# 3.3.1.10. NXcrystal¶

Status:

base class, extends NXobject, version 1.0

Description:

A crystal monochromator or analyzer.

Permits double bent monochromator comprised of multiple segments with anisotropic Gaussian mosaic.

If curvatures are set to zero or are absent, array is considered to be flat.

Scattering vector is perpendicular to surface. Crystal is oriented parallel to beam incident on crystal before rotation, and lies in vertical plane.

Symbols:

These symbols will be used below to coordinate dimensions with the same lengths.

n_comp: number of different unit cells to be described

i: number of wavelengths

Groups cited:
NXdata, NXgeometry, NXlog, NXshape

Structure:

usage: (optional) NX_CHAR

How this crystal is used. Choices are in the list.

Any of these values:

• Bragg: reflection geometry
• Laue: The chemical formula specified using CIF conventions. Abbreviated version of CIF standard: * Only recognized element symbols may be used. * Each element symbol is followed by a ‘count’ number. A count of ‘1’ may be omitted. * A space or parenthesis must separate each cluster of (element symbol + count). * Where a group of elements is enclosed in parentheses, the multiplier for the group must follow the closing parentheses. That is, all element and group multipliers are assumed to be printed as subscripted numbers. * Unless the elements are ordered in a manner that corresponds to their chemical structure, the order of the elements within any group or moiety depends on whether or not carbon is present. * If carbon is present, the order should be: C, then H, then the other elements in alphabetical order of their symbol. If carbon is not present, the elements are listed purely in alphabetic order of their symbol. This is the Hill system used by Chemical Abstracts. See, for example: http://www.iucr.org/__data/iucr/cif/standard/cifstd15.html, http://www.cas.org/training/stneasytips/subinforformula1.html, or http://www.indiana.edu/~cheminfo/courses/471cnfs.html.

type: (optional) NX_CHAR

Type or material of monochromating substance. Chemical formula can be specified separately. Use the “reflection” field to indicate the (hkl) orientation. Use the “d_spacing” field to record the lattice plane spacing.

This field was changed (2010-11-17) from an enumeration to a string since common usage showed a wider variety of use than a simple list. These are the items in the list at the time of the change: PG (Highly Oriented Pyrolytic Graphite) | Ge | Si | Cu | Fe3Si | CoFe | Cu2MnAl (Heusler) | Multilayer | Diamond.

chemical_formula: (optional) NX_CHAR

The chemical formula specified using CIF conventions. Abbreviated version of CIF standard:

• Only recognized element symbols may be used.
• Each element symbol is followed by a ‘count’ number. A count of ‘1’ may be omitted.
• A space or parenthesis must separate each cluster of (element symbol + count).
• Where a group of elements is enclosed in parentheses, the multiplier for the group must follow the closing parentheses. That is, all element and group multipliers are assumed to be printed as subscripted numbers.
• Unless the elements are ordered in a manner that corresponds to their chemical structure, the order of the elements within any group or moiety depends on whether or not carbon is present.
• If carbon is present, the order should be: C, then H, then the other elements in alphabetical order of their symbol. If carbon is not present, the elements are listed purely in alphabetic order of their symbol.
• This is the Hill system used by Chemical Abstracts.

order_no: (optional) NX_INT

A number which describes if this is the first, second,.. $$n^{th}$$ crystal in a multi crystal monochromator

cut_angle: (optional) NX_FLOAT {units=NX_ANGLE}

Cut angle of reflecting Bragg plane and plane of crystal surface

space_group: (optional) NX_CHAR

Space group of crystal structure

unit_cell[n_comp, 6]: (optional) NX_FLOAT {units=NX_LENGTH}

Unit cell parameters (lengths and angles)

