External Uniaxial Pressure Research Articles

Influence of high pressure on mechanical and electronic properties of C3060 allotropes—A first-principles investigation

The influence of external uniaxial pressure, ranging from 0 GPa to 50 GPa, on (3,0)(6,0) carbon (C3060), is examined through first-principles calculation. The mechanical descriptors, including elastic constants, bulk modulus, shear modulus, and Young's modulus, are studied and reported. Moreover, these characteristics demonstrate the adaptable robustness of C3060 to mechanical stress under various pressure conditions. Also, the ductility and brittleness analysis is obtained based on Cauchy pressure, Poisson's ratio, and Pugh's criteria. The structural and dynamical stability of C3060 are ensured using cohesive formation energy, phonon band spectrum, and phonon density of states. Further, the thermodynamic properties of C3060 under high pressure are discussed with regard to Gibbs free energy and entropy. Also, the electronic properties of C3060 under pressure within the range of 0 GPa–50 GPa are explored based on the band structure and projected density of the state spectrum. In short, this work emphasizes how uniaxial pressure influences the mechanical characteristics and electronic attributes of C3060, providing information on the adaptability of the material's structural features with regard to mechanical attributes.

In-plane uniaxial pressure-induced out-of-plane antiferromagnetic moment and critical fluctuations in BaFe2As2

A small in-plane external uniaxial pressure has been widely used as an effective method to acquire single domain iron pnictide BaFe2As2, which exhibits twin-domains without uniaxial strain below the tetragonal-to-orthorhombic structural (nematic) transition temperature Ts. Although it is generally assumed that such a pressure will not affect the intrinsic electronic/magnetic properties of the system, it is known to enhance the antiferromagnetic (AF) ordering temperature TN ( < Ts) and create in-plane resistivity anisotropy above Ts. Here we use neutron polarization analysis to show that such a strain on BaFe2As2 also induces a static or quasi-static out-of-plane (c-axis) AF order and its associated critical spin fluctuations near TN/Ts. Therefore, uniaxial pressure necessary to detwin single crystals of BaFe2As2 actually rotates the easy axis of the collinear AF order near TN/Ts, and such effects due to spin-orbit coupling must be taken into account to unveil the intrinsic electronic/magnetic properties of the system.

Correlation Between the Indentation Properties and Microstructure of Dissimilar Capacitor Discharge Welded WC-Co/High-Speed Steel Joints.

The welding of cemented carbide to tool steel is a challenging task, of scientific and industrial relevance, as it combines the high level of hardness of cemented carbide with the high level of fracture toughness of steel, while reducing the shaping cost and extending the application versatility, as its tribological, toughness, thermal and chemical properties can be optimally harmonised. The already existing joining technologies often impart either insufficient toughness or poor high-temperature strength to a joint to withstand the ever-increasing severe service condition demands. In this paper, a novel capacitor discharge welding (CDW) process is investigated for the case of a butt-joint between a tungsten carbide-cobalt (WC-Co) composite rod and an AISI M35 high-speed steel (HSS) rod. The latter was shaped with a conical-ended projection to promote a high current concentration and heat at the welding zone. CDW functions by combining a direct current (DC) electric current pulse and external uniaxial pressure after a preloading step, in which only uniaxial pressure is applied. The relatively high heating and cooling rates promote a thin layer of a characteristic ultrafine microstructure that combines high strength and toughness. Morphological analysis showed that the CDW process: (a) forms a sound and net shaped joint, (b) preserves the sub-micrometric grain structure of the original WC-Co composite base materials, via a transitional layer, (c) refines the microstructure of the original martensite of the HSS base material, and (d) results in an improved corrosion resistance across a 1-mm thick layer near the weld interface on the steel side. A nano-indentation test survey determined: (e) no hardness deterioration on the HSS side of the weld zone, although (f) a slight decrease in hardness was observed across the transitional layer on the composite side. Furthermore, (g) an indication of toughness of the joint was perceived as the size of the crack induced by processing the residual stress after sample preparation was unaltered.

