RESUMEN
We investigated the polarization-switching pathway-dependent electrical transport behaviors in rhombohedral-phase BiFeO3 thin films with point contact geometry. By combining conducting-atomic force microscopy and piezoelectric force microscopy, we simultaneously obtained current-voltage curves and the corresponding domain patterns before and after the polarization switching. The results indicate that for the (001)-oriented film, the abrupt current (due to polarization reversing) increases with the enhanced switching voltage for 109° and 180° switching events. More importantly, the abrupt current can be further improved in (110)- and (111)-oriented thin films, which benefits from the stronger modulation of the interfacial Schottky barrier by the enhanced out-of-plane polarization magnitude. The current on-off ratio obtained in a â¼20 nm thick (111)-oriented BiFeO3 thin film at a readout voltage of â¼3 V exceeds (â¼6 × 105)%, which is close to the result from a previous report on ultrathin tetragonal BiFeO3 thin films.
RESUMEN
Extremely high temperature in a chip will severely affect the normal operation of electronic equipment; however, the traditional air conditioning cooling technology is unsuitable for integrated circuit cooling. It is necessary to develop convenient and high-efficiency cooling techniques. In this paper, PbHfO3 antiferroelectric (PHO AFE) film was fabricated by a sol-gel method and was first found to be a promising electrocaloric (EC) material with high temperature change (ΔT â¼ -7.7 K) and acceptable EC strength (|ΔT/ΔE| â¼ 0.023 K cm kV-1) at room temperature. In addition to the negative EC effect (ECE), a large positive ECE can be observed at high temperature. The outstanding ECEs and their combination will make the PHO film one of the potential candidates for next-generation solid-state refrigeration. To understand the underlying physical mechanism for positive and negative ECEs in the PHO AFE film, a modified Ginzburg-Landau-Devonshire free-energy theory is adopted.
RESUMEN
In this work, a Co-N doped carbon nanotube (CNT) catalyst was fabricated via a simple pyrolysis approach and the effects of solvothermal processing on the catalytic activity of the as-prepared material were investigated in detail. The results show that after solvothermal processing (Co-NC) the catalyst has a more homogeneous anemone structure, a higher nitrogen content, a larger BET surface area and a higher degree of graphitization compared to the catalyst produced after non-solvothermal processing (Co-MA). The results of electrochemical tests indicate that Co-NC, compared to commercial 20% Pt/C and Co-MA, has an improved mass transfer process and sufficient active site exposure, which brings about superb oxygen reduction electrocatalytic activity, a higher reduction potential (-0.2 V vs. Ag/AgCl), a limiting diffusion current (5.44 mA cm-2) and excellent stability in 0.1 M KOH solution.