unit_cell_a: (optional) NX_FLOAT {units=NX_LENGTH}

Unit cell lattice parameter: length of side a

unit_cell_b: (optional) NX_FLOAT {units=NX_LENGTH}

Unit cell lattice parameter: length of side b

unit_cell_c: (optional) NX_FLOAT {units=NX_LENGTH}

Unit cell lattice parameter: length of side c

unit_cell_alpha: (optional) NX_FLOAT {units=NX_ANGLE}

Unit cell lattice parameter: angle alpha

unit_cell_beta: (optional) NX_FLOAT {units=NX_ANGLE}

Unit cell lattice parameter: angle beta

unit_cell_gamma: (optional) NX_FLOAT {units=NX_ANGLE}

Unit cell lattice parameter: angle gamma

unit_cell_volume: (optional) NX_FLOAT {units=NX_VOLUME}

Volume of the unit cell

orientation_matrix[3, 3]: (optional) NX_FLOAT

Orientation matrix of single crystal sample using Busing-Levy convention: W. R. Busing and H. A. Levy (1967). Acta Cryst. 22, 457-464

wavelength[i]: (optional) NX_FLOAT {units=NX_WAVELENGTH}

Optimum diffracted wavelength

d_spacing: (optional) NX_FLOAT {units=NX_LENGTH}

spacing between crystal planes of the reflection

scattering_vector: (optional) NX_FLOAT {units=NX_WAVENUMBER}

Scattering vector, Q, of nominal reflection

reflection[3]: (optional) NX_INT {units=NX_UNITLESS}

Miller indices (hkl) values of nominal reflection

thickness: (optional) NX_FLOAT {units=NX_LENGTH}

Thickness of the crystal. (Required for Laue orientations - see “usage” field)

density: (optional) NX_NUMBER {units=NX_MASS_DENSITY}

mass density of the crystal

segment_width: (optional) NX_FLOAT {units=NX_LENGTH}

Horizontal width of individual segment

segment_height: (optional) NX_FLOAT {units=NX_LENGTH}

Vertical height of individual segment

segment_thickness: (optional) NX_FLOAT {units=NX_LENGTH}

Thickness of individual segment

segment_gap: (optional) NX_FLOAT {units=NX_LENGTH}

segment_columns: (optional) NX_FLOAT {units=NX_LENGTH}

number of segment columns in horizontal direction

segment_rows: (optional) NX_FLOAT {units=NX_LENGTH}

number of segment rows in vertical direction

mosaic_horizontal: (optional) NX_FLOAT {units=NX_ANGLE}

horizontal mosaic Full Width Half Maximum

mosaic_vertical: (optional) NX_FLOAT {units=NX_ANGLE}

vertical mosaic Full Width Half Maximum

curvature_horizontal: (optional) NX_FLOAT {units=NX_ANGLE}

Horizontal curvature of focusing crystal

curvature_vertical: (optional) NX_FLOAT {units=NX_ANGLE}

Vertical curvature of focusing crystal

is_cylindrical: (optional) NX_BOOLEAN

Is this crystal bent cylindrically?

cylindrical_orientation_angle: (optional) NX_NUMBER {units=NX_ANGLE}

If cylindrical: cylinder orientation angle

polar_angle[i]: (optional) NX_FLOAT {units=NX_ANGLE}

Polar (scattering) angle at which crystal assembly is positioned. Note: some instrument geometries call this term 2theta.

azimuthal_angle[i]: (optional) NX_FLOAT {units=NX_ANGLE}

Azimuthal angle at which crystal assembly is positioned

bragg_angle[i]: (optional) NX_FLOAT {units=NX_ANGLE}

Bragg angle of nominal reflection

temperature: (optional) NX_FLOAT {units=NX_TEMPERATURE}

average/nominal crystal temperature

temperature_coefficient: (optional) NX_FLOAT {units=NX_ANY}

how lattice parameter changes with temperature

(geometry): (optional) NXgeometry

Position of crystal

temperature_log: (optional) NXlog

log file of crystal temperature

reflectivity: (optional) NXdata

crystal reflectivity versus wavelength

transmission: (optional) NXdata

crystal transmission versus wavelength

shape: (optional) NXshape

A NXshape group describing the shape of the crystal arrangement
NXDL Source:
https://github.com/nexusformat/definitions/blob/master/base_classes/NXcrystal.nxdl.xml