Origin of thermally stable ferroelectricity in a porous barium titanate thin film synthesized through block copolymer templating

Abstract

A porous barium titanate (BaTiO3) thin film was chemically synthesized using a surfactant-assisted sol-gel method in which micelles of amphipathic diblock copolymers served as structure-directing agents. In the Raman spectrum of the porous BaTiO3 thin film, a peak corresponding to the ferroelectric tetragonal phase was observed at around 710 cm−1, and it remained stable at much higher temperature than the Curie temperature of bulk single-crystal BaTiO3 (∼130 °C). Measurements revealed that the ferroelectricity of the BaTiO3 thin film has high thermal stability. By analyzing high-resolution transmission electron microscope images of the BaTiO3 thin film by the fast Fourier transform mapping method, the spatial distribution of stress in the BaTiO3 framework was clearly visualized. Careful analysis also indicated that the porosity in the BaTiO3 thin film introduced anisotropic compressive stress, which deformed the crystals. The resulting elongated unit cell caused further displacement of the Ti4+ cation from the center of the lattice. This displacement increased the electric dipole moment of the BaTiO3 thin film, effectively enhancing its ferro(piezo)electricity.

Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain

“…The spectrum of a bulk BT single crystal is also included for reference. This figure has been modified from Suzuki, N. et al 13 in accordance with the Creative Commons Attribution (CC BY) license. Please click here to view a larger version of this figure.…”

Synthesis and applications of nanoporous perovskite metal oxides

“…Recently, some researchers applied a modified EISA method using precipitant or chelating agents ( e.g. , citric acid, 16 urea, 20 , 21 acetic acid 22 , 23 ) to prepare nanoporous perovskite oxides without associating the dip-coating technique. The addition of these chelating agents would lead to a more homogeneous solution and better cation dispersion during the evaporation process but also affected the self-assembly of surfactants and their interaction with metal ions.…”

“…The addition of these chelating agents would lead to a more homogeneous solution and better cation dispersion during the evaporation process but also affected the self-assembly of surfactants and their interaction with metal ions. As a result, using these modified EISA methods, hierarchically nanoporous perovskite oxides can be obtained, including La 1.7 Ca 0.3 Ni 1– x Cu x O 4 , 16 La 0.5 Sr 0.5 Co 0.5 Fe 0.5 O 3 , 20 Sm 0.5 Sr 0.5 CoO 3 , 21 La 0.68 Ca 0.30 Mn 1.02 O 3– δ , 22 BaTiO 3 ( ref. 23 and 24 ) and SrTiO 3 .…”

Structural Dependent Eu3+ Luminescence, Photoelectric and Hysteresis Effects in Porous Strontium Titanate

“…A decrease in the grain size of SrTiO 3 at the nanoscale leads to distinctive properties as compared to the bulk material [ 16 , 17 ]. In recent years, several attempts were made to synthesize porous perovskites SrTiO 3 and BaTiO 3 [ 18 , 19 ].…”

“…One of the synthesis techniques includes using templates, which control formation periodical porous SrTiO 3 structure and repeatable combs form [ 28 ]. Another approach is based on using alcoxides and influence of water on the morphology of xerogels [ 18 , 29 , 30 , 31 ]. This approach allows for the fabrication of porous perovskites with grains larger than 100 nm.…”