Improved and tunable optical absorption characteristics of MQW GaAs/AlGaAs nano-scale heterostructure

In this article, we report the significant improvement with the tunable character of optical absorption characteristics of MQW (multi quantum well) GaAs/AlGaAs nano-scale heterostructure. The improvement and tunability of the optical characteristics have been studied via optimization of composition of the barrier layer, quantum well width and external uniaxial pressure application on the structure. A six band Kohn-Luttinger (K–L) Hamiltonian has been solved to determine the electrons and hole’s wave functions, their localizations in the structure along with their discrete (dispersed) energies and finally the optical absorption characteristics. Under uniaxial (001) pressure in the range of 5 GPa to 25 GPa, a remarkable improvement in the optical absorption (6000 cm−1 to 9000 cm−1) along with red shift of wavelength has been reported in this paper. Thus, the proposed heterostructure with the optimized Al content can suitably be utilized in the designing of photo-detector and optical sensor operating in the visible-NIR (near infrared) wavelength region.

Piezoresistivities of vapor‐grown carbon fiber/silicone foams for tactile sensor applications

AbstractDue to the growing demand for tactile sensors, the possibility of detecting an external uniaxial pressure by the piezoresistive measuring of a conductive filler/elastomer composite was investigated. A series of piezoresistive models are discussed. Novel highly sensitive piezoresistive foams with excellent elasticity were fabricated using vapor‐grown carbon fiber (VGCF), two‐component silicone elastomer and a new type of thermally expandable micro beads foaming agent to overcome the disadvantages of the silicone elastomer in the utilization of a tactile sensor. Deformations of the foams caused by uniaxial pressure were observed using scanning electron microscopy from cross‐sections. Effects of the VGCF and the foaming agent on the piezoresistivitiy were investigated. The piezoresistive mechanisms of the foams are discussed according to the measurements, and good fit was found between the theoretical calculations and the experimental piezoresistivity measurements. It is found that the addition of the micro beads foaming agent can improve the piezoresistivity of the VGCF/silicone foam and increase the sensitivity and repeatability for its application in a tactile sensor. © 2016 Society of Chemical Industry

Giant reduction of the phase transition temperature for beryllium doped VO2

We propose a route to largely decrease the transition temperature for the insulator-metal transition of VO2 by doping with beryllium atoms. Our first-principles calculations show that the doped beryllium atoms can unprecedentedly decrease the phase transition temperature by 58 K per at% Be, which exceeds any doping attempts reported for VO2. Furthermore, it is found that the transition temperature of the Be-doped VO2 can be further lowered by applying external uniaxial pressure. A combination of Be-doping and external pressure realizes the occurrence of the phase transition at the desired room temperature. The nature of these findings is revealed to be essentially relevant to the strain-induced dimerization of V-V chains in the R-phased VO2.

Resistance Pressure Sensor Based on Ag/Cu&lt;sub&gt;2&lt;/sub&gt;O-PEPC-NiPc/Al Composite

This work reports on the fabrication and investigation of pressure sensor based on Ag/Cu2O-PEPC-NiPc/Al composite. The active layer of the composite was deposited by drop-casting of the blend Cu2O-PEPC-NiPc on flexible substrate. The thin film of the blend consist of cuprous oxide (Cu2O) micropowder, (5 wt. %), poly-N-epoxypropylcarbazole (PEPC), (2 wt. %) and nickel phthalocyanine (NiPc) micropowder, (3 wt. %) in benzol (1 ml). The film thickness of the composite is in the range of 20-30 μm. It is found that the fabricated sensor is sensitive to pressure and showed good repeatability. The decrease in resistance of the sensor is observed 10 times by increasing the external uniaxial pressure up to 11.7 kNm-2. The experimentally obtained results are compared with the simulated results and showed reasonable agreement with each other.

