ICDD Powder Diffraction File

The data are taken from the ICDD powder diffraction file, record No. 4-836 H.E. Swanson, E. Tatge, National Bureau of Standards (US), Circular 359, 1 (1953). 

Figure 4.18. Example of a record extracted from the ICDD Powder Diffraction File. ...

Recently the ICDD Powder Diffraction File underwent a substantial and useful upgrade calculated patterns based on single crystal data from the ICSD file have been included into the PDF-2/PDF-4 Full File calculated patterns of structures stored in the CSD file, have been included into the PDF-4 Organics (see Table 4.3). These additions make it possible to conduct searches and find matches with computed digitized powder patterns in addition to experimentally measured powder diffraction data, thus improving automation, simplifying phase identification process and considerably expanding the applicability of the powder method for a qualitative phase analysis. 

ICDD Powder Diffraction Files on CD-ROM http //www.icdd.com/ IC-POWLS E-mail Winfried Kockelmann (W.Kockelmann rl.ac.uk)... 

International Centre for Diffraction Data- ICDD, Powder Diffraction File, Newtown Square, Pennsylvania, 1997. 

Sea.rch-Ma.tch. The computer identifies which crystalline phases (components) match the unknown pattern by using a file of known powder patterns maintained by the International Center for Diffraction Data (ICDD). The Powder Diffraction File contains interplanar t5 -spacings d = A/(2sin0)] and intensities of the diffraction maxima for each crystalline powder pattern submitted to the ICDD. Currendy there are about 65,000 patterns in the file. Current search—match programs can successfully identify up to seven components in an unknown pattern. A typical diffraction pattern of an unknown sample and the components identified by the computer search-match program is shown in Figure 15. 

The first collection of the powder diffraction data appeared in 1938, known as ASTM cards. Later, the International Centre for Diffiaction Data (ICDD) issued the data in electronic form, which became known as the Powder Diffraction File (PDF). Majority of the users currently use the so called Pdf-2 version, updated in different years. It contains both measured and computed diffiaction data in a flat-file structure. Beside some additional... 

International Centre for Diffraction Data (ICDD) (2006). Powder diffraction file Organic and organometallic phases search manual for experimental patterns. International Centre for Diffraction Data, Newton Square, PA. 

X-ray powder diffraction files (PDFs) for explosive materials are available as subsets of PDF libraries, such as Xpowder and that of the International Centre for Diffraction Data (ICDD). Commercial X-ray diffractometers can yield lattice spacings, d, to a precision of 0.0001 A. At this accuracy, it is not difficult to distinguish uniquely between many thousands of chemical compounds. Hence, XRD is a standard analytical technique for precisely identifying crystalline materials. 

ICDD, International Centre for Diffraction Data, Powder Diffraction File—2 Sets 1 7, Card iS-ii 7 (1997a). 

ICDD, Powder Dijfraction File, ed. W. F. McClune (Newton Square, PA International Centre for Diffraction Data, 2000). CIF from library of crystal files in Centre for Innovation Enterprise, CrystalMaker Software Limited (Oxford Oxford University, 2006). See example in Section 14.7. 

FIGURE 16.5. Data for two salts from the Powder Diffraction File. The crystal system, unit-cel] dimensions, space group and bibliographic references are given together with experimental details. Listed on the tight ate dhki, I hkl) and hkl for the most intense Bragg reflections. Courtesy, JCPDS — International Centre for Diffraction Data (ICDD), publishers of the Powder Diffraction File. 

The optimal counting time depends on the requirements imposed by the desired quality of diffraction data. For example, the International Centre for Diffraction Data (ICDD), which maintains and distributes the most extensive database of powder diffraction data, has established the following requirements for the submission of new experimental powder diffraction patterns to be added to the Powder Diffraction File ... 

The most complete and most often used powder diffraction database is the Powder Diffraction File (PDF), which is maintained and periodically updated by the fritemational Centre for Diffraction Data (ICDD ). PDF is a commercial database, and complete information about both the ICDD and Powder Diffraction File is available on the Web at http //www.icdd.com. This database is quite unique it contains either or both the experimentally measured and calculated digitized powder patterns for hundreds of thousands of compounds, including minerals, metals and alloys, inorganic materials, organic compounds and pharmaceuticals. The PDF is available as a whole or in subsets. Each record in the database is historically called the card."... 

