Artificial pinning in films, melt-textured and MgB2

Adrian CrisanSchool of Metallurgy and Materials, University of Birmingham, UK

andNational Institute of Materials Physics, Bucharest, Romania

CONTENTS

• Motivation

• YBCO (REBCO) films and coated conductors

• MgB2

• Melt-textured 123

MotivationEnergy efficient devices and equipment (magnets, motors, transformers, power lines)

High Tc superconductors Low cost, High critical current

Losses (dissipation): Movement of flux lines (Lorenz force, Thermal fluctuations)

Solution: blocking flux lines (pinning) on various types of defects, natural and/or artificial

Nanoengineered pinning centres

YBCO(REBCO) films and coated conductors

YBCO films (Coated Conductors) have many types of natural pinning centres (i.e., they may occur naturally during growth process

However, for many foreseen applications, especially in high magnetic fields, critical current still need improvement, hence larger FP, hence ARTIFICIAL PINNING CENTRES

S.R. Foltyn et al, Nat Mater 6/9 (2007) 631.

Substrate decoration

1

2

4

3

5

1- substrate; 2- nanodots; 3- SC film; 4- columnar defects; 5- dislocations

2001 – A. C. and H. Ihara, Jap. Patent #3622147, EU and USA; A. C. et al. APL 79, 4547 (2001), APL 80, 3566 (2002), IEEE Trans. Appl. Supercond. 13, 3726 (2003); M. Ionescu,…, and A.C. J. Phys. D: Appl. Phys. 37, 1824 (2004)

Quasi-superlattices (quasi-multilayers)2002 – A. C., seminar AIST (unpublished)

2004 – T. Haugan et al, (USAFRL), Nature, 430, 867

2005 – B. Holzapfel group (Dresden) J. Appl. Phys. 98, 123906.

Nanostructured targets (secondary phase nano-inclusions)

Materials used up to now on Tl-based films, YBCO, ErBCO• substrate decoration: Ag – AIST Tsukuba (A. C.), Univ. Wollongong Australia (Ionescu, Dou,

A. C.); MgO - AIST Japan (Badica and A. C.); Y2O3 – CREST Japan (Matsumoto), Barcelona (Puig,

Obradors), Dresda (Holzapfel); Ce2O3 – AIST Tsukuba (Nie, Yamasaki); Ir – USA Univ. and Nat. Lab.

consortium.; Au, Pd, LaNiO3 – Univ. Birmingham (A. C.)

• quasi-superlattices approach: Y2BaCuO5 – USAFR, Wright-Patterson (Houghan); Y2O3 – USAFR, Dresda; YSZ; BaTMO3 (TM = transition metal = Ir, Ti, Zr, Hf); TM – Dresda;

Au, Ag, Pd, LNO, PrBCO, ns-YBCO - Univ. Birmingham (A. C.)

• impurity addition to targets: BaZrO3 – many groups (Cambridge & Los Alamos,

ORNL, CREST-Japan, Univ. Birmingham & Univ. Turku Finland, etc..); BaNb2O6 ,BaSnO3 – CREST

Japan (Matsumoto); RE3TaO7 (RE = rare earth = Er, Gd, Yb); - Univ. Cambridge & Los Alamos (J.

McManus-Driscoll); double-perovskites YBa2NbO6 (Cambridge) Gd2Ba4CuWOy – Univ. Birmingham & Cambridge (A. C.); combination of two-three types of impurities

Dimensionality and strength of PCs

Pinning centres in films obtained by PLD

Substrate decoration

Distribution of the Ag nano particles deposited at 400o C by 15 laser pulses

Field dependence of critical current density at 77.3 K of pure YBCO film (open squares) and of the film grown on substrate decorated with 15 laser pulses substrate (full circles).

Columnar growth of YBCO on Ag Nanodots

YBCO

STO

AFM-side view- of YBCO grown on (from left to right): Au nano—dots decorated substrate, Ag nano—dots decorated substrate and on bare substrate.

Ag/YBCO quasi-multilayer films

Y2O3

HRTEM showing the Cu-O planes and a large Y2O3 precipitate

Cross-sectional TEM image, showing c-axis correlated defects, arrow indicates c-axis.

Mis-orientation in the boundary area

High-resolution cross-sectional TEM image of the substrate-film boundary. A nano-particle can be seen near the substrate

High-resolution cross-sectional TEM image of the substrate-film boundary.

Columnar structure formed from the substrate Columnar structure

Nanoscale particles

a) STEM image and element mapping of b) O2, c) Ba, d) Ag, e) Cu, f) Y

PBCO/YBCO quasi-multilayer films

High-resolution TEM image of PBCO/YBCO multilayer near the film substrate interface, arrow and circle point to a PBCO nano-particle.

A grain boundary along the c-axis.

Mis-orientated grain observed in the cross section TEM image.

