This timeline of discovery of superconducting materials shows how dramatic the discovery of high-Tc YBCO was. Credit: Wikipedia.
Do you recall where you were the weekend before the Super Bowl in 1987? Me neither. No matter, let’s play some Jeopardy, shall we?
Me: “Alex, I’ll take Super Bowl Weekends for $100.”
Alex: “The answer is YBCO.”
Me: “What is the abbreviated formula for the first high-temperature superconductor?”
Alex: “That is correct. The next answer is January 29, 1987.”
Me: “When were high-temperature superconductors discovered?”
Alex: “That’s right! Next answer: Jim Ashburn.”
Me: “Who was the graduate student that discovered high-temperature superconductors?”
Alex: “Right again! Next answer: M.K. Wu, University of Alabama in Hunstville.”
Me: “Who was Ashburn’s supervising professor and at what university did he work?”
Alex: “Right again! Next answer: Phil Simms.”
Me: “Ummmmm – Who was Wu’s postdoc?”
Alex: “No, so sorry. Phil Simms was the winning quarterback of Super Bowl XXI, leading the NY Giants to a 39-20 win over the Denver Broncos.”
If you were part of the ceramic science or physics world in 1987, you will recall it was a heady time. This new material rocked the world of solid state physics, and it was thought that an oxide material would be a disruptive technology for electricity transmission and other applications. In the 25 years since its discovery, we’ve seen that high Tc superconductor applications are not so easy to deploy, but progress is underway.
To mark the 25th anniversary of the historic discovery, the UAHuntsville unveiled a plaque in a recent ceremony.
A story on the university’s website recounts the events and thinking that led to Ashburn’s discovery. A physics graduate student at the time, Ashburn knew he was onto something that could be really big. With a good understanding of fundamental principles, especially the Periodic Table of the Elements, some coaching from a friend studying ceramic engineering, two textbooks and some fortunate bad luck, he formulated the first YBCO and demonstrated superconductivity at 93 K. (The story refers to one of the textbooks as “The Ceramic Bible,” which, presumably, is Introduction to Ceramics, by Kingery, Bowen and Uhlmann.)
Jim Ashburn and the new historic marker at UA Huntsville. Credit UA Huntsville.
The breakthrough that led Ashburn to the right formulation was the idea of “volume matching,” where atoms are substituted into a crystal lattice with compensations for their size. He says in the story, “I was learning that you have to put in things that were the right size with the right charge. It was basic crystal chemistry.” Knowing he wanted to try yttrium in the crystal, Ashburn turned to barium to get the required volume matching.
A little bit of fortunate bad luck followed. The usual furnace was unavailable for firing the compound, so Ashburn had to use the lab’s other furnace, which had a maximum temperature of 1,000°C, whereas the preferred furnace had a maximum firing temperature of 1,500°C. Later research would show that YBCO has a narrow processing sweet spot and melts at higher temperatures and solidifies into two separate compounds.
Ashburn has become an unofficial, self-appointed curator of the history of the discovery of high-temperature superconductors, however, he did not pursue a career in the field. He says, “My main interest is designing algorithms. I like to model things with math. That’s what I did then. It’s my job and it’s my happy place.”