Lead Apatites Research Articles

Impact of sulfur doping on copper-substituted lead apatite

Impact of sulfur doping on copper-substituted lead apatite

Integrating Superconductivity in Cu Replace Lead Apatite by Nuclear Magnetic Moment Theory of RBL

Recently, scientists proclaimed superconductivity under ambient conditions of room temperature and 1 atmosphere pressure in Cu partial substituted lead apatite: Pb(10-x)Cux(PO4)6. This paper highlights the application of RBL’s stable isotope of positive and negative nuclear magnetic moments (NMMs) theory for explaining the heavy isotopic enrichment of this materials as {207Pb{10-x}63Cux(‘31PιO4)6}, where ι = 17 or 18 and the resulting superconductivity and novel room temperature atmospheric pressure superconductivity of this heavy isotopic enriched substance. On the basis of such analysis by RBL theory, the synthesis of high temperature, regular pressure superconductivity can be explained and this recent experimental observation of ambient pressure and temperature superconductivity in 207Pb{10-x}63Cux(‘31PιO4)6, where ι = 17 or 18, proves RBL’s NMMs theory of high temperature superconductivity. After 1 month on July 22, 2023 of the archiving of such data for superconductivity Pb(10-x)Cux(PO4)6 by Lee and coworkers, a huge experimental effort by hundreds of researchers around the world has attempted to replicate this room temperature, ambient pressure superconductivity in Pb(10-x)Cux(PO4)6 without success. The resulting inability to replicate the ambient superconductivity and note of some fractional component in the mixture causing the ambient superconductivity is explained by RBL’s theory as the fractional component may be clumped isotopes as in {207Pb{10-x}63Cux(‘31PιO4)6}, where ι = 17 or 18, and RBL here notes the vapor deposition process alleged by Lee and coworkers for producing the superconductivity was previously predicted by RBL to cause isotopic fractionation during solid to liquid and liquid to gas and gas to solid physical changes.

Electronic structure and vibrational stability of copper-substituted lead apatite LK-99

Electronic structure and vibrational stability of copper-substituted lead apatite LK-99

Exploration of superconductivity in LK-99 synthesized under different cooling conditions

The claim of superconductivity above room temperature at ambient pressure in Cu-doped lead apatite (LK-99, Pb10-xCux(PO4)6O) has attracted considerable attention. In this paper, we present the results of synthesized LK-99 using a systematic approach based on quenching method variations. A slower cooling rate resulted in an increased LK-99 phase and a decreased Cu2S phase, with the slowest cooling method achieving the highest concentration of the LK-99 phase. Magnetic levitation was observed in certain specimens, with one end adhering to the magnet and the other end floating, which was distinguished from the Meissner effect. The majority of samples synthesized under different conditions exhibited no response to the magnet. The slowest cooled sample exhibited mostly insulating behavior. The samples synthesized in the other conditions had metallic behaviors, which contained a significant amount of Cu2S. No evidence of superconductivity was observed within the temperature range of 4 K–300 K in our samples.

The 1/4 occupied O atoms induced ultra-flatband and the one-dimensional channels in the Pb10−xCux(PO4)6O4 (x = 0, 0.5) crystal

The search for room-temperature superconductors has been a long-standing goal in condensed matter physics. In this study, we investigate the electronic and geometric properties of lead apatite with and without Cu doping within the framework of the density functional theory. Based on our calculations, we found that without Cu doping, the lead apatite PPOO shows an insulator character with flatbands that straddle the Fermi level. Once we introduce O1 vacancies, the flatbands disappear. Furthermore, we analyze the effects of Cu doping on the crystal structure and the electronic band structure of the material PCPOO4. Our calculations reveal the presence of one-dimensional channels induced by fully occupied O1 atoms that are only 1/4 occupied in the literature, which may play a crucial role in the realization of room-temperature superconductivity. Based on our findings, we propose a possible solution to improve the quality of superconductivity by annealing the material in an oxygen atmosphere. These results contribute to a better understanding of the unusual properties of Cu-doped lead apatite PCPOO4 and will pave the way for further exploration of its potential as a room-temperature superconductor.