ICDD makes limited funds available to researchers interested in processing and submitting new experimental patterns for incorporation into the Powder Diffraction File. More information about the ICCD s Grant-in-Aid program can be found at... 

ICDD" - Powder Diffraction PDF-2 or PDF-4 Full File. Both -149,000 ... 

The reference intensity ratio method is based on the experimentally established intensity ratio between the strongest Bragg peaks in the examined phase and in a standard reference material. The most typical reference material is corundum, and the corresponding peak is (113). The reference intensity ratio k) is quoted for a 50 50 (wt. %) mixture of the material with corundum, and it is known as the corundum number . The latter is commonly accepted and listed for many compounds in the ICDD s Powder Diffraction File. Even though this method is simple and relatively quick, careful account and/or experimental minimization of preferred orientation effects are necessary to obtain reliable quantitative results. 

See section 4.4 in Chapter 4 and http //www.icdd.com/ for more information about the Powder Diffraction File. 

When the unit cell is found, it can be used to search multiple databases in addition to the ICDD s Powder Diffraction File. A positive search result usually confirms indexing, while a negative outcome does not necessarily mean that the indexing is wrong - a particular crystal structure may be novel and/or not yet included in a database. 

Throughout the long history of the technique, its emphasis underwent several evolutionary and revolutionary transformations. Remarkably, none of the new developments have taken away nor diminished the value of earlier applications of the powder diffraction method on the contrary, they enhanced and made them more precise and dependable. A noteworthy example is phase identification from powder diffraction data, which dates back to the late 1930 s (Hanawalt, Rinn, and Frevel). Over the years, this application evolved into the Powder Diffraction File containing reliable patterns of some 300,000 crystalline materials in a readily searchable database format (Powder Diffraction File is maintained and distributed by the International Centre for Diffraction Data, http //www.icdd.com). 

In modern powder diffraction the measurement delivers a raw-file of some thousand step-scan data of counted X-ray photons per step. This raw file contains all the needed information to carry out a crystallographic analysis, but in a way that requires follow up. More informative is a list of distinguishable reflections that includes the position (mostly in the form of f-values) and intensity of each reflection. This dif-file (d-values and intensities) contains some tens to hundreds of reflections. The number of reflections depends on the complexity of the structure and the crystal symmetry the more atoms per cell and the lower the symmetry the more reflections can be identified. But the number of detectible reflections also depends on the resolving power of the equipment, best documented by the half-width of the reflections (more accurately half-width at half-maximum, FWHM). Reflections nearer together than this half-width (or even two half-widths) cannot be resolved. In a second step, very often the Miller indices of the originating lattice planes are added to the dif-file. For this the knowledge of the unit cell is necessary (though not of the crystal structure itself). The powder diffraction file PDF of the International Centre for Diffraction Data (ICDD) contains over 100000 such dif-files for the identification and discrimination of solid state samples. 

ICDD, The Powder Diffraction File, Database of the International Center for Diffraction Data, Sets 1-49 and 70-86, ICDD, 12 Campus Boulevard, Newton Square, Pennsylvania 19073-3273, USA, 1999. 

International Centre for Diffraction Data — Maintains and distributes the Powder Diffraction File (PDF), a file of over 500,000 X-ray powder diffraction patterns used for identification of crystalline materials. The ICDD also distributes the NIST Crystal Data file, which contains lattice parameters for over 235,000 inorganic, organic, metal, and mineral crystalline materials. Address 12 Campus Blvd., Newton Square, PA 19073-3273 [www.icdd.com]. 

Every crystalline powder produces a characteristic diffraction pattern. This is the basis of qualitative analysis by powder diffraction. Identification is usually accomplished by systematic comparison of an unknown pattern with a catalog of standard data such as the Powder Diffraction File published by the International Centre for Diffraction Data (ICDD). Specialized techniques have been designed for certain situations. 

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