scholarly journals Relation between Crystal Structure and Transition Temperature of Superconducting Metals and Alloys

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 158 ◽  
Author(s):  
Michael Rudolf Koblischka ◽  
Susanne Roth ◽  
Anjela Koblischka-Veneva ◽  
Thomas Karwoth ◽  
Alex Wiederhold ◽  
...  
Keyword(s):  
High Temperature Superconductors ◽  
Resonance Effect ◽  
Calculated Data ◽  
Electronic Configuration ◽  
Metallic Alloys ◽  
Charge Carriers ◽  
Superconducting Transition ◽  
Tetragonal Unit Cell ◽  
Straight Line ◽  
Unit Cells

Using the Roeser–Huber equation, which was originally developed for high temperature superconductors (HTSc) (H. Roeser et al., Acta Astronautica 62 (2008) 733), we present a calculation of the superconducting transition temperatures, T c , of some elements with fcc unit cells (Pb, Al), some elements with bcc unit cells (Nb, V), Sn with a tetragonal unit cell and several simple metallic alloys (NbN, NbTi, the A15 compounds and MgB 2 ). All calculations used only the crystallographic information and available data of the electronic configuration of the constituents. The model itself is based on viewing superconductivity as a resonance effect, and the superconducting charge carriers moving through the crystal interact with a typical crystal distance, x. It is found that all calculated T c -data fall within a narrow error margin on a straight line when plotting ( 2 x ) 2 vs. 1 / T c like in the case for HTSc. Furthermore, we discuss the problems when obtaining data for T c from the literature or from experiments, which are needed for comparison with the calculated data. The T c -data presented here agree reasonably well with the literature data.

Direct imaging of charge transfer

1996 ◽  
Vol 54 ◽  
pp. 680-681
Author(s):  
Yimei Zhu ◽  
J. Tafto
Keyword(s):  
Charge Transfer ◽  
Electron Diffraction ◽  
Scattering Amplitude ◽  
High Temperature Superconductors ◽  
Charge Carriers ◽  
Image Charge ◽  
Net Charge ◽  
Long Time ◽  
Electron Holes ◽  
First Time

The electron holes confined to the CuO2-plane are the charge carriers in high-temperature superconductors, and thus, the distribution of charge plays a key role in determining their superconducting properties. While it has been known for a long time that in principle, electron diffraction at low angles is very sensitive to charge transfer, we, for the first time, show that under a proper TEM imaging condition, it is possible to directly image charge in crystals with a large unit cell. We apply this new way of studying charge distribution to the technologically important Bi2Sr2Ca1Cu2O8+δ superconductors.Charged particles interact with the electrostatic potential, and thus, for small scattering angles, the incident particle sees a nuclei that is screened by the electron cloud. Hence, the scattering amplitude mainly is determined by the net charge of the ion. Comparing with the high Z neutral Bi atom, we note that the scattering amplitude of the hole or an electron is larger at small scattering angles. This is in stark contrast to the displacements which contribute negligibly to the electron diffraction pattern at small angles because of the short g-vectors.

scholarly journals Enhancing Superconductivity of the Nonmagnetic Quasiskutterudites by Atomic Disorder

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5830
Author(s):  
Andrzej Ślebarski ◽  
Maciej M. Maśka
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Superconducting Transition Temperature ◽  
High Temperature Superconductors ◽  
Superconducting Phase ◽  
Length Scale ◽  
Superconducting Transition ◽  
Atomic Disorder ◽  
Strong Inhomogeneity ◽  
Related Compounds

