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PRESENTED BYH.SIVATHANU

DEPARTEMENT OF PHARMACEUTICAL ANALY

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X-ray powder diffraction (XRD) is a rapidanalytical technique primarily used for phaseidentification of a crystalline material and canprovide information on unit cell dimensionsThe analyzed material is finely ground,homogenized, and average bulk compositionis determined.

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Max von Laue, in 1912, discovered thatcrystalline substances act as three-dimensional diffraction gratings for X-raywavelengths similar to the spacing of planes in a crystal lattice. X-ray diffractionis now a common technique for the study of crystal structures and atomic spacing

X-ray diffraction is based on constructiveinterference of monochromatic X-rays and acrystalline sample

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These X-rays are generated by a cathode raytube, filtered to produce monochromaticradiation, collimated to concentrate, anddirected toward the sampleThe interaction of the incident rays with thesample produces constructive interference(and a diffracted ray) when conditions satisfy

Bragg's Law(n =2 d sin )ected toward thesample

http://serc.carleton.edu/research_education/geochemsheets/BraggsLaw.htmlhttp://serc.carleton.edu/research_education/geochemsheets/BraggsLaw.html

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This law relates the wavelength of electromagnetic radiation to the diffractionangle and the lattice spacing in a crystallinesampleThese diffracted X-rays are then detected,processed and counted. By scanning thesample through a range of 2 angles, all

possible diffraction directions of the latticeshould be attained due to the randomorientation of the powdered material. .

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Conversion of the diffraction peaks to d-spacings allows identification of the mineralbecause each mineral has a set of unique d-spacings. Typically, this is achieved bycomparison of d-spacings with standard refeAll diffraction methods are based ongeneration of X-rays in an X-ray tuberencepatterns

http://serc.carleton.edu/research_education/geochemsheets/xrays.htmlhttp://serc.carleton.edu/research_education/geochemsheets/xrays.htmlhttp://serc.carleton.edu/research_education/geochemsheets/xrays.htmlhttp://serc.carleton.edu/research_education/geochemsheets/xrays.html

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These X-rays are directed at the sample, andthe diffracted rays are collected. A keycomponent of all diffraction is the anglebetween the incident and diffracted rays.Powder and single crystal diffraction vary ininstrumentation beyond this.

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X-ray diffractometers consist of three basicelements: an X-ray tube, a sample holder,and an X-ray detectorX-rays are generated in a cathode ray tube byheating a filament to produce electrons,accelerating the electrons toward a target byapplying a voltage, and bombarding thetarget material with electrons.

http://serc.carleton.edu/research_education/geochemsheets/xrays.htmlhttp://serc.carleton.edu/research_education/geochemsheets/xrays.htmlhttp://serc.carleton.edu/research_education/geochemsheets/xrays.htmlhttp://serc.carleton.edu/research_education/geochemsheets/xrays.html

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When electrons have sufficient energy todislodge inner shell electrons of the targetmaterial, characteristic X-ray spectra areproduced.These spectra consist of several components,the most common being K and K. K consists, in part, of K 1 and K 2. K 1 has aslightly shorter wavelength and twice theintensity as K 2.

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The specific wavelengths are characteristic of the target material (Cu, Fe, Mo, Cr).Filtering, by foils or crystal monochrometers,is required to produce monochromatic X-raysneeded for diffractionK 1and K 2 are sufficiently close inwavelength such that a weighted average of

the two is used.

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Copper is the most common target materialfor single-crystal diffraction, with CuK radiation = 1.5418. These X-rays arecollimated and directed onto the sample.As the sample and detector are rotated, theintensity of the reflected X-rays is recorded.

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When the geometry of the incident X-raysimpinging the sample satisfies the BraggEquation, constructive interference occursand a peak in intensity occurs. A detectorrecords and processes this X-ray signal andconverts the signal to a count rate which isthen output to a device such as a printer orcomputer monitor.

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The geometry of an X-ray diffractometer issuch that the sample rotates in the path of thecollimated X-ray beam at an angle while theX-ray detector is mounted on an arm to collect

the diffracted X-rays and rotates at an angle of 2 .The instrument used to maintain the angle

and rotate the sample is termed a goniometer For typical powder patterns, data is collected

at 2 from ~5 to 70, angles that are preset inthe X-ray scan.

