Material consideration: On the LK-99 ‘superconductor’ episode

Subject :Science and technology

Section: Msc

Context:

A group of South Korean scientists have recently claimed the discovery of a material they named LK-99. According to their reports, LK-99 is a superconductor at room temperature and pressure.

What does the Claim on Discovery of LK-99 Suggest?

Exploring Apatite Materials: The South Korean group’s discovery involved a rather unexpected material called apatite.
- Apatites are minerals with a phosphate scaffold in a tetrahedral or pyramidal motif(one phosphorus atom is surrounded by four oxygen atoms).
- The scientists started with lead apatite and substituted some of the lead atoms with copper, resulting in copper-substituted lead apatite, which they named LK-99.
Evidence of Superconductivity: The group reported that at 10% copper substitution, LK-99 exhibited the characteristics of a superconductor.
The material also maintained superconductivity in the presence of an external magnetic field, up to a certain critical threshold, a behavior consistent with known superconductors.

Why has the scientific community rejected the claim?

The scientific community is now confident that the material known as LK-99 is not a room-temperature and ambient-pressure superconductor.
There were two reasons why the material was not a superconductor.
- First, as conventional superconductors inside a weak magnetic field are cooled to induce a superconducting state, they expel the field from their bulk at and under the transition temperature. So, a magnet near the superconductor will be pushed away during the transition. The South Korean group had shared a video in which LK-99 appeared to half-repel a magnet. But independent researchers found that the material was an insulator whose impurities could be magnetised, leading to the half-repulsion seen in the video.
- Second, the South Koreans reported that the electrical resistivity of LK-99 dropped sharply at around 104° Celsius, a potential sign of superconductivity. But scientists observed the drop if the material contained copper sulphide as an impurity; copper sulphide undergoes a phase transition at that temperature, distorting the resistivity.

Superconductors:

Superconductors are materials that exhibit zero electrical resistance when cooled to extremely low temperatures. This property allows them to conduct electricity with no loss of energy.
Example: Lanthanum-Barium-Copper Oxide, Yttrium-Barium-Copper Oxide, Niobium-Tin etc.

What are Room temperature superconductors?

A room-temperature superconductor is a material capable of displaying superconductivity at temperatures above 0 °C (273 K; 32 °F), which are commonly encountered in everyday settings.
As of 2023, the material with the highest accepted superconducting temperature was highly pressurized lanthanum decahydride, whose transition temperature is approximately 250 K (−23 °C) at 200 GPa.
At standard atmospheric pressure, cuprates currently hold the temperature record, manifesting superconductivity at temperatures as high as 138 K (−135 °C).
The concept of “near-room temperature” transient effects has been a subject of discussion since the early 1950s.

Significance:

The discovery of a room-temperature superconductor would have enormous technological significance.
It has the potential to address:
- Global energy challenges,
- Enhance computing speed,
- Enable innovative memory-storage devices, and
- Create highly sensitive sensors, among a multitude of other possibilities.