Artificial pinning in films, melttextured and MgB2
Adrian Crisan
School of Metallurgy and Materials, University of Birmingham, UK
and
National Institute of Materials Physics, Bucharest, Romania
CONTENTS
• Motivation
• YBCO (REBCO) films and coated conductors
• MgB2
• Melt-textured 123
Motivation
Energy 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
S.R. Foltyn et al, Nat Mater 6/9 (2007) 631.
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
Substrate decoration
1- substrate; 2- nanodots; 3- SC film; 4- columnar defects; 5- dislocations
4
5
3
2
1
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(unpublished)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
STO
YBCO
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 nanoparticles are visible, and marked by circles.
Cu-O
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
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 BZOdoped 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 BZOdoped 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-rods
BZO 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 nanosized REBa2CuZrOy particles and 35 mol% of submicron Gd-211 precipitates led to the supercurrent 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 melttextured 123