In the transport studies of topological insulators, microflakes exfoliated from bulk single crystals are often used because of the convenience in sample preparation and the accessibility to high carrier mobilities. He...In the transport studies of topological insulators, microflakes exfoliated from bulk single crystals are often used because of the convenience in sample preparation and the accessibility to high carrier mobilities. Here, based on finite element analysis, we show that for the non-Hall-bar shaped topological insulator samples, the measured four-point resistances can be substantially modified by the sample geometry, bulk and surface resistivities,and magnetic field. Geometry correction factors must be introduced for accurately converting the four-point resistances to the longitudinal resistivity and Hall resistivity. The magnetic field dependence of inhomogeneous current density distribution can lead to pronounced positive magnetoresistance and nonlinear Hall effect that would not exist in the samples of ideal Hall bar geometry.展开更多
Sodium-ion batteries(SIBs),as the low-cost and large-scale energy storage devices,have attracted wide attention,but their capacity and cycle performance are limited by cathode materials.Here,P2-Na0.7MnO2.05microflakes...Sodium-ion batteries(SIBs),as the low-cost and large-scale energy storage devices,have attracted wide attention,but their capacity and cycle performance are limited by cathode materials.Here,P2-Na0.7MnO2.05microflakes with the diameter 500 nm to 1μm are synthesized by an improved solid-state reaction.The as-prepared P2-Na0.7MnO2.05microflakes exhibit excellent electrochemical performance when tested as a cathode material of SIBs.It delivers a considerably reversible capacity of 142.7 mA h g-1at a current density of 0.3C(1C=180 mA g-1)with a slow capacity decay to121.5 mA h g-1after 50 cycles.Even at a high current density of 2C,the P2-Na0.7MnO2.05microflakes still show a specific capacity of 88.9 mA h g-1with a capacity retention of 75%after 100 cycles.The above performance of Na0.7MnO2.05microflakes are better than Na0.7MnO2.05with large block morphology,which is mainly attributed to the lamellar morphology of P2-Na0.7MnO2.05alleviating structural deformation and accelerating reaction kinetics.This strategy will provide new opportunities to develop stable oxide cathodes for SIBs.展开更多
基金Supported by the National Natural Science Foundation of China (Grant No. 11961141011)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB28000000)the National Key Research and Development Program of China(Grant No. 2016YFA0300600)。
文摘In the transport studies of topological insulators, microflakes exfoliated from bulk single crystals are often used because of the convenience in sample preparation and the accessibility to high carrier mobilities. Here, based on finite element analysis, we show that for the non-Hall-bar shaped topological insulator samples, the measured four-point resistances can be substantially modified by the sample geometry, bulk and surface resistivities,and magnetic field. Geometry correction factors must be introduced for accurately converting the four-point resistances to the longitudinal resistivity and Hall resistivity. The magnetic field dependence of inhomogeneous current density distribution can lead to pronounced positive magnetoresistance and nonlinear Hall effect that would not exist in the samples of ideal Hall bar geometry.
文摘Sodium-ion batteries(SIBs),as the low-cost and large-scale energy storage devices,have attracted wide attention,but their capacity and cycle performance are limited by cathode materials.Here,P2-Na0.7MnO2.05microflakes with the diameter 500 nm to 1μm are synthesized by an improved solid-state reaction.The as-prepared P2-Na0.7MnO2.05microflakes exhibit excellent electrochemical performance when tested as a cathode material of SIBs.It delivers a considerably reversible capacity of 142.7 mA h g-1at a current density of 0.3C(1C=180 mA g-1)with a slow capacity decay to121.5 mA h g-1after 50 cycles.Even at a high current density of 2C,the P2-Na0.7MnO2.05microflakes still show a specific capacity of 88.9 mA h g-1with a capacity retention of 75%after 100 cycles.The above performance of Na0.7MnO2.05microflakes are better than Na0.7MnO2.05with large block morphology,which is mainly attributed to the lamellar morphology of P2-Na0.7MnO2.05alleviating structural deformation and accelerating reaction kinetics.This strategy will provide new opportunities to develop stable oxide cathodes for SIBs.
