Controlled Porosity in Ferroelectric BaTiO3 Photoanodes

Determination of Imprint Effects in Ferroelectrics from the Quantified Phase and Amplitude Response

Piezoresponse force microscopy (PFM) is a robust characterization technique to explore ferroelectric properties at the nanoscale. However, the PFM signal can lead to misinterpretation of results due to the dominant electrostatic interaction between the tip and the sample. In this work, a detailed calibration process is presented and a procedure to identify the parasitic phase offset is demonstrated. To obtain artifact-free phase-amplitude loops, a methodology is developed by combining the outcomes from switching spectroscopy-PFM (SS-PFM) and Kelvin probe force microscopy (KPFM). It is demonstrated that the phase and amplitude loops obtained from SS-PFM at a specific read voltage, ascertained from the surface potential by KPFM, can convey accurate electromechanical information. These methodologies are applied to quantify the imprint voltage in BaTiO3 and BiFeO3, along with vertically aligned BaTiO3:Sm2O3 and BaTiO3:MgO nanocomposites. The variation of the imprint voltage measured under different tip voltages demonstrates the importance of selecting the correct read voltage in determining the local imprint voltage. Additionally, 2D imprint voltage maps in each domain of a BaTiO3 single crystal are obtained using the datacube-PFM technique, which allows pixel-by-pixel determination of artifact-free spatial variation of PFM phase-amplitude response.

Understanding the impact of Bi stoichiometry towards optimised BiFeO3 photocathodes: structure, morphology, defects and ferroelectricity

BiFeO3 thin films have been widely studied for photoelectrochemical water splitting applications because of its narrow bandgap and good ferroelectricity which can promote the separation of photo-generated charges. Bismuth is well known as a volatile element and excess bismuth is usually added into the precursor to compensate the loss of bismuth during heat treatment, but the amount of excess bismuth required and how excess bismuth will affect PEC performance have not been clearly studied. Herein, self-doped Bi1+x FeO3 thin films are prepared via simple chemical solution deposition method with excess bismuth from 0-30% in the precursor. The loss of bismuth after annealing is confirmed by EDX and XPS. Multiple factors were investigated and it was found that non-stoichiometric Bi resulted in changes of structure, morphology, defects, electronic properties and PEC performance. An enhanced photocurrent is observed in bismuth-rich BiFeO3 films, which can be ascribed to the larger grain size, decreased oxygen vacancies, lattice distortion and supported charge separation. Moreover, the photocathodic performance can be further enhance by ferroelectric poling. Our work indicates that deficient bismuth should be carefully avoided during heat treatment and moreover, a slight excess of Bi is beneficial for PEC performance. Therefore, we offer a simple way to enhance PEC performance of BiFeO3-based ferroelectric materials through careful control of their stoichiometry.

Porous PZT Films: How Can We Tune Electrical Properties?

Porous ferroelectric lead zirconate titanate (PZT) films are a promising material for various electronic applications. This study focuses on understanding how the structure-directing agent, polyvinylpyrrolidone, can alter the structure and electrical properties of porous PZT films prepared through chemical solution deposition. Films with various porosities of up to ~40 vol.% and pore connectivities from 3-0 to 3-3 were prepared and studied by capacitance-voltage, dielectric hysteresis, transient current, photocurrent, and local current techniques. We have found that a linear decrease in material volume in a porous film is not the only factor that determines film properties. The creation of new internal grain boundaries plays a key role in changing electrical properties. This research expands the understanding of physical phenomena in porous ferroelectric films and may facilitate the development of new materials and devices.