Upload
warren-wilson
View
217
Download
0
Tags:
Embed Size (px)
Citation preview
Beauty, Form and Function: An Exploration of SymmetryBeauty, Form and Function: An Exploration of Symmetry
Asset No. 36
Lecture III-9
Laboratory Studies of Crystal Symmetry
PART IIISymmetry in Crystals
By the end of this lecture, you will be introduced to:
• the basic principles and methods of collecting X-ray diffraction patterns to determine crystal symmetry
• scanning electron of small facetted crystals demonstrating that symmetry of hand-held mineral samples can be replicated at micro- and nano-scales
Objectives
Preparing Crystals
A synthetic, single crystal rod of an ‘apatite’ containing neodymium and silicon. Apatite is hexagonal P63/m.
A tiny crystal fragment of ‘apatite’ glued to head of a
glass fiber ready for the diffraction experiment.
The X-ray Diffractometer
X-ray detector
X-ray source
crystal
The goniometer that precisely rotates the crystal through 3D
space
Collecting X-ray Diffraction Patterns
The apatite X-ray crystal diffraction patterns collected at
different orientations.
A close-up of the apatite crystal mounted on a glass fiber
Symmetry and Crystal Structure DeterminationAn hexagonal apatite X-ray crystal diffraction pattern collected along the [001] projection. This is consistent with P63/m.
Through modelling both the position and intensity of the diffraction spots the
crystal structure of the apatite is revealed, including all atom types (Nd, Si, O) and their fractional co-ordinates
inside the unit cell.
Scanning Electron Microscopy
Low magnification showing entire crystal
High magnification of one facet of the crystal
SEM of ‘hybrid’ perovskites useful as solar electricity collectors.
Large crystals are not suitable for X-ray diffraction as most of the X-rays are absorbed instead of diffracted
Small crystals deliver X-ray diffraction patterns with sharp and intense peaks.
The position of the diffraction spots gives the unit cell size
The intensity of the diffraction spots gives the symmetry
The scanning electron microscope is an ideal tool for studying micro and nano-crystal shape
The principles of symmetry hold at all scales.
Summary