Materials Physics at Extreme
Pressure-Temperature Conditions
We operate various versatile miniature diamond anvil cells (DACs) for the in situ characterisation of materials under extreme pressure-temperature (P-T) conditions. Pressure is considered as a “clean and controlled” fine-tuning parameter of the physical properties of materials by progressively changing the inter-atomic spacing. These DACs, transparent to a wide range of probing radiation, also readily fit into cryostats , under microcopes, in furnaces and so on. We then exploit the availability of existing characterisation facilities like Raman or Brillouin spectrometers for investigating mechanical-elastic properties, 57Fe Mössbauer spectroscopy to probe magnetic-electronic properties, XRD for structural evolution, electrical-resistance for carrier transport properties, as a function of pressure in various materials comprised of mainly 3d transition metal compounds. These include (i) strongly correlated electron systems (SCES) like Mott insulators which actually have considerable overlap with the physics involved in deep Earth materials of the geo-sciences, (ii) pressure response of nano-materials as well as (iii) potentially new ultra-hard and stable materials.
We are able to use the above mentioned techniques on a routine basis to pressures of ~30 GPa ( = 300 kbar = 300000 atm) in the DAC. Where necessary this can be extended to much higher pressures into the megabar (~100 GPa) regime corresponding to energy densities of 0.5 – 1.0 eV/Å3. Aside from these laboratory based capabilities we also have various contacts at synchrotrons for the application of synchrotron radiation specific techniques like X-ray absorption spectroscopy (XANES and EXAFS) and magnetic dichroism (XMCD) under such extreme P-T conditions.
We have international collaborations with German and French groups. Future plans are for collaborations with Japanese colleagues.
Some of the projects that we tackle involve pressure:
1. tuning of the crystal field to effect spin crossover (e.g., Fe molecular complexes) ,
2. induced magnetic collapse in Mott antiferromagnetic-insulators and other SCES (e.g., transition metal compounds),
3. instigated structural phase transformations and subsequent magnetism of the high pressure phases (e.g., Fe-oxides) ,
4. response of nanophase materials (e.g., TiO2 ) ,
5. stabilised phases of .potential new ultra-hard compounds in the laser heated DAC (e.g., ZrO2/HfO2 compounds).
Future projects and intentions:
1. megabar (>100 GPa) studies corresponding to deep Earth conditions, perhaps by exploiting synchrotron based techniques,
2. pressure response of new Fe based superconductors,
3. alternative magnetic characterisation techniques (SQUID based) under extreme high-pressure low-temperature conditions,
4. pressure effects in multiferroic related compounds.
Research Highlights
Link to poster
Links to related webpages
http://en.wikipedia.org/wiki/Diamond_anvil_cell;
http://cdac.gl.ciw.edu
GRH March 2011