The characteristics of Cu-doped lead apatite (LK-99) synthesized with the removal of Cu2S using ammonia solution: A diamagnetic semiconductor

This study evaluated the superconducting properties of Cu-doped lead apatite “LK-99” and synthesized LK-99 samples using the process proposed by a team from Korea, who first described the process. Additionally, whether the results of this Korean team were related to Cu2S was also examined using an ammonia solution (NH3·H2O) to remove Cu2S. Through x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDX) analyses, a distinct Cu2S phase was identified in the LK-99 samples. This phase was effectively eliminated through a subsequent treatment using an ammonia solution. The appearance of blue Cu+2 ions in the solution and the elimination of the Cu2S peak in XRD supported the conclusion. The magnetic and electrical properties of LK-99 with and without Cu2S suggest that the superconductor-like behavior in LK-99 predominantly arises from a transition in resistivity due to the influence of Cu2S. As such, LK-99 is better classified as a diamagnetic semiconductor than a room-temperature superconductor. The room-temperature superconductors still require further research.

On the dynamical stability of copper-doped lead apatite

The recent claim of room temperature superconductivity in a copper-doped lead apatite compound, called LK-99, has sparked remarkable interest and controversy. Subsequent experiments have largely failed to reproduce the claimed superconductivity, while theoretical works have identified multiple key features including strong electronic correlation, structural instabilities, and dopability constraints. A puzzling claim of several recent theoretical studies is that both parent and copper-doped lead apatite structures are dynamically unstable at the harmonic level, questioning decades of experimental reports of the parent compound structures and the recently proposed copper-doped structures. In this work, we demonstrate that both parent and copper-doped lead apatite structures are dynamically stable at room temperature. Anharmonic phonon–phonon interactions play a key role in stabilizing some copper-doped phases, while most phases are largely stable even at the harmonic level. We also show that dynamical stability depends on both volume and correlation strength, suggesting controllable ways of exploring the copper-doped lead apatite structural phase diagram. Our results fully reconcile the theoretical description of the structures of both parent and copper-doped lead apatite with the experiment.

Exceptional metal-semiconductor-metal transition of lead apatites via oxygen defect tuning.

Lead apatites, distinguished and compelling bulk materials with the stoichiometric arrangement as Pb10(POx)6Oy, are renowned for their structural complexity. Recently, the discovery of possible room-temperature superconductivity under ambient pressure in copper-substituted lead apatites has engendered considerable interest within both the physics community and beyond. Nevertheless, exploration of pristine Pb10(POx)6Oy parent structures has hitherto remained elusive. In this study, we employ density functional theory (DFT) calculations to investigate the effects of oxygen defects on the electronic structures of Pb10(POx)6Oy and Pb9Cu(POx)6Oy. We scrutinize two distinct categories of defects: oxygen atoms enmeshed within POx groups (Ox) and solitary oxygen atoms (Oy). Our investigation uncovers a profound influence of these defects on the band structure. Specifically, the introduction of Oy defects prompts a remarkable transition in Pb10(PO4)6Oy from a metal to semiconductor to metal state, accompanied by pivotal shifts in the principal electronic contributors from p orbitals of Oy to those of Pb atoms. Furthermore, the introduction of Ox defects in Pb10(POx)6O1 engenders metamorphosis in the band structure, transmuting it from a semiconductor to a metallic state. Significantly, our findings pinpoint the suitable range of x in the Pb10(POx)6O1 configuration as lying between 2 and 4. Additionally, our study also demonstrates that the oxygen defects (Ox/Oy) do not affect the metallic properties of copper-substituted lead apatites. This study elucidates the significant role of oxygen defects in modulating the electronic properties of apatite materials, offering insights into potential interdisciplinary applications. This establishes a crucial link between material composition and electronic behavior, revealing key mechanisms for engineering functionality in lead apatites and other advanced materials.

Doubly charged single Weyl pair with complete spin polarization

An ideal charge-two single Weyl pair with complete spin polarization has been unveiled in the Cu-doped lead apatite Pb9Cu(PO4)6O, laying the groundwork for exploring the topological properties with both magnetic ordering and high-order dispersion.

Non-Fermi liquid to charge-transfer Mott insulator in flat bands of copper-doped lead apatite.