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X-ray powder diffraction is most widely usedfor the identification of unknown crystallinematerials (e.g. minerals, inorganiccompounds). Determination of unknownsolids is critical to studies in geology,environmental science, material science,engineering and biology. Other applicationsinclude:

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characterization of crystalline materialsidentification of fine-grained minerals suchas clays and mixed layer clays that aredifficult to determine opticallydetermination of unit cell dimensionsmeasurement of sample purity

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With specialized techniques, XRD can be usedto: determine crystal structures using Rietveldrefinementdetermine of modal amounts of minerals(quantitative analysis)characterize thin films samples by: determining lattice mismatch between film and

substrate and to inferring stress and strain

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determining dislocation density and quality of thefilm by rocking curve measurements measuring superlattices in multilayered epitaxial

structures

determining the thickness, roughness and densityof the film using glancing incidence X-rayreflectivity measurements

make textural measurements, such as the

orientation of grains, in a polycrystallinesample

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StrengthsPowerful and rapid (< 20 min) technique foridentification of an unknown mineralIn most cases, it provides an unambiguousmineral determinationMinimal sample preparation is requiredXRD units are widely available

Data interpretation is relatively straightforward

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LimitationsHomogeneous and single phase material isbest for identification of an unknownMust have access to a standard reference fileof inorganic compounds (d-spacings, hkl s)Requires tenths of a gram of material whichmust be ground into a powder

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For mixed materials, detection limit is ~ 2% of sampleFor unit cell determinations, indexing of patterns for non-isometric crystal systems iscomplicatedPeak overlay may occur and worsens for highangle 'reflections'

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Determination of an unknown requires: the material, an instrument for grinding, and a sample holder. Obtain a few tenths of a gram (or more) of the material, as pure as possibleGrind the sample to a fine powder, typically ina fluid to minimize inducing extra strain(surface energy) that can offset peak

positions, and to randomize orientation.Powder less than ~10 m(or 200-mesh) insize is preferred

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Place into a sample holder or onto the samplesurface: Show captionHidePacking of fine powder into a sample holder.Photo courtesy of USGS.Details smear uniformly onto a glass slide, assuring a flat

upper surface pack into a sample container sprinkle on double sticky tape.

http://serc.carleton.edu/details/images/8417.htmlhttp://serc.carleton.edu/details/images/8417.html

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Typically the substrate is amorphous to avoidinterferenceCare must be taken to create a flat uppersurface and to achieve a random distributionof lattice orientations unless creating anoriented smear.For analysis of clays which require a single

orientation, specialized techniques forpreparation of clay samples are given byUSGS.

http://pubs.usgs.gov/of/2001/of01-041/htmldocs/methods.htmhttp://pubs.usgs.gov/of/2001/of01-041/htmldocs/methods.htmhttp://pubs.usgs.gov/of/2001/of01-041/htmldocs/methods.htmhttp://pubs.usgs.gov/of/2001/of01-041/htmldocs/methods.htm

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For unit cell determinations, a small amountof a standard with known peak positions (thatdo not interfere with the sample) can beadded and used to correct peak positions.

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Data Collection The intensity of diffracted X-rays is continuously recorded as the sampleand detector rotate through their respectiveangles. A peak in intensity occurs when themineral contains lattice planes with d-spacings appropriate to diffract X-rays at thatvalue of .

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Although each peak consists of two separatereflections (K 1 and K 2), at small values of 2 the peak locations overlap with K 2 appearing as a hump on the side of K 1.Greater separation occurs at higher values of . Typically these combined peaks are treatedas one. The 2 position of the diffractionpeak is typically measured as the center of the peak at 80% peak height.

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Data Reduction Results are commonlypresented as peak positions at 2 and X-raycounts (intensity) in the form of a table or anx-y plot (shown above). Intensity (I ) is eitherreported as peak height intensity, thatintensity above background, or as integratedintensity, the area under the peak. Therelative intensity is recorded as the ratio of the peak intensity to that of the most intensepeak ( relative intensity = I/I 1 x 100 ).

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Determination of an Unknown The d-spacingof each peak is then obtained by solution of the Bragg equation for the appropriate valueof . Once all d-spacings have beendetermined, automated search/matchroutines compare the d s of the unknown tothose of known materials.

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Because each mineral has a unique set of d-spacings, matching these d-spacingsprovides an identification of the unknownsample.A systematic procedure is used by orderingthe d-spacings in terms of their intensitybeginning with the most intense peak.

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Files of d-spacings for hundreds of thousands of inorg anic compounds areavailable from the International Centre forDiffraction Dataas the Powder Diffraction File

(PDF).Many other sites contain d-spacings of minerals such as the American MineralogistCrystal Structure Database.