We investigated the effect of enhancement of superconducting transition temperature Tc by nonmagnetic atom disorder in the series of filled skutterudite-related compounds (La3M4Sn13, Ca3Rh4Sn13, Y5Rh6Sn18, Lu5Rh6Sn18; M= Co, Ru, Rh), where the atomic disorder is generated by various defects or doping. We have shown that the disorder on the coherence length scale ξ in these nonmagnetic quasiskutterudite superconductors additionally generates a non-homogeneous, high-temperature superconducting phase with Tc⋆>Tc (dilute disorder scenario), while the strong fluctuations of stoichiometry due to increasing doping can rapidly increase the superconducting transition temperature of the sample even to the value of Tc⋆∼2Tc (dense disorder leading to strong inhomogeneity). This phenomenon seems to be characteristic of high-temperature superconductors and superconducting heavy fermions, and recently have received renewed attention. We experimentally documented the stronger lattice stiffening of the inhomogeneous superconducting phase Tc⋆ in respect to the bulk Tc one and proposed a model that explains the Tc⋆>Tc behavior in the series of nonmagnetic skutterudite-related compounds.

scholarly journals Potential high-Tc superconducting lanthanum and yttrium hydrides at high pressure

2017 ◽  
Vol 114 (27) ◽  
pp. 6990-6995 ◽  
Author(s):  
Hanyu Liu ◽  
Ivan I. Naumov ◽  
Roald Hoffmann ◽  
N. W. Ashcroft ◽  
Russell J. Hemley
Keyword(s):  
Group Structure ◽  
High Temperature Superconductors ◽  
Face Centered Cubic ◽  
Superconducting Transition ◽  
High Tc ◽  
Structure Search ◽  
Systematic Structure ◽  
Face Centered ◽  
Fcc Structure ◽  
Very High

A systematic structure search in the La–H and Y–H systems under pressure reveals some hydrogen-rich structures with intriguing electronic properties. For example, LaH10 is found to adopt a sodalite-like face-centered cubic (fcc) structure, stable above 200 GPa, and LaH8 a C2/m space group structure. Phonon calculations indicate both are dynamically stable; electron phonon calculations coupled to Bardeen–Cooper–Schrieffer (BCS) arguments indicate they might be high-Tc superconductors. In particular, the superconducting transition temperature Tc calculated for LaH10 is 274–286 K at 210 GPa. Similar calculations for the Y–H system predict stability of the sodalite-like fcc YH10 and a Tc above room temperature, reaching 305–326 K at 250 GPa. The study suggests that dense hydrides consisting of these and related hydrogen polyhedral networks may represent new classes of potential very high-temperature superconductors.

Electron-Doped High Tc Superconductors

MRS Bulletin ◽  
1990 ◽  
Vol 15 (6) ◽  
pp. 60-67 ◽  
Author(s):  
M. Brian Maple
Keyword(s):  
High Temperature ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Building Blocks ◽  
The United States ◽  
Charge Carriers ◽  
Critical Temperatures ◽  
High Tc ◽  
Prevailing View ◽  
Identical Crystal

Since the discovery of high temperature superconductivity in layered copper-oxide compounds in the latter part of 1986, an enormous amount of research has been carried out on these remarkable materials. Prior to 1989, the prevailing view was that the charge carriers responsible for superconductivity in these materials were holes that move through conducting CuO2 planes. The CuO2 planes are the basic building blocks of the crystal structures of all the presently known oxides with superconducting critical temperatures Tc greater than ~30 K. Recently, new superconducting materials have been discovered in Japan and the United States in which the charge carriers involved in the superconductivity appear to be electrons, rather than holes, that reside within the conducting CuO2 planes. These findings could have important implications regarding viable theories of high temperature superconductivity as well as strategies for finding new high temperature superconductors.The new electron-doped materials have the chemical formula Ln2-xMxCuO4-y and exhibit superconductivity with superconducting critical temperatures Tc as high as ~25 K for x ≍ 0.15 and y ≍ 0.02. Superconductivity has been discovered for M = Ce and Ln = Pr, Nd, Sm, and Eu, and for M = Th and Ln = Pr, Nd, and Sm. A related compound with the identical crystal structure, Nd2CuO4-x-y Fx, has also been found to display superconductivity withTc ≍ 25 K. Recently, it has been observed that superconductivity with Tc ≍ 25 K can even be induced in nonsuperconducting Nd2-xCexCuO4-y compounds by substituting Ga or In for Cu. Thus, it appears that the CuO2 planes can be doped with electrons, rendering the Ln2CuO4-y parent compounds metallic and superconducting, by substituting electron donor elements at sites within, as well as outside, the CuO2 planes; i.e., by substituting (1) Ce4+ or Th4+ ions for Ln3+ ions; (2) F1- ions for O2- ions; and (3) Ga3+ or In3+ ions for Cu2+ ions.

