Papers by Keyword: Oxygen Vacancy

Abstract: This review focuses on the recent developments of high temperature stable anatase TiO₂ photocatalyst. Eventhough TiO₂ exists in different forms anatase, rutile and brookite, anatase phase stabilization is often the key to obtain the highest photocatalytic performance for TiO₂, particularly for the use as an antibacterial and self-cleaning coatings in high temperature processed ceramics. Different methods available for the anatase stabilization in literature are critically reviewed and emphasis is placed on relatively recent developments. Currently available methods of anatase stabilizations are classified in to four categories viz (i) doping with metal ions (ii) doping with non-metal ions (iii) co-doping with metal and non-metal ions and (iv) dopant free stabilization by oxygen richness. Further to this, the application of these high temperature stabilized anatase TiO₂ photocatalyst on various ceramics substrates such as tile, glass and sanitary wares as self-cleaning and antibacterial coatings are also been briefly discussed.

Abstract: Pt/HfO_x/Pt resistive switching devices with symmetric electrodes were fabricated. Bipolar resistive switching (RS) behaviors and unipolar behaviors were then observed under a positive/negative bias applied to the top electrode (TE). A comparison and analysis of bipolar/unipolar RS behaviors under different voltage polarities was then performed.The results demonstrated that bipolar RS was achieved via a drift of anion (O^2-) under the electric field resulting in the rupture and recovery of filaments at the interface. When the filaments dissolved and formed at the interface near BE, the performance of the bipolar RS devices was better. However, for unipolar RS devices, when filaments dissolved and formed at the interface near TE, the performance was even better. These results indicated that a drift of O^2- caused by electric field and a diffusion of O^2- induced by Joule heat were the main reasons for unipolar RS. The different characteristics of the bipolar and unipolar devices can be attributed to the existence of a different number of defects at the active interface of the devices. This was where the rupture and recovery of filaments occurred. The results also indicate that the active interface is more important than other interfaces for RRAM performance.

Abstract: Ce_0.8Pr_0.2-xSm_xO_2-δ(x=0.02, 0.05, 0.1) solid solutions were synthesized by the sol-gel method. The XRD results show that all powders calcined at 800 °C are crystallized in a single cubic fluorite structure. The average grain sizes are between 19 nm and 28 nm. The Raman spectra analysis reveals that the solid solution Ce_0.8Pr_0.2-xSm_xO_2-δ has a cubic fluorite structure with oxygen vacancies. The oxygen vacancy concentration is increased by doping Sm in Ce_0.8Pr_0.2-xSm_xO_2-δ. Impedance spectra shows that the conductivity of rare earth co-doped ceria Ce_0.8Pr_0.15Sm_0.05O_2-δ is higher than that of single rare earth doped ceria Ce_0.83Sm_0.17O_2-y. The results also show that Ce_0.8Pr_0.15Sm_0.05O_2-δ possess maximum conductivity. At 600 °C, the conductivity is 1.20×10^-2S/cm, which is assigned to the higher oxygen vacancy concentration and the hopping electron transition of small polarons in the sample Ce_0.8Pr_0.15Sm_0.05O_2-δ.

Abstract: Ce_0.8Pr_0.2–xNd_xO_2-δ(x = 0.02, 0.05, 0.1) solid solutions were synthesized by the sol-gel method. The XRD results show that all powders calcined at 800 °C are crystallized in a single cubic fluorite structure. The average grain sizes are between 20 nm and 25 nm. The Raman spectra analysis reveals that the solid solution Ce_0.8Pr_0.2–xNd_xO_2-δ has a cubic fluorite structure with oxygen vacancies. The oxygen vacancy concentration is increased by doping Nd in Ce_0.8Pr_0.2–xNd_xO_2-δ. Impedance spectra shows that the conductivity of rare earth co-doped ceria Ce_0.8Pr_0.18Nd_0.02O_2-δ is higher than that of single rare earth doped ceria Ce_0.83Sm_0.17O_2−y. The results also show that Ce_0.8Pr_0.18Nd_0.02O_2-δ possess maximum conductivity. At 600 °C, the conductivity is 1.85×10^-2S/cm, which is assigned to the higher oxygen vacancy concentration and the hopping electron transition of small polarons in the sample Ce_0.8Pr_0.18Nd_0.02O_2-δ.

