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Zhou W.,East China Normal University | Deng H.,Shanghai Research Institute of Materials | Yang P.,East China Normal University | Chu J.,East China Normal University
Applied Physics Letters | Year: 2014

Structural phase transition, narrow band gap (Eg), and room-temperature ferromagnetism (RTFM) have been observed in the [KNbO3]1-x[BaNi1/2Nb1/2O3-δ]x(KBNNO) ceramics. All the samples have single phase perovskite structure, but exhibit a gradual transition behaviour from the orthorhombic to a cubic structure with the increase of x. Raman spectroscopy analysis not only corroborates this doping-induced change in normal structure but also shows the local crystal symmetry for x 0.1 compositions to deviate from the idealized cubic perovskite structure. A possible mechanism for the observed specific changes in lattice structure is discussed. Moreover, it is noted that KBNNO with compositions x = 0.1-0.3 have quite narrow Egof below 1.5 eV, much smaller than the 3.2 eV band gap of parent KNbO3(KNO), which is due to the increasing Ni 3d electronic states within the gap of KNO. Furthermore, the KBNNO materials present RTFM near a tetragonal to cubic phase boundary. With increasing x from 0 to 0.3, the magnetism of the samples develops from diamagnetism to ferromagnetism and paramagnetism, originating from the ferromagnetic-antiferromagnetic competition. These results are helpful in the deeper understanding of phase transitions, band gap tunability, and magnetism variations in perovskite oxides and show the potential role, such materials can play, in perovskite solar cells and multiferroic applications. © 2014 AIP Publishing LLC. Source


Background: A connection between a low alloy steel pressure vessel nozzle and a stainless steel main pipe safe-end in a pressurized water reactor (PWR) nuclear power plant is a dissimilar metal weld, which is at key location of pressure boundary and serves in high temperature primary water environments. Since 1990, cracking failure incidents happened on the welds in the primary water coolant of several PWRs in the countries such as USA, Sweden and Japan. Purpose: This paper is to briefly review the typical cases involving this problem in engineering and relevant researches. Methods: Methods such as nondestructive testing, crack and microstructure observation, finite element analysis were used in the failure analysis. Results: The cause of the failure cases was primary water stress corrosion cracking (PWSCC). Conclusions: It is concluded that the welds of 600 Alloy type such as 82/182 are susceptible to PWSCC but those of 690 Alloy Type such as 52/152 have excellent resistance to the cracking, and more researches are necessary. Source


Huang D.,East China Normal University | Deng H.,Shanghai Research Institute of Materials | Yang P.,East China Normal University | Chu J.,East China Normal University
Materials Letters | Year: 2010

Single-phase multiferroic BiFeO 3 thin films have been prepared on LaNiO 3/Si(100) and Si(100) wafer via sol-gel technique. The films are polycrystalline with preferring orientation of (101). The film has a conspicuous absorption in the blue and green light region, and band gap of 2.74 eV. The refractive index and the extinction coefficient of the film is about 2.36 and 0.06 at 600 nm, 2.26 and close to zero in the range of 800-1200 nm, respectively. The films also exhibit favorable ferroelectric and dielectric properties. A large photo induced open-circuit voltage was observed, indicating that the film exhibits photovoltaic behaviours. © 2010 Elsevier B.V. All rights reserved. Source


Ding N.,East China Normal University | Deng H.,Shanghai Research Institute of Materials | Yang P.,East China Normal University | Chu J.,East China Normal University
Materials Letters | Year: 2012

Multiferroic BiFe 1 - xZn xO 3 (0 ≤ x ≤ 0.10) thin films were prepared on LaNiO 3 coating Si substrates by pulsed laser deposition. X-ray diffraction data confirmed the substitutions of Zn into the Fe site. The films are the dominant orientation of (101). Three A 1 and five E modes are observed in Raman spectra. With increasing x, the position of the Raman active modes shift to higher wavenumber, and the full width at half maximum becomes smaller. At the photon energy of 2 eV, the refractive index is 2.71, and the extinction coefficient is close to zero. The band gap increases with the Zn amount, which may be caused by Burstein-Moss effect. © 2012 Elsevier B.V. All rights reserved. Source


Yu M.,Shanghai JiaoTong University | Zhu P.,Shanghai JiaoTong University | Ma Y.,Shanghai Research Institute of Materials
Computational Materials Science | Year: 2012

Tensile properties are critical to the engineering applications of hollow spheres filled syntactic foams. The potential of such composites cannot be fully realized unless their fracture modes and failure mechanisms under tension are fully understood, and appropriate modeling strategies for failure prediction are developed and verified. In this study, both experimental and numerical methods were employed to investigate the tensile behaviors of epoxy-ceramic microspheres syntactic foams with different volume fractions of filler phase. The experimental results indicate that mechanical behaviors of syntactic foams are dominated by brittle fracture mechanism under tensile load. To predict the mechanical properties of syntactic foams in terms of tensile strength and associated failure modes, a three-dimensional microstructure based finite element model was developed by means of a representative volume element (RVE). Cohesive elements were introduced into the finite element model to capture the progressive damage behavior of the microsphere-matrix interface. Complex failure modes of syntactic foams including microspheres fracture, interfacial debonding and the interaction of both features were well characterized according to the simulation results. The proposed model interprets the entire failure process from damage to fracture under tension and provides predictive capabilities for the strength properties of hollow spheres filled syntactic foams. By comparison, the simulation results and the experimental data are found to be in good agreement. © 2012 Elsevier B.V. All rights reserved. Source

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