Defects in the middle of the film

BZO-doped YBCO and multilayer architectures of BZO-doped YBCO films

BZO nano-particles in the YBCO matrix of the film deposited at 780o C

High resolution of cross section TEM image of the film deposited at low temperature, BZO nano-particles are visible, and marked by circles.

Cross section TEM image of BZO-doped YBCO film deposited at 800o C, clearly visible columnar structures (nano-rods) along the c-axis are formed

Formation of Cu-O nano-particle found in the YBCO matrix of the film

Cu-O

EDX mapping of the BZO-doped YBCO film using STEM mode, a) STEM image, b) mapping of Ba, c) mapping of Cu, d) mapping of O, e) mapping of Y and f) mapping of Zr

Cross section TEM image of BZO-doped YBCO film near the substrate, arrow shows the c-axis of YBCO

Formation of BZO nano-rods in the mildle area of the film, arrow shows c-axis

Short and long nano-rods grows together inside the YBCO matrix, along the c-axis.

The BZO nano-rods started growing from the STO substrate, along the c-axis (arrow)

Some of the nano-rods are long, larger than the cross section of the image, arrow indicates c-axis

Stacking fault found in high resolution TEM image

15Ag/BZO-doped YBCO multilayer architecture

Cross section image of (15Ag/1 μm BZO-doped YBCO)x2, arrow shows c direction

BZO nano-rods and nanoparticles in the YBCO matrix

Co-existence of Y2O3 (circle) and Cu rich phase (rectangular) and/or BZO phase.

Defects caused by CuO2 and/or BZO phase observed in the middle area of the film.

A cross section TEM image near the STO substrate, arrow show the c-axis of YBCO A distorted area near the STO substrate,

the c-axis is indicated by arrow

BZO nanoparticles and nano-rodsBZO nano-rods entangled with columns of YBCO due to Ag-induced columnar growth

1.5 μm BZO doped YBCO / 30 nm STO/ 1.5 μm BZO doped YBCO on Ag decorated (15 pulses) STO substrates

Pinning in MgB2

• MgB2 wires are produced by various variants of Powder-In-Tube (PIT) process

• Increase of Hc2 and Jc using nano—phase additions in the precursors in the initial stage

• Carbon doping: amorphous, nano-diamond, carbon nanotubes

• Ta, Ti, Zr impurity atoms used for absorbtion of H, to form e.g., ZrH2, preventing the formation of harmful MgH2 impurity

• Addition of nano-Silicon• Best doping: SiC nanoparticles

(up to 13-14 mol%)- B-rich phase- Mg2Si secondary phase- O- and Si- containing matrix

• Silicon oil liquid precursor- Si formed Mg2Si- C substitutes B sites

• Many other substitutions tried

Melt-textured REBa2Cu3O7

• Elemental 123: YBa2Cu3O7, NdBa2Cu3O7

• Mixed ternary light rare earth LRE–Ba2Cu3Oy (LRE = Nd, Eu, Sm, Gd) compounds (NEG-123, NSG-123, SEG-123) have twice irreversibility line (critical current density).

• All these elements tend to sit on both the rare earth- and Ba-sites in the matrix and to form so called LRE/Ba solid solution.

• Moreover, one can vary the LRE elemental ratio. Due to differences in the LRE ion sizes, the LRE ratio variation, especially in ternary composites can affect the local tensions in the matrix and contribute to the pinning performance.

• Microstructure observations clarified that one can create nanoscale arrays in these materials and dramatically improve pinning at high magnetic fields

• Besides, the melt-process technology enables introduction of non-superconducting secondary phase particles, RE2BaCuO5 “RE-211” that were found to enhance pinning at low magnetic fields.

• ZrO2 ball milling of LRE-211 particles led to nanoscale 211 phase

• Such particles (in the size of 70–150 nm) not only survived the melt-texturing process but also further reduced their size up to 20–50 nm.

• Micro-chemical analysis identified these defects as Zr-rich ZrBaCuO and (NEG, Zr) BaCuO ones

• The effect of Zr in the particles size diminution stacks obviously in the chemical inertia of Zr in the superconductor matrix

• Creating nanoscale particles based on some other inert elements, like MgO or adding fine Y2Ba4CuZrOy particles to RE-123 confirmed validity of this hypothesis.

• Use of the initial powder composed of the nano-sized REBa2CuZrOy particles and 35 mol% of sub-micron Gd-211 precipitates led to the super-current density around 270 kA/cm2 at 77 K.

• nanoparticles from the same chemical group, namely Mo, and Nb: MoO3 and Nb2O5

• Other family of nanoscale inclusions (RE)2Ba4CuMOy (where RE = Y, Sm, Gd, Nd, and M = Nb, Ta, W, Mo, Zr, Hf, Ag, Sb, Sn, Bi) were shown to improve drastically the properties of melt-textured 123