X-Ray Analytical Methods
X-rays were discovered by W.C. R?entgen in 1895, and led to three major uses:
• X-ray radiography is used for creating images of light-opaque materials. It relies on the
relationship between density of materials and absorption of x-rays. Applications include
a variety of medical and industrial applications.
• X-ray crystallography relies on the dual wave/particle nature of x-rays to discover
information about the structure of crystalline materials.
• X-ray fluorescence spectrometry relies on characteristic secondary radiation emitted by
materials when excited by a high-energy x-ray source and is used primarily to determine
amounts of particular elements in materials.
This course is primarily concerned with the x-ray crystallography of powders. In course
materials you will commonly find X-ray Diffraction, X-ray powder diffraction, and the
abbreviation XRD used interchangeably. Though intellectually somewhat sloppy, it is also
common practice.
Uses of X-Ray Powder Diffraction
The most widespread use of x-ray powder diffraction, and the one we focus on here, is for the
identification of crystalline compounds by their diffraction pattern. Listed below are some
specific uses that we will cover in this course:
• Identification of single-phase materials – minerals, chemical compounds, ceramics or
other engineered materials.
• Identification of multiple phases in microcrystalline mixtures (i.e., rocks)
• Determination of the crystal structure of identified materials
• Identification and structural analysis of clay minerals
• Recognition of amorphous materials in partially crystalline mixtures
Below are some more advanced techniques. Some of these will be addressed in an introductory
fashion in this course. Many are left for more advanced individual study.
• Crystallographic structural analysis and unit-cell calculations for crystalline materials.
• Quantitative determination of amounts of different phases in multi-phase mixtures by
peak-ratio calculations.
• Quantitative determination of phases by whole-pattern refinement.
• Determination of crystallite size from analysis of peak broadening.
• Determine of crystallite shape from study of peak symmetry.
• Study of thermal expansion in crystal structures using in-situ heating stage equipment.
Introduction to X-ray Powder Diffraction
(prepared by James R. Connolly, for EPS400-002, Introduction to X-Ray Powder Diffraction, Spring 2007)
(Material in this document is borrowed from many sources; all original material is ©2007 by James R. Connolly)
(Updated: 1-Jan-07) Page 2 of 9
XRD for Dummies: From Specimen to analyzed sample with minimal math
The physics and mathematics describing the generation of monochromatic X-rays, and the
diffraction of those X-rays by crystalline powders are very complex (and way beyond my limited
abilities to expound upon them). Fortunately a complete understanding of the mathematics
involved is not required to obtain, interpret and use XRD data. What is required is a basic
understanding of how the X-rays interact with your specimen, the sources and characteristics of
possible errors, and what the data tell you about your sample1.
What follows is a generalized explanation of the process of going from X-rays to diffraction data
for math-challenged geologists like me. Some of these processes will be treated a bit more
rigorously later in the course. For those who want to delve into the physics of X-ray diffraction,
any of the books in the bibliography at the end of this chapter will provide all that you desire
(and probably more). The intent here is to provide a conceptual framework for what is
happening.
Below is a schematic diagram of a diffractometer system and on the next page is a photograph of
our Scintag PAD V goniometer with many of the parts discussed below labeled.
The schematic diagram above is from the Siemens (now Brukker AXS) manual for the D5000 diffractometer.
While placement and geometry is somewhat different between different systems, all the basic elements of a Bragg-
Brentano diffractometer are present:
1 It is important to understand the difference between the terms sample and specimen. “Sample” refers to the
material, in Toto, that you want to analyze. “Specimen” refers to the prepared fraction of your sample that you will
be analyzing in a particular diffraction experiment. Though we frequently mix these terms in conversation, this is a
very important distinction. An ideal specimen will exactly represent your sample in your experiment; if it does not,
it is important to at least understand how it deviates from that ideal.