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Injection Seeding of a Ti:Al2O3 unstable resonator using both a pulsed single-mode Ti:Al2O3 laser and a continuous wave laser diode has been characterized. Results are compared with a theory which calculates injection seeding as function of seed and resonator alignment, beam profiles, and power.
Microstructural changes occurring during sliding wear of self-mated Al2O3 SiC whisker-reinforced composites were studied using optical, scanning electron microscopy and transmission electron microscopy. Pin-on-disc specimens were slid in air at 2.7 m/s sliding velocity under a 26.5 N load for 1 h. Wear tests were conducted at 23, 600, 800 and 1200 C. Mild wear with a wear factor of 2.4 x 10 exp -7 - 1.5 x 10 exp -6 cu mm /N per m was experienced at all test temperatures. The composite showed evidence of wear by fatigue mechanisms at 800 C and below. Tribochemical reaction (SiC oxidation and reaction of SiO2 and Al2O3) leads to intergranular failure at 1200 C. Distinct microstructural differences existing at each test temperature are reported.
The mechanisms for fiber damage in single crystal Al2O3 fiber-reinforced composites were investigated. Both fiber fragmentation and fiber strength degradation were observed in composites with a variety of matrix compositions. Four mechanisms that may be contributing to the fiber strength loss have been proposed and include matrix reaction, reaction with binders, residual stress-induced damage, and pressure from hot pressing. The effect of matrix reaction was separated from the other three effects by sputter-coating the matrices on cleaned fibers and annealing with a temperature profile that simulates processing conditions. These experiments revealed that Y and Cr in FeCrAlY base alloys and Zr in NiAl alloys reacted with the fiber, and grooves and adherent particles were formed on the fiber surface which were responsible for the strength loss. The effects of the matrix reaction appeared to dominate over the other possible mechanisms, although evidence for reaction with binders was also found. Ridges on the fiber surface, which reflected the grain boundaries of the matrix, were also observed. In order for single-crystal Al2O3 to be used as a fiber in MMC's and IMC's, a matrix or protective coating which minimizes matrix reaction during processing will be necessary. Of the matrices investigated, the Thermo-span(sup TM) alloy was the least damaging to fiber properties.
Natural pyroxene and garnet starting material are used to study the effects of joint Fe and Al substitution into MgSiO3 perovskite at approxmiately 50 GPa. Garnet is found to coexist with perovskite in samples containing both Fe and Al to pressures occurring deep into the lower mantel (approximately 1200 km depth). The volume of the perovskite unit cell is V(sub o(Angstrom(exp 3)) = 162.59 + 5.95x(sub FeSiO3) + 10.80x(sub Al2O3) with aluminum causing a significant increase in the distortion from the ideal cubic cell. On the basis of a proposed extension of the MgSiO3-Al2O3 high-pressure phase diagram toward FeSiO3, Fe is shown to partition preferentially into the garnet phase. The stability of garnet deep into the lower mantel may hinder the penetration of subducted slabs below the transition zone.
Sixteen ply unidirectional zirconia coated single crystal Al2O3 fiber reinforced polycrystalline Al2O3 was tested in uniaxial tension at temperatures to 1400 C in air. Fiber volume fractions ranged from 26 to 31%. The matrix has primarily open porosity of approximately 40%. Theories for predicting the Young's modulus, first matrix cracking stress, and ultimate strength were applied and evaluated for suitability in predicting the mechanical behavior of Al2O3/Al2O3 composites. The composite exhibited pseudo tough behavior (increased area under the stress/strain curve relative to monolithic alumina) from 22 to 1400 C. The rule-of-mixtures provides a good estimate of the Young's modulus of the composite using the constituent properties from room temperature to approximately 1200 C for short term static tensile tests in air. The ACK theory provides the best approximation of the first matrix cracking stress while accounting for residual stresses at room temperature. Difficulties in determining the fiber/matrix interfacial shear stress at high temperatures prevented the accurate prediction of the first matrix cracking stress above room temperature. The theory of Cao and Thouless, based on Weibull statistics, gave the best prediction for the composite ultimate tensile strength.
