Highly Conductive Carbon Nanotube‐Graphene Hybrid Yarn

An efficient procedure for the fabrication of highly conductive carbon nanotube/graphene hybrid yarns has been developed. To start, arrays of vertically aligned multi‐walled carbon nanotubes (MWNT) are converted into indefinitely long MWNT sheets by drawing. Graphene flakes are then deposited onto the MWNT sheets by electrospinning to form a composite structure that is transformed into yarn filaments by twisting. The process is scalable for yarn fabrication on an industrial scale. Prepared materials are characterized by electron microscopy, electrical, mechanical, and electrochemical measurements. It is found that the electrical conductivity of the composite MWNT‐graphene yarns is over 900 S/cm. This value is 400% and 1250% higher than electrical conductivity of pristine MWNT yarns or graphene paper, respectively. The increase in conductivity is asssociated with the increase of the density of states near the Fermi level by a factor of 100 and a decrease in the hopping distance by an order of magnitude induced by grapene flakes. It is found also that the MWNT‐graphene yarn has a strong electrochemical response with specific capacitance in excess of 111 Fg^?1. This value is 425% higher than the capacitance of pristine MWNT yarn. Such substantial improvements of key properties of the hybrid material can be associated with the synergy of MWNT and graphene layers in the yarn structure. Prepared hybrid yarns can benefit such applications as high‐performance supercapacitors, batteries, high current capable cables, and artificial muscles.     

Al-doped zinc oxide nanocomposites with enhanced thermoelectric properties

ZnO is a promising high figure-of-merit (ZT) thermoelectric material for power harvesting from heat due to its high melting point, high electrical conductivity σ, and Seebeck coefficient α, but its practical use is limited by a high lattice thermal conductivity κ(L). Here, we report Al-containing ZnO nanocomposites with up to a factor of 20 lower κ(L) than non-nanostructured ZnO, while retaining bulklike α and σ. We show that enhanced phonon scattering promoted by Al-induced grain refinement and ZnAl(2)O(4) nanoprecipitates presages ultralow κ ～ 2 Wm( -1) K(-1) at 1000 K. The high α～ -300 μV K(-1) and high σ ～ 1-10(4) Ω(-1 )m(-1) result from an offsetting of the nanostructuring-induced mobility decrease by high, and nondegenerate, carrier concentrations obtained via excitation from shallow Al donor states. The resultant ZT ～ 0.44 at 1000 K is 50% higher than that for the best non-nanostructured counterpart material at the same temperature and holds promise for engineering advanced oxide-based high-ZT thermoelectrics for applications.     

The four-particle harmonic-oscillator brackets: Compact expressions and updated Fortran program

We present a new version of the four-particle harmonic-oscillator transformation brackets (4HOB) calculation program, where marginal cases of mass-ratio parameters d=0, d→∞ and d₁=0, which cannot be calculated in previous version, are presented. The simplified 4HOB calculation formulas for these cases are given.

Program summary

Program title: HOTBCatalogue identifier: AEFQ_v2_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFQ_v2_0.htmlProgram obtainable from: CPC Program Library, Queen?s University, Belfast, N. IrelandLicensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 3998No. of bytes in distributed program, including test data, etc.: 65 088Distribution format: tar.gzProgramming language: Fortran 90Computer: Any computer with FORTRAN 90 compilerOperating system: Windows, Linux, FreeBSD, True64 UnixRAM: 8 MBClassification: 17.17Catalogue identifier of previous version: AEFQ_v1_0Journal reference of previous version: Comput. Phys. Comm. 181 (2010) 420Does the new version supersede the previous version?: YesNature of problem: Calculation of the four-particle harmonic-oscillator transformation brackets for cases of mass-ratio parameters d=0, d→∞ and d₁=0.Solution method: The method is based on compact expressions of the four-particle harmonics oscillator brackets, presented in [1] and its simplifications presented in this paper.Reasons for new version: We simplified the four-particle harmonic-oscillator transformation brackets expressions in cases d=0, d→∞ and d₁=0. It gives shorter calculation times and the possibility of calculating the four-particle harmonics oscillator brackets in these cases, which was not possible in the previous version of the program.Summary of revisions: New subroutines for the calculation of the harmonic-oscillator transformation brackets in cases d=0, d→∞ and d₁=0. In case d=0 subroutine HOB4_d_0(e1, l1, e2, l2, l12, e3, l3, e1s, l1s, e2s, l2s, l12s, e3s, l3s, l) is used. In this case and . In case d→∞ subroutine HOB4_d_infinity(e1, l1, e2, l2, l12, e3, l3, e1s, l1s, e2s, l2s, l12s, e3s, l3s, l) is used. In this case and . In case d₁=0 subroutine HOB4_d1_0(e1, l1, e2, l2, l12, e3, l3, e1s, l1s, e2s, l2s, l12s, e3s, l3s, l) is used. For theoretical issues of the revision see section ‘Theoretical aspects’.Restrictions: The four-particle harmonic-oscillator transformation brackets up to e=28.Running time: Less than one second for the single harmonic-oscillator transformation bracket.References:

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  [1] D. Germanas, S. Mickevi?ius, R.K. Kalinauskas, Calculation of four-particle harmonic-oscillator transformation brackets, Computer Physics Communications 181 (2010) 420-425.

     

Calculation of four-particle harmonic-oscillator transformation brackets

A procedure for precise calculation of the three- and four-particle harmonic-oscillator (HO) transformation brackets is presented. The analytical expressions of the four-particle HO transformation brackets are given. The computer code for the calculations of HO transformation brackets proves to be quick, efficient and produces results with small numerical uncertainties.