Powder X-Ray Diffraction Data for the Superconducting Phase TlCaBa2Cu2O7−δ

1992 ◽  
Vol 7 (2) ◽  
pp. 115-116 ◽  
Author(s):  
Terry L. Aselage ◽  
Michael O. Eatough
Keyword(s):  
Cuprate Superconductors ◽  
General Interest ◽  
Superconducting Transition ◽  
X Ray Diffraction ◽  
Pure Compound ◽  
Group 14 ◽  
X Ray ◽  
Superconducting Phases ◽  
The Family ◽  
Unit Cells

High temperature superconducting phases in the Tl-Ca-Ba-Cu-O system are ideally represented by the formula TlmCan−1Ba2CunO2(n+1)+m, with m either 1 or 2 and n = 1 to at least 3 (Parkin et at., 1988). Each of these phases contains one or more of the nearly planar CuO2sheets common to the cuprate superconductors. A single Ca atom separates adjacent CuO2sheets (n > 1). Single or double rock salt-like Tl-O layers are separated from the Can−1CunO2nregions by single Ba-O layers. Each of the Ca-containing members of this family crystallizes in a tetgragonal unit cell, with space group 14/mmm for the m = 2 series and P4/mmm for the m = 1 series.Despite the general interest in this family of superconductors, little has been reported about the m = 1, n = 2 member, TlCaBa2Cu2O7−δ, hereafter called 1122. This lack of work is due at least in part to the difficulty in synthesizing the pure compound (Michel et at., 1991). Additionally, technological interest has focused on members of the family with higher superconducting transition temperatures, particularly Tl2Ca2Ba2Cu3Oywith Tcup to 125 K. The critical temperature of 1122 has been reported from as low as 50 K (Hervieu et al., 1988) to as high as 103 K (Morosin et al., 1988), and at several values in between (Ganguli et al., 1988; Liang et al., 1988). Most of the samples had other superconducting phases in addition to 1122. Because of the nearly identical a axis lengths of the unit cells of the Tl-family of superconductors, syntactic intergrowths may be present in such multiphase samples.

Atomic Dynamics in Complex Metallic Alloys

2013 ◽  
Vol 1517 ◽  
Author(s):  
Holger Euchner ◽  
Stephane Pailhès ◽  
Tsunetomo Yamada ◽  
Ryuji Tamura ◽  
Tsutomu Ishimasa ◽  
...  
Keyword(s):  
Lattice Dynamics ◽  
Structural Complexity ◽  
Building Blocks ◽  
Metallic Alloys ◽  
Strong Reduction ◽  
Large Numbers ◽  
Unit Cells ◽  
Dynamics Simulations ◽  
The Impact ◽  
Complex Metallic Alloys

ABSTRACTComplex Metallic Alloys (CMAs) are metallic solids of high structural complexity, consisting of large numbers of atoms in their unit cells. Consequences of this structural complexity are manifold and give rise to a variety of exciting physical properties. The impact that such structural complexity may have on the lattice dynamics will be discussed. The surprising dynamical flexibility of Tsai-type clusters with the symmetry breaking central tetrahedron will be addressed for Zn6Sc, while in the Ba-Ge-Ni clathrate system the dynamics of encaged Ba guest atoms in the surrounding Ge-Ni host framework is analysed with respect to the experimentally evidenced strong reduction of lattice thermal conductivity. For both systems experimental results from neutron scattering are analyzed and interpreted on atomistic scale by means of ab initio and molecular dynamics simulations, resulting in a picture with the respective structural building blocks as the origin of the peculiarities in the dynamics.

