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Yokohama-shi, Japan

Takahashi M.,Ehime University | Okabe N.,Ehime University | Abe Y.,Toshiba Material Co. | Fujiki K.,Ehime University | Kanbayashi R.,Ehime University
Fatigue and Fracture of Engineering Materials and Structures | Year: 2012

Ceramic balls have been used as components of devices, such as those found in high-pressure pumps for automobiles and industrial machines. In the backflow valve, for example, a ceramic ball is in contact with a conical surface. Fractures of ceramic balls are extremely rare. It is important to investigate the cause of these rare fractures to guarantee higher reliability in the backflow valve. In this paper, the fracture mechanism and strength are discussed for an equivalent normal stress σ eq beneath the contact region and the maximum principal stress σ p near the contact boundary using stress intensity from fracture mechanics. The fracture surface of the ceramic ball was formed perpendicular to load direction. We assumed that fracture origins (defect/crack) existed on lines through three high stresses that analysed by finite element method. Actual fracture of a ceramic ball was found to be caused by the equivalent normal stress beneath contact region and not to be caused by the Hertz principal stress. Stress intensity factor (SIF) was clarified to depend on pressure, taper angle, CrN-coating thickness and the friction factor of the inside of the valve hole. A pre-existing defect size involved in failure was estimated by the SIF using three-dimensional elliptic defects and equivalent normal stress. Therefore, the actual fracture of a ceramic ball, which rarely occurs, could be evaluated by considering three-dimensional elliptic defects and the Weibull distribution of defects. © 2011 Blackwell Publishing Ltd.

Fukuda Y.,Toshiba Corporation | Matsuda N.,Toshiba Corporation | Matsuda N.,Toshiba Material Co. | Okada A.,Toshiba Corporation | Mitsuishi I.,Toshiba Corporation
Japanese Journal of Applied Physics | Year: 2012

We have successfully developed a white light-emitting diode (LED) for a wide-color-gamut backlight composed of a green-emitting phosphor Sr 3Si13Al3O2N21:Eu 2+ combined with a blue LED and a red-emitting phosphor CaAlSiN 3:Eu2+. This white LED showed a discrete spectrum with distinct separation of red, green, and blue primary colors due to a narrow emission band of around 525nm for the green phosphor. 94.2% of the wide color gamut of the National Television System Committee standard was attained by applying typical color filters of LCDs. The power LED module composed of 16 of these white LEDs revealed their excellent power dependence. The LED is expected to replace cold cathode fluorescent lamp (CCFL), and find a suitable application as a backlight in large-scale LCDs for in-vehicle use or for flat-panel television sets. © 2012 The Japan Society of Applied Physics.

Sasaki A.,Toshiba Material Co. | Kataoka Y.,Toshiba Material Co. | Aoki K.,Toshiba Material Co. | Saito S.,Toshiba Material Co. | And 4 more authors.
Japanese Journal of Applied Physics | Year: 2015

We studied a novel method of increasing the efficiency of solar cells using BaSi2 as a semiconductor. BaSi2 could be deposited by RF magnetron sputtering using a polycrystalline BaSi2 target, followed by annealing at 500°C for 30 min in N2 ambient. Furthermore, Schottky-type solar cells using BaSi2 were fabricated. The crucial point is that Al-Nd was used to form the Schottky junction between the BaSi2 film and the Al-Nd electrode. Additionally, Si3N4 (3-5 nm) was used as an oxidation prevention layer. Under irradiation at 90 K, resulting in a short-circuit current density (Jsc) of 3.19 mA/cm2, an open-circuit voltage (Voc) of 0.76 V, and a fill factor (FF) of 0.28 were obtained. © 2015 The Japan Society of Applied Physics.

Li W.,Tokyo Institute of Technology | Sasaki A.,Toshiba Material Co. | Oozu H.,Toshiba Material Co. | Aoki K.,Toshiba Material Co. | And 8 more authors.
Microelectronics Reliability | Year: 2015

Although a large amount of research on Li ion transportation has been carried out with the aim of improving the properties of lithium ion batteries, there has been little detailed research on electron conduction. Hence, we have been focusing on improving the charge/discharge performance of lithium ion batteries by increasing the electron conductivity of the electrodes. The electron conductivity of crystalline tungsten trioxide (WO3) was found to be increased by N2 annealing owing to the generation of oxygen vacancies. It was clarified that increasing the conductivity of the electrodes can improve the performance of lithium ion batteries, particularly their charge/discharge speed and reversibility. Additionally, the best performance was observed in a sample subjected to high-temperature annealing at 700 °C in N2 ambient, which decreased the resistivity of the WO3 electrode by five orders of magnitude and simultaneously changed the monoclinic crystalline structure into a cubiclike structure into which Li ions are more easily intercalated. Therefore, to enhance the charge/discharge performance of lithium ion batteries, electron conduction should be a focus of research. Crystalline WO3 was also demonstrated to be a promising material for electrodes since oxygen vacancy generation can be induced by a simple annealing treatment, improving the electron conduction and Li ion transportation. © 2014 Elsevier Ltd.

Li W.,Tokyo Institute of Technology | Sasaki A.,Toshiba Material Co. | Oozu H.,Toshiba Material Co. | Aoki K.,Toshiba Material Co. | And 8 more authors.
Microelectronics Reliability | Year: 2015

We report a new approach for improving the recharging and discharging speed of lithium ion batteries based on understanding of the electron conduction mechanism of tungsten trioxide (WO3) powder thin films fabricated from nanoparticles and used in lithium ion battery electrodes. Resistivity measurements are carried out after annealing in N2 or 5% O2 + 95% N2 ambient. Annealing in N2 ambient decreases the resistivity owing to the increased number of oxygen vacancies in the WO3 thin film. Fitting results obtained from the resistivity are used to propose the simultaneous existence of two types of electron conduction mechanism, band conduction and nearest-neighbor hopping (NNH) conduction, contributing to electron conduction in WO3 thin films. © 2014 Elsevier Ltd.

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