The thermally and optically stimulated luminescence (TL and OSL) response to high energy heavy-charged particles (HCPs) was investigated for two types of Al2O3:C luminescence dosimeters. The OSL signal was measured in both continuous-wave (CW) and pulsed mode. The efficiencies of the HCPs at producing TL or OSL, relative to gamma radiation, were obtained using four different HCPs beams (150 MeV/u 4He, 400 MeV/u 12C, 490 MeV/u 28Si, and 500 MeV/u 56Fe). The efficiencies were determined as a function of the HCP linear energy transfer (LET). It was observed that the efficiency depends on the type of detector, measurement technique, and the choice of signal. Additionally, it is shown that the shape of the CW-OSL decay curve from Al2O3:C depends on the type of radiation, and, in principle, this can be used to extract information concerning the LET of an unknown radiation field. The response of the dosimeters to low-LET radiation was also investigated for doses in the range from about 1-1000 Gy. These data were used to explain the different efficiency values obtained for the different materials and techniques, as well as the LET dependence of the CW-OSL decay curve shape. c2003 Elsevier Ltd. All rights reserved.
This paper examines the effect of high-dose irradiation on the optically stimulated luminescence (OSL) of Al2O3:C, principally on the shape of the OSL decay curve and on the OSL sensitivity. The effect of the degree of deep trap filling on the OSL was also studied by monitoring the sensitivity changes after doses of beta irradiation and after step-annealing of samples previously irradiated with high doses. The OSL response to dose shows a linear-supralinear-saturation behavior, with a decrease in the response for doses higher than those required for saturation. This behavior correlates with the sensitivity changes observed in the samples annealed only to 773 K, which show sensitization for doses up to 20-50 Gy and desensitization for higher doses. Data from the step-annealing study leads to the suggestion that the sensitization is caused by the filling of deep electron traps, which become thermally unstable at 1100-1200 K, whereas the desensitization is caused by the filling of deep hole traps, which become thermally unstable at 800-875 K, along with a concomitant decrease in the concentration of recombination centers (F+ -centers). Changes in the shape of the OSL decay curves are also observed at high doses, the decay becoming faster as the dose increases. These changes in the OSL decay curves are discussed in terms of multiple overlapping components, each characterized by different photoionization cross-sections. However, using numerical solutions of the rate equations for a simple model consisting of a main trap and a recombination center, it is shown that the kinetics of OSL process may also be partially responsible for the changes in the OSL curves at high doses in Al2O3:C. Finally, the implication of these results for the dosimetry of heavy charged particles is discussed. c2004 Elsevier Ltd. All rights reserved.
Al2O3-SiO2 aerogels are of interest as constituents of thermal insulation systems for use at high temperatures. Al2O3 and mullite aerogels are expected to crystallize at higher temperatures than their SiO2 counterparts, hence avoiding the shrinkages that accompany the formation of lower temperature SiO2 phases and preserving pore structures into higher temperature regimes. The objective of this work is to determine the influence of processing parameters on shrinkage, gel structure (including surface area, pore size and distribution) and pyrolysis behavior.
Al2O3 is Corundum structured and crystallizes in the trigonal R-3c space group. The structure is three-dimensional. Al3+ is bonded to six equivalent O2- atoms to form a mixture of corner, edge, and face-sharing AlO6 octahedra. The corner-sharing octahedra tilt angles range from 48–60°. There is three shorter (1.87 Å) and three longer (1.99 Å) Al–O bond length. O2- is bonded to four equivalent Al3+ atoms to form a mixture of distorted corner and edge-sharing OAl4 trigonal pyramids.
Al2O3 is Corundum-like structured and crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Al3+ is bonded to six O2- atoms to form a mixture of face, edge, and corner-sharing AlO6 octahedra. The corner-sharing octahedra tilt angles range from 51–71°. There are a spread of Al–O bond distances ranging from 1.87–2.03 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Al3+ atoms to form a mixture of distorted edge and corner-sharing OAl4 tetrahedra. In the second O2- site, O2- is bonded to four equivalent Al3+ atoms to form a mixture of distorted edge and corner-sharing OAl4 trigonal pyramids.
