Earticle

We investigated Pb10-xCux(PO4)6 (0.9 < x < 1.1) (LK-99) and Cu2S, presumed to be contained as an impurity in LK-99, in a wide spectral range from far infrared to ultraviolet using optical spectroscopy. The optical conductivity spectra of both samples were obtained from measured reflectance spectra at various temperatures from 80 to 434 K. Both samples showed several infrared-active phonons in the far and mid-infrared regions. LK-99 showed typical insulating features with a band gap of ~1 eV. Cu2S showed a nonmonotonic temperature-dependent trend and two energy gaps: one energy gap of ~93 meV and a band gap of 2.42 eV. Our results indicate that LK-99 cannot be a superconductor because it is an insulator with a large band gap.

Recently, Lee et al. claimed that LK-99 is the first room-temperature superconductor at ambient pressure, which quickly captured the attention of both the scientific community and the general public. We tried to replicate Pb10−xCux(PO4)6O, called as LK-99, and characterized its physical properties by measuring the electrical resistance and Meissner effect. The electrical resistance results for different batches exhibited structural phase transitions at different temperatures, and the magnetic measurements indicated weak diamagnetism at 300 K, which is weaker than that of water. Taken together with the structural analysis, these results suggest that the resistivity transitions are incurred by Cu-S compound generated as a byproduct during the synthesis of LK-99 and LK-99 is not a room-temperature superconductor.

The current study deals with the possible interplay between superconductivity and spin density wave in two band model high temperature iron based superconductor (FeBSC) Ba1-xNaxFe2As2. The electron and hole bands in the presence of the inter-band interaction between the two bands is becoming a vital issue to deal with the high temperature physics of the iron-based superconductors. In this research work, a model Hamiltonian appropriate for the system under consideration has been developed and the temperature dependent Green's function technique has been employed to get the solution for the equations of motion constructed for the two band model high temperature FeBSC Ba1-xNaxFe2As2. By making use of the decoupling procedure, the equations of motion for the dependence of superconducting transition temperature (TC) on spin density wave(SDW) order parameter (ΔSDW) in the electron intra-band (Δ𝑠𝑐(𝑒)) , hole intra-band (Δ𝑠𝑐(ℎ)) and inter-band (Δ𝑠𝑐(𝑒ℎ)) for Ba1-xNaxFe2As2 have been obtained. We have also obtained the expression for the dependence of spin density wave transition temperature(TSDW) on ΔSDW for Ba1-xNaxFe2As2. Using some plausible approximations and appropriate experimental values for the parameters in the obtained equations of motion, phase diagrams of TC versus Δ𝑠𝑐(𝑒), Δ𝑠𝑐(ℎ) and Δ𝑠𝑐(𝑒ℎ) are plotted. Furthermore, a phase diagram of TSDW versus Δ𝑆𝐷𝑊 is plotted for the material under consideration. Finally, using the above mentioned phase diagrams, the interplay between superconductivity and spin density wave in the two band model high temperature FeBSC Ba1-xNaxFe2As2 has been demonstrated to be a very distinct possibility. The agreement of the current finding with the experimental observations is quite commendable.

3D printing has the advantage of being able to process various types of parts by layering materials. In addition to these advantages, 3D printing technology allows models to be processed quickly without any special work that can be used in different fields to produce workpieces for various purposes and shapes. This paper deals to not only increase the utilization of 3D printing technology, but also to revitalize 3D printing technology in applications that require similar cryogenic environments. The goal of this study is to identify the mechanical properties of polylactic acid and photopolymer resin processed by Fused Deposition Modeling (FDM) and Digital Light Processing (DLP) respectively. The entire process is meticulously examined, starting from getting the thermal contraction using an extensometer. A uniaxial tensile test is employed, which enables to obtain the mechanical properties of the samples at both room temperature (RT) and cryogenic temperature of 77 K. As the results, photopolymer resin exhibited higher tensile properties than polylactic acid at RT. However, at cryogenic temperatures (77 K), the photopolymer resin became brittle and failure occurred due to thermal contraction, while polylactic acid demonstrated superior tensile properties. Therefore, polylactic acid is more suitable for lower temperatures.

Metal 3D printing is utilized in various industrial fields due to its advantages, such as fewer restrictions on production shape and reduced production time and cost. Existing research on 3D printing metal materials focused on changes in material properties depending on manufacturing conditions and was mainly conducted in a room temperature environment. In order to apply metal 3D printing products to cryogenic applications, research on the properties of materials in cryogenic environments is necessary but still insufficient. In this study, we evaluate the properties of stainless steel (STS) 316L and CuCr1Zr manufactured by Laser Powder Bed Fusion (LPBF) in a cryogenic environment. CuCr1Zr is a precipitation hardening alloy, and changes in material properties were compared by applying various heat treatment conditions. The mechanical properties of materials manufactured using the LBPF method are evaluated through tensile tests at room temperature and cryogenic temperature (77 K), and the thermal properties are evaluated by deriving the thermal conductivity of CuCr1Zr according to various heat treatment conditions. In a cryogenic environment, the mechanical strength of STS 316L and CuCr1Zr increased by about 150% compared to room temperature, and the thermal conductivity of CuCr1Zr after heat treatment increased by about 6 to 10 times compared to before heat treatment at 40 K.