# Presentation: 266945

## Twin and Defect Engineering for Strong c-axis Flux Pinning in Superconducting YBCOSiu-Wai Chan, Columbia University, DMR-0214650

- Twin boundaries, being strong magnetic-flux pinning centers, are engineered to appear in high density. To begin, the boundary energy is measured showing a decrease with increasing processing temperature. This knowledge is exploited  to refine twins by increasing annealing temperature with a concomitant increase of  the critical current density, and the pinning force. Twin spacing reduces to one fourth as the annealing temperature increases to 680oC with a pinning-force increases by 150% to 3.4 x 108 N/m3 at 77K & 1T. With scientists at ONRL, we generate beneficial extended defects in coated conductor tapes by first decorating substrates with nano-ceria. Important for applications,  improved Jc in YBCO with magnetic field along c-axis is observed,.

- Twin and Defect Engineering for Strong c-axis Flux Pinning in Superconducting YBCOSiu-Wai Chan, Columbia University, DMR-0214650

**Notes:**
Principle of method 
In order to realize the technological promises of high temperature superconductors (HTSC), their critical current density (Jc) need to be greatly improved. Among all HTSC’s, YBa2Cu3O7- (YBCO) still shows the greatest promise because it holds the record of the highest flux-pinning forces despite a lower transition temperature among other HTSC’s. Twin boundaries in YBCO are ubiquitous.  The flux pinning by twin boundaries is highly anisotropic and temperature dependent.  Between 50-80K twin boundaries do pin traversing vortices parallel to c-axis.  Thier presence may have helped the YBCO to exhibit higher critical current densities (Jc's) at high temperatures and high magnetic fields than those of the Bi, Hg and Tl cuprates.  Therefore, the increase in twin density and other extended defects can lead to higher Jc .  In order to refine the twin structure, we need to know the value of twin boundary energy and how it changes with oxygenation temperature, 

## Education and Research: Four undergraduates
(Mahnaz Milani-Baladi,
Johnny Lin,  Sumesh
Bhaskaran, & Hoda Mirafzal ),  four graduate students (O. Jongprateep, Josh Hao-Yung Chao, L. Mei & Joan M. Raitano), and one post-doc (Feng Zhang) have contributed. 

- (*Mahnaz Milani-Baladi,*
*Johnny Lin,  Sumesh*
*Bhaskaran, & **Hoda Mirafzal* ),  four graduate students (*O. Jongprateep, **Josh Hao-Yung Chao, L. Mei & Joan M. Raitano*), and one post-doc (*Feng Zhang) *have contributed.

- RET:Carla Brauthwaite Summers of 2004 and 2005 Science Teacher at Midwood High School, Brooklyn NYC  REU: Christina Diaz , NCSU 2005 Summer. Both Carla and Christina worked on oxide nanoparticles

- Education and Outreach from DMR Project on SuperconductivitySiu-Wai Chan, Columbia University, DMR-0214650

**Notes:**
Impact: New methods for engineering twin morphology will emerge from this proposed work that can be applied to YBCO coated tapes. Twinning as a material phenomenon affects important material properties in ferroelectrics, ferromagnetics, ferroelastics and intermetallic compounds with martensitic-transformation.  As such, what we learn from twinning in YBCO, can be directly applied to these technologically important materials to optimize their properties.  

Synergy: Research results and samples from proposed project have been used in PI's courses on lattice vibration, microscopy and microstructure design, providing vivid images of property-structure relation. PI encourages undergraduate students to participate in research and has advised 29 undergraduates’ research projects. A great number of them have since gone on to graduate schools.  Superconducting samples are  used in a material module for PI’s outreach program to New York City high schools.