Al2O3 crystallizes in the orthorhombic Pna2_1 space group. The structure is three-dimensional. there are four inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with eight AlO6 octahedra and corners with two equivalent AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 56–67°. There are a spread of Al–O bond distances ranging from 1.76–1.80 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO6 octahedra, corners with three equivalent AlO4 tetrahedra, and edges with seven AlO6 octahedra. The corner-sharing octahedra tilt angles range from 15–50°. There are a spread of Al–O bond distances ranging from 1.82–1.97 Å. In the third Al3+ site, Al3+ is bonded to six O2- atoms to form distorted AlO6 octahedra that share corners with four equivalent AlO6 octahedra, corners with four equivalent AlO4 tetrahedra, and edges with four AlO6 octahedra. The corner-sharing octahedra tilt angles range from 13–57°. There are a spread of Al–O bond distances ranging from 1.82–2.22 Å. In the fourth Al3+ site, Al3+ is bonded to six O2- atoms to form distorted AlO6 octahedra that share corners with six AlO6 octahedra, a cornercorner with one AlO4 tetrahedra, and edges with five AlO6 octahedra. The corner-sharing octahedra tilt angles range from 13–57°. There are a spread of Al–O bond distances ranging from 1.83–2.27 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded to four Al3+ atoms to form OAl4 tetrahedra that share a cornercorner with one OAl5 square pyramid, corners with two equivalent OAl4 tetrahedra, edges with two equivalent OAl5 square pyramids, and an edgeedge with one OAl4 tetrahedra. In the second O2- site, O2- is bonded to four Al3+ atoms to form distorted OAl4 tetrahedra that share a cornercorner with one OAl5 square pyramid, corners with four OAl4 tetrahedra, edges with two equivalent OAl5 square pyramids, and an edgeedge with one OAl4 tetrahedra. In the third O2- site, O2- is bonded to five Al3+ atoms to form distorted OAl5 square pyramids that share corners with two OAl4 tetrahedra, edges with two equivalent OAl5 square pyramids, and edges with four OAl4 tetrahedra. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to three Al3+ atoms. In the fifth O2- site, O2- is bonded in a trigonal planar geometry to three Al3+ atoms. In the sixth O2- site, O2- is bonded in a trigonal planar geometry to three Al3+ atoms.
Al2O3 is beta indium sulfide-like structured and crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are twenty-six inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with four AlO4 tetrahedra and edges with six AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.85–1.97 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with three equivalent AlO4 tetrahedra and edges with six AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.82–2.08 Å. In the third Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 49–59°. There are a spread of Al–O bond distances ranging from 1.76–1.83 Å. In the fourth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with four AlO4 tetrahedra and edges with six AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.84–1.99 Å. In the fifth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.82–2.03 Å. In the sixth Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 55–61°. There is one shorter (1.74 Å) and three longer (1.87 Å) Al–O bond length. In the seventh Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra and edges with four AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.91–1.96 Å. In the eighth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.86–1.96 Å. In the ninth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.82–2.02 Å. In the tenth Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 55–60°. There is one shorter (1.77 Å) and three longer (1.85 Å) Al–O bond length. In the eleventh Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 53–59°. There are a spread of Al–O bond distances ranging from 1.76–1.83 Å. In the twelfth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.85–2.00 Å. In the thirteenth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.85–1.97 Å. In the fourteenth Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 49–59°. There are a spread of Al–O bond distances ranging from 1.76–1.87 Å. In the fifteenth Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 50–58°. There are a spread of Al–O bond distances ranging from 1.76–1.85 Å. In the sixteenth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.84–2.02 Å. In the seventeenth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.83–2.00 Å. In the eighteenth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra and edges with four AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.90–1.98 Å. In the nineteenth Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 53–62°. There is one shorter (1.74 Å) and three longer (1.84 Å) Al–O bond length. In the twentieth Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 54–59°. There is three shorter (1.76 Å) and one longer (1.86 Å) Al–O bond length. In the twenty-first Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.81–2.06 Å. In the twenty-second Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 56–60°. There are a spread of Al–O bond distances ranging from 1.76–1.87 Å. In the twenty-third Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with five AlO4 tetrahedra and edges with six AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.80–2.01 Å. In the twenty-fourth Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 49–59°. There are a spread of Al–O bond distances ranging from 1.76–1.90 Å. In the twenty-fifth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with five AlO4 tetrahedra and edges with six AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.81–1.96 Å. In the twenty-sixth Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 56–64°. There are a spread of Al–O bond distances ranging from 1.77–1.86 Å. There are thirty-six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted T-shaped geometry to three Al3+ atoms. