An acceleration search method of higher Tc superconductors by a machine learning algorithm

We propose a method to efficiently search for superconductors with higher critical temperature Tc by machine learning based on a superconductor database. The Tc prediction and the search for new superconductors are still difficult problems. With the progress of computer power and calculation algorithms, the possibility of finding new materials with higher Tc at high throughput is emerging. Using the obtained Tc prediction model, the scope is expanded to the search space of multielement materials that have never been searched, and candidates for superconductors with higher Tc that can be synthesized are proposed

Nonlocal self-organization of long stacking faults from highly strained nanocomposite film of complex oxide

Elastic strain and defects are important key words for controlling structure and properties in films. While epitaxial strain and misfit dislocations have been discussed in conventional films, the evolution of strain and defect can be significantly varied by nanocomposite strain and complicated defects in oxides. In the present study, long stacking faults with a spacing of 5–30 nm and a length of >500 nm were self-organized by ex situ annealing highly strained nanocomposite films of YBa2Cu3O7–δ (YBCO) + BaMO3 (M = Hf, Sn). It is surprising that the nonlocal nature of stacking faults, namely, the structural correlation over >500 nm, was observed in spite of the local configuration of the nanocomposite interface. This kind of structural variation was not observed in the pure YBCO film without nanorods, even when the same annealing was performed. A strain energy analysis showed that the stacking fault formation led to the strain energy minimum by reducing the nanocomposite strain. The layered structure of YBCO stacking faults and the large nanocomposite strain realized the present nonlocal self-organization, which is not observed in the conventional systems with epitaxial strain and misfit dislocations

Influence of matching field on critical current density and irreversibility temperature in YBa2Cu3O7 films with BaMO3(M=Zr, Sn, Hf) nanorods

The influence of the matching field (BΦ) on critical current density (Jc) and irreversibility temperature (Tirr) in YBa2 Cu3O7 films containing BaMO3 (M=Zr, Sn, Hf) nanorods was investigated. It was revealed that the irreversibility temperature normalized by the critical temperature (Tirr/Tc) was influenced by BΦ, for B>BΦ, but Tirr/Tc did not depend on which BaMO3 material was used for B<BΦ, i.e., there was no dependence on nanorod density, diameter, interface sharpness, or Tc in the case of ideal nanorods. However, Jc/Jc(0 T) was found to decrease with increasing BΦ at low magnetic field strengths and to improve at high magnetic field strengths. In addition to Jc being dependent on BΦ, the Tc term in Tirr and Jc(0 T) were also found to have an effect on Jc

Deposition-Temperature Dependence of Vortex Pinning Property in YBa2Cu3O7+BaHfO3 Films

Improvement of critical current density (Jc) in magnetic fields is required in YBa2Cu3O7 films, and process parameters should be optimized for controlling pinning centers. In the present study, a deposition temperature was varied in pulsed laser deposition of YBa2Cu3O7+BaHfO3 films to control the nanorod structure, and its influence on Jc was analyzed. The YBa2Cu3O7+BaHfO3 film deposited at 850°C exhibited pinning force maximum (Fp,max) as high as 413 GN/m3 at 40 K, while the Fp,max for the deposition temperature of 850°C at 77 K was smaller than that in the YBa2Cu3O7+BaHfO3 film deposited at 900°C. A critical temperature decreased and matching field increased with decreasing the deposition temperature. Increase in deposition temperature is effective in improving the Fp,max in high temperatures, since the critical temperature and matching field dependences of Jc value dominate the Fp,max. On the other hand, low deposition temperature improves the Fp,max in low temperatures since the Fp shift in accordance with matching field is dominant to the Fp,max. Thus, the deposition temperature should be set in pulsed laser deposition of YBa2Cu3O7 films containing nanorods considering the Jc variation with critical temperature and matching field

Control of the glass-liquid transition temperature in YBa2Cu3O7-x films

Magnetic field dependences of the glass-liquid transition temperature (Tg) were studied in YBa2Cu3O7−x films containing various types of nanoinclusions. The vortex configuration entangled or straight and pinning strength for each vortex are crucial to the behaviors of Tg. c-axis correlated pinning centers optimize these factors and achieve the upper limit of Tg, which is determined by loss of line tension of vortices, if they are elongated through a thickness of a sample. By optimizing pinning centers, critical temperature, and a matching field, a Tg value of 77 K can be obtained in YBa2Cu3O7−x in a magnetic field as high as 27 T

Pin potential effect on vortex pinning in YBa2Cu3O7-δ films containing nanorods: Pin size effect and mixed pinning

The pin size effect and mixed pinning of nanorods and matrix defects are discussed for YBa2Cu3O7-δ films containing nanorods. BaSnO3 nanorods with a diameter of 11 nm and BaHfO3 nanorods with a diameter of 7 nm were prepared, and critical current density (Jc) and resistivity were measured in the films. When the coherence length was larger than the nanorod size at high temperatures near the critical temperature, the trapping angle and activation energy of the vortex flow depended on the nanorod diameter. At a moderate temperature of 65-77K, the pin size effect on Jc disappeared since the coherence length became smaller than the nanorod size. At a low temperature of 20K, the contribution from matrix pinning became comparable to that of nanorods in a high magnetic field due to the small coherence length. Thus, the temperature-dependent coherence length caused the pin potential situation to vary significantly, namely, the pin size effect and mixed pinning, which strongly affected vortex pinning in YBa2Cu3O7-d containing nanorods

