Directing again?!
The “Zhihu Daopai” bigwigs from institutions such as the Chinese Academy of Sciences, Huazhong University of Science and Technology, Beijing University of Science and Technology, and South China University of Technology (with online names such as “Zhen Keai Dai” and “Xi Zhixi”) have jointly released their latest research results.
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As soon as the news came out, related topics once rushed to the topNo. 1 on Zhihu Hot List.
Xi Zhixi, that is, Professor Yao Yao of South China University of Technology, summarized the original words in the provincial version as follows:
A blend of variant apatite and covellite was synthesized. Among them, the variant apatite component showsNear-room-temperature superconductivityThe transition temperature is about 250-260K (-23.15℃ ~ -13.15℃), and covellite may also be induced to produce another low-temperature superconducting phase of about 30K (−243.15∘C).
In addition, Professor Xi also emphasized that except for the apatite structure of this new sample which is similar to LK-99 reported by the Korean team last year, it is different from LK-99 in many aspects such as synthesis process, raw materials, element composition and ratio, and structure.
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It can basically be considered a brand new research result.
What's in the paper?
First, let’s look at what everyone is most concerned about.Resistance curve.
In the experiment, the researchers synthesized two parallel samples, labeled S1 and S2, the only difference between them is that the sulfur doping ratio in S2 is slightly higher than that in S1. For comparison, a lead-free sample was also synthesized, labeled S3.
The figure below shows the structure and element distribution information of the S1 sample. From the XRD analysis, we can see that the sample is a mixture of variant apatite and covellite (copper sulfide). During the sulfur doping process, the original apatite lattice shrinks and distorts significantly, and the lattice constant decreases, so this new compound is called “variant apatite”.
The EPMA microscopic quantitative results in (b) show that phosphorus and oxygen are gradually replaced by sulfur. The EPMA WDS mapping shown in (d)-(h) clearly shows three compounds: undoped apatite (A), sulfur-doped variant apatite (VA), and covellite (C).
The IV curves of the S1 sample at eight temperatures are shown below. The electrical transport was measured using a four-probe technique on an Aglient B2912A, and the temperature was controlled by an Oxford OptiStatDN.
Despite the initial voltage drop caused by the very large compensation resistance of the instrument, the voltage plateau phenomenon that appears in the current-voltage (IV) curve, that is, the voltage on the sample remains unchanged as the applied current increases, can be safely attributed to quantum transport, i.e.Zero resistance effect.
Exceeding the so-called critical current Ic After that, the voltage starts to rise and increases rapidly, and then turns into a normal linear IV curve in the normal metallic state, which indicates the transition from the superconducting phase to the normal phase.
As can be seen from Figures (b)–(g), the typical superconducting IV curve from 140–240 K (-133.15°C ~ -33.15°C) is clearly observed, and the critical current basically decreases with increasing temperature, which can be roughly fitted by a quadratic function.
Based on the current experiments, the researchers estimated from the results that the resistivity below 240K (-33.15°C) is at least 10−8 The magnitude of Ω・m is even smaller.The authors believe this indicates that the resistivity of the sample is at least comparable to or even smaller than that of copper, strongly suggesting that a zero-resistance effect has been achieved.
The research team used the MPMS-3 SQUID to detect DC magnetic susceptibility.
Under zero-field cooling (ZFC) measurement at 25 Oe, the magnetic susceptibility-temperature (MT) curve shows significant diamagnetic properties below 260 K (-13.15 ° C), while the field-cooled (FC) curve is paramagnetic. The bifurcation between ZFC and FC appears at 250-260 K (-23.15 ° C ~ -13.15 ° C), which can be regarded as the critical temperature Tc.
The MT curve of the S2 sample shows similar characteristics under ZFC, but the FC susceptibility also exhibits diamagnetic behavior, which indicates that increasing sulfur doping in variant apatite can enhance superconducting properties.
Interestingly, the two samples did not show a plateau-like line shape at low temperatures. On the contrary, the magnetic susceptibility decreased rapidly as the temperature decreased, so the Meiners effect (one of the characteristics of superconductivity) could not be observed.
Therefore, the research team reviewed the MT curve of the S3 sample and found that there were two obvious stages: the first was from 130-230K (-143.15°C to -43.15°C), which can be regarded as the variant apatite.Near room temperature superconducting phase; The second one is below 30K (-243.15°C), which can be considered as a low-temperature superconducting phase mainly caused by covellite.
Since the two phases of variant apatite and covellite are related, the researchers suspected that the superconductivity of covellite is induced by variant apatite through the proximity effect.
Figures (d)-(h) show the magnetic susceptibility-magnetic field (MH) curves at different temperatures. At 250K and 200K, the linear diamagnetic background is subtracted to show the superconducting hysteresis loop more clearly.
Essentially, this pronounced hysteresis has never been observed in other materials at such high temperatures and under conventional conditions, and it is reasonable to assume that this isThe main characteristics of near-room-temperature superconductivity.
The lower and upper critical magnetic fields (Hc1 and Hc2), they basically increase with decreasing temperature.
For other details, the research team adoptedHigh pressure hydrothermal methodTo prepare materials.
All samples reported previously were synthesized using sintered apatite (the method used by the Korean LK-99 team), but the sintering process cannot guarantee purity. In this new study, the research team used a high-pressure hydrothermal method to synthesize the samples, which are soft and brittle but easier to purify.
The raw materials include copper nitrate, lead nitrate, ammonium phosphate and potassium sulfide. There are two steps, the first step is to synthesize the raw lead apatite and co-dope it with copper and sulfur, and the second step is to further dope it with sulfur. After final filtration and drying, the sample should be pure black with no visible metallic luster.
And thisBlack is crucialwhich is also the reason why it is difficult to reproduce.
“The laboratory is about to become a visual laboratory”
The authors note that the final black color of the sample is crucial.
In the words of Teacher Xi, it was really cute to write down every step and ask the junior to help synthesize it, but the result was not good. The samples all looked black, but each one was different, “their laboratory is about to become a visual laboratory.”
Zhen Keai Dai even said bluntly, “If the color is not right in the first step of synthesis, the sample can be thrown away.”
Really cute Dai also said:
As for whether it is a superconductor, we think it is based on the results. If it is not, can you tell me what it is? As for the error, please tell me how it is wrong, and we will improve it and try again.
In summary,rigorousTwo words full.
Netizens were also very serious about eating melons. Many netizens said not to rush to open champagne and it would be possible to verify it only after the official publication.
The team said that the samples are open for provision and some have already been sent out to peers.
Finally, there is one reserved item. Teacher Xi came up with a name for this new material, “Xuanpo Stone”. Xuan refers to black and also has a bit of metaphysical color. Poshi is the transliteration of thiophosphate POS.
But Dai always disagrees with this name (doge).
Paper link:https://arxiv.org/abs/2406.17525
Reference Links:https://www.zhihu.com/question/659946224
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