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Although the mechanical properties of CoCrFeNi system high entropy alloys (HEAs) could be enhanced with the increase of Al content, it is inevitable to produce a gradual transformation of multiphase microstructure with chemical segregations. It will lead to the change of work function and the appearance of localized corrosion. The present work investigates the correlation between the corrosion behavior and the microstructure of Al x (CoCrFeNi) 100−x (x = 0–20) HEAs in 0.5 M H 2 SO 4 solution by immersion test, electrochemical measurement, SKPFM and SEM. The microstructure of CoCrFeNi system HEAs with increasing the content of Al has been transformed from single FCC phase to mixture of FCC and BCC duplex phases, and then to BCC phase. The detected value of work function gradually decreases with Al addition. The addition of a little amount of Al which retains the single FCC phase structure is beneficial to improve the corrosion resistance of Al-containing CoCrFeNi system HEAs, and the addition of excessive Al elements which promotes the formation and growth of BCC phase weakens the corrosion resistance of Al-containing CoCrFeNi system HEAs. • The relationship between the microstructure and corrosion resistance of Al x (CoCrFeNi) 100−x was systematically studied. • The microstructure of Al x (CoCrFeNi) 100−x changes from single FCC phase to FCC + BCC, and then to BCC phase. • Little Al addition without phase change improves the corrosion resistance, while excessive Al addition weakens. [ABSTRACT FROM AUTHOR]

Abstract We present extensive investigations of the crystallographic phase diagram and electronic properties of the Fe-based superconductor FeSe under extreme conditions (high pressure (HP) and low temperature (LT)) by synchrotron X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). An isostructural phase transition (Tetragonal (T) →high-pressure Tetragonal (Tʹ)) is discovered in FeSe at ∼2.8 GPa based on the axial ratio c/a with finer pressure step as observed in Fe-As-based superconductor such as EuFe 2 As 2. We also find a pressure-induced Tʹ → MnP-type phase transition at 7.6 GPa in FeSe, which is consistent with the documented pressure-induced high-spin → low-spin transition (∼6–7 GPa). These results reveal the pressure-induced structural phase transition sequence in FeSe at room temperature to be T → Tʹ → Tʹ+MnP-type at pressures of 0–10.6 GPa, enriching the crystallographic phase diagram. The HPLT XRD data also indicate that a sluggish structural phase transition (Cmma → Pnma) begins at 7.5 GPa, and these two phases coexist up to 26.5 GPa. The HP X-ray absorption near-edge spectroscopy (XANES) measurement shows that E o of Se experiences a pressure-induced shift to high energy, evidencing strongly charge transfer between Fe and Se under high pressure. Our results shed lights on the correlation between crystallographic/electronic structure and superconductivity in this material. Highlights • An isostructural phase transition (T → Tʹ) is discovered in FeSe at ∼2.8 GPa. • Another pressure-induced Tʹ → MnP-type phase transition at 7.6 GPa in FeSe. • A sluggish structural transformation (Cmma → Pnma) begins at 7.5 GPa (10 K). • XANES results show pressure-induced charge transfer between Fe and Se. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric thin films are urgently needed in microelectronic and microelectromechanical systems. In this work, (1- x)(0.94Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3)- x (Sr 0.7 Bi 0.2 □ 0.1)TiO 3 (abbreviated as BNT-BT- x SBT) piezoelectric thin films were prepared successfully. The optimal piezoelectric performance can be achieved when x = 0.02 at morphotropic phase boundary (MPB). Further, to explore the impacts of orientation control on the properties of thin films, (100), (110), and (111)-oriented BNT-BT-0.02SBT thin films were prepared on Nb-SrTiO 3 single crystal. The (110) preferred orientation thin film can achieve a high inverse piezoelectric coefficient (d 33 *) of 170 pm/V, which has a great improvement contrasted with non-oriented films. From the perspective of engineering domain configuration, the high d 33 * of (110)-oriented thin film can be characterized that the ferroelectric domain can get a complete flip in the direction of non-easily polarized axes. In short, orientation regulation is of great importance in improving the piezoelectric properties of thin films and has important applications in microelectronic sensing. • BNT-BT- x SBT ternary thin films at MPB were prepared by sol-gel method. • (100), (110) and (111)-oriented thin films were prepared on Nb-SrTiO 3 single crystal. • Grain growth can be promoted along with the densely stacking plane orientation. • (110)-oriented thin film obtains the optimal inverse piezoelectric coefficient (170 pm/V). • The ferroelectric domain get complete flip in the direction of non-easily polarized axes. [ABSTRACT FROM AUTHOR]

