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BackgroundTwo X-ray diffractometers manufactured by HUBER company are installed at BL02U2 beamline of Shanghai Synchrotron Radiation Facility (SSRF).PurposeThis study aims to develop a new grazing incidence diffractometer installed between the two HUBER diffractometers to further satisfy the needs of users for grazing incidence diffraction experimental methods.MethodsThe overall scheme of the grazing incidence diffractometer was introduced, followed by detail discussion on several important modules such as high-precision, high-load and large-stroke linear stage, three-dimensional adjustment platform for a detector, sample stage system, and the control system. A compatible operation of the three diffractometers was realized, and the MoS2 sample was taken as an example to obtain a typical experimental result of the grazing incidence diffractometer.ResultsThe grazing incidence X-ray diffractometer has been in operation for more than two years. The X-ray energy range of the diffractometer is 4.8~28 keV. The temporal resolution of the detector is 50 ms, and the maximum detection angle is 52°. Experimental results of MoS2 sample shown that the nanosheets are more likely to accumulate on the surface of silicon wafers along the (001) crystal plane.ConclusionsThe grazing incidence X-ray diffractometer developed in this study improves the experimental conditions for grazing incidence diffraction and expands the experimental platform for material surface science research at SSRF.

Area detectors have been widely used in X-ray diffraction (XRD) to improve the acquisition speed and data quality. Here, an accurate, high efficiency, low distortion approach with a large angle range for collecting powder X-ray diffraction data is developed which is carried out by rotating a small area detector on the detector arm of the diffractometer. A series of collected images are spliced and converted into one 1D XRD pattern. The calculation of the 2θ value and intensity corresponding to every pixel are shown in detail. The calibration of the detector and experimental geometry was carried out. Finally, the reliability of this method has been demonstrated by the X-ray diffraction measurements of a standard LaB6 powder and Rietveld refinement results. [ABSTRACT FROM AUTHOR]

Invar alloys with zero thermal expansion (ZTE), isotropy, high operation temperature, and wide temperature range are of great significance in fields such as aerospace and modern industry. However, it is difficult to simultaneously meet the above characteristics in one material. The traditional methods like element or vacancies doping would increase the operation temperature but at the expense of ZTE behavior. Here, by the coherent coupling between two cubic phases, the isotropic ZTE metallic material with the higher cut‐off temperature (560 K) and a wide operation temperature range (ΔT = 200 K) is obtained in Fe2.75Co0.25PtB0.25. The operation temperature range is much higher than that of commercial Fe0.65Ni0.35 Invar alloy and meets the applications at elevated temperatures. High‐angle annular dark field images and synchrotron X‐ray diffraction prove that by the coherent interfacial coupling between the A1 and its coherent L12 nanodomains, the original negative thermal expansion or positive thermal expansion performances for them can be changed into the same ZTE performances. This thermal expansion regulation strategy realized by coherent coupling will lead to an innovative and significant revolution for ZTE design and promote its development and application. [ABSTRACT FROM AUTHOR]

In this work, we confirmed the electric-induced transition (EPT) in (K,Na)NbO3-based ceramics through experiment and theory. Through in situ X-ray diffraction measurements, electric field-induced phases (EPs) could be observed in the ceramics. To explain the appearance of EPs, a new function λ(Eex) was introduced into the six order Devonshire theory when the external electric field was applied. 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 T-EP plays a more positive role than R-EP in terms of the piezoelectric response. Also, a giant piezoelectricity (d33 = 435–490 pC N−1), a high Curie temperature (TC = 205–234 °C), and a converse piezoelectric coefficient (dSTACKABOVE*/ABOVEBELOW33/BELOW/STACK = 500–890 pm V−1) can be achieved by choosing optimum metal oxides as well as their content. We believe that such work could help to further study the physical mechanisms of giant piezoelectricity in potassium–sodium niobate. [ABSTRACT FROM AUTHOR]

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.