XRD analysis • Instruments and data acquisition • Getting data and data formats • Analysis software • Phase ID
Equipment • Scintag PAD-V • Pole-Figure attachment • Scintillation detector • Scintag XDS-2000 • Theta-Theta goniometer • i-Ge energy-dispersive detector • Bruker D8 • GADDS area detector • Philips XRD-3000 generator • Laue camera and film recording
Data Acquisition • Assumption: infinite, randomly distributed particles • Size < ~30mm (320 grit) • watch for preferred orientation • Sample on rotation axis • Good statistics! • Standards important for precision work
Acquisition issues • Statistics
Poisson distribution • Describes processes where each event is independent and has a constant probability of occurring within a time interval. • Standard Deviation (s) = (I)½ • Var (I) = s2 = I
S/N ratio • Any point on a scan will have a fixed count rate total counts (I) are proportional to time.
S/N continued… • We usually want NET intensity rather than GROSS intensity. • Need to subtract the background • What uncertainty do we have in the NET intensity?
Variances add Cross terms = 0 for independent variables Relative Variances add Uncertainty propagation Source: P.R. Bevington Data Reduction and Analysis for the Physical Sciences, 2nd ed., p. 50
Case when absolute variances add If B is large, then the remainder after subtraction will be small and the relative uncertainty will be very large.
Acquisition issues • Statistics • Fluorescence effects
Acquisition issues • Statistics • Fluorescence effects • Geometric Effects • Off-axis • Absorption depth (sampling depth)
Aberrations • Bragg-Brentano goniometer is a para-focusing geometry. • All elements must be precisely located. • If the sample is displaced from the rotation axis, there is a peak shift
Displacement Shift h < 100mm Illustrate correction process later
Absorption Equation Where r is the density and m is the mass absorption coefficient.
Absorption Depth Where G is the fraction of the diffracted signal and m is the linear (not mass) absorption coefficient.
Acquisition issues • Statistics • Fluorescence effects • Geometric Effects • Off-axis • Absorption depth (sampling depth) • Spectral Contamination • Cu Kb, W La radiation
Ni Filter • Ka/Kb intensity ratio is 9 • Ni filter attenuates Kb more than Ka • MAC of Ni for Cu Kb = 283 cm2/g • MAC of Ni for Cu Ka = 49 cm2/g • A 20mm Ni filter will produce a Kb/Ka ratio of about 500 while attenuating the Ka by a factor of ~2. • Kb intensity is not 0!
Spectral Contamination • Multiple Cu peaks • Ka1 = 1.540562Å • Ka2 = 1.54439Å • Average =1.5418Å • CuKb = 1.392218Å • W deposits on anode (filament contamination) • W La1 = 1.47639Å
W La Cu Kb MgO
Data Format • EVA needs “.RAW” • Scintag - creates “.RD” • VAX data acquisition computer. Need to download data. • Convert to .RAW with ALL2EVA • Convert to ASCII with RD2ASCII (to read into Excel) • Bruker - .RAW
ALL2EVA • Converts all .RD files (up to 100) in a folder to .RAW • DOS program - 8 character filename • Tips: • Set up your ftp program to download to one directory. • Setup an ALL2EVA shortcut to point to the appropriate directory
Set to your download directory ALL2EVA shortcut
Phase ID • EVA or Jade software • EVA available in er6 lab • EVA & Jade in CEOF computer lab • ICDD database (formerly JCPDS) • Tutorials • www.matter.org.uk/diffraction/x-ray • www.ccp14.ac.uk/educate.htm
er6 procedure • Download and convert data • Go to the CEOF web page (www.ceof.ohio-state.edu) , select “file servers” and the Scintag window. Enter the appropriate username and password. • Copy the file to the C:\TEMP. Ensure that the saved filename conforms to the DOS 8 character format, that the extension is .RD, and that there is no “;1” appended to the extension. • Select Start | All Programs | Databases | X-ray Diffraction | All2EVA. • Copy these .RD and .RAW files to your home directory on the Z: drive. • Select Start | All Programs | Databases | X-ray Diffraction | DIFFRAC Plus Evaluation | Eva • Select File | Open, set the file type to .RAW, and select your file name. • Select View | Settings | Master Database File. Enter “G:\Diffplus\PDF1\JCP2.CAT”.
EVA • tour
EVA • displacement_1.eva
Phase ID steps • Read .RAW file • Subtract background, Strip Ka2 (append) • Use background subtracted scan for Peak Search; Use Ka2 stripped scan for Peak Match. • Match dominant peaks; displacement shift if necessary • If displacement shift; return to RAW data and correct.
EVA • Single phase (min11-01.raw) • Elements: Mg and O
EVA • TQ019-01.raw • Pure Mg, Si, O used in the processing
EVA • DA029.raw • Multi component, initially unknown elements • SEM EDS
EVA • DA029.raw • SEM EDS • Ti, Si, Mn, O, F • K, Na, Al, Mg, Fe