The direct measurement of flexoelectric coefficients in epitaxial thin films is an unresolved problem, due to the clamping effect of substrates which induces a net strain (and hence parasitic piezoelectricity) in addition to strain gradients and flexoelectricity. Herein, we propose and demonstrate the use of van der Waals epitaxy as a successful strategy for measuring the intrinsic (clamping-free = flexoelectric coefficients of epitaxial thin films. We have made, measured, and compared BaTiO 3 and SrTiO 3 thin film capacitor heterostructures grown both by conventional oxide-on-oxide epitaxy and by van der Waals oxide-on-mica epitaxy, and found that, whereas the former is dominated by parasitic piezoelectricity, the response of the latter is truly flexoelectric. The results are backed by theoretical calculations of the film-substrate mechanical interaction, as well as by direct measurements that confirm the strain-free state of the films. van der Waals epitaxy thus emerges as powerful new tool in the study of flexoelectricity and, in particular, they finally allow exploring flexoelectric phenomena at the nanoscale (where strain gradients are highest) with direct experimental knowledge of the actual flexoelectric coefficients of thin films.

This paper proposes a new assessment method for lightning trip-out of transmission lines that includes an improved analytic hierarchy process (IAHP) algorithm based on a lift in association rules. First, the k-means clustering algorithm is used to discretize the geomorphic information along transmission lines, and ten feature factors are obtained. Next, by analysing the correlation between each feature factor and a lightning trip-out event using the lift algorithm, the strong correlation factors are extracted. On this basis, an IAHP algorithm optimized by lift is proposed to establish an objective judgment matrix. Then, multiple indexes are combined as a criterion layer of the IAHP, and a lightning risk assessment model of transmission lines is established. Finally, the proposed method is validated by simulations using 28 transmission lines with 220 kV voltage grade of a provincial power grid of China. An assessment model is established using the lightning trip-out data in the period 2010-2014, and then this model is employed to estimate the lightning trip-out risk in the period 2015-2018. Based on the number of phase faults, the agreement between the estimation results and the actual values is 76%. The proposed model provides a new method for the lightning risk assessment of transmission lines.

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The recently discovered large flexoelectricity in relaxor ferroelectrics has rekindled considerable research interest. In this paper, several Sm-doped Pb(Mg2/3Nb1/3)O3–xPbTiO3 (PMN–xPT) ferroelectric ceramics were prepared and the relationship between flexoelectricity and PT content was systematically investigated. The largest flexoelectric response (∼550 μC/m) was observed in the Sm-doped PMN–32PT ceramic, which should be accounted for in the reorientation of the polar nanoregions. At room temperature, the flexoelectric response of Sm-doped PMN–32PT ceramic is an order of magnitude higher than that of the parent PMN–PT ceramics and even 50% higher than that of Bi–PMN–32PT ceramic (∼300 μC/m). Such a big increment is directly related to the greater local structural heterogeneity caused by Sm3+ ions into PMN–PT. Therefore, the result presented in this paper verifies that introducing local structural heterogeneity is a feasible approach to achieve ultrahigh flexoelectricity.