Determination of Unit Cell Dimensions Fordetermination of unit cell parameters, eachreflection must be indexed to a specific hkl .

http://www.icdd.com/http://www.icdd.com/http://www.icdd.com/http://www.icdd.com/http://rruff.geo.arizona.edu/AMS/amcsd.phphttp://rruff.geo.arizona.edu/AMS/amcsd.phphttp://rruff.geo.arizona.edu/AMS/amcsd.phphttp://rruff.geo.arizona.edu/AMS/amcsd.phphttp://rruff.geo.arizona.edu/AMS/amcsd.phphttp://rruff.geo.arizona.edu/AMS/amcsd.phphttp://www.icdd.com/http://www.icdd.com/

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The following literature can be used tofurther explore X-ray Powder Diffraction(XRD)Bish, DL and Post, JE, editors. 1989. ModernPowder Diffraction. Reviews in Mienralogy, v.20. Mineralogical Society of America.Cullity, B. D. 1978. Elements of X-raydiffraction. 2nd ed. Addison-Wesley, Reading,Mass.

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Klug, H. P., and L. E. Alexander. 1974. X-raydiffraction procedures for polycrystalline andamorphous materials. 2nd ed. Wiley, NewYork.Moore, D. M. and R. C. Reynolds, Jr. 1997. X-Ray diffraction and the identification andanalysis of clay minerals. 2nd Ed. OxfordUniversity Press, New York.

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For more information about X-ray PowderDiffraction (XRD) follow the links below.For more information on XRD Methods, visitthe USGS website

For additional information on X-ray basics;Materials Research Lab, University of California- Santa BarbaraRigaku Journal; an on-line journal that

describes and demonstrates a wide range of applications using Xray diffraction.Cambridge University X-ray Tutorial

http://pubs.usgs.gov/of/2001/of01-041/index.htmhttp://pubs.usgs.gov/of/2001/of01-041/index.htmhttp://www.mrl.ucsb.edu/mrl/centralfacilities/xray/xray-basics/index.htmlhttp://www.rigaku.com/downloads/journal/http://www.esc.cam.ac.uk/teaching/content.htmlhttp://www.esc.cam.ac.uk/teaching/content.htmlhttp://www.esc.cam.ac.uk/teaching/content.htmlhttp://www.esc.cam.ac.uk/teaching/content.htmlhttp://www.rigaku.com/downloads/journal/http://www.rigaku.com/downloads/journal/http://www.rigaku.com/downloads/journal/http://www.mrl.ucsb.edu/mrl/centralfacilities/xray/xray-basics/index.htmlhttp://www.mrl.ucsb.edu/mrl/centralfacilities/xray/xray-basics/index.htmlhttp://www.mrl.ucsb.edu/mrl/centralfacilities/xray/xray-basics/index.htmlhttp://pubs.usgs.gov/of/2001/of01-041/index.htmhttp://pubs.usgs.gov/of/2001/of01-041/index.htm

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International Union of Crystallography (IUCr)Teaching Pamphlets Introduction to X-ray Diffraction--Universityof California, Santa BarbaraIntroduction to Crystallography--from LLNLX-ray Crystallography Lecture Notes--fromSteve Nelson, Tulane University

Interactive Tutorial About X-ray diffraction--University of Erlangen

http://www.iucr.org/iucr-top/comm/cteach/pamphlets.htmlhttp://www.iucr.org/iucr-top/comm/cteach/pamphlets.htmlhttp://www.mrl.ucsb.edu/mrl/centralfacilities/xray/xray-basics/index.htmlhttp://ruppweb.dyndns.org/Xray/101index.htmlhttp://www.tulane.edu/~sanelson/eens211/x-ray.htmhttp://www.lks.physik.uni-erlangen.de/diffraction/http://www.lks.physik.uni-erlangen.de/diffraction/http://www.lks.physik.uni-erlangen.de/diffraction/http://www.lks.physik.uni-erlangen.de/diffraction/http://www.tulane.edu/~sanelson/eens211/x-ray.htmhttp://www.tulane.edu/~sanelson/eens211/x-ray.htmhttp://www.tulane.edu/~sanelson/eens211/x-ray.htmhttp://ruppweb.dyndns.org/Xray/101index.htmlhttp://www.mrl.ucsb.edu/mrl/centralfacilities/xray/xray-basics/index.htmlhttp://www.mrl.ucsb.edu/mrl/centralfacilities/xray/xray-basics/index.htmlhttp://www.mrl.ucsb.edu/mrl/centralfacilities/xray/xray-basics/index.htmlhttp://www.iucr.org/iucr-top/comm/cteach/pamphlets.htmlhttp://www.iucr.org/iucr-top/comm/cteach/pamphlets.htmlhttp://www.iucr.org/iucr-top/comm/cteach/pamphlets.htmlhttp://www.iucr.org/iucr-top/comm/cteach/pamphlets.html

