OPTIMIZING XRD DATA. By: Matthew Rayner

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1 OPTIMIZING XRD DATA By: Matthew Rayner 1

2 XRD Applications PANalytical classifies XRD applications in 4 groups 1. Powders 2. Nanomaterials 3. Solid objects 4. Thin films Many day-to-day samples cross these application boundaries R&D requirements continuously stimulates new hardware & software development 2

3 Powder applications The most commonly used configuration Phase identification Phase quantification - fixed irradiated volume Care has to be taken with sample preparation 3

4 Sample preparation errors Contamination Usually from sample preparation equipment (cross-contamination) Dusty environments and penetration depth Material loss Non-quantitative transfer of binders / grinding aids Loss of sample due to handling Static charges removing magnetic materials from samples Alteration of composition Induced chemical reactions upon grinding or pressing Decomposition Induced lattice changes Due to over-grinding, pressure or heat Surface effects Segregation, adhering samples, smearing, surface roughness etc. Preferred orientation 4

5 An ideal powder sample for diffraction in Bragg- Brentano (reflection) geometry should be finely ground and homogeneous since the average penetration depth is approximately 100 μm (Cu Kα), the average grain size of 5 μm with a maximum size of 25 μm (for mixtures of hard and soft materials pressing is recommended over grinding) be infinitely thick usually 2 3 mm (depends on the radiation being used) have a completely flat surface backloading sample holders are recommended No preferred orientation (often impossible) 5

6 STEP 1 Good sample preparation 6

7 Unusual / small samples 7

8 Impressive example of small samples 8

9 Sample spinning Increases particle statistics by bring more samples into diffraction positions 9

10 Optical considerations 10

11 STEP 2 Optimizing incident beam optics Fixed volume vs. fixed irradiated area? W is imposed by the soller slits and beam mask Soller slits also limit axial divergence 11

12 STEP 2 Optimizing incident beam optics L is imposed by the choice of divergence slit L will change with the incident beam angle Over-radiation (onto the sample holder) will cause a significant increase in the background signal Optimize divergence slit at lowest angle of measurement 12

13 STEP 3 Optimizing diffracted beam optics Receiving slit size = divergence slit size Use an antiscatter slit size that is just large enough not to influence the intensity of your peaks Incident beam soller = diffracted beam soller 13

14 STEP 3 Optimizing diffracted beam optics Diffracted beam monochromator is considered oldfassioned but is excellent if there are elements in the sample that may fluoresce due to the incident radiation It also decreases the background signal by removing white radiation Example: Fe in samples when using Cu Kα 14

15 STEP 3 Optimizing diffracted beam optics In this configuration a point detector would be perfectly adequate but extremely slow (especially due to the monochromator) 15

16 STEP 3 Optimizing diffracted beam optics The solution is to include a linear detector Multiple receiving slits and detectors measure multiple peaks at the same time Massive reduction in measurement time (> 90 times faster) 16

17 We are the only manufacturer that offers diffracted beam monochromators for linear detectors 17

18 Transmission Geometry - Spinning Ideal for samples with light to medium elemental composition Lower preferred orientation effects Fixed irradiated volume quantitative analysis Low angle diffraction and SAXS 18

19 19

20 Transmission Geometry - Capillary Ideal for samples with light to medium elemental composition Often used for air-sensitive samples Minimal preferred orientation problems Fixed irradiated volume quantitative analysis Low angle diffraction and SAXS Care must be taken with regards to crystal shape 20

21 Non-standard Powder Geometries - Cu Kα 1 Pure Cu Kα 1 radiation from the tube Excellent resolution Usually constant irradiated area (programmable slits) Crystal structure solutions from powder diffraction data 21

22 Non-standard Powder Geometries II Beam No focusing geometry, therefore, no effect from sample height variations 1-dimensional diffracted beam optics slow Benefit from removal of white (background) radiation from the tube Ideal for powder samples with a large amount of surface roughness Ideal for solid objects Fixed irradiated volume quantitative analysis but not ideal 22

23 Summary 3 major steps in optimizing powder diffraction experiments 1. Sample preparation Is this the best way to prepare this specific sample? Have I taken every possibility into account? 2. Incident beam optics - Is this the optimal configuration for my experiment and have I optimized the individual optics correctly? 3. Diffracted beam optics and detector - Is this the optimal configuration for my experiment? Have I optimized the individual optics correctly? Do I need a monochromator? Am I using the correct detector? 23

24 Thank You Thank you for your kind attention Questions? 24