Large piezoelectric properties in KNN-based lead-free single crystals grown by a seed-free solid-state crystal growth method

We report lead-free single crystals with a nominal formula of (K₀.₄₅Na₀.₅₅)₀.96Li₀.₀₄NbO₃grown using a simple low-cost seed-free solid-state crystal growth method (SFSSCG). The crystals thus prepared can reach maximum dimensions of 6 mm × 5 mm × 2 mm and exhibit a large piezoelectric coefficient d₃₃ of 689 pC/N. Moreover, the effective piezoelectric coefficient d₃₃*, obtained under a unipolar electric field of 30 kV/cm, can reach 967 pm/V. The large piezoelectric response plus the high Curie temperature (TC) of 432 °C indicate that SFSSCG is an effective approach to synthesize high-performance lead-free piezoelectricsingle crystals.This work was supported by the National Natural Science Foundation of China (NSFC, Nos. 51332009 and 51172257), National Basic Research Program of China 973- Projects (2012CB619406), the CAS/SAFEA International Partnership Program for Creative Research Teams, and Science and Technology Commission of Shanghai Municipality (15ZR1445400). Y.L. appreciates the financial support from the Australian Research Council in the form of Future Fellowship

On the validity of the local Fourier analysis

Local Fourier analysis (LFA) is a useful tool in predicting the convergence factors of geometric multigrid methods (GMG). As is well known, on rectangular domains with periodic boundary conditions this analysis gives the exact convergence factors of such methods. In this work, using the Fourier method, we extend these results by proving that such analysis yields the exact convergence factors for a wider class of problems

Anomalous Photovoltaic Effect in Centrosymmetric Ferroelastic BiVO4

The anomolous photovoltaic (APV) effect is an intriguing phenomenon and rarely observed in bulk materials that structurally have an inversion symmetry. Here, the discovery of such an APV effect in a centrosymmetric vanadate, BiVO4, where noticeable above‐bandgap photovoltage and a steady‐state photocurrent are observed in both ceramics and single crystals even when illuminated under visible light, is reported. Moreover, the photovoltaic voltage can be reversed by the stress modulation, and a sine‐function relationship between the photovoltage and stress directional angle is derived. Microstructure and strain‐field analysis reveal localized asymmetries that are caused by strain fluctuations in bulk centrosymmetric BiVO4. On the basis of the experimental results, a flexoelectric coupling via a strain‐induced local polarization mechanism is suggested to account for the APV effect observed. This work not only allows new applications for BiVO4 in optoelectronic devices but also deepens insights into the mechanisms underlying the APV effect.This work was financially supported by the National Key R&D Program of China (2016YFA0201103), the Natural Science Foundation of China (Grant Nos. 21577143, 51502289, 51872311, and 51502325), the Natural Science Foundation of Fujian Province (Grant Nos. 2017J05031 and 2018I0021), the Frontier Science Key Project of the Chinese Academy of Sciences (QYZDB-SSW-JSC027), and the Instrument Developing Project of Chinese Academy of Sciences (Grant No. ZDKYYQ20180004). Y.L. thanks the Australian Research Council for support in the form of an ARC discovery program grant

High-Performance Non-enzymatic Glucose Sensors Based on CoNiCu Alloy Nanotubes Arrays Prepared by Electrodeposition

Transition metal alloys are good candidate electrodes for non-enzymatic glucose sensors due to their low cost and high performance. In this work, we reported the controllable electrodeposition of CoNiCu alloy nanotubes electrodes using anodic aluminum oxide (AAO) as template. Uniform CoNiCu alloy arrays of nanotubes about 2 μm in length and 280 nm in diameter were obtained by optimizing the electrodeposition parameters. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) measurements indicated that the as-prepared alloy nanotubes arrays are composed of 64.7 wt% Co-19.4 wt% Ni-15.9 wt% Cu. Non-enzymatic glucose sensing measurements indicated that the CoNiCu nanotubes arrays possessed a low detection limit of 0.5 μM, a high sensitivity of 791 μA mM−1 cm−2 from 50 to 1,551 μM and 322 μA mM−1 cm−2 from 1,551 to 4,050 μM. Besides, they showed high reliability with the capacity of anti-jamming. Tafel plots showed that alloying brought higher exchange current density and faster reaction speed. The high performance should be due to the synergistic effect of Co, Ni, and Cu metal elements and high surface area of nanotubes arrays