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the third O2- site, O2- is bonded in a distorted T-shaped geometry to three Al3+ atoms. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the fifth O2- site, O2- is bonded to four Al3+ atoms to form distorted edge-sharing OAl4 trigonal pyramids. In the sixth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the eighth O2- site, O2- is bonded to four Al3+ atoms to form distorted edge-sharing OAl4 trigonal pyramids. In the ninth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the tenth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the eleventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the twelfth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the fourteenth O2- site, O2- is bonded to four Al3+ atoms to form distorted edge-sharing OAl4 trigonal pyramids. In the fifteenth O2- site, O2- is bonded to four Al3+ atoms to form distorted edge-sharing OAl4 trigonal pyramids. In the sixteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the seventeenth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the eighteenth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the nineteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the twentieth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the twenty-first O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the twenty-second O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the twenty-third O2- site, O2- is bonded to four Al3+ atoms to form a mixture of distorted edge and corner-sharing OAl4 trigonal pyramids. In the twenty-fourth O2- site, O2- is bonded to four Al3+ atoms to form distorted edge-sharing OAl4 trigonal pyramids. In the twenty-fifth O2- site, O2- is bonded to four Al3+ atoms to form a mixture of distorted edge and corner-sharing OAl4 trigonal pyramids. In the twenty-sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the twenty-seventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the twenty-eighth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the twenty-ninth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the thirtieth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the thirty-first O2- site, O2- is bonded in a trigonal non-coplanar geometry to three Al3+ atoms. In the thirty-second O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the thirty-third O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the thirty-fourth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the thirty-fifth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the thirty-sixth O2- site, O2- is bonded in a distorted trigonal pyramidal geometry to four Al3+ atoms.
Al2O3 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six O2- atoms to form a mixture of corner and edge-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 57°. There are a spread of Al–O bond distances ranging from 1.86–2.01 Å. In the second Al3+ site, Al3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Al–O bond distances ranging from 1.87–2.14 Å. In the third Al3+ site, Al3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Al–O bond distances ranging from 1.87–2.13 Å. In the fourth Al3+ site, Al3+ is bonded to six O2- atoms to form a mixture of corner and edge-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 57°. There are a spread of Al–O bond distances ranging from 1.86–2.01 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted square co-planar geometry to four Al3+ atoms. In the second O2- site, O2- is bonded to four Al3+ atoms to form corner-sharing OAl4 tetrahedra. In the third O2- site, O2- is bonded in a 4-coordinate geometry to four Al3+ atoms. In the fourth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the fifth O2- site, O2- is bonded to four Al3+ atoms to form corner-sharing OAl4 tetrahedra. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to four Al3+ atoms.
Al2O3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with seven equivalent AlO6 octahedra and corners with two equivalent AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 56–63°. There is three shorter (1.77 Å) and one longer (1.81 Å) Al–O bond length. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with seven equivalent AlO4 tetrahedra and edges with four equivalent AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.89–2.02 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to three Al3+ atoms. In the second O2- site, O2- is bonded in a trigonal planar geometry to three Al3+ atoms. In the third O2- site, O2- is bonded to four Al3+ atoms to form a mixture of distorted edge and corner-sharing OAl4 tetrahedra.
