what do x-ray powder diffraction patterns look like?
DESCRIPTION
What do X-ray powder diffraction patterns look like?. What do X-ray powder diffraction patterns look like?. What do X-ray powder diffraction patterns look like?. Each peak in pattern is a reflection from a different set of planes. - PowerPoint PPT PresentationTRANSCRIPT
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What do X-ray powder diffraction patterns look like?What do X-ray powder diffraction patterns look like?
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What do X-ray powder diffraction patterns look like?What do X-ray powder diffraction patterns look like?
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What do X-ray powder diffraction patterns look like?What do X-ray powder diffraction patterns look like?
Each peak in pattern is a reflection from a different set of planes
Each peak in pattern is a reflection from a different set of planes
By determining 2 for a peak, can use Braggs' law to get d for that set of planes
By determining 2 for a peak, can use Braggs' law to get d for that set of planes
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Powder patterns - what information available in pattern?
Powder patterns - what information available in pattern?
1. peak positions2. peak intensities3. peak shape4. background structure
1. peak positions2. peak intensities3. peak shape4. background structure
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Powder patterns - what information available in pattern?
Powder patterns - what information available in pattern?
1. peak positions - give unit cell shape, size, and symmetry1. peak positions - give unit cell shape, size, and symmetry
Simple example - P cubic:Simple example - P cubic:
Naming each peak with Miller indices is called " indexing the pattern" Naming each peak with Miller indices is called " indexing the pattern"
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Indexing Indexing
Message: indexing cubic patterns is usually pretty easyespecially, if done visually
Message: indexing cubic patterns is usually pretty easyespecially, if done visually
Why:usually, relatively few reflectionsreflections evenly spacedonly one lattice parameter to guess
Why:usually, relatively few reflectionsreflections evenly spacedonly one lattice parameter to guess
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Indexing Indexing
In cubic:
dhkl = a/(h2 + k2 + l2)1/2 = a/s1/2
a = s1/2 dhkl
s is an integer …… 1, 2, 3, 4….
In cubic:
dhkl = a/(h2 + k2 + l2)1/2 = a/s1/2
a = s1/2 dhkl
s is an integer …… 1, 2, 3, 4….
Since = 2dhkl sin hkl, smallest means largest dhkl
Since a = s1/2 dhkl, largest dhkl means smallest s value
Thus, lowest 2reflections in pattern are those with small s values
Since = 2dhkl sin hkl, smallest means largest dhkl
Since a = s1/2 dhkl, largest dhkl means smallest s value
Thus, lowest 2reflections in pattern are those with small s values
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Indexing Indexing Fill in the (hkl)s for these s valuesFill in the (hkl)s for these s values
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IndexIndex
Indexing Indexing
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(110)
(111)
(200)
(210)
(211)
(220)
(221)
(310)
(311)
(320)
(321)(222) (400)
(410)
(411)
(331)
(420)
IndexIndex
Indexing Indexing
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Slight complication: 3 different Bravais lattices in cubic
P cubic
I cubic
F cubic
Slight complication: 3 different Bravais lattices in cubic
P cubic
I cubic
F cubic
Translational symmetry gives missing planes - thus missing reflections
Translational symmetry gives missing planes - thus missing reflections
All planes, reflections possibleAll planes, reflections possible
(hkl) present only if h + k + l = even(hkl) present only if h + k + l = even
(hkl) present only if h,k,l all even or all odd(hkl) present only if h,k,l all even or all odd
Indexing Indexing
These are "extinction rules"These are "extinction rules"
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Indexing Indexing Fill in the (hkl)s for these I cubic (h + k + l = even) & F cubic (h,k,l all even or all odd)Fill in the (hkl)s for these I cubic (h + k + l = even) & F cubic (h,k,l all even or all odd)
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Indexing Indexing Indexing Indexing
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IndexIndex
Indexing Indexing
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How to know indexing is correct?How to know indexing is correct?
