Indications of superconductivities in blend of variant apatite and covellite

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China’s room temperature superconductor research continues. Here is the latest published work from the team from multiple universities and labs.

This is the same teams that found stronger magnetic indications of Meissner effect in LK99 variant materials.

Through heavily doping sulfur into an apatite framework, chinese researchers synthesized a new blend mainly comprising variant apatite and covellite (copper sulfide). Magnetic measurement exhibits that significant diamagnetism appears at around 260 K and drops dramatically below 30 K implying coexistence of two superconducting phases. The upper critical magnetic field is larger than 1000 Oe at 250 K. Electric measurement manifests that the current-voltage curves deviate from the normal linear lineshape suggesting the presence of zero-resistance effect, and the critical current is around 50 μA at 140 K. These exotic magnetic and electric features strongly indicate these two components, variant apatite and covellite, individually trigger two superconducting phases at near-room and low temperatures.

They believe the properties of superconductivities can be largely improved in the near future and promising applications can be soon established.

They have also measured the resistance–temperature (RT) curves of S1 and S2 samples. Subtracting the compensating resistance, the resistance of sample is 1–3 mΩ at room temperature, meaning that the resistivity is in the order of 10^−6–10^−7 Ω · m. Considering the short electrode distance in the setup and the large fluctuation of initial voltage U0, the resistance is too small to be precisely measured, so it is difficult to determine critical temperature by RT curves.

The whole reaction process of the synthesis is a nonequilibrium dynamic process. Following continuous doping of sulfur, the apatite in the raw material will gradually evolve to covellite. They can divide the process into five steps and in each step there is a main effective component in the blend: Raw material of apatite, sulfur doped apatite, variant apatite as main phase blended with covellite, covellite as main phase doped with variant apatite, and covellite.

S1 and S2 samples belong to the third and fourth category, respectively. They have also synthesized three other samples, S4, S5 and S6, individually terminated at relevant steps to show the change during the variant process. The XRD of them can be seen in Fig. 4(a),
and from Fig. 4(b) it is clear that during the reaction the lattice is continuously shrunk and distorted.

The doped apatite basically holds the main framework of apatite, though the lattice distortion has been very strong. In the overdoped phases including variant apatite and covellite the framework gets close to collapse. The EPMA of covellite exhibits the main phase is indeed copper sulfide and also some persulfide particles are observed. Although both variant apatite and copper persulfide are unstable by themselves in ambient
conditions, the distortion of lattice stabilizes them implying the association between them.

The magnetization of additional samples are shown in Fig. 4(c)–(e). The undoped apatite manifests paramagnetism, and the covellite has no magnetic response except below 30 K. The doped apatite and covellite below 30 K exhibit diamagnetism which is what they want. Consequently, the most important component, variant apatite, is generated as an intermediate in step 2, 3 and 4. In order to optimize the synthesis, therefore, the manipulation of doping and defect concentration plays the essential role.