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High pressure - high temperature synthesis and studies of nitride materials

High pressure - high temperature synthesis and studies of nitride materials

T ransition m etal nitrides provide im portant refractory m aterials, such as "superhard" cerm ets for m echanically-resistant coatings, force-transm itting elem ents, and as useful m agnetic and conductive m aterials, including high-Tc superconductors [3, 7]. T hroughout the years, the scientific com m unity has m easured m any o f the relevant m aterial properties o f transition m etal nitride com pounds and com posites, such as the hardness, shear m oduli, superconducting transition tem perature. H ow ever, there is little inform ation on the bulk m odulus o f the pure m aterials, w hich gives direct inform ation on the volum e com pressibilities o f the nitride com pounds, that one can correlate w ith their electronic properties, and especially the cohesive energy [3, 7]. In this, chapter we present com pressibility m easurem ents for five transition m etal nitrides that constitute im portant m aterials (5-M oN, y-M oiN , TaN , TIN and C r2N ), using in situ X -ray structure determ inations using synchrotron radiation in the diam ond anvil cell. Industry already uses all o f these nitrides as "super-hard" coating m aterials because o f their high hardness properties and their chem ical stability. H ow ever, the volum e com pressibility rem ains unknow n even though it is an im portant param eter.
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Evolution of the low temperature Fermi surface of superconducting FeSe1−xSx across a nematic phase transition

Evolution of the low temperature Fermi surface of superconducting FeSe1−xSx across a nematic phase transition

We thank J. C. A. Prentice for computational support, N. Davies and A. Narayanan for preliminary sample preparation and R. Valenti, A. Chubukov and A. Shekhter for useful discussions. This work was mainly supported by EPSRC (EP/L001772/1, EP/ I004475/1, EP/I017836/1). A.A.H. acknowledges the fi nancial support of the Oxford Quantum Materials Platform Grant (EP/M020517/1). A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1157490 and the State of Florida. This research was supported in part by the National Science Foundation under Grant No. NSF PHY17-48958. Part of this work was supported by HFML-RU/FOM and LNCMI-CNRS, members of the European Magnetic Field Laboratory (EMFL) and by EPSRC (UK) via its membership to the EMFL (grant no. EP/N01085X/1). Part of this work was supported by Programme Investissements d’ Avenir under the programme ANR-11-IDEX-0002-02, reference ANR-10-LABX-0037- NEXT. The authors would like to acknowledge the use of the University of Oxford Advanced Research Computing (ARC) facility in carrying out part of this work. A.I.C. thanks the hospitality of KITP supported by the National Science Foundation under Grant No. NSF PHY- 1125915. A.I.C. acknowledges an EPSRC Career Acceleration Fellowship (EP/I004475/1).
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Band Structure, Metallization and Superconducting Transition Of Group III V Semiconductors AlP And AlAs Under High Pressure

Band Structure, Metallization and Superconducting Transition Of Group III V Semiconductors AlP And AlAs Under High Pressure

the effect of pressure on the band structure of these compounds.[13] We have analyzed the phenomena of metallization and superconductivity for high pressure (CsCl) structure of these materials. It is hoped that this analysis will enable us to make some general statement regarding the path to high Tc superconductivity in covalent compounds. In Section 2, we give the details of the calculational procedure, electronic band structure and density of states corresponding to various pressures. The ground-state properties, structural phase transition, metallization and superconducting transition temperature Tc and its variation under pressure are discussed in Section 3. Concluding remarks are given in Section 4.
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Minimizing of Fault Current Using SFCL Technology

Minimizing of Fault Current Using SFCL Technology

In today’s scenario there are tremendous growths in power system and interconnected networks such as grids. These growths are expected to continue in future. As there is any occurrence of accidental events like lightning, a large amount of power flows through the grid which results in a failure of the system. These faults can generate surge currents more than one hundred times the normal operating current, hence damage the expensive grid-connected equipments. Therefore protection of the system is an important consideration to avoid harm to the system parameters and system equipments from large amount of current during fault [1] [3]. A Fault Current Limiter (FCL) is a device which limits the short circuit current during fault in a power transmission network. Fault current limiters (FCL) provide an effective way to suppress fault current and result in considerable saving in the investment of high capacity circuit breakers. A various types of fault current limiters uses variety of new techniques for limiting excess fault current [4]. However focus is on superconducting technologies i.e. Superconducting Fault current Limiters (SFCL). Whereas non-superconducting technologies contain devices like simple inductors or variable resistors are also known as Fault Current Controllers. Due to the rapid growth in the power generation systems there is a growth in fault current level, which may cross the rated capacity of available circuit breaker. Replacement of these existing switchgears due to increased fault level will not be the feasible option by considering cost parameter. By considering all these parameters it is necessary to use some reliable means to minimize fault current level and hence allow the circuit breaker to operate at lower fault Currents. Superconducting Fault current Limiters provides an effective way to suppress fault current [3], [6]. Current limiting behavior of these superconductors depends on their non-linear characteristics with Temperature, current and magnetic field variations. If there is Increase in any one of these three parameters can cause transition of superconducting state to normal state. As per the development of superconducting materials SFCLs are of three types [3],
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Support vector regression approach of 
		modeling the superconducting transition temperature of borocarbide based 
		superconductors

