Polar metal

A polar metal, metallic ferroeletric,[1] or ferroelectric metal[2] is a metal that contains an electric dipole moment. Its components have an ordered electric dipole. Such metals should be unexpected, because the charge should conduct by way of the free electrons in the metal and neutralize the polarized charge. However they do exist. One substance family that can produce a polar metal is the nickelate perovskites. One example is lanthanum nickelate, LaNiO3.[3][4] A thin film of LaNiO3 grown on the (111) crystal face of lanthanum aluminate, (LaAlO3) was interpreted to be both conductor and a polar material at room temperature.[3] Also, when grown 3 or 4 unit cells thick (1-2 nm) on the (100) crystal face of LaAlO3, the LaNiO3 can be a polar insulator or polar metal depending on the atomic termination of the surface.[4] Lithium osmate,[5] LiOsO3 also undergoes a ferrorelectric transition when it is cooled below 140K. The point group changes from R3c to R3c losing its centrosymmetry.[6] At room temperature and below lithium osmate is an electric conductor, in single crystal, polycrystalline or powder forms, and the ferroelectric form only appears below 140K. Above 140K the material behaves like a normal metal.[7]

P. W. Anderson and E. I. Blount predicted that a ferroelectric metal could exist in 1965.[6] They were inspired to make this prediction based on superconducting transitions, and the ferrorelectric transition in barium titanate. The prediction was that atoms do not move far and only a slight crystal non-symmetrical deformation occurs, say from cubic to tetragonal. This transition they called martensitic. They suggested looking at sodium tungsten bronze and InTl alloy. They realised that the free electrons in the metal would neutralise the effect of the polarization at a global level, but that the conduction electrons do not strongly affect transverse optical phonons, or the local electric field inherent in ferroelectricity.[8]

References

  1. ↑ Drexel University (2 April 2014). "Researchers open path to finding rare, polarized metals". phys.org. Retrieved 23 April 2016.
  2. ↑ Benedek, Nicole A.; Birol, Turan (2016). "'Ferroelectric' metals reexamined: fundamental mechanisms and design considerations for new materials". Journal of Materials Chemistry C. doi:10.1039/C5TC03856A.
  3. 1 2 Kim, T. H.; Puggioni, D.; Yuan, Y.; Xie, L.; Zhou, H.; Campbell, N.; Ryan, P. J.; Choi, Y.; Kim, J.-W.; Patzner, J. R.; et al. (20 April 2016). "Polar metals by geometric design". Nature. doi:10.1038/nature17628.
  4. 1 2 Kumah, D.P.; Malashevich, A.; Disa, A.S.; Arena, D.A.; Walker, F.J.; Ismail-Beigi, S.; Ahn, C.H. (6 November 2015). "Effect of Surface Termination on the Electronic Properties of LaNiO3 Films". Physical Review Applied. 2: 054004. Bibcode:2014PhRvP...2e4004K. doi:10.1103/PhysRevApplied.2.054004.
  5. ↑ "When is a ferroelectric not a ferroelectric?". www.isis.stfc.ac.uk. 2013. Retrieved 21 April 2016.
  6. 1 2 Shi, Youguo; Guo, Yanfeng; Wang, Xia; Princep, Andrew J.; Khalyavin, Dmitry; Manuel, Pascal; Michiue, Yuichi; Sato, Akira; Tsuda, Kenji; Yu, Shan; et al. (22 September 2013). "A ferroelectric-like structural transition in a metal". Nature Materials. 12 (11): 1024–1027. arXiv:1509.01849Freely accessible. Bibcode:2013NatMa..12.1024S. doi:10.1038/nmat3754.
  7. ↑ Shi, Youguo; Guo, Yanfeng; Wang, Xia; Princep, Andrew J.; Khalyavin, Dmitry; Manuel, Pascal; Michiue, Yuichi; Sato, Akira; Tsuda, Kenji; Yu, Shan; et al. (22 September 2013). "A ferroelectric-like structural transition in a metal supplementary information" (PDF). Nature Materials. doi:10.1038/nmat3754-s1.
  8. ↑ Anderson, P. W.; Blount, E. I. (15 February 1965). "Symmetry Considerations on Martensitic Transformations: "Ferroelectric" Metals?". Physical Review Letters. 14 (7): 217–219. Bibcode:1965PhRvL..14..217A. doi:10.1103/PhysRevLett.14.217.
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