Control of orbital ordered state in strained Nd0.25Sr1.75MnO4 films

Epitaxial strain effect has been studied for Nd0.25Sr1.75MnO4 thin films on (100) surfaces of two different isostructural (single-layered perovskite) substrates, LaSrAlO4 and LaSrGaO4. Due to the anisotropic strain in the MnO2 plane, the orientation-controlled films were stabilized with the structure consistent with that of C-type antiferromagnetic and d3x2−r2 ferro-orbital-ordered state. Measurements of highly anisotropic optical spectra show that the tensile strain in the MnO2 plane aligns ferroically the direction of d3x2−r2 orbitals parallel to the film plane, whereas compressive strain does those vertical to the film plane. These results indicate that the direction of the ferroic ordering of d3x2−r2 orbitals can be controlled by external uniaxial pressure, implying a potential for a switching device.

Pressure effect study on the I–V property of the GaAs-based resonant tunnelling structure by photoluminescence measurement

This paper discusses the I–V property of the GaAs-based resonant tunnelling structure (RTS) under external uniaxial pressure by photoluminescence studies. Compressive pressure parallel to the [110] direction, whose value is determined by Hooke's law, is imposed on the sample by a helix micrometer. With the increase of the applied external uniaxial compressive pressure, the blue shift and splitting of the luminescence peaks were observed, which have some influence on the I–V curve of RTS from the point of view of the energy gap, and the splitting became more apparent with applied pressure. Full width at half maximum broadening could also be observed.

Effects of uniaxial stress on orbital stripe direction in half-doped layered manganites:Eu0.5Ca1.5MnO4andPr(Sr,Ca)2Mn2O7

We have studied the uniaxial-stress effects on the half-doped charge-orbital ordered (CO-OO) manganites ${\text{Eu}}_{0.5}{\text{Ca}}_{1.5}{\text{MnO}}_{4}$ and $\text{Pr}{({\text{Sr}}_{1\ensuremath{-}y}{\text{Ca}}_{y})}_{2}{\text{Mn}}_{2}{\text{O}}_{7}(y\ensuremath{\sim}0.9)$. ${\text{Eu}}_{0.5}{\text{Ca}}_{1.5}{\text{MnO}}_{4}$ with single Mn-O layer structure is ferroelastic and the application of weak uniaxial stress $(&lt;8.5\text{ }\text{MPa})$ along the orbital stripe direction drives a rotation of the orbital stripes by $90\ifmmode^\circ\else\textdegree\fi{}$ through the lattice orthorhombicity channel. For $\text{Pr}{({\text{Sr}}_{1\ensuremath{-}y}{\text{Ca}}_{y})}_{2}{\text{Mn}}_{2}{\text{O}}_{7}(y\ensuremath{\sim}0.9)$ with double Mn-O layer structure, it is revealed that the phase stability of two CO-OO states with different orbital stripe direction can be controlled by the external uniaxial pressure. In addition, the application of higher uniaxial pressure also causes a rotation of the lattice orthorhombicity itself and hence rotates the orbital stripes as well as the electric polarization axis in the low-temperature CO-OO state.

Model for the domain state of Ti‐rich titanomagnetites

Domain structure observations on synthetic and natural Ti‐rich titanomagnetites (≈TM60), some of which were made under external uniaxial pressure, lead to a new model for the domain state of such materials. Instead of a classical domain configuration, we observed in most cases a more complicated micromagnetic structure with multidomain particles consisting of a conglomerate of quasi‐single domain, multi‐domain and spin cluster zones due to an inhomogeneous anisotropy field caused by internal stress. Pseudo‐single domain properties such as stable TRM can be explained by spin rotation processes as in single domain particles.

Multimagnon absorption in the optical spectrum of antiferromagnetic RbMnF3

The spectrum of optical electrodipolar absorption of antiferromagnetic RbMnF3 in the region of the 6 A 1g ( 6 S)→ 4 E g , 4 A 1g ( 4 G) transition has been studied experimentally in strong magnetic fields (up to300 kOe) and at the external uniaxial pressure. Employing the parameters of earlier studies of the single-particle pure exciton transition 6 A 1g ( 6 S)→ 4 E g ( 4 G), the dipolar moments of the transition and the absorption maxima of its two- and three-magnon sidebands have been calculated. Also, the exciton dispersion for translationally equivalent ions and exciton-magnon interactions have been estimated. It has been shown that the whole main part (200 cm −1 ) of the absorption bands under consideration is likely to be formed by single-, two-, and three-magnon sidebands of this transition.