Practical X-Ray Diffraction

Transcription

1 Typical Example Practical X-Ray Diffraction White powder sample of NaCl,KCl,KNO 3 (trace of H 2 O) Département de chimie Université Laval Prof. Josée BRISSON Dr. Wenhua BI Powder X-Ray Diffraction in 10 mins. 1 Part 2: Polycrystalline X-Ray Diffraction Theory Powder Sample Structural information 2 Bragg s Law: 3 The Pattern The Reality > 99% of applications The basic function of XRD Blue Exp. Red Cal. 4 Truth: PXRD is more complicated than SCXRD. Software: DiffractWD 5 1

2 Possible Applications Checking purity; Identification of impurities; Following phase transitions; Determining phase diagram; Crystallinity and crystal size; Quantitative analysis; Strain, preferred orientation, and texture; RDF (Radiation Distribution Function) ab initio Structural determination. General Procedure for Serious XRD 1. Choose and Calibrate Instrument 2. Prepare and Mount the sample 3. Perform Primary Data Acquisition 4. Adjust the Configuration 5. Compose Data Collection Strategy 6. Collect the Diffraction Pattern 7. Transfer the Format of the Pattern 8. Analyze and Refine the Structural Model against the Pattern 9. Evaluate the Results of Refinement 10. Document Files and Plot Figures Search the Database Consult extra information 6 In the chemical X-ray lab 7 (PXRD) Single crystal X-ray diffractometers (SCXRD) are able to handle powder samples. But only for phase identification. 8 Rigaku Ultima III@Département des sols et de génie agroalimentaire, UL. 9 Bruker D8 Advance@ 10 Bench-top style 11 2

3 Sample holder 12 Bragg-Brentano Configuration (reflection) 13 Debye-Scherrer Configuration (transmission). 14 Bragg-Brentano Configuration (reflection) 15 Area Sensitive Diffractometer PSD (position-sensitive detector), slit and knife: 16 Bruker D8 Discovery 17 3

4 Choice of Suitable Diffractometer Choose of Suitable Diffractometer Transparent Shift 18 Debye-Scherrer VS. Bragg-Brentano 19 Calibration of Diffractometer Sample Preparation Agate mortar Ball-mill in hardened steel or agate Standard samples from NIST (National Institute of Standards and Technology) 20 Size, thickness, loading, roughness. www2.arnes.si 21 Sample Loading Primary Diffraction Side-load, Backload; Si(510), Quartz(001^6 o ). 22 To get a general idea about the capability of diffraction. 23 4

5 Set the Strategy for Data Collection Classical PXRD Pattern Wavelength; Range of 2 Theta ; Exposure time; Scan speed; Step size; Rotation speed; Size of the slits; Temperature; 24 Information from the XRD pattern and composition of an individual peak. 25 Classical PXRD Pattern Pattern Treatment Integration (if necessary); Theta calibration; Smoothing; Background subtraction; Removal of K alpha2 contribution; File format transfer (for plotting); Information from the XRD pattern, From Powder diffraction- theory and practice Edited by Robert E. Dinnebier and Simon J. L. Billinge., RSC, Qualitative Analysis PDF Files from ICDD ($$$) Check purity and identify impurities. Main Function: Video 28 ICDD (International Center of Diffraction Data), PDF (Powder diffraction file) 29 5

6 Follow a Phase Transition Phase Diagram Temperature Doping Unit cell of Ni x Cu (1-x) O in ICSD Peak-Shift Due to Doping [NiO_Fm-3m_ raw] PowderCell 2.2 [CuO_Fm-3m_ raw] PowderCell 2.2 [CuNiO raw] PowderCell Compound Cu0.05Ni0.95O Cu0.10Ni0.90O Cu0.15Ni0.85O Cu0.20Ni0.80O Cu0.25Ni0.75O Reduced Unit Cell 2.954, 2.954, 2.954, 60, 60, 60, , 2.956, 2.956, 60, 60, 60, , 2.959, 2.959, 60, 60, 60, , 2.961, 2.961, 60, 60, 60, , 2.963, 2.963, 60, 60, 60, Intensity(%) Two-Theta (deg) 32 Powder Pattern from Powder Cell 2.4 (Free!) 33 Crystal Size Scherrer Equation in 1918: K B 2 L cos Peak width (B) is inversely proportional to crystallite size (L) K depends on: 1. How the width is determined, 2. Crystal shape, 3. Size distribution K normally varies from 0.62 to Peak profile: Convolution of following contributions Instrumental Peak Profile Crystallite Size Microstrain Non-uniform Lattice Distortions Faulting Dislocations Antiphase Domain Boundaries Grain Surface Relaxation Solid Solution Inhomogeneity Temperature Factors Scott A. Speakman@MIT:

7 Crystallinity ab initio Structure Determination I crist I I crist amorphe 100 X-ray diffraction in polymer science. Video 36 The "last chance" method! Far away from routine in the chemical lab. 37 Number of Structures from PXRD Quality of Pattern sdpd.univ-lemans.fr 38 ESRF: European Synchrotron Radiation Facility (Grenoble, France) 39 XRD for Non-Crystalline Materials XRD for Amorphous Polymer Radial distribution curves for liquid gallium at different temperatures 40 Polystyrene 41 7

8 XRD for Polymer XRD for Amorphous Polymer r (Å) XRD for Amorphous Polymer XRD for Semi-Crystalline Polymer Crystals are very small 100 nm thick, 1 m in other directions No single crystals for X-ray diffraction No need to grind Powders, fibers, films,as is (1-2mm thick) Limited diffraction at large 2 angles 44 Large peak width (Fourier transform of something small.) 45 Maleic acid vs isoprene: which is which? JB1 Example of a paint R. Li, Societyof Plastics Engineers, Plastic research on line, I.D.H. Oswald, I. Chataigner, S. Elphick, F.P.A. Fabbiani, A.R. Lennie, J. Maddaluno, W.G. Marshall, T.J. Prior, C.R. Pulham. R.I. Smith CrystEngComm, 2009,11, Amorphous polymer halo Circles : dotted, narrow and go to high 2 angle: mineral pigment 47 8

9 Diapositive 48 JB1 Josée Brisson, 3/19/2014

10 Small Angle X-Ray Scattering (SAXS) Orientation and texture analysis Small angle = higher d-spacing ; Diffraction = not crystal; Crystal-amorphous phase stacks = long period; Other forms of order also studied. Uniaxial or biaxial orientation determined from relative intensity of a specific hkl diffraction spot Michel H. J. Kocha,Chem. Soc. Rev., 2006,35, Munk, P. Aminabhavi, T. M. Introduction to Macromolecular Science, 2e 49 ed, Wiley-Liss,New York, 2002, Summary All kinds of samples are acceptable; Abundant structural information; Fast for the basic qualitative analysis; Instrument needs to be carefully calibrated; Standard samples are indispensable; Database of PDF2/4 is very useful for identifying unknowns; ab initio structure determination from powder pattern possible but complicated Many thanks for your attention! We will talk about solutions, textbooks, and resources for X-ray diffraction after the break