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Short-range order can be developed in multi-principal element alloys and influences the point defect behavior due to the large variation of the local chemical environment. The effect of short-range order on vacancy and interstitial formation energy and migration behavior was studied in body-centered cubic multi-principal element alloy NbZrTi by first-principles calculations. Two short-range order structures created by density functional theory and Monte Carlo method at 500 and 800 K were compared with the structure of random solid solution. Both vacancy and interstitial formation energies increase with the degree of short-range order. Point defect formation energies tend to be higher in regions enriched in Nb and lower in regions enriched in Zr and Ti. Both vacancies and interstitials prefer to migrate toward Zr,Ti-rich regions and away from Nb-rich regions, suggesting that Zr,Ti-rich regions can potentially act as recombination centers for point defect annihilation. Compared to an ideal random solid solution, the short-range order increases the spatial inhomogeneity of point defect energy landscape. Tuning the degree of short-range order by different processing techniques can be a viable strategy to optimize the point defect behavior to achieve enhanced radiation resistance in multi-principal element alloys. [ABSTRACT FROM AUTHOR]

We report on the enhancement of photovoltaic performance in a graphene/polycrystalline BiFeO3 (BFO)/Pt heterojunction for the first time. The unique properties of the graphene electrode lead to a short circuit current density of 61 μA/cm2 and an open circuit voltage of 0.52 V in the heterojunction. These values are much higher than the results reported in polycrystalline BFO with indium tin oxide as the top electrode. A theoretical band diagram model and an equivalent electrical model considering the ferroelectric polarization, interface states, and energy band bending effect are constructed to depict the carrier transport behavior. Important photovoltaic parameters, such as conversion efficiency, illumination intensity response, ON/OFF characteristics, minority carrier lifetime, and external quantum efficiency, are investigated experimentally and theoretically. To improve the photovoltaic performance of the graphene/polycrystalline BFO/Pt heterojunction, HNO3 treatment, and CdSe quantum dots (QDs) filling/sensitizing, as two independent chemical and physical routines, were processed and compared. It can be seen that the photocurrent density exhibits a significant improvement from 61 μA/cm2 to 8.67 mA/cm2 (∼150 fold) after HNO3 treatment, while a considerable enhancement of ∼5 fold is seen with QDs filling/sensitizing. We also present and investigate an optical application of our graphene/polycrystalline BFO/Pt heterojunction as a photosensitive detector. [ABSTRACT FROM AUTHOR]

Domain witching of ferroelectrics under mechanical or electric load in vacuum or dry air has been intensively studied. However, the effects of environments on the domain switching in ferroelectrics have not been well understood. Here, we demonstrate that domain configurations in BaTiO3 single crystal under sustained load can be significantly affected by the humidity due to the decrease in surface energy and electrostatic energy upon adsorption of polar water molecules. Consequently, the crack propagation behaviors of the ferroelectrics under sustained load can be remarkably altered. [ABSTRACT FROM AUTHOR]

The authors report the study of polarization fatigue in Pb(Zr,Ti)O3 (PZT) ferroelectric thin films using in situ high-resolution grazing incidence x-ray specular reflectivity of synchrotron radiation. The results demonstrate that there is no formation of a region of different electron densities in the film growth direction with subnanometer depth resolution during fatigue. The upper bounds on the theoretically predicted interfacial accumulation of oxygen vacancies at the interfaces between PZT and Pt electrodes are determined by the comparison of experimental results and theoretical simulations. [ABSTRACT FROM AUTHOR]