Copper-doped lead apatite, called LK-99, was initially claimed to be a room temperature superconductor driven by flat electron bands, but was later found to be a wide gap insulator. Despite the lack of room temperature superconductivity, there is growing evidence that LK-99 and related compounds host various strong electron correlation phenomena arising from their flat electron bands. Depending on the copper doping site and crystal structure, LK-99 can exhibit two distinct flat bands crossing the Fermi level in the non-interacting limit: either a single or two entangled flat bands. We explore potential correlated metallic and insulating phases in the flat bands of LK-99 compounds by constructing their correlation phase diagrams, and find both non-Fermi liquid and Mott insulating states. We demonstrate that LK-99 is a charge-transfer Mott insulator driven by strong electron correlations, regardless of the flat band type. We also find that the non-Fermi liquid state in the multi-flat band system exhibits strange metal behaviour, while the corresponding state in the single flat band system exhibits pseudogap behaviour. Our findings align with available experimental observations and provide crucial insights into the correlation phenomenology of LK-99 and related compounds that could arise independently of superconductivity. Overall, our research highlights that LK-99 and related compounds offer a compelling platform for investigating correlation physics in flat band systems.

Pressure-induced one-dimensional oxygen ion diffusion channel in lead apatite

Pressure-induced one-dimensional oxygen ion diffusion channel in lead apatite

Metallization and spin fluctuations in Cu-doped lead apatite

Metallization and spin fluctuations in Cu-doped lead apatite

Ab initio investigations on the electronic properties and stability of Cu-substituted lead apatite (LK-99) family with different doping concentrations (x = 0, 1, 2)

The pursuit of room-temperature ambient-pressure superconductivity in novel materials has sparked interest, with recent reports suggesting such properties in Cu-substituted lead apatite, known as LK-99. However, these claims lack comprehensive experimental and theoretical support. In this study, we address this gap by conducting ab initio calculations to explore the impact of varying doping concentrations (x = 0, 1, 2) on the stability and electronic properties of five compounds in the LK-99 family. Our investigations confirm the isolated flat bands that intersect the Fermi level in LK-99 (Pb9Cu(PO4)6O:Cu<Pb(1)>). In contrast, the other four parent compounds exhibit insulating behavior with wide band gaps. X-ray diffraction spectra based on the DFT simulations at 0 K confirm the presence of Cu substitution on Pb(1) sites in the originally synthesized LK-99 sample, while an extra peak suggests potential alternative like Pb8Cu2(PO4)6 phases due to compositional variations in the original LK-99 samples. Furthermore, the LK-99 structure undergoes substantial lattice constriction, resulting in a significant 5.5% reduction in volume and 6.8% in area of two mutually inverted triangles formed by Pb(2) atoms. Meanwhile, energy calculations reveal a marginal energy preference for substituting Cu on Pb(2) sites over Pb(1) sites, with a difference of approximately 0.010 eV per atom (roughly 0.9645 kJ/mol). Intriguingly, at pressures exceeding 73 GPa, stability shifts towards LK-99 containing Cu substitutions on Pb(1) sites. Despite exhibiting higher electronic conductivity than parent compounds, Pb9Cu(PO4)6O:Cu<Pb(1)> falls short of the conductivity levels observed in metals or advanced oxide conductors with the simulation based on the Boltzmann transport theory.

Synthesis of possible room temperature superconductor LK-99: Pb9Cu(PO4)6O

The quest for room temperature superconductors has been teasing scientists and physicists, since its inception in 1911 itself. Several assertions have already been made about room temperature superconductivity, but have never been verified or reproduced across the labs. The cuprates were the earliest high transition temperature (T c) superconductors, and it seems that copper has done the magic once again. In July 2023, a Korean group synthesized a lead apatite based compound LK-99, showing a T c of above 400 K (Lee et al 2023 arXiv: 2307.12008; 2023 arXiv: 2307.12037; Lee et al 2023 J. Korean Cryst. Growth Cryst. 33 61). The signatures of superconductivity in the compound are very promising, in terms of resistivity (ρ = 0) and diamagnetism at T c. Although, the heat capacity (C p) did not show the obvious transition at T c. Inspired by the interesting claims of the above room temperature superconductivity in LK-99, in this article, we report the synthesis of polycrystalline samples of LK-99, by following the same heat treatment as reported in Lee et al (2023 arXiv: 2307.12008; 2023 arXiv: 2307.12037) using a two-step precursor method. The phase is confirmed through x-ray diffraction measurements, performed after each heat treatment. The room temperature diamagnetism is not evidenced by the levitation of a permanent magnet over the sample or vice versa. The isothermal magnetization measurement at 280 K shows that as synthesized sample of LK-99 is paramagnetic. Further measurements for the confirmation of bulk superconductivity in variously synthesized samples are underway. Our results on the present LK-99 sample, synthesized at 925 °C, as of now do not confirm the appearance of bulk superconductivity at room temperature. Further studies with different heat treatments are underway.

