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International
Tables for Crystallography Volume G Definition and exchange of crystallographic data Edited by S. R. Hall and B. McMahon © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. G. ch. 3.3, p. 118
Section 3.3.4.1. Characterization and preparation of the sample
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NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8562, USA |
The data items in these categories are as follows:
![[Scheme scheme1]](/schemes/Gach3o3scheme1.gif)
![[Scheme scheme2]](/schemes/Gach3o3scheme2.gif)
The PD_CHAR data items describe information known about the sample from observation and chemical analysis. For example, a description of the sample morphology can be specified using _pd_char_particle_morphology. Note that there are data items in the core dictionary that are appropriate for use with powder diffraction. For example, _atom_type_analytical_mass_% can be used for chemical analysis results and _chemical_melting_point for the melting point. Several similar data items occur in the pdCIF and core dictionaries. _exptl_crystal_colour and _pd_char_colour both describe the sample colour, but _pd_char_colour is more systematic. Also, _pd_char_atten_coef_mu_calc and _exptl_absorpt_coefficient_mu describe similar properties, but _pd_char_atten_coef_mu_calc is adjusted for the sample packing fraction, so it can be compared with the experimental value, _pd_char_atten_coef_mu_obs, when a direct measurement is made.
The PD_PREP data items describe how the sample was collected or prepared. For example, _pd_prep_pressure and _pd_prep_temperature describe the pressure and temperature used to prepare the sample. Note that these will probably differ from the pressure and temperature conditions at which diffraction measurements are made. Measurement conditions are recorded in _diffrn_ambient_pressure and _diffrn_ambient_temperature.