Abstract: A series of composites of the high photoactivity of {001} facets exposed BiOCl and grapheme sheets (GS) were synthesized via a one-step hydrothermal reaction. The obtained BiOCl/GS photocatalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), Ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy. The as-prepared BiOCl/GS photocatalyst showed enhanced photocatalytic activity for the degradation of methyl orange (MO) under UV and visible light (λ > 400 nm). The enhanced photocatalytic activity could be attributed to oxygen vacancies of the {001} facets of BiOCl/GS and the high migration efficiency of photo-induced electrons, which could suppress the charge recombination effectively.

Abstract: In this paper, the ZrInZnO thin film has been prepared by solution method. The influence of heat treatment conditions on film properties has been analyzed. With the treatment temperature and time increase, the Hall mobility and square resistance of the film were increased and reduced respectively. In addition, we analyzed the role of heavy metal Zr on oxygen vacancies in the semiconductor oxide combined with heat treatment results and the chemical reaction process. It has been found that heavy metal Zr has binding effect on oxygen, it effectively inhibits the generation of oxygen vacancies, thereby reducing the number of oxygen vacancies, but at the same time causing certain binding effect to carriers.

Abstract: Single crystal of ferroelectric (Bi,Na)TiO₃BaTiO₃ (BNTBT) with tetragonal P4mm structure grown by a top-seeded solution growth (TSSG) method at a high oxygen pressure (PO₂) of 0.9 MPa and their properties were compared with those of the crystals grown at a PO₂ of 0.1 MPa. The crystals obtained at PO₂ = 0.9 MPa exhibited a remanent polarization (P_r) of 54 μC/cm², which was much larger than those of the crystals grown at PO₂ = 0.1 MPa (20 μC/cm²). It is suggested that the large P_r is attributed to a low oxygen vacancy concentration.

Abstract: The insulation degradation of BaTiO₃-based ceramics under direct-current field is caused by the migration of oxygen vacancies. To improve the reliability of BaTiO₃-based ceramic capacitors, conventional approaches are focusing on dielectrics, mainly working on suppressing the total amount of oxygen vacancies towards the cathode. In this study, we newly focus NOT on the dielectrics but on the electrodes, and tried to improve the reliability of BaTiO₃-based ceramics by suppressing the segregation of migrated oxygen vacancies. La_0.8Sr_0.2MnO₃ (LSM) is a mixed ionic-electronic conductor that generates oxide ions from gas-phase oxygen. We expected that LSM would compensate for migrated oxygen vacancies when using it as the cathode of a BaTiO₃-based ceramic capacitor. The results of our highly-accelerated life tests indicate that the reliability of BaTiO₃-based ceramics improved when LSM porous ceramics was used only as the cathode, (NOT the anode).

Abstract: In this study oxygen vacancy concentration on 3Y TZP ceramics was compared for sintered and aged samples in air and argon gas atmosphere. The sintering study was conducted over the temperature range 1250°C - 1500°C. Photoluminescence (PL) spectrums of the sintered samples were taken by laser with excitation wavelength 325nm. Two distinctive sharp and broad peaks were observed for the wavelength ~ 615 nm and ~ 580 600nm. The sample sintered at 1250 °C showed higher oxygen vacancy in both atmospheres. At the same time, argon gas sintered sample showed higher oxygen vacancy than air sintered sample. The emission band blue shifted after 1 h ageing for the sample sintered in 1500 °C in both atmospheres. XRD results on 1 hour aged sample sintered in argon gas atmosphere showed higher monoclinic phase than air sintered sample.

Abstract: To enhance the conductivity and reduce the surface roughness of ZnO films, electrodeposition of ZnO films on the ITO substrate had been studied for the application of inverted organic solar cells. ZnO films with the grain size range from 0.4 to 2 μm had been fabricated by varying the temperature, ion concentration and deposition potentials. Moreover, ZnO films with the impurity energy level of 2.28±0.20 eV origin from the oxygen vacancy, had been found in the PL emission. It is found that as the applied potential went more negative, the concentration of the oxygen vacancies increased, and the emission peak of the impurity level had higher intensity. By changing the ion concentration and temperature of the electrolyte, the controllable microstructure and impurity levels of ZnO thin films had been achieved.