PDF-4+ - Purchase

Identify and Quantitate

PDF-4 products are advanced databases containing the data from multiple database sources. These databases are advanced in that they have an array of tools that supplement conventional analyses. These tools include a full suite of data simulation programs enabling the use of neutron, electron, or synchrotron data, in addition to X-ray data. The simulations can also be tailored for various instrumental and specimen characteristics, such as the high resolution available in some synchrotrons and the ability to simulate nanoparticles for any reference material. The databases have simulations for standard powder diffraction, as well as EBSD and spot pattern electron diffraction. Several different algorithms are automatically employed by the programs depending on whether atomic coordinates, powder data, or scattering factors are available from the entry information.

There are two new simulation features for Release 2009. The electron diffraction simulation has been enhanced to adapt for space group conditions and electron form-factor intensities. An interactive panel shown on the far right in Figure 5 can change several key instrumental parameters (i.e., radius, voltage, wavelength) and recalculate the pattern on-the-fly. These features were added based on input from users of the PDF who work in electron diffraction. In Figure 5 on the left, you will see a 2D pattern simulator that can be used to display X-ray, neutron or electron diffraction data.

For quantitative analysis, the PDF-4 product line offers the critical data needed to perform quantitation by the Reference Intensity Ratio (RIR) method, Rietveld analysis or total pattern analysis. The simulation package above can be used to create digital patterns for export into pattern fitting routines or cluster analyses. ICDD is also including digitized experimental patterns with particular attention to characterizing semicrystalline materials (clays, powders) that are not well described by a crystalline model.

Two features of the Powder Diffraction File are shown in Figure 7. The top pattern is the experimental pattern for polypropylene, the bottom pattern is the crystallite size broadening simulation of the crystalline component. The difference in the two patterns, between 12 and 25 degrees two theta, is predominately due to the amorphous content. In this manner, PDF-4+ can be used to examine both crystallinity and crystallite size effects.

Data Mining

ICDD continues to add new searches and display fields to the search and display software used in PDF-4+, as shown below. All searches and displays can be combined, providing a nearly endless variety of choices for data mining. The results of any search and display can be graphically plotted. In 2009, nearly all the new features were suggested by ICDD members and users of the database.

Another new useful feature is the enhancement of the “coordinates” display field. This is a flag that shows all the materials that have an atomic coordinate set with the entry. New in 2009 is a second flag, shown in Figure 9 as a gray check that indicates that there is a cross-reference to a structure with atomic coordinates. By editorial definition, cross-references must have similar cell dimensions, volumes and diffraction patterns with identical space groups and empirical formula. In such a manner, over 40,000 materials without atomic coordinate sets are now cross-referenced to atomic coordinates to facilitate Rietveld analyses. A mouse click on the entry with the gray check would pull up the entry data with an active link to the atomic coordinates in the cross-reference section of the PDF card.

Figure 10 also demonstrates one of several new display options. This figure shows the molecular volume, which is a cell volume divided by Z. As shown in the graph, this representation clearly distinguishes between the known polymorphs of silicon nitride. Using the point and click option, any point on the graph can display either the diffraction data for that entry or a full entry display. Table 1 (above) outlines both standard options, as well as many new options for both searches and displays.