Al2O3 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are ten inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with six AlO6 octahedra, corners with two equivalent AlO5 square pyramids, and an edgeedge with one AlO5 square pyramid. The corner-sharing octahedra tilt angles range from 14–71°. There are a spread of Al–O bond distances ranging from 1.75–1.84 Å. In the second Al3+ site, Al3+ is bonded to five O2- atoms to form distorted AlO5 square pyramids that share corners with six AlO6 octahedra, a cornercorner with one AlO5 square pyramid, corners with two equivalent AlO4 tetrahedra, and an edgeedge with one AlO6 octahedra. The corner-sharing octahedra tilt angles range from 47–54°. There are a spread of Al–O bond distances ranging from 1.81–2.01 Å. In the third Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra, an edgeedge with one AlO6 octahedra, and edges with three AlO5 square pyramids. There are a spread of Al–O bond distances ranging from 1.86–2.23 Å. In the fourth Al3+ site, Al3+ is bonded to five O2- atoms to form AlO5 square pyramids that share a cornercorner with one AlO5 square pyramid, corners with three AlO4 tetrahedra, edges with three AlO6 octahedra, and an edgeedge with one AlO4 tetrahedra. There are a spread of Al–O bond distances ranging from 1.82–1.93 Å. In the fifth Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with ten AlO6 octahedra and a cornercorner with one AlO5 square pyramid. The corner-sharing octahedra tilt angles range from 55–62°. There are a spread of Al–O bond distances ranging from 1.80–1.84 Å. In the sixth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO5 square pyramids, corners with four AlO4 tetrahedra, and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.82–2.00 Å. In the seventh Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six AlO4 tetrahedra, edges with four AlO6 octahedra, and an edgeedge with one AlO5 square pyramid. There are a spread of Al–O bond distances ranging from 1.83–2.06 Å. In the eighth Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with eight AlO6 octahedra and corners with two equivalent AlO5 square pyramids. The corner-sharing octahedra tilt angles range from 51–60°. There are a spread of Al–O bond distances ranging from 1.76–1.84 Å. In the ninth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO5 square pyramids, corners with four AlO4 tetrahedra, and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.82–2.07 Å. In the tenth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO5 square pyramids, corners with four AlO4 tetrahedra, and edges with five AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.83–2.01 Å. There are fifteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the second O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the third O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the fourth O2- site, O2- is bonded in a T-shaped geometry to three Al3+ atoms. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the sixth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the seventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the ninth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the tenth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the eleventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the twelfth O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to four Al3+ atoms. In the thirteenth O2- site, O2- is bonded in a tetrahedral geometry to four Al3+ atoms. In the fourteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the fifteenth O2- site, O2- is bonded in a trigonal planar geometry to three Al3+ atoms.
Al2O3 crystallizes in the orthorhombic Cmc2_1 space group. The structure is three-dimensional. Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. There are a spread of Al–O bond distances ranging from 1.69–1.82 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Al3+ atoms. In the second O2- site, O2- is bonded in a trigonal planar geometry to three equivalent Al3+ atoms.
Al2O3 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to five O2- atoms to form AlO5 trigonal bipyramids that share corners with four equivalent AlO4 tetrahedra, an edgeedge with one AlO4 tetrahedra, and edges with two equivalent AlO5 trigonal bipyramids. There are a spread of Al–O bond distances ranging from 1.82–2.02 Å. In the second Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with two equivalent AlO4 tetrahedra, corners with four equivalent AlO5 trigonal bipyramids, and an edgeedge with one AlO5 trigonal bipyramid. There are a spread of Al–O bond distances ranging from 1.76–1.79 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to three Al3+ atoms. In the third O2- site, O2- is bonded in a distorted T-shaped geometry to three Al3+ atoms.
Al2O3 is Corundum-like structured and crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are three inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six equivalent O2- atoms to form a mixture of edge and corner-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 43°. All Al–O bond lengths are 1.93 Å. In the second Al3+ site, Al3+ is bonded to six equivalent O2- atoms to form a mixture of corner and face-sharing AlO6 octahedra. The corner-sharing octahedra tilt angles range from 43–53°. All Al–O bond lengths are 1.94 Å. In the third Al3+ site, Al3+ is bonded to six equivalent O2- atoms to form a mixture of distorted edge, corner, and face-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 53°. There is three shorter (1.85 Å) and three longer (2.03 Å) Al–O bond length. O2- is bonded to four Al3+ atoms to form a mixture of edge and corner-sharing OAl4 trigonal pyramids.