Nanostructures and flux pinning properties in YBa2Cu3O7−y thin films with double perovskite Ba2LuNbO6 nanorods

Double perovskite Ba2LuNbO6 (BLNO)-doped YBa2Cu3O7−y (YBCO) thin films are fabricated on a SrTiO3 (001) substrate by pulsed laser deposition, and their nanostructures are characterized by transmission electron microscopy and scanning transmission electron microscopy. Cross-sectional observations and elemental mapping reveal that BLNO self-assembles during thin film deposition, and consequently, nanorods extending straight from the substrate to the surface are formed in the YBCO thin films. It is confirmed that stacking faults perpendicular to the growth direction disturb the formation of BLNO nanorods. Strain maps extracted by geometric phase analysis reveal that the tensile strain occurs in the YBCO matrix around the BLNO nanorods. Misfit dislocations are periodically introduced at the interface between the nanorod and the matrix, which results in the inhomogeneous strain of YBCO around the BLNO nanorods. The superconducting properties of the YBCO + BLNO thin films are compared with those of other previously reported YBCO thin films with normal perovskite and double perovskite nanorods

Tuning the microstructure and vortex pinning properties of YBCO-based superconducting nanocomposite films by controlling the target rotation speed

We report the controlled incorporation of perovskite, BaSnO3 (BSO), and double-perovskite, YBa2NbO6 (YBNO), nanocolumnar structures into a YBa2Cu3O7−δ (YBCO) film matrix by controlling the target rotation speed. A surface modified target approach has been employed to deposit YBCO+BSO and YBCO+YBNO nanocomposite films using a laser ablation technique. The effect of target rotation speed on the microstructure and subsequently on the superconducting properties has been studied in detail. The density of BSO and YBNO nanocolumnar structures is found to depend on the target rotation speed, which subsequently affects the vortex pinning properties of the superconducting films in the absence and presence of applied magnetic fields. Three rotation speeds, 3, 2 and 1 s/rot., have been attempted in this study. Compared to pure YBCO, the YBCO+BSO and YBCO+YBNO nanocomposite films exhibit superior in-field critical current density (JC) and also exhibit a strong JC peak for H ∥ c-axis, indicating strong c-axis pinning. The irreversibility line has also been found to improve significantly in the nanocomposite films. For both the target combinations (YBCO+BSO and YBCO+YBNO), the target rotation speed of 2 s/rot. has been found to give the optimum superconducting properties

Systematic Variation of Hybrid APCs Into YBCO Thin Films for Improving the Vortex Pinning Properties

The effect of hybrid (columnar and spherical) artificial pinning centers (APCs) on the vortex pinning properties of YBCO thin films is studied in this paper on the basis of variation of critical current density JC with applied magnetic held and also with the orientation of the applied magnetic held. YBCO+BSO3% composite target is used for preparing film with 1-D (columnar) APCs, whereas the same composite target is modified by putting two differently sized (2.2 area% and 3 area%) Y2O3 sectored pieces for preparing films having different concentrations of 3-D (spherical) APCs along with 1-D APCs. Film consisting of only 1-D APCs exhibits enhanced in-held JC values as compared to the one without any APC, and the ones consisting of hybrid APCs exhibit even better JC-B characteristics with increase in the fraction of 3-D APCs. Fp max. values increase systematically with incorporation of 1-D and 1-D + 3-D APCs, and it also shifts toward higher applied magnetic fields. Film with 1-D APCs exhibits strong JC peak at Θ = 0° (H//c-axis), whereas films consisting of hybrid APCs exhibit enhanced JC at all the investigated angular regime. A possible mechanism of vortex pinning in samples with hybrid APCs is also discussed, suggesting the role of 1-D and 3-D APCs

Tailoring the vortex pinning strength of YBCO thin films by systematic incorporation of hybrid artificial pinning centers

The effect of hybrid (columnar and spherical together) artificial pinning centers (APCs) on the vortex pinning properties of YBa2Cu3O7−δ (YBCO) thin films is investigated in detail on the basis of variation of critical current density (J C ) with applied magnetic field and also with the orientation of the applied magnetic field at 65 K and 77 K. Premixed YBCO + BaSnO3 composite targets are used for the deposition of the YBCO films which consist of self-assembled BaSnO3 nanocolumns (1D APCs); on the other hand, for the deposition of the YBCO films with hybrid APCs (BaSnO3 nanocolumns together with Y2O3 nanoparticles), the surface of the premixed YBCO + BaSnO3 composite targets are modified by putting a thin Y2O3 sectored piece on the premixed YBCO + BaSnO3 composite targets by means of silver paste. F pmax value increases systematically with incorporation of 1D and 1D and 3D APCs and it also shifts towards higher applied magnetic fields. Films with 1D APCs exhibit a strong J C peak at Θ = 0° (H//c-axis) whereas films consisting of hybrid APCs exhibit enhanced J C at all the investigated angular regimes. A possible mechanism of vortex pinning in samples with hybrid APCs is also discussed suggesting the role of 1D and 3D APCs