The crystal structure of LiOsO3
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Ferroelectrics are insulating materials with an electrical polarisation that can be switched by an applied voltage. Ferroelectricity cannot occur in metals because polarisation would be screened by the conduction electrons. Typically materials only demonstrate ferroelectricity below a certain temperature known as the phase transition temperature where lack of inversion symmetry occurs.
In an article published in Nature Materials, an international team including members from Oxford Physics, ISIS, China and Japan report the discovery of a new material called lithium osmate (LiOsO3) which remains a metal down to the lowest temperatures and yet undergoes a structural phase transition that is identical to the ferroelectric transition in the well-known ferroelectrics LiNbO3 and LiTaO3.
Using a variety of techniques including neutron diffraction on the WISH diffractometer at the ISIS Facility which allowed measuring structural parameters with a great precision, the team found that the phase transition in LiOsO3 is characterised by a large shift in the position of the Li ions thereby breaking inversion symmetry. The same structural effect has been known for many years to cause ferroelectricity in insulating LiNbO3 and LiTaO3.
The discovery represents the first clear-cut example of a so-called “ferroelectric” metal, a concept first postulated over 50 years ago by Nobel prize-winner Philip Anderson together with his co-worker Blount. It is also scientifically interesting because the mechanisms for structural phase transitions are usually quite distinct in metals and insulators, so it is surprising to find a metal (LiOsO3) that undergoes the same structural transition as occurs in the insulating analogues. The discovery of a “ferroelectric” metal establishes a new class of materials which could have interesting properties, such as the possibility of non-centrosymmetric superconductivity stabilised by the “ferroelectric” structural instability.
For further information please contact Pascal Manuel
Research date: September 2013
This Research has been published in Nature Materials
Reference: Y. Shi et al., Nature Materials 10.1038/nmat3754
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