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===Lattice periodicity and X-ray crystallinity===
===Lattice periodicity and X-ray crystallinity===
晶格周期性与 x 射线结晶度
'''晶格周期性与 x 射线结晶度'''
The strictest form of order in a solid is lattice periodicity: a certain pattern (the arrangement of atoms in a unit cell) is repeated again and again to form a translationally invariant tiling of space. This is the defining property of a crystal. Possible symmetries have been classified in 14 Bravais lattices and 230 space groups.
The strictest form of order in a solid is lattice periodicity: a certain pattern (the arrangement of atoms in a unit cell) is repeated again and again to form a translationally invariant tiling of space. This is the defining property of a crystal. Possible symmetries have been classified in 14 Bravais lattices and 230 space groups.
固体中秩序的最严格形式是'''晶格周期性''': 某种模式('''<font color="#ff8000">单元格 Unit Cell</font>'''中原子的排列)一次又一次地重复，形成一个平移不变的空间'''<font color="#ff8000">平铺 Tiling</font>'''。这就是'''<font color="#ff8000">晶体 Crystal</font>'''的定义属性。可能的对称性已在14个'''<font color="#ff8000">布拉维斯晶格 Bravais Lattice</font>'''和230个'''<font color="#ff8000">空间群 Space Group</font>'''中分类。
Lattice periodicity implies long-range order: if only one unit cell is known, then by virtue of the translational symmetry it is possible to accurately predict all atomic positions at arbitrary distances. During much of the 20th century, the converse was also taken for granted – until the discovery of quasicrystals in 1982 showed that there are perfectly deterministic tilings that do not possess lattice periodicity.
Lattice periodicity implies long-range order: if only one unit cell is known, then by virtue of the translational symmetry it is possible to accurately predict all atomic positions at arbitrary distances. During much of the 20th century, the converse was also taken for granted – until the discovery of quasicrystals in 1982 showed that there are perfectly deterministic tilings that do not possess lattice periodicity.
格点周期性意味着'''长程有序''': 如果只知道一个单位单元，那么借助于平移对称性，就有可能在任意距离上精确地预测所有原子的位置。在20世纪的大部分时间里，相反的情况也被认为是合理的——直到1982年'''<font color="#ff8000">准晶体 Quasicrystal</font>'''的发现表明，完全确定性的倾斜并不具有晶格周期性。
Besides structural order, one may consider charge ordering, spin ordering, magnetic ordering, and compositional ordering. Magnetic ordering is observable in neutron diffraction.
Besides structural order, one may consider charge ordering, spin ordering, magnetic ordering, and compositional ordering. Magnetic ordering is observable in neutron diffraction.
除了结构有序外，还可以考虑'''<font color="#ff8000">电荷有序 Charge Ordering</font>'''、'''<font color="#ff8000">自旋 Spin</font>'''有序、'''<font color="#ff8000">磁有序 Magnetic Ordering</font>'''和成分有序。磁顺序可以在'''<font color="#ff8000">中子衍射 Neutron Diffraction</font>'''中观察到。