# Reflection conditions

### From Online Dictionary of Crystallography

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(1) ''General conditions''. They apply to all Wyckoff positions of a space group, ''i.e.'' they are always obeyed, irrespective of which Wyckoff positions are occupied by atoms in a particular crystal structure. They are due to one of three effects: | (1) ''General conditions''. They apply to all Wyckoff positions of a space group, ''i.e.'' they are always obeyed, irrespective of which Wyckoff positions are occupied by atoms in a particular crystal structure. They are due to one of three effects: | ||

- | + | *''Centred cells''. | |

The resulting conditions apply to the whole three-dimensional set of reflections hkl. Accordingly, they are called ''integral reflection conditions''. They are given in [[Integral reflection conditions| Table 1]]. | The resulting conditions apply to the whole three-dimensional set of reflections hkl. Accordingly, they are called ''integral reflection conditions''. They are given in [[Integral reflection conditions| Table 1]]. | ||

- | + | *''Glide planes''. | |

The resulting conditions apply only to twodimensional sets of reflections, ''i.e.'' to reciprocal-lattice nets containing the origin (such as hk0, h0l, 0kl, hhl). For this reason, | The resulting conditions apply only to twodimensional sets of reflections, ''i.e.'' to reciprocal-lattice nets containing the origin (such as hk0, h0l, 0kl, hhl). For this reason, | ||

- | they are called ''zonal reflection conditions''. They are listed in Table 2. | + | they are called ''zonal reflection conditions''. They are listed in Table 2.2.13.2 of ''International Tables of Crystallography, Volume A''. |

- | + | *''Screw axes''. | |

The resulting conditions apply only to onedimensional sets of reflections, ''i.e.'' reciprocal-lattice rows containing the origin (such as h00, 0k0, 00l). They are called ''serial | The resulting conditions apply only to onedimensional sets of reflections, ''i.e.'' reciprocal-lattice rows containing the origin (such as h00, 0k0, 00l). They are called ''serial | ||

- | reflection conditions''. They are listed in Table 2. | + | reflection conditions''. They are listed in Table 2.2.13.2 of ''International Tables of Crystallography, Volume A''. |

(2) ''Special conditions'' (‘extra’ conditions). They apply only to special Wyckoff positions and occur always in addition to the general conditions of the space group. | (2) ''Special conditions'' (‘extra’ conditions). They apply only to special Wyckoff positions and occur always in addition to the general conditions of the space group. | ||

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==See also == | ==See also == | ||

- | Section 2.2.13 of ''International | + | Section 2.2.13 of ''International Tables of Crystallography, Volume A'' |

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[[Category:X-rays]]<br> | [[Category:X-rays]]<br> |

## Revision as of 06:40, 19 April 2006

Conditions de réflexion (*Fr*).

## Definition

The reflection conditions describe the conditions of occurence of a reflection (structure factor not systematically zero). There are two types of systematic reflection conditions for diffraction of crystals by radiation:

(1) *General conditions*. They apply to all Wyckoff positions of a space group, *i.e.* they are always obeyed, irrespective of which Wyckoff positions are occupied by atoms in a particular crystal structure. They are due to one of three effects:

*Centred cells*.

The resulting conditions apply to the whole three-dimensional set of reflections hkl. Accordingly, they are called *integral reflection conditions*. They are given in Table 1.

*Glide planes*.

The resulting conditions apply only to twodimensional sets of reflections, *i.e.* to reciprocal-lattice nets containing the origin (such as hk0, h0l, 0kl, hhl). For this reason,
they are called *zonal reflection conditions*. They are listed in Table 2.2.13.2 of *International Tables of Crystallography, Volume A*.

*Screw axes*.

The resulting conditions apply only to onedimensional sets of reflections, *i.e.* reciprocal-lattice rows containing the origin (such as h00, 0k0, 00l). They are called *serial*
reflection conditions*. They are listed in Table 2.2.13.2 of *International Tables of Crystallography, Volume A*. *

(2) *Special conditions* (‘extra’ conditions). They apply only to special Wyckoff positions and occur always in addition to the general conditions of the space group.

## See also

Section 2.2.13 of *International Tables of Crystallography, Volume A*