Chapter 516: Several thorny problems

2019, January 14th.

Xu Qingzhou was messing with models and stroking his cat at home when Carson's call came.

On the 7th, the performance of the new set of samples plummeted. Carson didn't believe in evil, so he continuously made 6 sets of samples and finally concluded: it won't work.

6 experiments, 24 samples were all scrapped.

Xu Qingzhou drove to the laboratory, ready to see it on the spot. Just as he stepped into the laboratory, Carson reported the situation.

"Of the 24 samples, only d04, when the magnetic field strength is 10T, the Jc can reach 1×10^5 A/cm. The magnetic field dependence of the critical current density is insufficient, and the mechanical stability and durability are also difficult to reach the theoretical level."

"That is to say, our best results are still stuck at 8 days ago. Once the ALD precursor pulse ratio is adjusted according to the plan, the performance not only fails to attack the commercial level but drops a lot, and various problems follow one after another."

Xu Qingzhou stared at the data in the computer, and then picked up the X-ray diffraction pattern and transmission electron microscope (TEM) display image on the side.

【Preparation Batch 1

Tc(K)——18.2±0.8——fluctuation exceeds the standard.】

After bending cycles (10 times, r=1mm), the thin film showed cracking.

"Moreover, the process sensitivity of the critical temperature is also too high... problems are everywhere."

Xu Qingzhou narrowed his eyes, the tip of his pen tapped lightly, and his brain ran at high speed.

To put it simply, it's like blowing a balloon. Xu Qingzhou's model shows, or theoretically speaking, it can continue to inject air into the balloon, but the current situation is that the balloon reached the maximum expansion threshold in advance.

Injecting air slightly will "bang" and explode.

The easiest thing to solve is the process sensitivity problem. Adjust the precursor dynamic feedback control system and detect the fluctuation of the precursor pulse ratio.

The magnetic field dependence and mechanical stability problems are the hard bones that need to be gnawed down.

Because the grain boundary weak-link effect is significant... this part of the content seems to have no solution.

Carson pulled the chair over, sat on one side of Xu Qingzhou, poured a few mouthfuls of water, and said: "Judging from the data, according to previous parameters, industrial-grade superconducting thin film is our limit."

"No, this is not our limit."

As someone who stays in the laboratory every day, Xu Qingzhou is accustomed to such unsatisfactory experiments, and at this moment, he is calm.

His gaze fell on the structure diagram of the sample, mechanical stability and durability are insufficient...

Maybe he can start from the performance of graphene.

The interface binding energy between graphene and NbSn is low, less than 1J/m, leading to weak resistance to stress and radiation.

Xu Qingzhou pondered for a moment and said directly: "Carson, regarding the insufficient mechanical stability and durability, what do you think if we design a transition layer?"

Interface gradient design, a method he often used in experiments before.

This is the importance of experience, and it can even be said that accumulating experience is more important than the experiment itself.

"Transition layer?" Carson was stunned.

"That's right."

Xu Qingzhou turned the signature pen in his hand and explained further: "It's like adding a screw washer, which can increase the contact area, reduce pressure, and also provide friction and damping effects, reducing mechanical stability damage caused by vibration or external force."

"Oh, Professor, super great idea!"

Carson's eyes lit up, feeling that it was promising, but soon hesitated: "However, what material should we use for this 'washer'?"

"WS, NbC, and NbSn, you guys try these three materials."

The layered crystal structure of WS has a specific crystal plane epitaxial relationship with the sapphire substrate, NbC is chemically inert at high temperatures and can prevent element interdiffusion between WS and NbSn, and NbSn is currently the A15 superconductor with the highest known critical temperature.

These three are the materials Xu Qingzhou can think of right now.

He continued: "If these three materials don't work, you can look at others yourself. In essence, it is multi-dimensional optimization through lattice matching, thermal expansion gradient, chemical stability, and process compatibility."

Carson nodded, having no opinion. After doing experiments with Xu Qingzhou for several months, he found that 90% of Xu Qingzhou's decisions were correct, and he could learn a lot of knowledge.

It turns out geniuses are so terrible.

Xu Qingzhou said: "Leave other problems to me."

"Good."

Carson greeted Sun Simin and Ma Ersi to take materials, while he sat down to design how to make the transition layer.

After arranging the tasks, Xu Qingzhou's gaze fell on the data of the characterization test. Mechanical problems were left to Carson and the others, so it should be fine. The insufficient magnetic field dependence of the critical current density is the really troublesome thing.

To put it simply, it means that the speed of current in the superconducting thin film is reduced.

The superconducting coherence at the grain boundary breaks, forming a resistive region, becoming a current bottleneck under high fields. The grain boundary is like an old toll station on the highway, a series of problems, narrow lanes (grain boundary atomic arrangement is chaotic), toll collectors are inefficient (grain boundary resistance is high). Traffic flow (current) is forced to slow down or even stop here, becoming a bottleneck for the entire road network.

To solve this problem, the "traffic system" of the superconducting thin film must jump from chaotic and disordered to an efficient and intelligent network, finally realizing JC compliance.

Quite thorny, at least, their current means won't work, and they need to think of other ways.

Xu Qingzhou felt a bit of a headache and could only sigh that it was indeed not so easy.

Thinking about it, he simply packed up his things and went to the library.

Problems are everywhere. For example, according to database statistics, the defect rate of large-scale preparation is still too high, and the scrap rate is greater than 40%.

Of course, this is not urgent, it can be dragged back later, wait for the performance of subsequent samples to stabilize, and then slowly iterate and repair defects.

Now how to build a smooth traffic system is the big thing.

However, at the intersection, Xu Qingzhou simply took a turn, preparing to go to the Mathematics Department to get a free cup of coffee first.

There was only Hoern in the office.

"Good afternoon."

Xu Qingzhou ordered a latte, sat down and chatted with Hoern, only to learn that their project progress was not bad, and it could be concluded in another half a year.

The project matter was finished. Hoern brought the coffee he made and asked curiously: "Xu, have you researched the supersymmetric Z-function?"

"No."

Xu Qingzhou shook his head and said helplessly: "The physics experiment is enough to give me a headache, no time to research other content."

"Tsk tsk, do you know, quite a few mathematicians in the mathematical community are researching your supersymmetric theory. However, you, the proposer, are actually doing other research."

Hoern sighed, no wonder the mathematical community called Xu Qingzhou and Riemann the same, leaving fishhooks in the mathematical community all over the world.

Clearly a mathematician, but always thinking about irrelevant physics.

(End of chapter) ===== CHAPTER 517 =====