Early phase effects of silicate and orthophosphate on lead (Pb) corrosion scale development and Pb release

Orthophosphate is widely used to control lead (Pb) release in drinking water distribution systems, but phosphorus addition is not sustainable. Alternative corrosion control treatments are needed, and sodium silicate is one possibility. Here, pre-corroded Pb coupons—with and without free chlorine—were used to examine early-phase corrosion scale development after silicate addition, with orthophosphate as a reference corrosion inhibitor. Scale development was evaluated in terms of total Pb release, phase transformation, electrochemical impedance, morphological changes, Pb dissolution kinetics, and short-term Pb–Cu galvanic corrosion. Elevated Pb release occurred for approximately one month after silicate addition, and total Pb release peaked at 1968.1 μg/L and 1176.9 μg/L from systems with and without free chlorine, respectively. In contrast, orthophosphate-treated coupons exhibited fewer, less pronounced spikes in Pb release. By day 354, the median total Pb release from orthophosphate-treated coupons with and without free chlorine had decreased to 3.7 and 5.0 μg/L, respectively, while the median total Pb release from corresponding silicate-treated coupons was much higher, at 44.9 μg/L and 34.3 μg/L. Calcium lead apatite (Ca0.56Pb3.77(PO4)3OH0.67) was identified in orthophosphate-treated scales, with hydroxylpyromorphite (Pb5(PO4)3OH) present in the absence of free chlorine. Plattnerite occurred on coupons in all chlorinated systems. Pb silicate compounds were not detected, but Ca2SiO4 and Na2Ca2(SiO3)3 were identified by X-ray powder diffraction. The charge transfer: film resistance ratio characterizing the orthophosphate-treated coupons decreased slowly while that of the silicate-treated coupons increased after silicate was added. These variations suggest orthophosphate provided better corrosion control than silicate did. Silicate treatment generally caused degradation of the top Pb scale layer, resulting in elevated Pb release, while orthophosphate encouraged the growth of more structured, generally thicker, corrosion scales that were effective in limiting Pb release.

Time constraints on experimental studies of lead apatites

The paper presents the results of experimental studies on the synthesis and thermodynamic stability of selected Pb-apatites in terms of criteria determining termination of the experiments. Based on the case study, we indicate difficulties in analysing the obtained experimental data. Time-resolved sampling of precipitate formed during a dropwise synthesis of pyromorphite was performed and the results were compared to the literature data. It has been concluded that the Ostwald ripening time for synthesized solids depends primarily on the chemical composition of the intended Pb-apatite phase. We presented that heterogeneity of precipitate affects its dissolution in terms of repeatability of the results and equilibrating time. A unique 9-year-long experiment on vanadinite stability at a pH range from 2.0–6.0 revealed that among all tested dissolution conditions only the reactions at the pH = 3.5 can perform as the basis for some thermodynamic calculations. It has been concluded that the rate of phase transitions in the Pb-apatites group can be misleading in terms of determining the equilibrium of the system, and the experimental setup designed particularly to provide reliable controls in this aspect should be involved. Means in this respect have been proposed.

Lead apatites: structural variations among Pb5(BO4)3Cl with B = P (pyromorphite), As (mimetite) and V (vanadinite).