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Teaching activities, labs, and resourcespertaining to X-ray Powder Diffraction (XRD).X-ray techniques lab exercises from the SERCTeaching Mineralogy Collections

Weathering of Igneous, Metamorphic, andSedimentary Rocks in a Semi-Arid Climate - AnEngineering Application of Petrology- Thisproblem develops skills in X-ray diffractionanalysis as applied to clay mineralogy, reinforceslecture material on the geochemistry of weathering, and demonstrates the role of petrologic characterization in site engineering.

http://serc.carleton.edu/NAGTWorkshops/mineralogy/activities.html?q1=sercvocabs__8:37http://serc.carleton.edu/NAGTWorkshops/mineralogy/activities.html?q1=sercvocabs__8:37http://serc.carleton.edu/NAGTWorkshops/petrology/teaching_examples/24566.htmlhttp://serc.carleton.edu/NAGTWorkshops/petrology/teaching_examples/24566.htmlhttp://serc.carleton.edu/NAGTWorkshops/petrology/teaching_examples/24566.htmlhttp://serc.carleton.edu/NAGTWorkshops/petrology/teaching_examples/24566.htmlhttp://serc.carleton.edu/NAGTWorkshops/petrology/teaching_examples/24566.htmlhttp://serc.carleton.edu/NAGTWorkshops/petrology/teaching_examples/24566.htmlhttp://serc.carleton.edu/NAGTWorkshops/petrology/teaching_examples/24566.htmlhttp://serc.carleton.edu/NAGTWorkshops/petrology/teaching_examples/24566.htmlhttp://serc.carleton.edu/NAGTWorkshops/petrology/teaching_examples/24566.htmlhttp://serc.carleton.edu/NAGTWorkshops/petrology/teaching_examples/24566.htmlhttp://serc.carleton.edu/NAGTWorkshops/petrology/teaching_examples/24566.htmlhttp://serc.carleton.edu/NAGTWorkshops/mineralogy/activities.html?q1=sercvocabs__8:37http://serc.carleton.edu/NAGTWorkshops/mineralogy/activities.html?q1=sercvocabs__8:37http://serc.carleton.edu/NAGTWorkshops/mineralogy/activities.html?q1=sercvocabs__8:37http://serc.carleton.edu/NAGTWorkshops/mineralogy/activities.html?q1=sercvocabs__8:37

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Teaching Guide to X-ray Diffraction atCambridge A Powerpoint presentation on use of XRD inSoil Science(PowerPoint 1.6MB Sep7 07) byMelody Bergeron,Image and ChemicalAnalysis Laboratoryat Montana StateUniversity

http://www.esc.cam.ac.uk/teaching/pow.htmlhttp://www.esc.cam.ac.uk/teaching/pow.htmlhttp://serc.carleton.edu/files/research_education/geochemsheets/techniques/xrd_soils.ppthttp://serc.carleton.edu/files/research_education/geochemsheets/techniques/xrd_soils.ppthttp://www.physics.montana.edu/ICAL/ICAL.htmlhttp://www.physics.montana.edu/ICAL/ICAL.htmlhttp://www.physics.montana.edu/ICAL/ICAL.htmlhttp://www.physics.montana.edu/ICAL/ICAL.htmlhttp://serc.carleton.edu/files/research_education/geochemsheets/techniques/xrd_soils.ppthttp://serc.carleton.edu/files/research_education/geochemsheets/techniques/xrd_soils.ppthttp://serc.carleton.edu/files/research_education/geochemsheets/techniques/xrd_soils.ppthttp://serc.carleton.edu/files/research_education/geochemsheets/techniques/xrd_soils.ppthttp://serc.carleton.edu/files/research_education/geochemsheets/techniques/xrd_soils.ppthttp://www.esc.cam.ac.uk/teaching/pow.htmlhttp://www.esc.cam.ac.uk/teaching/pow.htmlhttp://www.esc.cam.ac.uk/teaching/pow.htmlhttp://www.esc.cam.ac.uk/teaching/pow.html

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THANKYOU