Narrow Results

Oxygen defects of nanoflower TiO₂ photo-catalyst was fabricated at the presence of hydrogen at different temperatures (100–600^∘C) and the concentrations of oxygen defects were firstly quantitatively analyzed by hydrogen programmed temperature reduction techniques (H₂-TPR). Total oxygen defect concentration and surface oxygen defect concentration were consistent with XPS and EPR results, respectively. Even at the hydrogen thermal temperature of 600^∘C, the shape of TiO₂ was still kept as nanoflower structure as characterized by SEM. However, the rutile and anatase coexist in the composition of crystal phase when hydrogen reduction temperature of the TiO₂ catalyst reached 400^∘C to 600^∘C as proved by Raman and XRD results. TiO₂ sample with oxygen defects shows excellent photo-catalytic activity for degradation of Direct Blue 78(DB) regardless of ultraviolet light (the maximum degradation rate achieved within 100min was 93.27%) or visible light (the maximum degradation rate achieved within 100min was 88.25%). The photo-catalytic activity seems to be highly correlated with the surface oxygen defects of TiO₂ catalyst. With surface oxygen-defect concentrations increase, the degradation ability on DB was significantly enhanced, while bulk oxygen defects had negligible effect on the photo-catalytic activity. The enhanced photo-catalytic performance of TiO₂ with a fixed amount of oxygen defects was attributed to the strong capturing capability of the photo-generated electrons. In addition, the surface defects could also improve the photo-catalytic reaction efficiency.

Ti₂${\text{Nb}}_{10}$${\text{O}}_{29}$ (TNO) is considered as a potential anode material due to its high capacity/power density and reliable safety. However, its poor electronic conductivity restricts its rate performance, which is important for its application in electric vehicles (EVs). In this study, we fabricated a hybrid of Ti₂${\text{Nb}}_{10}$${\text{O}}_{29-x}$/holey-reduced graphene oxide (TNO_x/HRGO) by a two-step method. In the structure of TNO_x/HRGO, TNO_x microspheres with oxygen vacancies are wrapped by gossamer-like HRGO. The oxygen vacancies of TNO_x and the high conductivity of HRGO can effectively enhance the electronic conductivity of the TNO_x/HRGO hybrid, and the HRGO holes are beneficial for the transmission of lithium-ion (${\text{Li}}^{+}$). The synergy effect of above features improves the rate performance of the TNO_x/HRGO hybrid. In addition, the existence of HRGO can buffer volume expansion during the insertion processes of ${\text{Li}}^{+}$, which can improve cyclic stability of the TNO_x/HRGO hybrid. Consequently, the TNO_x/HRGO electrode has excellent lithium-ion storage capacity, with high-rate performance (242mAh/g at 10^∘C, 225mAh/g at 20^∘C and 173mAh/g at 40^∘C) and excellent cyclic stability (98.0% capacity retention after 300 cycles at 10^∘C). This work reveals that TNO_x/HRGO can be a potential anode material for high-rate-performance lithium-ion storage.

Lead free (K_0.5Na_0.5)NbO₃ (KNN) ceramics were prepared by conventional solid state reaction route. For single perovskite phase formation, calcination temperature was optimized at 850°C for 6 h, whereas for dense morphology the sintering of the ceramic was carried out at 1120°C for 4 h. X-ray diffraction XRD analysis confirmed the formation of single phase with orthorhombic structure at room temperature. Impedance analysis and AC conductivity studies of the KNN sample was carried out in the temperature range of 703–773 K. Impedance study showed the increase in conducting behavior at higher temperature. The temperature dependence of AC conductivity indicated that the conduction process is due to doubly ionized oxygen vacancies in the higher temperature region.

Solid solutions on the base of composition from morphotropic phase boundary (1–x)BiScO₃–xPbTiO₃ with x = 0.64, 0.645, 0.65 were prepared from nitrates solutions. Variations in phase content, structure parameters, microstructure, dielectric and piezoelectric properties of dense ceramic samples were studied. The first-order phase transitions were observed at temperatures near 700 K. The influence of the processing conditions on the morphology, temperature of phase transitions, and dielectric parameters was observed. In some ceramics effect of dielectric relaxation was observed at high temperatures. This effect was explained by the contribution from ionic transport due to the oxygen vacancies creation during high temperature sintering.

The theoretical possibility of the temperature-activation process of the temperature dependence of the dielectric constant of samples of ferroelectric ceramics lead zirconate titanate (PZT) at temperatures below the Curie point is considered. The model takes into account the 180° motion of the domain wall, which is located in the potential well. The values of activation energies ($\sim$ 0.01, 0.1, 1 eV) were obtained from the experimental dependences of the logarithm of the dielectric constant on the reciprocal temperature. This is associated with three processes: initial vibrations of domain walls; separation of domain walls (DWs) from oxygen vacancies; the motion of DWs as a result of the motion of oxygen vacancies.

High-density ferroelectric BiFeO₃ (BFO) nanodot arrays were developed through template-assisted tailoring of epitaxial thin films. By combining piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM) imaging techniques, we found that oxygen vacancies in nanodot arrays can be transported in the presence of an electric field. Besides triple-center domains, quadruple-center domains with different vertical polarizations were also identified. This was confirmed by combining the measurements of the domain switching and polarization vector distribution. The competition between the accumulation of mobile charges, such as oxygen vacancies, on the interface and the geometric constraints of nanodots led to the formation of these topological domain states. These abnormal multi-center topological defect states pave the way for improving the storage density of ferroelectric memory devices.

Most widely used dielectrics for MLCC are based on BaTiO₃ composition which inevitably shows performance degradation during the application due to the migration of oxygen vacancies ($V_{\mathrm{o}}^{\cdot \cdot }$). Here, the BaTiO₃, (${\text{Ba}}_{0.97}$${\text{Ca}}_{0.03}$)TiO₃, Ba(${\text{Ti}}_{0.98}$${\text{Mg}}_{0.02}$)O₃, (${\text{Ba}}_{0.97}$${\text{Ca}}_{0.03}$)(${\text{Ti}}_{0.98}$${\text{Mg}}_{0.02}$)O₃, (${\text{Ba}}_{0.96}$${\text{Ca}}_{0.03}$${\text{Dy}}_{0.01}$)(${\text{Ti}}_{0.98}$${\text{Mg}}_{0.02}$)O₃ ceramics (denoted as BT, BCT, BTM, BCTM and BCDTM, respectively) were prepared by a solid-state reaction method. The core-shell structured grains ($\sim$200 nm) featured with 10-20 nm wide shell were observed and contributed to the relatively flat dielectric constant-temperature spectra of BTM, BCTM and BCDTM ceramics. The TSDC study found that the single/ mix doping of Ca${}^{2+}$, especially the Mg${}^{2+}$, Mg${}^{2+}$/Ca${}^{2+}$ and Mg${}^{2+}$/Ca${}^{2+}$/Dy${}^{3+}$ could limit the emergence of $V_{\mathrm{o}}^{\cdot \cdot }$ during the sintering and suppress its long-range migration under the electric-field. Because of this, the highly accelerated lifetimes of the ceramics were increased and the value of BCDTM is 377 times higher than that of BT ceramics. The $p-n$ junction model was built to explain the correlation mechanism between the long-range migration of $V_{\mathrm{o}}^{\cdot \cdot }$ and the significantly increased leakage current of BT-based dielectrics in the late stage of HALT.