I am devoted to scientific research, but you want to trick me into having a love relationship?

Chapter 516: Some Difficult Questions

April 2019, 1.

Xu Qingzhou was working on models and petting a cat at home when Carson called.

On the 7th, the performance of a new set of samples dropped sharply. Carson refused to believe it, so he made 6 sets of samples in a row and finally came to the conclusion: it didn't work.

In 6 experiments, all 24 samples were discarded.

Xu Qingzhou drove to the laboratory and prepared to take a look at the scene. As soon as he stepped into the laboratory, Carson reported the situation.

“Among the 24 samples, only D04 can reach a Jc of 10×1 A/cm at a magnetic field strength of 10 T. The critical current density is not sufficiently dependent on the magnetic field, and its mechanical stability and durability are also difficult to reach the theoretical level.”

"That is to say, our best results are still the same as eight days ago. Once we adjusted the ALD precursor pulse ratio as planned, the performance not only did not reach the commercial level, but dropped a lot, and various problems followed."

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

Preparation batch 1
Tc (K)——18.2± 0.8——Fluctuation exceeds the standard.】

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

"Also, the process sensitivity of the critical temperature is too high. There are a lot of problems."

Xu Qingzhou squinted his eyes, tapped the pen tip lightly, and his brain worked rapidly.

To put it simply, it is like blowing up a balloon. Xu Qingzhou's model shows that, theoretically, air can continue to be injected into the balloon, but the current situation is that the balloon has reached its maximum expansion threshold ahead of time.

It exploded with a "bang" when a little air was injected.

The easiest problem to solve is the process sensitivity problem, which can be solved by adjusting the precursor dynamic feedback control system and detecting the fluctuation of the precursor pulse ratio.

The lack of magnetic field dependence and mechanical stability issues are the hard nuts to crack.

Because the weak connection effect of grain boundaries is significant, this part seems to have no solution.

Carson pulled a chair over and sat next to Xu Qingzhou. He gulped down a few gulps of water and said, "Based on the data and previous parameters, industrial-grade superconducting film is our limit."

“No, this is not our limit.”

As someone who spends every day in the laboratory, Xu Qingzhou is accustomed to such unsatisfactory experimental situations, and he is not at all concerned at the moment.

He looked at the structural diagram of the sample and found that its mechanical stability and durability were insufficient.
Perhaps we can start with the properties of graphene.

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

Xu Qingzhou thought for a moment and said directly: "Mr. Carson, regarding the lack of mechanical stability and durability, what do you think about us designing a transition layer?"

The gradient design of the interface is a method he used frequently in his previous experiments.

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

"Transition layer?" Carson was stunned.

"Yes."

Xu Qingzhou turned the pen in his hand and further explained: "Just like adding a screw gasket, it can increase the contact area, reduce pressure, and provide friction and damping effects, reducing the damage to mechanical stability caused by vibration or external forces."

"Oh, Professor, what a brilliant idea!"

Carson's eyes lit up, and he felt that there was great potential, but he soon hesitated and asked, "But what material should we use for this 'gasket'?"

"WS, NbC, and NbSn, you 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, which can prevent the mutual diffusion of elements between WS and NbSn. NbSn is the A15 superconductor with the highest known critical temperature.

These three are the materials Xu Qingzhou can think of at the moment.

He continued: “If these three materials don’t work, you can look at other materials yourself. Essentially, it is a multi-dimensional optimization through lattice matching, thermal expansion gradient, chemical stability and process compatibility.”

Carson nodded without any objection. After following Xu Qingzhou in the experiment for a few months, he found that 90% of Xu Qingzhou's decisions were correct and he could learn a lot of knowledge.

It turns out that genius is so terrible.

Xu Qingzhou said: "Leave the other questions to me."

"it is good."

Carson asked Sun Simin and Mars to get the materials, while he sat down to design how to make the transition layer.

After arranging the tasks, Xu Qingzhou turned his attention to the data of the characterization test. The mechanical problems were handed over to Carson and others, which should be no problem. The insufficient dependence of the critical current density on the magnetic field was the rather troublesome issue.

Simply put, the speed of electric current in the superconducting film is reduced.

The superconducting coherence breaks at the grain boundary, forming a resistive area, which becomes a current bottleneck under high fields. The grain boundary is like an old toll booth on the highway, with a series of problems, narrow lanes (disordered arrangement of atoms at the grain boundary), inefficient toll collectors (high resistance at the grain boundary). Traffic (current) is forced to slow down or even stagnate here, becoming a bottleneck for the entire road network.

To solve this problem, the "traffic system" of the superconducting film must be transformed from chaos and disorder to an efficient and intelligent network, and ultimately achieve unimpeded current flow under high magnetic fields, that is, Jc meets the standard.

It's quite tricky. At the very least, their current methods are not effective and they need to find another way.

Xu Qingzhou felt a little overwhelmed and could only sigh that it was not that easy.

After thinking about it, he simply packed up and went to the library.

There are a lot of problems. For example, according to database statistics, the defect rate of large-scale production is still too high, and the scrap rate is greater than 40%.

Of course, there is no rush for this. It can be delayed a bit until the performance of subsequent samples stabilizes, and then we can slowly iterate and fix the defects.

The big issue now is how to build a smooth transportation system.

However, at the intersection, Xu Qingzhou simply turned a corner and prepared to go to the Department of Mathematics to get a free cup of coffee.

Horn was still the only one in the office.

"good afternoon."

Xu Qingzhou ordered a latte and sat down to chat with Horn. He found out that their project was progressing well and would be completed in another half a year.

After finishing the topic, Horn brought over the coffee and asked curiously, "Xu, have you studied supersymmetric zeta functions?"

"No."

Xu Qingzhou shook his head and said helplessly: "Physics experiments are already giving me enough headaches. I don't have time to study other things."

"Tsk, tsk, you know, quite a few mathematicians in the mathematics community are studying your supersymmetry theory. But you, the proposer, are actually doing other research."

Horn sighed with emotion, no wonder the mathematics community praised Qingzhou and Riemann, leaving a fish hook in the mathematics community everywhere.

Although he is a mathematician, he is always thinking about irrelevant physics.

(End of this chapter)