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

Area of Science:

• Materials Science
• Solid-State Physics
• Crystallography

Background:

• Ferroic domain walls (DWs) exhibit distinct properties compared to bulk materials, offering potential for nanoelectronics.
• Domain wall engineering is a promising approach for developing novel nanodevice architectures.

Purpose of the Study:

• To report the discovery and characterization of a novel improper ferroelectric material, CsNbW₂O₉.
• To investigate the structural and electronic properties of this new material and compare it to existing systems.

Main Methods:

• Powder neutron diffraction was used to analyze the crystal structure.
• Symmetry mode analysis was employed to understand the ferroelectric transition mechanism.
• The material's domain microstructure was examined.

Main Results:

• A new improper ferroelectric, CsNbW₂O₉, with a hexagonal tungsten bronze structure was identified.
• The material undergoes an improper ferroelectric transition at 1100 K involving unit cell tripling.
• Symmetry breaking is electronically driven via the second-order Jahn-Teller effect, distinct from the geometrically driven mechanism in hexagonal rare earth manganites.
• CsNbW₂O₉ exhibits domain microstructures similar to manganites, including "cloverleaf" vertices and polar discontinuous domain walls.

Conclusions:

• The discovery of CsNbW₂O₉ provides a new material system for exploring domain wall functionality.
• Its unique electronic driving mechanism for symmetry breaking, coupled with known domain patterns, is significant for the field of domain wall nanoelectronics.