Support vector regression approach of modeling the superconducting transition temperature of borocarbide based superconductors

Support vector regression is a learning algorithm proposed by Vapnik to solve regression tasks [18]. SVR has a good sound mathematical framework that results in optimal solution for its optimization problem. In addition, SVR performs excellently by maintaining good generalization error when the input dataset is small as it does not over-fit. The input vector, 𝒙, corresponds to the training dataset employed to train the SVR model and are first mapped to a high-dimensional feature space using a non-linear mapping function, 𝜑 𝒙 [19]. Linear regression is then performed on the transformed data in this high- dimensional space by constructing a set of hypothesis. The linear model of SVR can thus be expressed as:
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Design of Ultra-Narrowband Miniaturized High Temperature Superconducting Bandpass Filter

Design of Ultra-Narrowband Miniaturized High Temperature Superconducting Bandpass Filter

Abstract—This paper proposes a novel clip-shaped meander-line resonator (CSMLR) to realize miniaturized ultra-narrowband (UNB) bandpass filter design. The main advantage is that it can achieve very weak coupling between adjacent resonators with keeping them very close and introduce transmission zeros (TZs). To further demonstrate the feasibility of using this configuration, a six-pole UNB filter with a fractional bandwidth (FWB) of 0.20% at the center frequency of 1915 MHz was designed on double-sided YBCO high temperature superconducting (HTS) thin films with a thickness of 0.5 mm and dielectric constant of 9.8. The measured responses agree rather well with the simulated ones. The measured results show a maximum insertion loss of 0.31 dB and return loss of 15.5 dB in the passband. Two TZs are generated to improve the passband selectivity, which causes the band-edge steepness better than 50 dB/MHz in both transition bands.
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A Review on Cuprate Based Superconducting Materials Including Characteristics and Applications

A Review on Cuprate Based Superconducting Materials Including Characteristics and Applications

superconductor is not the minimal resistance in the usual sense but is equal to zero. This is because carriers are not scattered by the crystal lattice, thus there is no energy dissipation in a superconductor carrying a DC current, which suggests that superconductivity is a kind of macroscopic quantum effect. Since the discovery of superconductivity in 1911, there have been many attempts to establish a theory to explain this phenomenon, and a number of models describing physical characteristics of superconductors have been established. Some simple and easily understandable models belong to phenomenological theories of which the two-fluid model is a relatively intuitive theory. This model can successfully describe motion of carriers and magnetic field distribution within the superconductor. Combined with the constitutive Maxwell’s electromagnetism equations, the two-fluid model explains some superconducting phenomena such as zero resistance and the Meissner effect. Based on a series of interaction hypotheses between electrons and lattice in quantum mechanics, in 1957, J. Bardeen, L.N. Cooper and J.R. Schrieffer proposed the concept of Cooper pairs and established the well-known Barden–Cooper–Schrieffer (BCS) theory, that is, the superconducting quantum theory that describes superconductivity from the microscopic point of view and successfully explains most of superconducting phenomena.
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A new ring-shape high-temperature superconducting trapped-field magnet

