The electronic structure of InGaZnO 4 , which has a layered structure with alternating laminated layers of InO 2 and GaZnO 2 , was calculated in order to investigate the mechanism of electrical conductivity. In the crystal structure obtained through relaxation calculations using classical two-center potentials, the Ga ion in the GaZnO 2 layer has pentagonal coordination forming a bipyramid with five oxygen ions, while the Zn ion in the same layer has tetrahedral coordination, losing a bond with the oxygen at the top of one pyramid. The molecular orbitals of model clusters for the relaxed structure, which were calculated by the discrete variational X␣ method using a model cluster, show strong two-dimensional structures. The electronic states at the edge of the conduction band are the result of overlapping between In 5s orbitals, and delocalize in the InO 2 layer. The energy in the Ga 4s and Zn 4s states in the GaZnO 2 layer was too large to be doped with electrons. The In 5s states are considered to be conduction paths for carrier electrons. A very high conductivity can be expected in the case where dopant ions are introduced into the GaZnO 2 layers.
The effect of the silicon content on the densification of Al-xSi binary alloys (x = 0, 1, 4, 7, 10, 12, and 20 mass%) fabricated using selective laser melting (SLM) were systematically studied. By optimizing laser scanning parameters for each Al-xSi powder, almost fully dense SLM samples (more than 99.5% relative density) could be achieved for the Al-0Si (pure aluminum), and Al-4~20Si alloys. The Al-1Si SLM sample, on the other hand, contained many microcracks, considered to be solidification cracks. The Al-1Si SLM sample, in the solid-liquid coexisting state, was brittle and no healing of
The properties of ceramic materials are strongly influenced by the presence of ultra-dilute impurities or dopants. The near-edge X-ray absorption fine structure (NEXAFS) method by the third-generation synchrotron can be a powerful tool for identifying impurities if a good theoretical tool for interpreting the spectra is provided. We have adopted a novel method to break the bottleneck for its wide application [1]. Local environments of a few 10 ppm levels of Ga in otherwise high-purity MgO ceramic samples were quantitatively examined by NEXAFS and the firstprinciples supercell calculation. Formation of Mg vacancy to compensate the extra charge of substitutional Ga at the Mg site is suggested by the analysis. It is then unambiguously confirmed by the combined study of positron lifetime measurements and plane-wave pseudopotentials calculations. The powerful combination of techniques with NEXAFS to identify the ultra-dilute dopant is fully demonstrated.The experiments were carried out at beamline BL01B1 with a bending magnet system with two mirrors and a fixed-exit double crystal monochromator utilizing Si (311) planes. X-ray fluorescence from the sample was detected by a 19-element Ge solid-state
First-principles molecular-orbital calculations for titanium-metalloid compounds TiB, TiB 2 , TiC, Ti 2 N, TiN, TiO, TiO 2 , TiSi, TiSi 2 , TiP, TiS, and TiS 2 have been made by the use of discrete-variational X␣ method with model clusters composed of about 100 atoms. In order to compare the covalent bonding quantitatively among these compounds with different crystal structures, we used covalent bond density in which both the strength and the number of each type of the bonds in the compounds are taken into account. The covalent bond density represents the strength of the covalent bonding per unit volume irrespective of crystal structures. The dominant covalent bonding in the titanium compounds except for TiO is found to be the Ti-X bonding, which mainly arises from the interaction between Ti-3d-X-np and Ti-4p-X-np orbitals. Each compound exhibits a wide variety of chemical bondings depending upon its crystal structure and local coordinations. However, their total covalent bond density simply decreases and the ionic character increases with rising the atomic number of X atoms. The trend agrees with a simple expectation from the electronegativity differences between Ti and X.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.