The Mineral Science Laboratories house a wide range of experimental facilities to support the varied research programmes followed by members of the department.
X-ray DiffractionThe X-ray laboratories contain both single crystal and powder diffractometers. In addition to high temperature Guinier and precession cameras we have a number of novel diffractometers which have been designed and constructed in the department. Further developments along these lines continue.
The main thrust of the work on the single-crystal diffractometers is to measure the intensity distribution of X-rays associated with diffuse scattering and superlattice reflections. The powder diffraction equipment is mostly used to determine, with high accuracy, the spontaneous strains that invariably accompany phase transitions.
Infrared SpectroscopyOne application of IR spectroscopy is to measure small changes in the frequencies, widths and intensities of the lines in the spectra as the sample is cycled through a phase transition. The measurements are precise enough to allow detailed information about the changes that accompany the phase transition to be determined.
Small samples of chemical profiles are studied using the infrared microscope. Alternatively we can use powder samples or macroscopic crystals in reflection or transmission mode. We are specialised in the study of thin films using Fourier transform infrared and Fourier transform Raman techniques. Typical materials are high-temperature superconductors, silicates, carbonates, metamict minerals and ceramics, and semiconducting oxides.We have two FT infrared spectrometers, one of which also has a Raman spectrometer attached. The larger spectrometer is able to measure samples held at both high and low temperatures. The equipment has a microscope stage.
The NMR is mostly used for measurement of changes in local ion environment or coordination associated with changing temperature, for example at a phase transition or in glass formation from the molten state.
We have a Varian 400 MHz Infinity NMR with 4 probes for high-resolution solid-state NMR and wideline solid-state NMR research.
Contact: Ian Farnan
Thermal and Mechanical AnalysisOne of our main interests is the study of temperature-dependent phase transitions in minerals and ceramics. We make use of a number of instruments for thermal analysis of materials, including a Perkin Elmer differential scanning calorimeter and a thermo-gravimetric balance. We also have two Perkin Elmer dynamic mechanical analysers for measuring changes in the visco-elastic properties of solids as a function of temperature. These facilities allow the study of critical phenomena from liquid nitrogen temperatures to more than 700 K.
We make use of Linkam heating and cooling stages for optical studies from liquid nitrogen temperatures up to 1500 K.
Our current projects in instrument development aim to integrate these facilities with those in the X-ray laboratory, to allow simultaneous thermal and structural analysis.
Second Harmonic GenerationWe can measure optical frequency doubling in solids in both transmission and reflection geometry as a function of temperature. Using a Nd-YAG Q-switched infrared laser we measure the green second harmonic light arising from non-centrosymmetric structure. This can be useful for space group determination in crystallographic studies, but is also a powerful technique for investigating defect structure and ferroelectric phase transitions in other polar materials.
Dielectric SpectroscopyWe have an HP4192A impedance analyser which allows measurement of the real and imaginary dielectric constant of materials in the frequency range 5 Hz to 13 MHz. This is useful for the study of transport phenomena in ionic conductors,
resonance phenomena in dielectrics, and critical phenomena at ferroelectric transitions. Samples are typically measured as a function of temperature between 300 and 1000 K.
High-Pressure FacilitiesHigh-pressure work is carried out using local laboratory based equipment and facilities at national laboratories. For local work we use diamond anvil cells, which enable a variety of measurements to be performed. These include both X-ray diffraction and IR/Raman spectroscopy measurements. Our diamond anvil cells can be heated, which gives the possibility of performing experiments over a wide range of pressures and temperatures simultaneously. We have a dedicated laboratory which contains appropriate sample preparation and loading equipment, together with pressure measurement by Ruby fluorescence. Members of our group are leading a consortium that has developed equipment to perform neutron diffraction measurements at simultaneous high pressures and temperatures. This is based on the PEARL beamline of the ISIS neutron source, and uses the Paris-Edinburgh opposed-anvil technology. One novel feature we have developed for this technology is the use of a radiographic method for determination of sample temperatures.
Computational FacilitiesThe computational work involves use of a broad range of facilities. For the most complex calculations there is a need for parallel supercomputers. Much of this need is met by the Hitachi SR2201 (256 nodes) and Silicon Graphics Origin 2000 (64 nodes) parallel computers of the University of Cambridge High Performance Computing Facility, of which the Mineral Sciences group is a contributing partner. We are also members of two consortia for the use of the CSAR Cray T3E supercomputing facility.
The large scale facilities are supported by a network of Silicon Graphics workstations, which are used for smaller scale calculations (lattice energy, lattice dynamics), and for testing simulations before being ported to the large high-performance computing facilities.
We are equipped with a wide range of simulation software. We use two types of ab initio quantum mechanical electronic structure calculations. Both use density functional theory, but one (CASTEP) uses plane wave basis functions to describe the electronic wave functions, and the other (SIESTA) uses localised atomic orbitals. We use the GULP code for calculations of structure, properties and lattice dynamics with empirical interatomic potentials. For studies of disordered materials, or where we need to take explicit account of temperature, we use the DLPOLY molecular dynamics code. Finally, for studies of cation ordering processes we use our own in-house OSSIA Monte Carlo code.
The workstations also provide an environment for visualisation, using the MSI Cerius2 package. This provides a software environment for generating configurations to be used in simulation studies, for visualising the results of simulations, and for producing animations of the dynamics of atoms obtained from molecular dynamics simulations.
See also our computational page
Contact: Martin Dove
In addition to our in-house facilities we are major users of national neutron and synchrotron radiation facilities. These complement in-house methods in a variety of ways.
Neutron Scattering and Synchrotron RadiationNeutron methods provide a unique probe of materials. The neutron interacts directly with the atomic nuclei in a way that is different, and hence complementary, to the interaction of X-rays with the atomic electrons. For example, neutrons are particularly sensitive to hydrogen, whereas X-rays are least sensitive to these atoms. The wavelength of a neutron beam is comparable to the interatomic distances, and the energy scale of neutron beams is comparable to the energy scale of atomic vibrations, so that neutron scattering can be used as a probe of both atom positions and dynamics. Different instruments are designed to exploit different features of the broad range of scattering processes.
The Mineral Sciences group has expertise in a wide range of neutron scattering methods. These include diffraction at high and low temperatures, diffraction at high pressures and simultaneous high pressures and temperature, total scattering methods, single crystal excitations, and incoherent quasielastic and inelastic spectroscopy. For diffraction we use the GSAS code to perform Rietveld refinement of crystal structures, and for total scattering measurements we have developed a modification of the Reverse Monte Carlo method to take explicit account of the Bragg scattering.
We primarily use the UK ISIS spallation neutron source at the Rutherford-Appleton Laboratory, Oxfordshire. We also use the ILL reactor neutron source, of which the UK is a major partner, together with other sources in the US and Canada.
Synchrotron radiation provides high-intensity monochromatic and polarised beams of X-rays. For our work, the important role is for high-energy (low wavelength) beams of sufficient intensity for high-pressure studies. We have mostly used the UK Synchrotron Radiation Facility at the Daresbury Laboratory, Cheshire, but also use the European Synchrotron Radiation Facility (ESRF) in Grenoble.
We also makes us of other facilities in the department for Mineral Science research, particularly:
Contact: Professor M.A. Carpenter
Contact: Iris Buisman
Contact: Richard Harrison
- Geochemistry Laboratories
- High Temperature Experimental Facilities
- Mineral Science Research Laboratories
- Sedimentary Laboratory
- Palaeontology Labs
Last updated on 25-Mar-15 13:08