Diffraction file

Powder Diffraction File, Sets 1—29, CPDS International Center for Diffraction Data, Swarthmore, Pa., 1985. 

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. 

By referring to the "POWDER DIFFRACTION FILE", published by the AMERICAN SOCIETY FOR TESTING AND MATERIALS, 1916 Race St., Philadelphia, Penna. 19103, we can look up the most probable composition. Usually, we will know how the material was made and the components used to make it. If not, we can analyze for constituents. In this case, we would find La and Al, and would surmize that we have an oxidic compound, since we made the compound by firing the two oxides together. 

Joint Committee on Powder Diffraction Standards (JCPDS) Powder Diffraction File, 6-675. 

Powder Diffraction File, Inorganic Phases, Organic and Organometallic Phases Search Manual, W. F. McClune, editor-in-chief, International Centre for Diffraction Data, Newtown Square, Pa., 1993. 

Recent developments and prospects of these methods have been discussed in a chapter by Schneider et al. (2001). It was underlined that these methods are widely applied for the characterization of crystalline materials (phase identification, quantitative analysis, determination of structure imperfections, crystal structure determination and analysis of 3D microstructural properties). Phase identification was traditionally based on a comparison of observed data with interplanar spacings and relative intensities (d and T) listed for crystalline materials. More recent search-match procedures, based on digitized patterns, and Powder Diffraction File (International Centre for Diffraction Data, USA.) containing powder data for hundreds of thousands substances may result in a fast efficient qualitative analysis. The determination of the amounts of different phases present in a multi-component sample (quantitative analysis) is based on the so-called Rietveld method. Procedures for pattern indexing, structure solution and refinement of structure model are based on the same method. 

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... 

Table 2.1 shows the crystal structure data of the phases existing in the Mg-H system. Pnre Mg has a hexagonal crystal structure and its hydride has a tetragonal lattice nnit cell (rutile type). The low-pressure MgH is commonly designated as P-MgH in order to differentiate it from its high-pressure polymorph, which will be discussed later. Figure 2.2 shows the crystal structure of p-MgH where the positions of Mg and H atoms are clearly discerned. Precise measurements of the lattice parameters of p-MgH by synchrotron X-ray diffraction yielded a = 0.45180(6) mn and c = 0.30211(4) nm [2]. The powder diffraction file JCPDS 12-0697 lists a = 0.4517 nm and c = 0.30205 nm. The density of MgH is 1.45 g/cm [3]. 

In the first phase, a data base is acquired from one of a variety of sources. Some of the CIS data bases have been developed specifically for the CIS, an example of this being the mass spectral data base (2). Others, such as the Cambridge Crystal File (4), are leased for use in the CIS and still others, such as the X-ray powder diffraction file (5), are operated within the CIS by their owners, in this case the )oint Committee on Powder Diffraction Standards. 

Joint Comlttee on Powder Diffraction Standards Powder Diffraction Files, ASTM, New York, 1967, Set 6-10, p 399. 

If the powder diffraction pattern is indeed a fingerprint for a given material, then it would seem desirable to have a library of the patterns for all known substances. In this way, the powder pattern of an unknown material could be compared to the known patterns in the library until a match is made. Such a file does exist. It is the JCPDS Powder Diffraction File (PDF) mentioned earlier (3). The PDF is published annually as a set of consecutively numbered "cards" (the idea of a card becoming somewhat... 

The data, obtained through use of the equipment mentioned above, is tabulated in the format used in the ASTM Powder Diffraction File (Refs 4,6,10,21 22). likewise, the format and conventions of the International Tables for X-Ray Crystallography (Ref 5) are usually also adhered to closely... 

The primary source of x-ray crystal diffract-tion reference data is the above-mentioned ASTM Powder Diffraction File , published by the Joint Committee on Powder Diffraction Standards. This file consists of over 38000 diffraction patterns of crystalline materials including expls and related materials. Scientists in the expls field routinely utilize this source. for the identification of expls and metastable phases by comparing the interplanar d spacings and intensities of exptl phases with those of known phases (Refs 4,10,21 22)... 

Smith et al, Eds, Index (Organic) to the Powder Diffraction File-1967 , ASTM PD1S-170, ASTM,... 

X-ray Powder Diffraction File, PDF-2 Database Sets 1-44. (International Centre for Diffraction Data, Pennsylvania, 1994) card 17-333, 15-457. 

American Society for Testing and Materials (ASTM) X-ray powder diffraction file, card No. 9-432, Philadelphia (1967). 

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. 

Faber, J., Fawcett, T and Goehner, R. (2005). Powder Diffraction File (2003). Newtown Square, PA The International Centre for Diffraction Data. http //jour-nals.cambridge.org/downloadphpfile. 

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