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Abstract: The atomic level mechanism of incorporation of Zn2+ into hydroxyapatite (HAp), which is a potential dopant to promote bone formation, was investigated, based on first principles total energy calculations and experimental X-ray absorption near edge structure (XANES) analyses. It was found that Zn2+-doped HAp tends to have a Ca-deficient chemical composition and substitutional Zn2+ ions are associated with a defect complex with a Ca2+ vacancy and two charge compensating protons. Moreover, first principles calculations demonstrated that Zn2+ incorporation into HAp can take place by occupying the Ca2+ vacancy of the defect complex. The Ca2+ vacancy complex is not only the origin of the calcium deficiency in HAp, but also plays a key role in the uptake of trace elements during mineralization. [Copyright &y& Elsevier]

First principles plane wave basis calculations were performed to investigate the atomic-scale mechanism of grain boundary (GB) sliding of the Al-terminated Σ13 pyramidal twin GB in α-Al2O3 in order to investigate the difference in sliding properties from the previously reported result of O-terminated GB. Atomistic mechanism of sliding process was found to be similar to the previously reported O-terminated GB, that is, the sliding takes place with successive breaking/rebonding of Al-O bonds across the GB core [Nakamura et al., Phys. Rev. B 75 (2007) p.184109]. On the other hand, it was found that sliding resistance of the Al-terminated GB is higher than that of the O-terminated one, though they have the identical orientation relationship. Quantitative chemical bonding analyses show that the difference in the sliding resistance originates from the local Al-O bonding characteristics of individual Al-O pairs across the GB plane. [ABSTRACT FROM AUTHOR]

Abstract: The effect of strong carbide forming elements (Ti, Zr) in the Cu matrix on interfacial bonding and electric conductivity of CNF/Cu composites has been studied. The chemical bonding states of C/Cu interfaces were calculated by using the first-principles molecular orbital method, which showed that the presence of Ti or Zr in the interface layer strongly increases chemical bonding strength across the interface. The CNF/Cu composites with the alloying elements have been fabricated successfully by liquid infiltration process. Tensile strength of composites with additional element has been increased. However, Ti addition compared with Zr addition resulted in great loss of electric conductivity. [Copyright &y& Elsevier]

Abstract: We report electrical conductivity of Ti-nanowires in sapphire fabricated by utilizing lattice dislocations. We evaporated metallic Ti on a sapphire plate containing high density of uniaxial dislocations, and annealed the plate at high temperatures. As a result, it was found that Ti atoms intensely segregated along the dislocations within about 5nm in diameter, indicating the formation of Ti-nanowires inside sapphire. Furthermore, the nanowires were confirmed to have significant electrical conductivity even in sapphire insulator. [Copyright &y& Elsevier]

Interfacial atomic structures of Cu/Al2O3(0001) and Cu/Al2O3(112¯0) systems prepared by a pulsed-laser deposition technique have been characterized by using high-resolution transmission electron microscopy (HRTEM). It was found that Cu metals were epitaxially oriented to the surface of Al2O3 substrates, and the following orientation relationships (ORs) were found to be formed: (111)Cu//(0001)Al2O3, [11¯0]Cu//[11¯00]Al2O3 in the Cu/Al2O3(0001) interface and (001)Cu//(112¯0)Al2O3, [11¯0]Cu//[0001]Al2O3 in the Cu/Al2O3(112¯0) interface. Geometrical coherency of the Cu/Al2O3 system has been evaluated by the coincidence of reciprocal lattice points method, and the result showed that the most coherent ORs were (111)Cu//(0001)Al2O3, [112¯]Cu//[11¯00]Al2O3 and (11¯0)Cu//(112¯0)Al2O3, [111]Cu//[0001]Al2O3, which are equivalent to each other. These ORs were not consistent with the experimentally observed ORs, and it was possible that crucial factors to determine the ORs between Cu and Al2O3 were not only geometrical coherency, but also other factors such as chemical bonding states. Therefore, to understand the nature of the interface atomic structures, the electronic structures of the Cu/Al2O3 interfaces have been investigated by electron energy-loss spectroscopy. It was found that the pre-edge at the lower energy part of the main peak appeared in the O-K edge spectra at the interface region in both the Cu/Al2O3(0001) and Cu/Al2O3(112¯0) systems. This indicates the existence of Cu–O interactions at the interface. In fact, HRTEM simulation images based on O-terminated interface models agreed well with the experimental images, indicating that O-terminated interfaces were formed in both systems. Since the overlapped Cu atomic density in the experimental ORs were larger than that in the most coherent OR, it is considered that the on-top Cu–O bonds stabilize the O-terminated Cu/Al2O3 interfaces. [Copyright &y& Elsevier]

Distribution and arrangement of nanopores in an YSZ (7 wt% Y2O3–ZrO2)-thermal barrier coating (TBC) deposited by an electron beam-physical vapor deposition (EB-PVD) have been investigated by means of transmission electron microscopy. The YSZ-TBC deposited by the EB-PVD showed a typical columnar structure normal to the bond coat surface on the substrate. It has been generally believed that one column is a single crystal and grows continuously from the substrate. In the present study, however, it was found that each column consisted of a number of subcolumns with different misorientations and contained nanopores at the subcolumn boundaries. In addition to the nanopores at the subcolumn boundaries, nanopores with smaller size were observed within subcolumns, and were arranged periodically perpendicular to the growth direction of the subcolumns. Such arrangement and distribution of nanopores may be due to the misorientation of YSZ plate-like grains in the formation and coalescence processes of the YSZ subcolumns. [Copyright &y& Elsevier]

Symmetrical Σ7 tilt grain boundaries of alumina (Al[sub 2]O[sub 3]) were studied using bicrystals. Three types of Σ7 boundaries were successfully fabricated, that is, rhombohedral twin (Σ7{1&1mac;02}) and two types of [0001] symmetrical tilt grain boundaries with grain-boundary planes {4&5macr;10} and {2&3macr;10} (Σ7{4&5macr;10} and Σ7{2&3macr;10}). Their atomic structures and grain-boundary energies were investigated using high-resolution transmission electron microscopy (HRTEM) and a thermal grooving technique, respectively. HRTEM observations showed that the Σ7{1&1macr;02} boundary had a completely symmetrical atomic arrangement with respect to the grain-boundary plane. In contrast, Σ7{2&3macr;10} and Σ7{4&5macr;10} boundaries exhibited asymmetrical atomic structures, which were confirmed by analyzing the atomic configurations using static lattice calculations. Thermal grooving experiments showed that the grain-boundary energies strongly depended on the properties of the grainboundary planes. [ABSTRACT FROM AUTHOR]