Definition Aurivillius phases are a class of layered perovskite materials characterized by a general chemical formula of (Bi₂O₂)²⁺(Aₙ₋₁BₙO₃ₙ₊₁)²⁻, where A and B represent different metal cations, and n denotes the number of perovskite-like octahedral layers stacked between bismuth oxide (Bi₂O₂) layers. These materials are known for their ferroelectric, piezoelectric, and dielectric properties.
Overview Aurivillius phases were first identified and structurally characterized in the 1940s and 1950s by the Swedish chemist Bengt Aurivillius, after whom they are named. They belong to the broader family of layered oxides and are structurally derived from the perovskite structure (ABO₃), but differ in their layering due to the presence of alternating (Bi₂O₂)²⁺ sheets and perovskite-like slabs. The structural versatility of Aurivillius phases allows for significant compositional tuning, making them of interest for applications in non-volatile memory devices, sensors, and high-temperature piezoelectrics.
Etymology/Origin The term "Aurivillius phases" derives from Bengt Aurivillius, a Swedish chemist who synthesized and described the crystal structures of several oxides with layered architectures in the mid-20th century. His early work on bismuth-containing oxides established the structural blueprint for this class of materials.
Characteristics Aurivillius phases exhibit several distinctive features:
- Crystal Structure: Composed of n layers of corner-sharing BO₆ octahedra forming a perovskite-like block, separated by fluorite-type (Bi₂O₂)²⁺ layers along the c-axis.
- Layer Number (n): The value of n ranges typically from 1 to 5, and influences the material's dielectric, ferroelectric, and thermal properties. Higher-n phases tend to have higher Curie temperatures and enhanced polarization.
- Chemical Flexibility: A-site cations are typically larger ions (e.g., Sr²⁺, Ba²⁺, Ca²⁺), while B-site cations are transition metals (e.g., Ti⁴⁺, Nb⁵⁺, Ta⁵⁺). Partial substitution at either site can modify electrical behavior.
- Ferroelectricity: Most Aurivillius phases are ferroelectric due to the displacement of B-site cations within the perovskite blocks and are stable at relatively high temperatures.
- Applications: Used in high-temperature piezoelectric sensors, as capacitors, and in ferroelectric random-access memory (FeRAM) due to their fatigue resistance compared to some perovskites like BaTiO₃.
Related Topics
- Perovskite structure
- Ferroelectric materials
- Piezoelectricity
- Layered oxides
- Bismuth titanate (Bi₄Ti₃O₁₂), a well-known n=3 Aurivillius phase
- Ruddlesden-Popper phases – another family of layered perovskite-related oxides
- Dielectrics and electronic ceramics