Phase identification

We saw in Chapter 1 that the nature and the positions of the atoms have a direct effect on the intensity of the diffraction peaks. Likewise, the interplanar distances, and hence the positions of the diffraction peaks, are directly related to the values of the cell parameters. This shows that the list of relative intensities and interplanar 

For each known phase, an entry is added, that corrstitutes some kind of ID for that phase. Such an entry is shown in Table 4.1 arrd it includes, for each characteristic peak, the values of the interplanar distances, the integrated interrsities and the Miller indices. Also, the crystal system, the cell parameters and the space group are mentioned. Generally, bibliographical information is included to specify the reference to the publication the entry was based on. 

1 The methods used to compare experimental results and the characteristics of known crystal phases have been described in detail in other books. Readers who wish to study this aspect further can refer in particular to Jenkins and Snyder [JEN 96] or to the more recent book by Pecharsky and Zavalij [PEC 03]. 

Electron microscopy study of epitaxial grown thin film of Zr02 (R.A. Ploc, Proc. Am. Meeting of Microscopy Soc. Canada Vol. VII, 34 (1980) give a = 5.135(5) CaF2 PSC cF12. To replace 14-534 and 7-337  

In the past few years, a new method was developed [CAU 88], It consists of directly modeling the pattern without determining beforehand the interplanar distances and the relative intensities. A calculated pattern is generated by gradually adding the contributions of the different possible phases. By adjusting the calculated pattern with the experimental data, the validity of the suggested phase combinations can be tested. This method seems to be particularly efficient. 

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Liquid crystal phases possess characteristic textures when viewed in polarized light under a microscope. These textures, which can often be used to identify phases, result from defects in tire stmcture. Compendia of micrographs showing typical textures exist to facilitate phase identifications [37, 38]. These monographs also discuss tire origins of defect stmctures in some detail. 

Element-selective phase identification and quandfica-tion, structural characterization of disordered states... 

Besides phase identification XRD is also widely used for strain and particle size determination in thin films. Both produce peak broadenings, but they are distinguishable. Compared to TEM, XRD has poor area resolution capability, although by using synchrotron radiation beam diameters of a few pm can be obtained. Defect topography in epitaxial films can be determined at this resolution. 

Examples of XRD Characterization of Thin Films Phase Identification... 

Other excellent methods of phase identification include TEM and electron diffraction. These may be more useful for low-Z materials, ultrathin films, and for characterizing small areas, including individual grains. For multiphase films with incomplete texture, these methods and XRD are complementary, since in commonly used geometries, they probe atomic planes perpendicular and parallel to the thin film surface, respectively. 

As with other diffraction techniques (X-ray and electron), neutron diffraction is a nondestructive technique that can be used to determine the positions of atoms in crystalline materials. Other uses are phase identification and quantitation, residual stress measurements, and average particle-size estimations for crystalline materials. Since neutrons possess a magnetic moment, neutron diffraction is sensitive to the ordering of magnetically active atoms. It differs from many site-specific analyses, such as nuclear magnetic resonance, vibrational, and X-ray absorption spectroscopies, in that neutron diffraction provides detailed structural information averaged over thousands of A. It will be seen that the major differences between neutron diffraction and other diffiaction techniques, namely the extraordinarily... 

Figure 4.4. X-rays scattered by atoms in an ordered lattice interfere constructively in directions given by Bragg s law. The angles of maximum intensity enable one to calculate the spacings between the lattice planes and allow furthermore for phase identification. Diffractograms are measured as a function of the angle 26. When the sample is a...

Bayne, S. C. Greener, E. H. (1985). ZnO cements phase identification by thermal analysis. Dental Materials, 1, 165-9. 

Figure 7.8 Dependence of the nigration tine for a 7 cn developnent in an unsaturated chamber for different Merck reversed-phase layers using water-acetonitrile as the nobile phase. Identification 1 - RP-18 HPTLC plate 2 - RP-2 HPTLC plate 3 - RP-18N HPTLC plate 4 =- RP-18 TLC plate and 5 RP-8 TLC plate.

The analytical power of XRF and XRD has lately been combined in an integrated XRF/XRD system, in which XRD powder measurements are examined for phase identification and Rietveld analysis on the basis of element concentrations. Process analysis, a former stronghold of XRF, can now be performed by highspeed XRD, which is supported by XRF element-analytical data. 

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

A room temperature powder X-ray diffraction pattern for Na8[GaSi04]6(C104)2 Sodalite with Si as an internal standard for phase identification in the reaction products has been studied. X-ray powder diffraction study confirms the cubic structure of Na8[GaSi04]6(C104)2 sodalite synthesized... 

X-ray powder diffractometry is a relatively straightforward technique for phase identification. There are, however, numerous sources of error in quantitative XPD. The issues that are of greatest relevance to pharmaceutical systems are enumerated in the following. 

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. 

XRD Characterization The powder x-ray diffraction of the mechano-chemically milled complex borohydride has been carried out by the Philips X pert diffractometer with Cu-Koi radiation of X= 5.4060 A. The incident and diffraction slit width used for the measurements are 1° and 2° respectively. The sample holder was covered with Polyethylene tape (foil) with an O-ring seal in an N2 filled glove box in order to avoid or at least minimize the 02/moisture pickup during the XRD measurements. The diffraction from the tape was calibrated without the actual sample and found to be occurring at 29 angles of 22° and 24°, respectively. The XRD phase identification and particle size calculation has been carried out using PANalytical X pert Highscore software, version l.Of. 

To determine the phase properties of the calcined bimetallic nanoparticles, a detailed x-ray diffraction (XRD) study was carried out. The XRD data of AuPt/C showed that the diffraction patterns for the carbon-supported nanoparticles show a series of broad Bragg peaks, a picture typical for materials of limited structural coherence. Nevertheless, the peaks are defined well enough to allow a definitive phase identification and structural characterization. The diffraction patterns of Au/C and Pt/C could be unambiguously indexed into an fcc-type cubic lattice occurring with bulk gold and platinum. We estimated the corresponding lattice parameters by carefully determining... 

PHASE IDENTIFICATION BY COMBINING LOCAL COMPOSITION FROM EDX WITH INFORMATION FROM DIFFRACTION DATABASE... 

Local composition is very useful supplementary information that can be obtained in many of the transmission electron microscopes (TEM). The two main methods to measure local composition are electron energy loss spectrometry (EELS), which is a topic of a separate paper in this volume (Mayer 2004) and x-ray emission spectrometry, which is named EDS or EDX after the energy dispersive spectrometer, because this type of x-ray detection became ubiquitous in the TEM. Present paper introduces this latter method, which measures the X-rays produced by the fast electrons of the TEM, bombarding the sample, to determine the local composition. As an independent topic, information content and usage of the popular X-ray powder dififaction database is also introduced here. Combination of information from these two sources results in an efficient phase identification. Identification of known phases is contrasted to solving unknown stmctures, the latter being the topic of the largest fiaction of this school. 

Phase identification by combining local composition from EDX... 

Qualitative phase identification with the ProcessDiffraction program... 

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