[en] The phase-change temperature and crystal structures of the δ-phase SbTe alloy for Sb contents of 64 at%, 72 at%, and 76 at% have been investigated. The δ-phase SbTe alloy has a rhombohedral crystal structure, and crystallization occurs in an extremely narrow temperature range of 140-145 C compared with Sb₄₀Te₆₀. We have determined the relationship between the Sb content and the crystalline structure using X-ray diffraction and selected area electron diffraction. When the Sb content increases, the number of Sb layers stacked with Sb₂Te₃ in the unit cell increases, which results in the lowering of the activation energy for crystallization and a lower ovonic threshold voltage. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Polycrystalline samples of Cu₃TaIn₃Se₇ and CuTa₂InTe₄ were synthesized by the usual melt and anneal technique. X-ray powder diffraction showed a single phase behavior for both samples with tetragonal symmetry and unit cell parameter values a=5.794±0.002 A, c=11.66±0.01 A, c/a=2.01, V=391±1 A³ and a=6.193±0.001 A, c=12.400 ±0.002A, c/a=2.00, V=475±1 A³, respectively. Differential thermal analysis (DTA) measurements suggested a complicated behavior near the melting point with several thermal transitions observed in the heating and cooling runs. From the shape of the DTA peaks it was deduced that the melting is incongruent for both materials. Magnetic susceptibility measurements (zero-field cooling and field cooling) indicated an antiferromagnetic character with transition temperatures of T=70 K (Cu₃TaIn₃Se₇) and 42 K (CuTa₂InTe₄). A spin-glass transition was observed in Cu₃TaIn₃Se₇ with T_f∼50 K. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Selective area metal-organic vapor phase epitaxy (SA-MOVPE) allows in-plane control of layer composition and thickness. The use of relatively wide (>10μm) selective masks brings about large wavelength modulation, taking advantage of vapor-phase diffusion of precursors. The wide masks, however, tend to induce nucleation on them, leading to much reduced and uncontrollable wavelength modulation. To obtain deposition selectivity between masks and crystal surface, hydrogen addition was proved to be effective by preventing GaN nucleation on masks. Consequently, the maximum growth rate enhancement of 4.8 and the photoluminescence peak shift of 54 nm (nominally 11% shift in the indium composition) were achieved for InGaN bulk layer. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

[en] Photoluminescence (PL) intensity of both a-plane and m-plane InN epilayers has been observed to strongly depend on polarization angle. The PL intensity for polarization perpendicular to c-axis (E perpendicular to c) is up to four times as that of polarization parallel to c-axis (E//c) for a-plane InN, and this ratio is up to seven times for m-plane InN. The absorption edges of a-plane samples for the two polarizations are separated by 19 meV, with (E//c) at higher energy side. The PL detected from sample edge also shows such anisotropy. X-ray diffraction experiments for a series of a-plane samples, taking orthorhombic distortion of lattice into account, have shown some samples are compressively strained along growth direction and others have negligible strain. With measured strain, the polarization anisotropy has been analyzed by comparing the experimental results with calculated transition energies and relative oscillator strengths including anisotropic in-plane strain. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

[en] Local lattice misorientations on crystalline substrates can be visualized by rocking curve imaging. Local deviations from Bragg peak positions are extracted from a series of digital topographs recorded by a CCD detector under different azimuths. Bragg peaks from surface regions such as crystallites with a larger local misorientation overlap on the detector, which requires a back-projection method in order to reconstruct the misorientation components on the sample surface from the measured angular position on the detector planes. From mathematical point of view, the reconstruction problem is an inverse problem. In this paper, we formulate the forward and back-projection problems and we prove the correctness of a particular solution. The usability of the method is demonstrated on a phantom data set. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

[en] Sliced SiC boule grown by physical vapor transport is investigated using synchrotron white beam phase contrast imaging combined with Bragg diffraction. The evolution of defects is revealed. In the early growth stage, foreign polytype inclusions not only induce massive generation of full-core dislocations and dislocated micropipes but also attract them, forming slit-type pores at the boundaries of inclusions. In the intermediate stage, when inclusions stop to grow and become overgrown by the matrix, the pore density significantly reduces, which is attributed to their transformation into new micropipes. In the later stage, the micropipe density decreases, providing evidence for their partial annihilation and healing. Mechanisms for the evolution from inclusions to pores and finally to micropipes during the crystal growth are further discussed. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] In this paper, a typical Li- and Ta/Sb-modified alkaline niobate-based ceramics prepared by conventional sintering were investigated in terms of different sintering temperatures and dwelling times. Compositional segregation phenomenon is found to exist in the alkaline niobate-based ceramics sintered at the temperatures above their melting points. As a result, microstructures of the ceramics become nonuniform, and electrical properties of them are degraded. Results indicate that compositional segregation is also a factor in the narrow sintering temperature window for alkaline niobate-based ceramics. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] The effects of donor dopants and acceptor dopants (A and B sites) on the resistivity of CaBi₂Nb₂O₉ (CBN) ceramics were studied. The results indicate that the dominant conduction mechanism of pure CBN is p-type. When the donor doping amount x < 0.05 on A site and x < 0.02 on B site, the resistivity increased with increasing donor doping. With a further increase of donor doping, the resistivity decreased since conductivity mechanism changes from p-type to n-type. The resistivity with acceptor doping is decreased at low temperature and equal to the pure CBN ceramic at high temperature since the resistivity of the grain boundary decreases. This work provides a way to obtain high-resistivity CBN ceramics by appropriate donor doping, which is benefit for use in high-temperature piezoelectrics. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] Composites consisting of SrTiO₃-based perovskite and either yttria-stabilized zirconia or ceria were investigated. The mechanical compatibility and possible inter-diffusion between phases were characterized by scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. A gradual disappearance of Ce-containing phases with an increase in the temperature of reduction in hydrogen was noticed. Moreover, a diffusion of Sr, Ti, and Ce was observed between the composites and the yttria-stabilized zirconia electrolyte support in the conditions of high temperature (1300-1400 C) reduction in H₂. (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] High-saturated red phosphors Mn⁴⁺-doped SrAl₁₂O₁₉ were prepared by solid-state reaction methods. The luminescent properties of SrAl₁₂O₁₉:Mn⁴⁺ were systematically investigated. The excitation spectra indicated that SrAl₁₂O₁₉:Mn⁴⁺ could be effectively excited by both NUV light and the blue light of LED chips. The emission spectra exhibit two sharp peaks in the deep-red region. The effects of codoping ions, M = Li⁺, Na⁺, K⁺, Mg²⁺, on the luminescent properties of SrAl₁₂O₁₉:Mn⁴⁺ were investigated, respectively. The results suggested that Mg²⁺ could significantly improve the luminescent properties of SrAl₁₂O₁₉:Mn⁴⁺, and the phosphor SrAl₁₂O₁₉:Mn⁴⁺,Mg²⁺ was demonstrated to be a potential candidate for high colour rendering white LEDs. CIE chromaticity diagram of different phosphors and luminescence of SrAl₁₂O₁₉:Mn⁴⁺,Mg²⁺ phosphor (a). A commercial blue LED chip coated with SrAl₁₂O₁₉:Mn⁴⁺,Mg²⁺ (b) and the luminance of SrAl₁₂O₁₉:Mn⁴⁺,Mg²⁺ excited by a 365-nm light source (c) (x: the CIE chromaticity of a blue chip LED+ YAG:Ce coated with SrAl₁₂O₁₉:Mn⁴⁺,Mg²⁺, 20 mA). (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)