A new ring-shape high-temperature superconducting trapped-field magnet

Second generation high temperature superconducting (2G HTS) trapped field magnets have significant potential for a variety of engineering applications to provide strong magnetic field and replace conventional permanent magnets, e.g. samarium-cobalt and neodymium-iron-boron. Bulk, single grain RE–Ba–Cu–O ((RE)BCO, where RE is a rare-earth element) superconductors have been a research focus for more than twenty years. Using the top seeded melt growth (TSMG) process and reinforcement technique, the record trapped field have exceeded 17 T for a single grain YBCO bulk [1,2]. Multiple seeding technique has been used to increase the size of YBCO bulks [3,4,5]. The 2G HTS bulks have been demonstrated as trapped field magnets for electrical machines [6,7], as well as self-stabilising bearings for energy storage flywheels and magnetic separation devices [8,9]. The magnetization of 2G HTS bulks has been studied extensively, partly because it is one of the key challenges. Pulsed field magnetization (PFM) has been identified as an effective and practical way to magnetize 2G HTS bulks [10,11,12,13]. Due to the heat generated in the stack, the trapped field and flux acquired by PFM is usually less than that acquired by field cooling or zero field cooling methods, especially at lower temperatures [14,15]. Therefore, effort has been devoted to optimize the PFM process to improve the trapped field with PFM. Recent study has shown higher trapped field can be achieved using flux jump-assisted PFM or using slit coils [16,17]. Thermally coupled numerical models have been developed to simulate the trapped field during PFM process and study the influence of grain boundaries [18,19].
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Role of Holes in Determining Resistivity and Hall Effect in Crystals of YB2Cu3O7 δ and Bi2Sr2CaCu2O8 δ

Role of Holes in Determining Resistivity and Hall Effect in Crystals of YB2Cu3O7 δ and Bi2Sr2CaCu2O8 δ

be temperature-independent constants of the materials under consideration. To apply Equation (8) to describe the measured Hall coefficient, it should be unders- tood that the Hall scattering rate is a function of the hole and electron resistivity components which determine the scattering rates for electrical transport. The model takes into account that ρ ( ) T and R H ( ) T can vary with T in the normal state and R H ( ) T is positive. In fact we cannot assume any definite

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Materials   for the High Temperature Reactor (HTR)

Materials for the High Temperature Reactor (HTR)

This is a key component and HTR-M investigations will establish the available information on a few selected vessel steels and a database for design and feasibility investiga[r]

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Disorder-driven electronic localization and phase separation in superconducting Fe1+yTe0.5Se0.5 single crystals

Disorder-driven electronic localization and phase separation in superconducting Fe1+yTe0.5Se0.5 single crystals

onal superconducting phase might contain these secondary phases in small quantities. Further, the synthesis procedure is prone to oxygen contamination and thus producing unwanted phases such as Fe 2 O 3 and Fe 3 O 4 . All these phases are mag- netic and detrimental to superconductivity. Another crucial issue in the case of FeSe superconductors is the role played by excess of Fe. It is exceedingly difficult to obtain perfectly stoichiometric Fe chalcogenides and excess of Fe appears to be always present in synthesized compounds. 4,5,9,10,12 The

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SUPERCONDUCTING MATERIALS AND ITS APPLICATIONS

SUPERCONDUCTING MATERIALS AND ITS APPLICATIONS

Superconducting is a phenomenon of exactly zero electrical resistance and expulsion of magnetic flux fields occurring in certain materials called superconductors when cooled below a characteristic critical temperature. It was discovered by Dutch physicist Heike kamerlingh onnes on April 18, 1911 in leiden. Superconductivity is a quantum mechanical phenomenon. It is characterized by meissner effect , the complete ejection of magnetic field lines from the interior of superconductors during its transitions into superconducting state. The electrical resistance of metallic conductor decreases gradually as temperature is lowered. In ordinary conductors, such as copper or silver, this decrease is limited by impurities and other defects. Even near absolute zero , a real sample of a normal conductor shows some resistance. In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current through a loop of superconducting wire can persist indefinitely with no power source.
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High Temperature Tests for Graphite Materials

High Temperature Tests for Graphite Materials

Graphite of the SGL brand according to the high-resolution scanning electron microscopy has a distinguished anisotropy of the structure (fig. 3, 4). This anisotropy supposedly connected by using of needle coke with a grain size of 20-30 mkm as a base material of graphite composite. The particles of coke are produced in grinding process with high anisometric, and pressing this powder into a matrix one can be obtained artificial graphite with high density, but combined with a very high and undesirable anisotropy of physical and mechanical properties. Direct confirmation of such anisotropy is an X-ray phase diagram for SGL graphite (fig. 1). The picture of graphite samples MPG and LeCL made in the destruction zone are shown on the fig. 5. The inset in this case at the upper right corner shows the photo of the original surface.
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Inventory of on-going high temperature materials research activities in Europe. Section 2: mechanical properties. EUR 8637 EN

Inventory of on-going high temperature materials research activities in Europe. Section 2: mechanical properties. EUR 8637 EN

Long term creep behaviour of high temperature strength gas turbine materials.. Crack growth in high temperature materials at elasticity exceeding conditions at high temperatures.[r]

