結(jié)晶學chap3symmgp-資料下載頁
2025-03-20 17:30本頁面
【正文】 ??????????????????????????111222101010001cbacbaa, b, c h, k, l reverse ???????????????????????????????222111101010001cbacbatranspose transpose a*, b*, c* x, y, z u, v, w ???????????????????????????????******222111101010101cbacba reverse ?????????????????????????????????******111222101010101cbacba???????????????????????????????PPPIIIcbacba011101110P I PF aa?????????????111111111P F F I IF aa???????????100011111Trigonal T RH aa?????????????111101110S ????????????11111212131 Rarhombohedral cell Hatrigonal cell obverse (positive) Ra??????????111101110????????????11111212131reverse (negative) Trigonal lattices ahex ? aR ? bR bhex ? bR ? cR chex ? aR ? bR ? cR ahex ? bR ? cR bhex ? cR ? aR chex ? aR ? bR ? cR or or ahex ? cR ? aR bhex ? aR ? bR chex ? aR ? bR ? cR As for the hexagonal cell, in the conventional trigonal cell the threefold axis is chosen parallel to c, with a ? b, unrestricted c, ? ? ? ? 90?, and ? ? 120?. Centred cells are easily amenable to the conventional P trigonal cell. Because of the presence of a treefold axis some lattices can exist which may be described via a P cell of rhombohedral shape, with unit vectors aR, bR, cR such that aR ? bR ?cR, ?R ? ?R ? ?R, and the three fold axis along the aR ? bR ? cR direction. Such lattices may also be described by three hexagonal cells with basis vectors ahex, bhex, chex defined according to These hexagonal cells are said to be in obverse setting. Three further triple hexagonal cells, said to be in reverse setting, can be obtained by changing ahex and bhex to ?ahex and ?bhex. The hexagonal cells in obverse setting have centring point at (0, 0, 0), (2/3, 1/3, 1/3), (1/3, 2/3, 2/3) While for reverse setting centring points are at (0, 0, 0), (1/3, 2/3, 1/3), (2/3, 1/3, 2/3) It is worth nothing that a rhombohedral description of a hexagonal P lattice is always possible. Six triple rhombohedral cells with basis vectors a’R, b’R Trigonal T RH aa?????????????111110101RH aa?????????????111110101Obverse (positive) Reverse (negative) ????????????11112111231????????????11112111231Ra?Rhombohedral Cell Ha?Trigonal Cell In direct space: czbyaxr ??? ☆ x, y, z fractional coordinates In reciprocal space: **** clbkahd h k l ???☆ h, k, l plane, miller indices ? ? ? ? ? ??????????????????lkhlkhclbkahclbkahd h k l ******2*? ? ? ? ? ??????????????????zyxzyxczbyaxczbyaxr 2cbaV ???
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