The crystal structure of four Pb apatite samples, Pb5(BO4)3Cl, was refined with synchrotron high-resolution powder X-ray diffraction data, Rietveld refinements, space group P63/m and Z = 2. For this isotypic series, B = P5+ is pyromorphite, B = As5+ is mimetite and B = V5+ is vanadinite. The ionic radius for As5+ (0.355 Å) is similar to that of V5+ (0.335 Å), and this is twice as large as that for P5+ (0.170 Å). However, the c unit-cell parameter for mimetite is surprisingly different from that of vanadinite, although their unit-cell volumes, V, are almost equal to each other. No explanation was available for this peculiar c-axis value for mimetite. Structural parameters such as average 〈B-O〉 [4], 〈Pb1-O9〉 [9] and 〈Pb2-O6Cl2〉 [8] distances increase linearly with V (the coordination numbers for the cations are given in square brackets). Mimetite has a short Pb2-O1 distance, so the O1 oxygen atom interacts with the 6s2 lone-pair electrons of the Pb2+ cation that causes the Cl-Cl distance (= c/2) to increase to the largest value in the series because of repulsion, which causes the c-axis to increase anomalously. Although Pb apatite minerals occur naturally in ore deposits, they are also formed as scaly deposits in lead water pipes that give rise to lead in tap water, as was found recently in Flint, Michigan, USA. It is important to identify Pb-containing phases in water-pipe deposits.

Structural and spectroscopic study of arsenate and vanadate incorporation into apatite group: Implications for semi-quantitative estimation of As and V contents in apatite

The solid solutions of mimetite-vanadinite series were synthesized at room temperature through aqueous precipitation method and were characterized with Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), X-ray diffraction (XRD), infrared and Raman spectroscopy. Based on the XRD analyses, it showed that all the samples crystallize with the same structure. A and c parameters vary smoothly with substitution of AsO43− for VO43−. In the FT-IR spectra of mimetite-vanadinite solid solutions series, the bands corresponding to stretching (v3) vibrations of AsO43− and VO43− ions were observed in the range 700–900cm−1, and the bending (v4) vibrations of OAsO and OVO were observed in the range 310–400cm−1. In the Raman spectra, the bands attributed to vibrations in the VO43− appeared at 830–700cm−1, 420–290cm−1. The bands attributed to vibrations in the AsO43− appeared in the ranges 740–820cm−1, 410–310cm−1. In addition, the peak positions of the dominant antisymmetric stretching (v3) of VO bond around 706cm−1 of IR spectra for the prepared solids also varies with the different As/(As+V) ratio, and the relationship is linear, which can be an implication for semi-quantitative estimation of As and V contents in lead apatites.

Carbonate substitution in lead hydroxyapatite Pb5(PO4)3OH

Synthetic carbonate lead hydroxyapatite Pb5(PO4,CO3)3(OH,CO3) was precipitated from aqueous solution and characterized. The maximum content of CO32− ion in lead apatites does not exceed 2.25 wt%. For precipitation from aqueous solutions this is even lower and controlled by the solubility of cerussite PbCO3. Carbonate substitution occurs simultaneously in two structural positions: at OH− sites (A-type substitution) and at PO43− sites (B-type substitution). This is the most pronounced in FTIR (Fourier Transform Infrared Spectroscopy) spectra at 865 cm−1 and within the range of 1300–1500 cm−1. The substitution results in slight increase of the unit cell parameter a from 9.874 to 9.904 A. The presence of CO32− in two structural positions results in two stages of the release of CO2 upon heating: at 300–350 °C and at 400 °C. The presence of carbonates has little effect on thermal decomposition of lead hydroxyapatite which starts at about 450 °C resulting in the formation of lead pyrophosphate.

Method development for the synthesis of large crystals of pyromorphite

In the UK, water utilities add phosphate to drinking water in order to prevent lead being released from older properties that are supplied by lead water pipes. The mechanism of reduction is thought to involve the formation of insoluble lead phosphates. This research was carried out to optimise the growth of large lead apatite crystals for use in future atomic force microscopy work. In this case study, pyromorphite crystals exhibiting both prismatic hexagonal and needle-like structures with sizes up to 0.2mm were successfully grown using a caesium chloride flux. They were produced both at lower temperatures and in less time than previous studies. All samples were characterised using a variety of analytical techniques such as X-ray diffraction, infrared spectrometry, energy dispersive X-ray analysis, scanning electron microscopy and thermogravimetric analysis.