相似文献