Standard "Shake and Bake" synthesis routes are usually employed to prepare powder samples for further investigation. High temperature muffle and tube furnaces are used to achieve firing temperatures of up to 1600 degrees and a variety of different atmospheres can be used including oxygen, nitrogen, argon and hydrogen. Single crystals are grown using flux methods,
The main techniques for characterising samples are:
- X-ray Powder Diffraction
- Neutron Powder Diffraction
- Electron Microscopy
- Magnetic Studies
- Conductivity studies
X-ray Powder Diffraction
Samples are characterised using the Departmental X-ray powder diffractometers. There are 4 instruments:
- one "workhorse" machine for monitoring reaction progress,
- three high resolution Siemens D5000 instruments:
- one operating with Cu Kalpha1 radiation in reflection geometry
- one operating with Cu Kalpha1 radiation in transmission geometry
- one operating with Cu Kalpha radiation with a high temperature stage allowing in situ studies at temperatures up to 1200 degrees
Neutron Powder Diffraction
The complemetary technique of neutron diffraction not only allows the detection of light atoms (e.g. oxygen) in a structure, it can also be extremely useful for resolving different cations with a similar number of valence electrons which appear identical in X-ray diffraction techniques.
Low temperature neutron diffraction experiments are crucial to gaining a full understaning of the nature of magnetic ordering present in a sample.
Neutron Powder Diffraction Experiments are carried out by the group at the ISIS facility at the Rutherford Appleton Laboratories near Didcot (Oxfordshire) and at the ILL in Grenoble (France).
Electron Microscopy
For probing individual crystallites on a smaller length scale than is achieveable with either X-ray or neutron powder diffraction (both of which are techniques which study the bulk material) electron microscopy is an extremely powerful technique. Both electron diffraction (where a diffraction pattern is collected from what is effectively a tiny single crystal) and high resolution lattice imaging (where it is possible to "see" individual columns of atoms) play a key role in structure determination. EDS (X-ray dispersive energy analysis) can also be a useful for probing the homogeneity of stoichiometry of the different crystallites in a sample.
The Department owns a Jeol 2000FX microscope which is located in Chemical Crystallography, and within the University excellent electron microscopy facilities are available.
Magnetic Studies
Magnetic characterisation is carried out using a SQUID magnetometer which operates in the range 1.8 - 350 K. Measurements of magnetisation both as a function of temperature and applied field are routinely made to help establish the nature of any magnetic interactions present. Low temperature neutron diffraction studies are essential for determing the structure of a long range mangetically ordered solid.
Conductivity Studies
Measurement of the electrical conductivity of sintered bars of samples can be carried out in-house from 5 - 300 K. Magnetoresistance data is collected in collaboration with Dr. S. Blundell of the Department of Physics.