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High Temperature XRD of Phase Transition in Piezoelectric PbNb2O6 across its Curie temperature

High Temperature XRD of Phase Transition in Piezoelectric PbNb2O6 across its Curie temperature

piezoelectric form (the meta-stable orthorhombic structure) in pure phase. Subsequently, various aspects have not been re-studied in modern times. We decided to investigate with high temperature (HT) x-ray diffraction (XRD) the structural changes during ferroelectric to paraelectric phase transition on heating across the Curie temperature and trace the cooling path also, of orthorhombic PbNb 2 O 6 , characterized at room temperature by XRD and TEM (Transmission Electron Microscopy). We have optimized preparation steps 3 including the quenching
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Field simulation studies for a high temperature superconducting synchronous generator with a coreless rotor

Field simulation studies for a high temperature superconducting synchronous generator with a coreless rotor

Abstract: A series of 2D and 3D modelling investigations have been undertaken to evaluate and optimise magnetic field distributions in a high temperature superconducting synchronous generator with a coreless rotor. Such design studies are essential to determine if the required air-gap flux density is achievable and at the same time maintaining the total harmonic voltage content within desirable limits. Moreover, due to the anisotropic properties of the superconducting tapes, the presence of carefully designed flux diverters is required in order to reduce the magnetic field normal to the broad face of the tape. It is therefore necessary to model and optimise the shape and position of the flux diverters to minimise the undesirable magnetic field components. Since a 2D model does not take into account the effect of the end leakage flux, a 3D model was used to confirm the effectiveness of the design changes.
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Piezoelectric materials for high temperature transducers and actuators

Piezoelectric materials for high temperature transducers and actuators

Modestly ( \ 5 %) donor doped modified ceramic powders of the 0.567BF-0.188KBT-0.245PT (D2) ternary system [87] were prepared by conventional solid-state synthesis, as it was expected to improve the resistivity and offer stable high temperature properties for metrology. Herein, this material nomenclature will be D2?, where as reported elsewhere in detail, stoichiometric quantities of the starting reagents were mixed with yttria stabilized zirconia balls in isopropyl alcohol using a high energy bead mill (Willy A. Bachofen, Basel, Switzerland) for 30 min, followed by drying and sieving through 200 lm. The subsequent powder was calcined at 800 °C for 4 h in covered cru- cibles. Binder was subsequently added and the powder pressed into 12 mm diameter pellets and sintered at 1050 °C for 2 h, before being ground and polished with SiC (Buehler, Germany) to 1 mm thick. Finished pellets were electroded by sputtering with 50 nm of Ti, and 200 nm of Au as layers (Quorum Technologies ltd. Lewes, UK). Density was measured using the Archimedes method and established to be 7700 kg/m 3 .
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Non-Linear Surface Impedance of YBCO Superconductors

Non-Linear Surface Impedance of YBCO Superconductors

We studied the different measurement techniques resonant used for microwave characterisation of high temperature superconducting samples and devices and the results are drawn in chapter [r]

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Fabrication of YBa2Cu3O7 Superconducting Film on {100}<001> Textured Cu Tape via Conductive Buffer Layers

Fabrication of YBa2Cu3O7 Superconducting Film on {100}<001> Textured Cu Tape via Conductive Buffer Layers

therefore, for reliable and safe application, it is necessary to attach low-resistivity metal layers, such as Cu and/or Ag, to the CCs to stabilize and protect them from damage due to quenching. Presently, insulative oxides are used for the buffer layers; thus, thick Ag and Cu layers are required to be deposited as stabilizer layers on the YBCO layer. However, the high material and process costs for obtaining the Ag and Cu lay- ers are one of the major obstacles to achieving low-cost CCs. The use of conductive buffer layers instead of insulative reduces the cost of CCs. In this paper, we propose a new configuration for CCs: YBCO deposited on a conductive Sr(Ti 0.95 Nb 0.05 )O 3 buffered Ni-electroplated
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Small ring testing of high temperature materials

Small ring testing of high temperature materials

Figure 6 shows a photograph of the experimental set-up shown in Figure 4 for the SR specimen test. The SR specimen is placed into the test machine and a load applied diametrically to the specimen via loading pins with large resulting deformations in comparison to that of the sub-size uniaxial and impression creep test types. This is due to the flexible nature of the SR specimen type which results in a large equivalent gauge length of the SR specimen type. These high levels of deformation allow for tests to be performed at lower equivalent stresses than the other specimen types and allows for low strains to be obtained from these relatively large deformations.
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