The high-pressure crystal structure and transporting properties of bismuthinite (Bi 2 S 3 ) have been studied with a combination of experimental and theoretical methods. The present experimental results show that the structure of orthorhombic Bi 2 S 3 stably exists in the experimental pressure range up to around 55 GPa. Upon compression, the X-Ray diffraction (XRD) patterns are dominated by broad Bragg features and seemingly pressure-induced structural amorphization or disorder occurs. However, by analyzing the XRD data obtained during the decompression cycle we suggest that the broad Bragg diffraction peaks under high pressure could be due to the nonhydrostatic conditions or crystal structural defects. To construct the correlation between the structural variation and the physical properties of Bi 2 S 3 , the transporting properties of Bi 2 S 3 were investigated under high pressure. With increasing pressure, the resistance value decreases sharply below 5 GPa and then decreases gently as the pressure further increasing. There is an obvious inflection point at about 5 GPa in the relationships of log ( R ) versus pressure. We speculate that the observed electrical variation is resulted from the pressure-induced second-order isostructural phase transition according to the reported literature. Temperature dependence of the resistance indicated that a pressure-induced semiconductor → metal transition in Bi 2 S 3 happens at around 20 GPa. The present high pressure resistance measurement indicated that high pressure could help to improve the thermoelectric properties. [ABSTRACT FROM AUTHOR]

In this study, Al-Cu alloy suitable for laser powder bed fusion (LPBF) is rapidly developed through casting and laser remelting. The microstructure of as-cast Al-Cu alloy is consisted of equiaxed grains, and it was significantly refined after remelting. The Vickers hardness in the remelted zone improved by approximately 33.7% compared with that of as-cast Al-Cu alloy. The effects of different element content on Al-Cu-Mg-Zr alloy were analyzed, and optimum alloy composition was obtained with Al-5Cu-2Mg-1Zr-0.3Mn-0.15Ti through comparing microstructure, the hardness and other properties after remelting. The nano-indentation hardness and Young's modulus of remelted Al-5Cu-2Mg-1Zr-0.3Mn-0.15Ti alloys were 1.86 and 86.7 GPa, respectively. The microstructure was dense without obvious crack after LPBF forming, and the tensile strength, yield strength and elongation values reach 483 MPa, 365 MPa and 13.4% after solution treatment. • The suitability of LPBF-fabricated alloys composition was judged by cast and laser remelting.. • The ultra-fine microstructure and Al2Cu dispersion distribution were observed in laser remelting alloy. • New composition Al-Cu alloy prepared by LPBF shows a dense structure and good mechanical behavior. [ABSTRACT FROM AUTHOR]

Te-doped Li 4 Ti 5 O 12 (LTO) was prepared by a ball milling-assisted solid-state method in air. The as-prepared powders were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy. Li 4 Ti 4.95 Te 0.05 O 12 powder sintered at 850 °C presented improved ionic and electronic conductivities of 2.20 × 10-7 S·cm-1 and 2.40 × 10-9 S·cm-1 at room temperature, respectively, an order of magnitude higher than those of intrinsic LTO. Electrochemical analysis showed that the discharge specific capacities of Li 4 Ti 4.95 Te 0.05 O 12 in Li half cells at 1 C and 5 C were 162.49 mAh·g-1 and 143.5 mAh·g-1, respectively, with capacity retention rates of 98.8% and 98.2% after 100 cycles. The Li 4 Ti 4.95 Te 0.05 O 12 /LiNi 0.5 Mn 0.3 Co 0.2 O 2 full cells also showed a good specific capacity of 101.8 mAh·g-1 at 1 C and delivered good temperature adaptability. This study provides an effective strategy for the preparation of high-performance LTO anodes for lithium-ion batteries. • Excellent transport characteristics of Li 4 Ti 4.95 Te 0.05 O 12 with an ionic conductivity of 2.20 × 10-7 S·cm-1. • High discharge specific capacity of 120.25 mAh·g-1 at high rate of 10 C in Li 4 Ti 4.95 Te 0.05 O 12 half cell. • Excellent capacity retention rate of 99.7% after 400 cycles and good specific capacity of Li 4 Ti 4.95 Te 0.05 O 12 /LiNi 0.5 Mn 0.3 Co 0.2 O 2 full cell. [ABSTRACT FROM AUTHOR]