An Electronically Driven Improper Ferroelectric: Tungsten Bronzes as Microstructural Analogs for the Hexagonal Manganites

• Published in: Advanced materials (Weinheim) Vol. 31; no. 40; pp. e1903620 - n/a
• Main Authors: McNulty, Jason A., Tran, T. Thao, Halasyamani, P. Shiv, McCartan, Shane J., MacLaren, Ian, Gibbs, Alexandra S., Lim, Felicia J. Y., Turner, Patrick W., Gregg, J. Marty, Lightfoot, Philip, Morrison, Finlay D.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01-10-2019
• Subjects: Apexes; Broken symmetry; Bronzes; Domain walls; Ferroelectric materials; Ferroelectricity; ferroelectrics; improper ferroelectricity; Jahn-Teller effect; Manganites; Materials science; Microstructure; Nanoelectronics; Nanotechnology devices; Neutron diffraction; structure‐property relationships; Tungsten bronze; Unit cell; ferroelectrics; domain walls; improper ferroelectricity; structure-property relationships
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201903620

Since the observation that the properties of ferroic domain walls (DWs) can differ significantly from the bulk materials in which they are formed, it has been realized that domain wall engineering offers exciting new opportunities for nanoelectronics and nanodevice architectures. Here, a novel improper ferroelectric, CsNbW2O9, with the hexagonal tungsten bronze structure, is reported. Powder neutron diffraction and symmetry mode analysis indicate that the improper transition (TC = 1100 K) involves unit cell tripling, reminiscent of the hexagonal rare earth manganites. However, in contrast to the manganites, the symmetry breaking in CsNbW2O9 is electronically driven (i.e., purely displacive) via the second‐order Jahn–Teller effect in contrast to the geometrically driven tilt mechanism of the manganites. Nevertheless CsNbW2O9 displays the same kinds of domain microstructure as those found in the manganites, such as the characteristic six‐domain “cloverleaf” vertices and DW sections with polar discontinuities. The discovery of a completely new material system, with domain patterns already known to generate interesting functionality in the manganites, is important for the emerging field of DW nanoelectronics.
A novel electronically driven improper ferroelectric hexagonal tungsten bronze, CsNbW2O9
is reported. This compound displays the same domain microstructure as the hexagonal manganites, such as the characteristic six‐domain “cloverleaf” vertices and domain wall (DW) sections with polar discontinuities. This new material class, with domain patterns already known to generate interesting functionality, is important for the emerging field of DW nanoelectronics.