Properties of Sapphire
Properties of Sapphire
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DOI：
10.1007/978-0-387-85695-7_2
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发表时间：
2009-01-01
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1}[1]。α-Al 2 O3的晶格由Al 3+和O2 −离子形成。如果把O2 −阴离子描绘成球状，那么晶格就呈现出最紧密的六方堆积形式（图2.1）。Al 3+离子位于没有对称中心的晶场中（由于晶格畸变）。这些阳离子位于紧密堆积的O2 −离子之间的八面体空洞中，占据了这些空洞的三分之二。八面体的空心被六个球包围着。如果每个球的半径都是一个单位，那么这个空心包含一个相对半径为0.41的球。由于O 2−和Al 3+的离子半径比（分别为1.40和0.57 Ω），阳离子位于阴离子填充的中空部分。它们轻微地扭曲晶格，但不会落在八面体位置的稳定极限之外。Al 3+和O 2−的配位数分别为6和4。八面体中上面的三个O 2−离子相对于下面的三个O 2−离子旋转了大约64.3 °，并且位于相互距离为2.164 <$m的平行平面（图2.2 a）中。最紧密堆积变形与
1}[1]. The crystal lattice of a-Al 2O 3 is formed by Al 3+ and O 2− ions. If the O 2− anions are depicted as balls, the crystal lattice takes the form of their closest hexagonal packing (Fig. 2.1). The Al 3+ cations are located in a crystalline field that has no symmetry center (due to crystal lattice distortions). These cations lie in the octahedral hollows between the closely packed O 2− ions, filling two thirds of these hollows. The octahedron hollow is surrounded by six balls. If the radius of each is taken as a unit, then the hollow contains a ball with a relative radius of 0.41. Due to the ratio of the ionic radii of O 2− and Al 3+(equal to 1.40 and 0.57 Å, respectively), the cations are located within the hollows of the anion packing. They slightly distort the lattice, but do not fall outside the stability limits of the octahedron position. The coordination numbers for Al 3+ and O 2− are 6 and 4, respectively. The three upper O 2− ions in the octahedron are turned about 64.3 with respect to the three lower O 2− ions and lie in parallel planes (Fig. 2.2 a) at a distance of 2.164 Å from each other. The closest packing distortion bound up with the discrepancy between