Crystal Growth of High Temperature Superconductors

MRS Bulletin ◽  
1988 ◽  
Vol 13 (10) ◽  
pp. 56-61 ◽  
Author(s):  
H.J. Scheel ◽  
F. Licci
Keyword(s):  
High Temperature ◽  
Critical Current Density ◽  
Single Crystals ◽  
Critical Current ◽  
Current Density ◽  
Large Scale ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Superconducting Transition ◽  
Theoretical Understanding

The discovery of high temperature superconductivity (HTSC) in oxide compounds has confronted materials scientists with many challenging problems. These include the preparation of ceramic samples with critical current density of about 106 A/cm2 at 77 K and sufficient mechanical strength for large-scale electrotechnical and magnetic applications and the preparation of epitaxial thin films of high structural perfection for electronic devices.The main interest in the growth of single crystals is for the study of physical phenomena, which will help achieve a theoretical understanding of HTSC. Theorists still do not agree on the fundamental mechanisms of HTSC, and there is a need for good data on relatively defect-free materials in order to test the many models. In addition, the study of the role of defects like twins, grain boundaries, and dislocations in single crystals is important for understanding such parameters as the critical current density. The study of HTSC with single crystals is also expected to be helpful for finding optimum materials for the various applications and hopefully achieving higher values of the superconducting transition temperature Tc than the current maximum of about 125 K. It seems unlikely at present that single crystals will be used in commercial devices, but this possibility cannot be ruled out as crystal size and quality improve.

scholarly journals Higher superconducting transition temperature by breaking the universal pressure relation

2019 ◽  
Vol 116 (6) ◽  
pp. 2004-2008 ◽  
Author(s):  
Liangzi Deng ◽  
Yongping Zheng ◽  
Zheng Wu ◽  
Shuyuan Huyan ◽  
Hung-Cheng Wu ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
High Temperature ◽  
Transition Temperature ◽  
Density Functional ◽  
High Temperature Superconductors ◽  
Density Functional Theory Calculations ◽  
Universal Relation ◽  
Superconducting Transition ◽  
Functional Theory ◽  
A Charge

By investigating the bulk superconducting state via dc magnetization measurements, we have discovered a common resurgence of the superconducting transition temperatures (Tcs) of the monolayer Bi2Sr2CuO6+δ(Bi2201) and bilayer Bi2Sr2CaCu2O8+δ(Bi2212) to beyond the maximum Tcs (Tc-maxs) predicted by the universal relation between Tcand doping (p) or pressure (P) at higher pressures. The Tcof underdoped Bi2201 initially increases from 9.6 K at ambient to a peak at 23 K at 26 GPa and then drops as expected from the universal Tc-P relation. However, at pressures above 40 GPa, Tcrises rapidly without any sign of saturation up to 30 K at 51 GPa. Similarly, the Tcfor the slightly overdoped Bi2212 increases after passing a broad valley between 20 and 36 GPa and reaches 90 K without any sign of saturation at 56 GPa. We have, therefore, attributed this Tcresurgence to a possible pressure-induced electronic transition in the cuprate compounds due to a charge transfer between the Cu 3dx2−y2and the O 2pbands projected from a hybrid bonding state, leading to an increase of the density of states at the Fermi level, in agreement with our density functional theory calculations. Similar Tc-P behavior has also been reported in the trilayer Br2Sr2Ca2Cu3O10+δ(Bi2223). These observations suggest that higher Tcs than those previously reported for the layered cuprate high-temperature superconductors can be achieved by breaking away from the universal Tc-P relation through the application of higher pressures.

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