Qingyuan Hu

Reverse boundary layer capacitor model in glass/ceramic composites for energy storage applications

Reverse boundary layer capacitor (RBLC) configuration model, where the grain boundary has a higher electrical conductivity than the grain, is proposed in glass/ceramic composites for dielectric energy storage applications. By introducing glass additives as grain boundaries with electrical conductivity higher than ceramic grains, the steady electric field across grains can be larger than grain boundaries as desired due to the conductivity difference. The breakdown field is thus expected to increase in the RBLC-type brick wall model because of the field distribution. The equivalent circuit, grain boundary conductivity dependence of energy density, low-loss frequency range of the RBLC model are discussed. The simulation results suggest that the RBLC approach has advantages in overall energy density, compared with normal insulating glass phase composites.

Symmetry changes during relaxation process and pulse discharge performance of the BaTiO3-Bi(Mg1/2Ti1/2)O3 ceramic

Lead free relaxor ferroelectrics have attracted continuing interest due to their outstanding and eco-friendly properties. In this paper, dielectric relaxation behavior of the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic (BT-40BMT), which is a typical lead free relaxor ferroelectric, is theoretically and experimentally investigated. At first, the observed dielectric relaxation was quantitatively characterized by a statistical model, indicating that the minority co-related polar nano regions (PNRs) dominate the total polarization. Kinetics of the PNRs were subsequently studied by micro-Raman measurements performed at various temperatures. Here, the relaxation of written domains formed by the piezoresponse force microscopy (PFM) tip-bias induced electric field was also studied, which describes the polarization retention performance of BT-40BMT. The absence of ferroelectric signal contribution in local switching was also confirmed by the contact mode Kelvin PFM technique, indicating the lack of local ferroelectricity. Moreover, the temperature insensitive energy storage property from 293 K to 443 K was obtained. High voltage pulsed discharge behavior was also investigated by using the pulsed current. A power density of 7.9 × 108 W/kg is obtained under a pulsed voltage of 50 kV. Combined with the fast discharge time, the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic is considered as a candidate material for high voltage pulse power applications.Lead free relaxor ferroelectrics have attracted continuing interest due to their outstanding and eco-friendly properties. In this paper, dielectric relaxation behavior of the 0.6BaTiO3-0.4Bi(Mg1/2Ti1/2)O3 ceramic (BT-40BMT), which is a typical lead free relaxor ferroelectric, is theoretically and experimentally investigated. At first, the observed dielectric relaxation was quantitatively characterized by a statistical model, indicating that the minority co-related polar nano regions (PNRs) dominate the total polarization. Kinetics of the PNRs were subsequently studied by micro-Raman measurements performed at various temperatures. Here, the relaxation of written domains formed by the piezoresponse force microscopy (PFM) tip-bias induced electric field was also studied, which describes the polarization retention performance of BT-40BMT. The absence of ferroelectric signal contribution in local switching was also confirmed by the contact mode Kelvin PFM technique, indicating the lack of local ferroelectricit...

Direct observation of the domain kinetics during polarization reversal of tetragonal PMN-PT crystal

Lead magnesium niobate-lead titanate (PMN-PT) solid solutions are intensively studied for the last two decades due to their outstanding piezoelectric properties. However, despite the strong interest, there is a lack of studies of domain kinetics and domain structure evolution, which are of great importance for the development of domain engineering in PMN-PT. We present the results of the domain kinetics study during polarization reversal in tetragonal PMN-PT single crystals by in situ optical visualization accompanied by analysis of the switching current. Three types of domain structure evolution have been revealed: (1) formation and growth of macroscopic a-domains, (2) formation of charged domain walls as a result of intersections of macroscopic a-domains, and (3) formation and growth of c-domains. The domain wall motion velocities were estimated. It has been shown by comparison of the switching current and optical one that the main switching current peak is related to the growth of c-domains, whereas the small one is caused by the capacitive input of the charged domain walls. The enhancement of dielectric permittivity by two orders of magnitude due to the appearance of the charged domain walls has been revealed. The difference of forward and reverse polarization reversals was attributed to the clamped switching conditions.Lead magnesium niobate-lead titanate (PMN-PT) solid solutions are intensively studied for the last two decades due to their outstanding piezoelectric properties. However, despite the strong interest, there is a lack of studies of domain kinetics and domain structure evolution, which are of great importance for the development of domain engineering in PMN-PT. We present the results of the domain kinetics study during polarization reversal in tetragonal PMN-PT single crystals by in situ optical visualization accompanied by analysis of the switching current. Three types of domain structure evolution have been revealed: (1) formation and growth of macroscopic a-domains, (2) formation of charged domain walls as a result of intersections of macroscopic a-domains, and (3) formation and growth of c-domains. The domain wall motion velocities were estimated. It has been shown by comparison of the switching current and optical one that the main switching current peak is related to the growth of c-domains, whereas th...