Powder diffraction software pattern calculation

Qualitative and quantitative analytical applications of X-ray diffraction both require reference diffraction patterns to identify and quantify the different polymorphic modifications. Experimental powder patterns may be suspect for their use as standards as a result of experimentally induced errors or aberrations or the lack of polymorphic purity in the sample itself (which may even result from the sample preparation). The availability of full crystal structure determinations for any or all of the polymorphic modifications can considerably facilitate generation of standard powder patterns. A variety of public domain software is now available for calculating powder diffraction patterns from single crystal data (ICDD 2001, lUCr 2001)." ... 

Most powder diffraction databases only serve angular dispersive X-ray diffraction. Energy dispersive X-ray diffraction data can be transformed into an angular dispersive equivalent that can then be used in conventional search-match software. Users of neutron diffraction data are currently limited to performing phase identification using a list of crystal structures imported into a Rietveld program. It is wise to first run samples destined for neutron diffraction sample in a powder XRD prior to confirm phase purity, and to use calculated patterns to assist in phase identification of possible undesired phases due to ancillary equipment or sample environment. 

H.M. Rietveld developed a practical method to analyze powder diffraction data. The Rietveld refinement method [6] is based on modeling a diffraction pattern according to structural information available for the phases previously identified in the pattern. This model is calculated by computer software after introduction of some crystallographic data space group symmetry, atomic species and positions within the cell, occupancies, lattice parameters, line broadening parameters, and experimental conditions. The term refinement refers to the cyclic improvement process used in the estimation of the set of parameters that can model the diffraction pattern as close as possible to the observed pattern. Usually, the Rietveld refinement is accomplished by minimizing the sum of the differences of calculated and observed intensities for each angular step of the diffraction pattern and by a... 

The powder X-ray diffraction patterns of the samples were recorded on a Philips PW 1820 diffractometer using nickel filtered Cu Ka radiation. The crystallinity of the samples was calculated by measuring the area under the (5 3 3) peak taking original NaY sample as reference. The unit cell size (So) of the samples were determined from XRD patterns using PDPll software. 

---