Powder Cell program

While most Rietveld programs can calculate powder patterns, it can be easier to use a dedicated program. An excellent program for pattern calculation is the Powder Cell program. However, if attempting to calculate accurate patterns for non-tube wavelengths, the Poudrix software should be considered (Table 17.31). 

Calculation of intensities of re fixes (1) and inter-plane distances (d) carried out with apphcation of standard software package EVA. Theoretical XRD spectra (X-ray patterns) were calculated under Powder Cell program described in [17, 18]. Optical density Ag-GIM was measured by means of Macbeth TD504 photometer (Kodak, USA) in range 0.15.0 units with accuracy of 2% (rel.). 

With CIF becoming a more used standard in the powder diffraction community, structure data conversion is becoming less needed on a day-to-day basis. The Powder Cell format is probably the next best format due to its relative simplicity compared to CIF. Most structure databases can export files into CIF format, and some to Powder Cell format. Eric Dowty s Cryscon software is currently the most comprehensive structure data conversion and transformation (Table 17.8). However, due care should be shown and results checked. Normally, the programs are robust, and it is more a case of users selecting options without understanding the consequences. 

POWDER CELL a program for the representation and manipulation of crystal structures and calculation of the resulting X ray powder patterns., W. Kraus and G. Nolze, J. Appl. Crystallogr., 1996, 29, 301 303... 

Powder Cell POWDER CELL a program for the representation and... 

Poudrix for LMGP Suite Suite of Programs for the Shelx, Powder Cell,... 

Gretep LMGP Suite Suite of Programs for the interpretation of X ray Experiments, by J. Laugier and B. Bochu, ENSP/ Laboratoire des Materiaux et du Genie Physique, BP 46. 38042 Saint Martin d Hcres, France Poudrix, Shelx, Lazy Pulvarix, Powder Cell, CIF... 

To answer on the question, whether the reCfexes indicated can belong to elemental silver with such a space stmcture in principle, theoretical XRD-pattems of assumed structure of element silver with use of program powder cell described in woric [18], have been constractedby us. These XRD-pattems ate presented in Figure 11. As may be seen from them, the theoretical d values calculated by us (333.6, 288.7, 204.2, 174.1, 166.7, 144.4, 132.5, 129.1, and 117.9 pm) for spedCbd above stmcture. 

Information content in a powder diffraction pattern is reduced as compared to that in single crystal diffraction, due to the collapse of the three dimensional reciprocal space into a one dimensional space where the only independent variable is the scattering angle. The poorer the resolution of the diffraction method, the less the information content in the pattern (Altomare et al. 1995 David 1999). As a consequence, structure of less complex phases can be determined from power diffraction alone (fewer atoms in the asymmetric unit of the unit cell). However, refinement of the structure is not limited so seriously with resolution issues, so powder diffraction data are used in Rietveld refinement more frequently than in structure determination. Electron powder diffraction patterns can be processed and refined using public domain computer programs. The first successful applications of electron diffraction in this field were demonstrated on fairly simple structures. 

The object of this experiment is to determine the crystal structure of a solid substance from x-ray powder diffraction patterns. This involves determination of the symmetry classification (cubic, hexagonal, etc.), the type of crystal lattice (simple, body-centered, or face-centered), the dimensions of the unit cell, the number of atoms or ions of each kind in the unit cell, and the position of every atom or ion in the unit cell. Owing to inherent limitations of the powder method, only substances in the cubic system can be easily characterized in this way, and a cubic material will be studied in the present experiment. However, the recent introduction of more accurate experimental techniques and sophisticated computer programs make it possible to refine and determine the structnres of crystals of low syimnetiy from powder diffraction data alone. 

Takaki Y., Taniguchi T., Nakata K. and Yamaguchi H., Program for Finding the Unit-cell Constants and the Space Group from X-ray Powder Diffraction Data - The Case Where Approximate Unit-cell Contants are Known, J.Ceram. Soc. Jpn., 97 (1989)pp.763-766. 

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