Phase Identification by X-ray Diffraction
(From Chapter 9 of Textbook 2)
Powder Diffraction Methods
• Qualitative Analysis
– Phase Identification
• Quantitative Analysis
– Lattice Parameter Determination
– Phase Fraction Analysis
• Structure Refinement
– Rietveld Methods
• Structure Solution
– Reciprocal Space Methods
– Real Space Methods
• Peak Shape Analysis
– Crystallite Size Distribution
– Microstrain Analysis
– Extended Defect Concentration
1930’s
Hanawalt, Rinn and Frevel (Dow Chemical): diffraction
data on about 1000 compounds
JCPDS, ICDD: Joint Committee on Powder Diffraction
Standards; 1978 was renamed International Center for
Diffraction Data.
Hanawalt Method: (Grouping scheme)
values of the three strongest lines (d1, d2, d3) and
intensities (I/I1)
File
number
three strongest lines
lowest-angle line
Chemical formula and
name of substance
Special
symbol
data on
diffraction
method used
crystallographic
data
optical and
other data
data on
specimen
diffraction pattern
Special symbols give extra information:
*: well-characterized chemistry, quantitative measure
of intensity, high-quality d-spacing data (3 to 4
significant digits, no serious systematic errors)
i: reasonable range and even spread of intensity,
“sensible” completeness of the pattern, good d-spacing
data (3 significant digits)
o: low precision data, possible multi-phase mixture,
possible poor chemical characterization
c: powder pattern calculated from structural parameters
Procedure
(1) Locate proper d1 group
(2) Find the closest match to d2 (±0.01 Å)
(3) Follow by matching d3
(4) Compare relative intensity
(5) Good agreement in search manual 
locate the proper PDF card 
compare the d and I/I1values of all the peaks
Examples: unknown pattern from measurement:
strongest lines in the powder pattern:
d1 = 2.82; d2 = 1.99; d3 = 1.63
Portion of the ICDD Hanawalt search manual:
d1 = 2.82; d2 = 1.99; d3 = 1.63
Matched, turn to card number 5-628
Very weak
K
(220) plane
higher
Intensity?
Discrepancies!!
2×2.18×sin = 1.54  = 20.68o
2×d×sin 20.68o = 1.392 d = 1.97
Not
listed
Absorption
effect
Identification of Phases in Mixtures
Examples: pattern of unknown
d:
3.01 2.47 2.13 2.09 1.80 1.50 1.29 1.28
I/I1: 5
72
28 100 52 20
9
18
d:
1.22 1.08 1.04 0.98 0.91 0.83 0.81
I/I1: 4
20
3
5
4
8
10
No substance matching (d1:2.09; d2:2.47; d3: 1.80) all
together  probably a mixture
Assume: d1 and d2 not the same phase.
d1 and d3 the same phase  find Cu
Check the Pattern of Cu:
d: 2.088 1.808 1.278 1.090 1.044 0.904 0.830 0.808
I/I1: 100
46
20
17
5
3
9
8
Remainder of pattern of unknown:
d: 3.01 2.47 2.13 1.50 1.29 1.28 0.98
I/I1: 5
72
28
20
9
4
5
I/I1: 7
100 39
28
13
6
7 Normalized
Following the steps of searching again  Cu2O
Overlapped diffraction lines  carefully subtract the
intensity from the already identified phases to help
further identification of other phases.
Example
 Computer searching of the PDF:
 Computerization has dramatically improved the
efficiency of searching the JCPDS database
 Cards are no longer printed –data are on CD-ROM
 Numerous third-party vendors have software for
searching the PDF database
 Computerized “cards” can contain much more
crystallographic information
Database is still expanding …
 New approach – whole pattern fitting
Special
symbol
Searching of the PDF requires high-quality data
Accurate line positions are a must!
Calibration of camera and diffractometer with standards
Careful measurement of line intensities
Elimination of artifacts (e.g. preferred orientation)
Solid solutions and strains shift peak positions
“Garbage in, garbage out”
Errors in database
EVA software
TOPAS software