A team from Korea University led by Lee Sukbae (이석배) and Kim Ji-Hoon (김지훈) began studying this material as a potential superconductor starting in 1999.

A prominent cause was a copper sulfide impurity[10] occurring during the proposed synthesis, which can produce resistance drops, lambda transition in heat capacity, and magnetic response in small samples.

[11][12][10][13][14][15][16] After the initial preprints were published, Lee claimed they were incomplete,[17] and coauthor Kim Hyun-Tak (김현탁) said one of the papers contained flaws.

First they produce lanarkite from a 1:1 molar mixing of lead(II) oxide (PbO) and lead(II) sulfate (Pb(SO4)) powders, and heating at 725 °C (1,000 K; 1,340 °F) for 24 hours: Then, copper(I) phosphide (Cu3P) is produced by mixing copper (Cu) and phosphorus (P) powders in a 3:1 molar ratio in a sealed tube under a vacuum and heated to 550 °C (820 K; 1,000 °F) for 48 hours:[19]: 3 Then, lanarkite and copper phosphide crystals are ground into a powder, placed in a sealed tube under a vacuum, and heated to 925 °C (1,200 K; 1,700 °F) for between 5‒20 hours:[19]: 3 There were a number of problems with the above synthesis from the initial paper.

[23] Some small LK-99 samples were reported to show strong diamagnetic properties, including a response confusingly[24] referred to as "partial levitation" over a magnet.

While initial preprints claimed the material was a room-temperature superconductor,[19]: 1  they did not report observing any definitive features of superconductivity, such as zero resistance, the Meissner effect, flux pinning, AC magnetic susceptibility, the Josephson effect, a temperature-dependent critical field and current, or a sudden jump in specific heat around the critical temperature.

[25] As it is common for a new material to spuriously seem like a potential candidate for high-temperature superconductivity,[14] thorough experimental reports normally demonstrate a number of these expected properties.

On 31 July 2023, Sinéad Griffin of Lawrence Berkeley National Laboratory analyzed LK-99 with density functional theory (DFT), showing that its structure would have correlated isolated flat bands, and suggesting this might contribute to superconductivity.

[35] Similarly presented research on room-temperature superconductors (but a completely different chemical system) by Ranga P. Dias had been published in Nature earlier that year, and received with skepticism—Dias's paper would subsequently be retracted in 2022 after its data was questioned as having been falsified.

[42] On 31 July 2023, a group led by Kapil Kumar published a preprint on arXiv documenting their replication attempts, which confirmed the structure using X-ray crystallography (XRD) but failed to find strong diamagnetism.

[20] On 11 Aug 2023, P. Puphal et al., released their preprint synthesizing the first single crystals of Pb9Cu(PO4)6O finally disproving superconductivity in this chemical stoichiometry published later in APL Materials.

[17] On the same day, Kim Hyun-Tak provided The New York Times with a new video presumably showing a sample displaying strong signs of diamagnetism.

On 4 August 2023, he informed SBS News that high-quality LK-99 samples may exhibit diamagnetism over 5,000 times greater than graphite, which he claimed would be inexplicable unless the substance is a superconductor.

Upon formation, the verification committee did not agree that the two 22 July arXiv papers by Lee et al. or the publicly available videos at the time supported the claim of LK-99 being a superconductor.

[41][16][50] A number of studies found that copper(I) sulfide contamination common to the synthesis process could closely replicate the observations that inspired the initial preprints.

[41] The Korean Society of Superconductivity and Cryogenics expressed concern on the social and economic impacts of the preliminary and unverified LK-99 research.

[55] A video from Huazhong University of Science and Technology uploaded on 1 August 2023 by a postdoctoral researcher on the team of Chang Haixin,[41] apparently showed a micrometre-sized sample of LK-99 partially levitating.

This went viral on Chinese social media, becoming the most viewed video on Bilibili by the next day,[56][41] and a prediction market briefly put the chance of successful replication at 60%.

[63] After the July 2023 publication's release, independent groups reported that they had begun attempting to reproduce the synthesis, with initial results expected within weeks.