Indexing Indexing
Correct indices give consistent set of lattice parameters
Example for cubic:
d(Å) (hkl) a(Å)
3.157 (100) 3.1571.931 (110) 2.7311.647 (111) 2.8521.366 (200) 2.732
Correct indices give consistent set of lattice parameters
Example for cubic:
d(Å) (hkl) a(Å)
3.157 (100) 3.1571.931 (110) 2.7311.647 (111) 2.8521.366 (200) 2.732
(hkl) a(Å)
(111) 5.468(220) 5.462(311) 5.462(400) 5.464
(hkl) a(Å)
(111) 5.468(220) 5.462(311) 5.462(400) 5.464
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Other types of translational symmetry also give missing planes
glide planes and screw axes
Other types of translational symmetry also give missing planes
glide planes and screw axes
Indexing Indexing
Ex: F 41/d 3 2/m
(0kl) present if k + l = 4n
(hhl) present if h + l = even
(hkl) if h + k + l = odd or 4n(for some structures w/ this space group)
Ex: F 41/d 3 2/m
(0kl) present if k + l = 4n
(hhl) present if h + l = even
(hkl) if h + k + l = odd or 4n(for some structures w/ this space group)
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What if it's not cubic?
Manual indexing methods usually very tedious - use computer indexing programs such as "Ito", "Treor", "Crysfire", "Dicvol", others
What if it's not cubic?
Manual indexing methods usually very tedious - use computer indexing programs such as "Ito", "Treor", "Crysfire", "Dicvol", others
Indexing Indexing
Computer indexing frequently not easy - sometimes have to use several, or all, indexing programs to figure out right answer
Computer indexing frequently not easy - sometimes have to use several, or all, indexing programs to figure out right answer
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Why index? Why index?
cubic: dhkl2 = a2/(h2 + k2 + l2)
tetragonal: 1/dhkl2 = (h2 + k2)/a2 + l2 /c2
hexagonal: 1/dhkl2 = (4/3)(h2 + k2 + hk)/a2 +
l2 /c2
orthorhombic: 1/dhkl2 = h2/a2 + k2/b2 + l2 /c2
etcetera
cubic: dhkl2 = a2/(h2 + k2 + l2)
tetragonal: 1/dhkl2 = (h2 + k2)/a2 + l2 /c2
hexagonal: 1/dhkl2 = (4/3)(h2 + k2 + hk)/a2 +
l2 /c2
orthorhombic: 1/dhkl2 = h2/a2 + k2/b2 + l2 /c2
etcetera
It can be fun! Like solving a puzzleIt can be fun! Like solving a puzzle
Indices needed to calculate lattice parametersneed (hkl) and dhkl for all reflections
use all reflections to get high precision
Indices needed to calculate lattice parametersneed (hkl) and dhkl for all reflections
use all reflections to get high precision
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Indexing Indexing
ATCF!!!ATCF!!!
But…… 小心But…… 小心
Looks cubicLooks cubic
But it is not!(C orthorhombic)But it is not!(C orthorhombic)
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Powder patterns - what information available in pattern?
Powder patterns - what information available in pattern?
1. peak positions2. peak intensities - how much?3. peak shape4. background structure
1. peak positions2. peak intensities - how much?3. peak shape4. background structure
Relatively recent increase in use of X-ray diffraction for quantitative analysis
Relatively recent increase in use of X-ray diffraction for quantitative analysis
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Year
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Papers publishedon quantitative analysisBy x-ray diffraction
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Powder patterns - what information available in pattern?
Powder patterns - what information available in pattern?
1. peak positions2. peak intensities - how much?3. peak shape4. background structure
1. peak positions2. peak intensities - how much?3. peak shape4. background structure
Quantitative analysis
Example: 2-phase mixtures of CaF2 & ZnO
Quantitative analysis
Example: 2-phase mixtures of CaF2 & ZnO
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67 wt% CaF2/33 wt% ZnO
23 wt% CaF2/77 wt% ZnO
CaF2
ZnO
CaF2
ZnO
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Iia =Iia =KiaXaKiaXa
aa
Main equation for quantitative analysisMain equation for quantitative analysis
Quantitative AnalysisQuantitative AnalysisUse measured intensities ….. but not simpleUse measured intensities ….. but not simple
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Iia =Iia =KiaXaKiaXa
aa
Iia = intensity of reflection i of phase a
Iia = intensity of reflection i of phase a
Quantitative AnalysisQuantitative AnalysisUse measured intensities ….. but not simpleUse measured intensities ….. but not simple
Main equation for quantitative analysisMain equation for quantitative analysis
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Iia =Iia =KiaXaKiaXa
aa
ais density of phase aais density of phase a
Quantitative AnalysisQuantitative AnalysisUse measured intensities ….. but not simpleUse measured intensities ….. but not simple
Main equation for quantitative analysisMain equation for quantitative analysis
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Iia =Iia =KiaXaKiaXa
aa
Kia contains structure factor, multiplicity, Lorentz-polarization factor, temperature factor + scale factor for reflection i of phase a
Kia contains structure factor, multiplicity, Lorentz-polarization factor, temperature factor + scale factor for reflection i of phase a
Quantitative AnalysisQuantitative AnalysisUse measured intensities ….. but not simpleUse measured intensities ….. but not simple
Main equation for quantitative analysisMain equation for quantitative analysis
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Iia =Iia =KiaXaKiaXa
aa
Xa = wt fraction of phase a (want this!!)Xa = wt fraction of phase a (want this!!)
