Papers by Keyword: Oxygen Vacancy

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Authors: B. Pajot, S.A. McQuaid, R.C. Newman, C. Song, R. Rahbi
Authors: Pradeepan Periyat, Binu Naufal, Sanjay Gopal Ullattil
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.
Authors: Atsushi Honda, Shin'ichi Higai, Takafumi Okamoto, Noriyuki Inoue, Yasuhiro Motoyoshi, Nobuyuki Wada, Hiroshi Takagi
Abstract: We performed first-principles calculations to examine the interaction among rare-earth (RE), alkaline-earth (AE) elements and oxygen vacancy (VO) in BaTiO3, in order to clarify the combined effects of VO trapping by two different elements. It was found that there is a synergistic effect of VO trapping by RE at Ba site and AE at Ti site, so that the co-doping is effective to improve insulating reliability of BaTiO3. We also verified that the local atomic structures around dopants obtained by calculations well agree with that obtained experimentally by extended X-ray absorption fine structure (EXAFS) analyses. The present work is the first one to clarify the structural environment around dopants including VO by both theoretical and experimental approaches.
Authors: Xiao Rong Chen, Jie Feng
Abstract: Pt/HfOx/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 (O2-) 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 O2- caused by electric field and a diffusion of O2- 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.
Authors: Takashi Oyama, Nobuyuki Wada, Hiroshi Takagi
Abstract: The role of grain boundaries (GBs) in the diffusion of oxygen vacancies (VO••s) in barium titanate (BaTiO3) and its mechanism were investigated using atomistic simulation techniques. It was found that GBs trapped VO••s at specific sites in the course of the diffusion, and the excess energy reflecting structural distortion of the GB was closely related to the availability of the trapping. GBs therefore act as a resistance of the diffusion of VO••s, suggesting that electrical degradation of multilayer ceramic capacitors (MLCCs), which is derived from vacancy diffusion, enables to be additionally improved by controlling GB structures in BaTiO3-based dielectrics.
Authors: Atsushi Oshiyama
Authors: Makito Nakano, Akira Saito, Nobuyuki Wada
Abstract: The electrical degradation mechanisms of BaTiO3-based ceramics were investigated by measuring the dependence of leakage current on high electric fields. Before the degradation, the leakage current predominately obeyed Ohm’s law and Poole-Frenkel relation. As the degradation progressed, the Poole-Frenkel emission current increased. Moreover, the total current at the high electric fields also comprised Schottky emissions between cathodes and dielectric layers.
Authors: Takumi Hijii, Hiroko Amasaki, Tomoyasu Eguchi, Jun Kuwano
Authors: Xiao Fei Niu, Fu Rong Tu
Abstract: The monodisperse popcorn-like CeO2 nanostructures with crude surface covered by wrinkles completely and a diameter of 150-300 nm have been successfully synthesized by a facile hydrothermal technology. XRD, SEM, XPS, Raman scattering and M-H curve were employed to characterize the samples. The results showed that the popcorn-like CeO2 nanostructures have a cubic fluorite structure and there are Ce3+ ions and oxygen vacancies existing in their surface. The magnetic measurement indicated that the popcorn-like CeO2 nanostructures possess excellent ferromagnetism at room temperature, which can be attributed to the influences of the morphology of the particles, Ce3+ ions and oxygen vacancies.
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