The structural origin of enhanced piezoelectric performance and stability in KNN-based ceramics can be attributed to the hierarchical nanodomain architecture with phase coexistence.

Mechanism of metal-insulator transition (MIT) in strained VO2 thin films is very complicated and incompletely understood despite three scenarios with potential explanations including electronic correlation (Mott mechanism), structural transformation (Peierls theory) and collaborative Mott-Peierls transition. Herein, we have decoupled coactions of structural and electronic phase transitions across the MIT by implementing epitaxial strain on 13-nm-thick (001)-VO2 films in comparison to thicker films. The structural evolution during MIT characterized by temperature-dependent synchrotron radiation high-resolution X-ray diffraction reciprocal space mapping and Raman spectroscopy suggested that the structural phase transition in the temperature range of vicinity of the MIT is suppressed by epitaxial strain. Furthermore, temperature-dependent Ultraviolet Photoelectron Spectroscopy (UPS) revealed the changes in electron occupancy near the Fermi energy EF of V 3d orbital, implying that the electronic transition triggers the MIT in the strained films. Thus the MIT in the bi-axially strained VO2 thin films should be only driven by electronic transition without assistance of structural phase transition. Density functional theoretical calculations further confirmed that the tetragonal phase across the MIT can be both in insulating and metallic states in the strained (001)-VO2/TiO2 thin films. This work offers a better understanding of the mechanism of MIT in the strained VO2 films.

The phase problem is reduced to a sign problem once the anomalous-scatterer or the replacing-heavy-atom sites are located.OASISadopts theCCP4 format [Collaborative Computational Project, Number 4 (1994).Acta Cryst.D50, 760–763]. It applies a direct-method procedure to break the phase ambiguity intrinsic to one-wavelength anomalous scattering (OAS) or single isomorphous replacement (SIR) data.

In this work, we confirmed the electric -induced transition (EPT) in (K,Na)NbO 3 -based ceramics through experiment and theory. Through in-situ x-ray diffraction measurement, electric field -induced phases (EP) could be observed in the ceramics. To explain the appearance of EP, a new function ex E λ ( ) was introduced to the six order Devonshire theory when the external electric field was applied. The further studies indicate that EPT had two possible forms, i.e., tetragonal -electric induced phase transition (T-EP) and rhombohedral -electric induced phase transition (R-EP), and then T-EP plays a more positive role than R-EP in terms of piezoelectric response. Also, a giant piezoelectricity (d 33 =435~490 pC/N), a high Curie temperature (T C =205~235°C), and converse piezoelectric coefficient (d 33 * =500~890 pm/V) can be achieved by choosing optimum metal oxides as well as their content. We believe that a) Corresponding