Quantitative AnalysisQuantitative AnalysisUse measured intensities ….. but not simpleUse measured intensities ….. but not simple
Main equation for quantitative analysisMain equation for quantitative analysis
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Iia =Iia =KiaXaKiaXa
aa
Xa = wt fraction of phase a (want this!!)Xa = wt fraction of phase a (want this!!)measure
this!!measure this!!
Quantitative AnalysisQuantitative AnalysisUse measured intensities ….. but not simpleUse measured intensities ….. but not simple
Main equation for quantitative analysisMain equation for quantitative analysis
But what do we do with ?But what do we do with ?
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Iia =Iia =KiaXaKiaXa
aa
But what do we do with ?But what do we do with ?
Xa = wt fraction of phase a (Want this!!)
Xa = wt fraction of phase a (Want this!!)
Measure this!!Measure this!!
is mass attenuation coefficient for mixture …. unknown, unless we know is mass attenuation coefficient for mixture …. unknown, unless we know
Quantitative AnalysisQuantitative AnalysisUse measured intensities ….. but not simpleUse measured intensities ….. but not simple
Main equation for quantitative analysisMain equation for quantitative analysis
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mix = X1phase1 + X2phase 2 + X3phase 3 + ………mix = X1phase1 + X2phase 2 + X3phase 3 + ………
for each phase may be calculated from the chemical composition of each phase for each phase may be calculated from the chemical composition of each phase
compd = X11 + X22 + X33 + ………compd = X11 + X22 + X33 + ………
Iia =Iia =KiaXaKiaXa
aa
If sample contains > one phase, then unknown if wt fractions unknownIf sample contains > one phase, then unknown if wt fractions unknown
Quantitative AnalysisQuantitative AnalysisUse measured intensities ….. but not simpleUse measured intensities ….. but not simple
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Iia =Iia =KiaXaKiaXa
aa
would also be nice not to calc Kia or get a
would also be nice not to calc Kia or get a
Quantitative AnalysisQuantitative AnalysisUse measured intensities ….. but not simpleUse measured intensities ….. but not simple
Main equation for quantitative analysisMain equation for quantitative analysis
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Use measured intensities ….. but not simpleUse measured intensities ….. but not simple
Simple example: rutile/anatase polymorphs since polymorphs have same composition:
Simple example: rutile/anatase polymorphs since polymorphs have same composition:
mix = rutile = anatasemix = rutile = anatase
Quantitative AnalysisQuantitative Analysis
Iirutile =Iirutile =KirutileXrutileKirutileXrutile
rutile rutile
Iirutile =Iirutile =KirutileKirutile
rutile rutilerutile rutile
Suppose we measure Iirutile of pure rutile
can eliminate mix (& other stuff)
Suppose we measure Iirutile of pure rutile
can eliminate mix (& other stuff)
= Xrutile= Xrutile
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Iia =Iia =KiaXaKiaXa
aa
Quantitative AnalysisQuantitative AnalysisUse measured intensities ….. but not simpleUse measured intensities ….. but not simple
For mixtures that are not polymorphs, many single & multiple peak procedures have been developed that use known amounts ofinternal standards - mixed with unknownexternal standards - run separate x-ray patternof standard material
For mixtures that are not polymorphs, many single & multiple peak procedures have been developed that use known amounts ofinternal standards - mixed with unknownexternal standards - run separate x-ray patternof standard material
Most analysis techniques tell only what elements are present & how much. X-ray diffraction tells how much of what PHASES are presentMost analysis techniques tell only what elements are present & how much. X-ray diffraction tells how much of what PHASES are present
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Quantitative AnalysisQuantitative Analysis
Rietveld analysis of fuel depositRietveld analysis of fuel deposit
Recently, whole pattern analysis methods for quantitative analysis have become popular. Example: Rietveld analysisRecently, whole pattern analysis methods for quantitative analysis have become popular. Example: Rietveld analysis
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Rietveld analysis of fuel depositRietveld analysis of fuel deposit
Quantitative AnalysisQuantitative Analysis