Program summary

Program title: HOTBCatalogue identifier: AEFQ_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFQ_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 1247No. of bytes in distributed program, including test data, etc.: 6659Distribution format: tar.gzProgramming language: FORTRAN 90Computer: Any computer with FORTRAN 90 compilerOperating system: Windows, Linux, FreeBSD, True64 UnixRAM: 8 MBClassification: 17.17Nature of problem: Calculation of the three-particle and four-particle harmonic-oscillator transformation brackets.Solution method: The method is based on compact expressions of the three-particle harmonics oscillator brackets, presented in [1] and expressions of the four-particle harmonics oscillator brackets, presented in this paper.Restrictions: The three- and four-particle harmonic-oscillator transformation brackets up to the e=28.Unusual features: Possibility of calculating the four-particle harmonic-oscillator transformation brackets.Running time: Less than one second for the single harmonic-oscillator transformation bracket.References:

[1]

G.P. Kamuntavi?ius, R.K. Kalinauskas, B.R. Barret, S. Mickevi?ius, D. Germanas, Nuclear Physics A 695 (2001) 191.

     

HOTB: High precision parallel code for calculation of four-particle harmonic oscillator transformation brackets

This new version of the HOTB program for calculation of the three and four particle harmonic oscillator transformation brackets provides some enhancements and corrections to the earlier version (Germanas et al., 2010) [1]. In particular, new version allows calculations of harmonic oscillator transformation brackets be performed in parallel using MPI parallel communication standard. Moreover, higher precision of intermediate calculations using GNU Quadruple Precision and arbitrary precision library FMLib [2] is done. A package of Fortran code is presented. Calculation time of large matrices can be significantly reduced using effective parallel code. Use of Higher Precision methods in intermediate calculations increases the stability of algorithms and extends the validity of used algorithms for larger input values.     

Preparation and characterization of hybrid conducting polymer-carbon nanotube yarn

Hybrid polypyrrole (PPy)-multi walled carbon nanotube (MWNT) yarns were obtained by chemical and electrochemical polymerization of pyrrole on the surface and within the porous interior of twisted MWNT yarns. The material was characterized by scanning electron microscopy, electrochemical, mechanical and electrical measurements. It was found that the hybrid PPy-MWNT yarns possessed significantly higher mechanical strength (over 740 MPa) and Young's modulus (over 54 GPa) than the pristine MWNT yarn. The hybrid yarns also exhibited substantially higher electrical conductivity (over 235 S cm(-1)) and their specific capacitance was found to be in excess of 60 F g(-1). Measurements of temperature dependence of electrical conductivity revealed semiconducting behaviour, with a large increase of band gap near 100 K. The collected low temperature data are in good agreement with a three-dimensional variable range hopping model (3D-VRH). The improved durability of the yarns is important for electrical applications. The composite yarns can be produced in commercial quantities and used for applications where the electrical conductivity and good mechanical properties are of primary importance.     

A Liquid‐Metal‐Based Magnetoactive Slurry for Stimuli‐Responsive Mechanically Adaptive Electrodes

Electrical communication between a biological system and outside equipment allows one to monitor and influence the state of the tissue and nervous networks. As the bridge, bioelectrodes should possess both electrical conductivity and adaptive mechanical properties matching the target soft biosystem, but this is still a big challenge. A family of liquid‐metal‐based magnetoactive slurries (LMMSs) formed by dispersing magnetic iron particles in a Ga‐based liquid metal (LM) matrix is reported here. The mechanical properties, viscosity, and stiffness of such materials rapidly respond to the stimulus of an applied magnetic field. By varying the intensity of the magnetic field, regulation within a factor of 1000 of the Young's modulus from ≈kPa to ≈MPa, and the ability to reach GPa with more dense iron particles inside the LMMS are demonstrated. With the advantage of high conductivity of the LM matrix, the functions of the LMMS are not only limited to the soft implanted electrodes or penetrating electrodes in biosystems: the electrical response based on the LMMS electrodes can also be precisely tuned by simply regulating the applied magnetic field.     

Surface Lattice-Matched Engineering Based on In Situ Spinel Interfacial Reconstruction for Stable Heterostructured Sodium Layered Oxide Cathodes

Layered transition metal oxide (Na_xTMO₂), being one of the most promising cathode candidates for sodium-ion batteries (SIBs), have attracted intensive interest because of their nontoxicity, high theoretical capacities, and easy manufacturability. However, their physical and electrochemical properties of water sensitivity, sluggish Na⁺ transport kinetics, and irreversible multiple-phase translations hinder the practical application. Here, a concept of surface lattice-matched engineering is proposed based on in situ spinel interfacial reconstruction to design a spinel coating P2/P3 heterostructure cathode material with enhanced air stability, rate, and cycle performance. The novel structure and its formation process are verified by transmission electron microscopy and in situ high-temperature X-ray diffraction. The electrode exhibits an excellent rate performance with the highly reversible phase transformation demonstrated by in situ charging/discharging X-ray diffraction. Additionally, even after a rigorous water sensitivity test, the electrode materials still retain almost the same superior electrochemical performance as the fresh sample. The results show that the surface spinel phase can play a vital role in preventing the ingress of water molecules, improving transport kinetics, and enhancing structural integrity for Na_xTMO₂ cathodes. The concept of surface lattice-matched engineering based on in situ spinel interfacial reconstruction will be helpful for designing new ultra-stable cathode materials for high-performance SIBs.