Search

Two new quaternary chalcogenides, Na6CdSb4S10 and Na3CdSbSe4, were successfully synthesized by the high-temperature solid-state reaction in vacuum-sealed silica tubes. Note that Na6CdSb4S10 crystallizes in the C2/c space group, whereas Na3CdSbSe4 crystallizes in the P21/c space group. As seen from their structures, Na6CdSb4S10 exhibits a three-dimensional (3D) framework structure composed by the interconnection of isolated [(Cd/Sb)2Sb2S10] clusters and two different layers formed by the NaSn (n = 4, 6) units; besides, the structure of Na3CdSbSe4 is composed of isolated ∞(Cd3Sb2Se12)n chains and 2D layers formed by the NaSen (n = 5, 6) units. Their optical performances (bandgap and Raman spectra) were also investigated. Moreover, theoretical calculation was used to analyze the structure–performance relationship of Na3CdSbSe4. [ABSTRACT FROM AUTHOR]

The read-cycle endurance of a magnetic tunneling junction (MTJ) has been investigated, focusing on the spin-dependent tunneling current at high temperatures. The MTJ structure used in this study consisted of Ta-NiFe-CoFe-AlOx-CoFe-IrMn-NiFe-Ta prepared on a thermally oxidized Si wafer. Both the tunneling current and tunneling magnetoresistance ratio showed no significant degradation during the 1E9 read-cycle test using unipolar voltage pulses of 0.5 V at room temperature. Temperature dependence of the MTJs resistance calculated from the measured tunneling current has also been examined in a temperature range from room temperature to 175 °C. Furthermore in the case of read-cycle tests for thermally stressed MTJs, the variation of the tunneling current was less than 2% after 1E9 cycles at a stress temperature of 175 °C. This indicates that MTJs have sufficient read-cycle endurance under high-temperature operation. [ABSTRACT FROM AUTHOR]

The first pyroborate in the Li 2 O-MgO-B 2 O 3 system, Li 3.366 Mg 0.317 B 2 O 5 , has been synthesized via high temperature solution method. The crystal structure can be described as isolated B 2 O 5 units connecting with the Li(2)O 5 chains to generate the 2 ∞ [Li 2 (2)B 2 O 5 ] layers, which condense alone a -axis, and the co-occupied Li(1)/Mg atoms fill into the voids between the layers. Interestingly, edge- and face-sharing Li(2)O 5 polyhedra are rarely found in Li 3.366 Mg 0.317 B 2 O 5 and its maternal compound β -Li 4 B 2 O 5 . Moreover, torsion and dihedral angles between two BO 3 triangles of B 2 O 5 in Li 4−2x Mg x B 2 O 5 (x = 0, 0.317, 2) are investigated to explore the structure regulation via introduction of the Mg 2+ cation. The structure refinement, thermal stability and infrared spectrum are presented in detail. [ABSTRACT FROM AUTHOR]

Two new isostructural lead borates, Pb 8 Mg(BO 3 ) 6 and Pb 8 Ca(BO 3 ) 6 , have been synthesized via high temperature solution method. The single crystal structures of title compounds contain ∞ [Pb 8 B 6 O 18 ] 2- double layers composed of planar BO 3 triangles, Pb(2)O 9 and distorted Pb(1)O 5 polyhedra, these layers condense in c -axis, and the MgO 6 (or CaO 6 ) polyhedra fill into the layers, forming a three-dimensional framework. The stereochemical activity of lone pair (SCALP) electrons were found in the Pb(1)O 5 polyhedra, which combine with the BO 3 units, generating strong optical anisotropy. The calculated birefringences of Pb 8 Mg(BO 3 ) 6 and Pb 8 Ca(BO 3 ) 6 using first-principles method are 0.15@1064 nm and 0.12@1064 nm, respectively, which are comparable to the commercial α -BaB 2 O 4 (α-BBO) crystal and imply that they probably can be used as birefringent materials. The electronic structures, density of states of title compounds were calculated by density functional theory (DFT). Meanwhile, the TG-DSC curves, infrared spectral and UV–Vis–NIR diffuse reflectance spectral were measured. [ABSTRACT FROM AUTHOR]

The transition between onion states and vortex states in exchange-coupled Ni–Fe/Mn–Ir asymmetric ring dots has been investigated. A direction of domain wall motion, during the transition from the single-domain state to the vortex state via the onion state, depends on a sweep direction of an external field. This dependence fixes the directions of vortical magnetizations in the vortex states. The derivative of the amount of the domain wall motion with respect to the external field depends on the sweep direction of external field, and thus the hysteresis loop becomes asymmetric. [ABSTRACT FROM AUTHOR]

Ni–Fe asymmetric ring dots with partially planed outer sides were investigated as candidates for high-density magnetic memory cells. The magnetic states, which were measured with magnetic force microscopy, show that in-plane magnetic fields can control the chirality, either clockwise or counterclockwise, of vortical magnetizations of the Ni–Fe asymmetric ring dots. This control facilitates applying ring dots to the magnetic random access memories. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Ni–Fe/Mn–Ir asymmetric ring dots with partially planed outer sides are investigated in order to confirm a method for obtaining pinned layers in magnetic memories with asymmetric ring shapes. Magnetic force microscopy revealed that the direction of vortical magnetization is pinned in Ni–Fe/Mn–Ir asymmetric ring dots despite the direction of the magnetic fields. This investigation shows that the Ni–Fe/Mn–Ir asymmetric ring dots can be applied to pinned layers in magnetic memories with asymmetric ring shapes. [Copyright &y& Elsevier]

[Display omitted] • Hollow carbon fibers (CFs) and ZnO/CFs composite derived from waste cotton were prepared by a green carbonization method. • The gas sensing properties of CFs and ZnO/CFs were achieved by changing carbonization temperatures for the first time. • The regulated CFs and ZnO/CFs showed the detection limits of 0.45 ppb and 0.17 ppb for CH 2 O vapor, respectively. • The sensor array of CFs and ZnO/CFs can identify five analytes within 15 s and recover within 4 s. Renewable waste cotton was carbonized into hollow carbon fibers (CFs) and ZnO/CFs composite by a simple carbonization method, which was studied as gas sensing materials for the first time. It was found that the carbonization destroyed the hydrogen bonds within the cotton fiber and changed their microstructure. Meanwhile, high temperature promoted the decomposition of zinc acetate adsorbed to cotton fibers into ZnO, forming lots of heterojunctions between ZnO and CFs, which further improved the gas sensitive properties. Accordingly, the gas sensing properties of CFs and ZnO/CFs were effectively tailored by controlling the carbonization temperatures, achieving the differential response to the target gases. The sensor array based on CFs and ZnO/CFs displayed the rapid, discriminative detection to target gases at room temperature. The response time and recovery time of sensor array are no more than 15 s and 4 s, respectively. The theoretical limit of detection of controlled CFs and ZnO/CFs to CH 2 O vapor was determined to be 0.45 ppb and 0.17 ppb, respectively. This work extended the application of cotton to the field of gas sensors and enriched the family of gas sensing materials. [ABSTRACT FROM AUTHOR]