arXiv subjects

Jingjun Qin

Publications and source records attributed to Jingjun Qin.

5 recordsLinked to original sources

arXiv2026

Superconductivity in Al-based high-entropy alloys TiHfNbTaAl and TaNbHfZrAl

Since the first report of a high entropy alloy (HEA) superconductor in 2014, HEAs have continued to captivate the interest of superconducting researchers. Owing to the significant degree of disorder inherent in these systems, they serve as exemplary models for examining the properties of materials that exist in states intermediate between crystalline and amorphous structures. Here we present the superconductivity properties and crystal structure of TaNbHfZrAl and TiHfNbTaAl HEAs, which both have the VEC of 4.2 and body centered cubic (BCC) structure. Through resistivity, magnetic, and specific heat measurements, we prove that both samples are the bulk type-II superconductors with a critical temperature Tc of 5.5 K for TaNbHfZrAl and Tc of 3.2 K for TiHfNbTaAl. The Tc of HEA superconductors is influenced by the VEC and the element composition. And the incorporation of Al in high disorder HEA superconductors causes a more crystallinelike Tc dependence.

cond-mat.supr-con↗

arXiv2026

Superconductivity in the A15-type V3(Os1-2xSixGex) medium-entropy alloys

Cubic A15-type superconducting alloys continue to fascinate the academic and industrial fields because they mainly support the largest market for low-temperature superconducting applications and show exotic physical properties. Medium-/high-entropy alloys (MEAs-HEAs) can be employed stably under extreme conditions due to their high mechanical hardness and excellent irradiation tolerance. Combining with the features of the A15-type superconductor and MEAs-HEAs, we design a series of previously unreported A15-type V3(Os1-2xSixGex) (x = 0.333, 0.375, 0.425) MEA superconductors, which can be obtained by an arc melting method. Resistivity, magnetic susceptibility, and specific heat measurements indicate that all of them are type-II bulk superconductors. The superconducting transition temperature (Tc) exhibits an upward trend with the systematic reduction of Os concentration. Additionally, the upper critical field of the V3(Os0.333Si0.333Ge0.333) sample is larger than the Pauli limit, suggesting it may be robust against magnetic fields due to spin-orbit coupling induced by the heavy Os atoms. These findings not only advance our understanding of emergent phenomena in entropy-stabilized A15-type alloys but also expand the members of new superconductors.

cond-mat.supr-con↗

arXiv2026

Oxygen permeability and stability in the entropy-stabilized Co-based Perovskite oxygen permeable membranes

Oxygen transport membranes (OTMs), enabling catalytic reaction and gas separation, support crucial chemical engineering processes and decarbonization technologies, but their applications are hindered by limited oxygen permeation fluxes and inadequate long-term stability during operation. Here, a series of high-entropy perovskite OTMs based on La0.5Sr0.5CoO3 were designed and synthesized by the simple sol-gel method. The impact of varying doping ratios on the structure, surface morphology, oxygen permeability, and stability of these high-entropy OTMs was thoroughly examined. At 950 {\deg}C, the optimal composition, La0.25Sr0.25Gd0.2Nd0.2Pr0.1CoO3, achieved oxygen permeation fluxes of 1.62 mL min-1 cm-2 under air/He gradient and 1.46 mL min-1 cm-2 under air/CO2, respectively. Remarkably, all high-entropy OTMs demonstrated stable operation for over 100 h in a pure CO2 environment without a significant decline in performance. This finding paves a new way to enhance the structural and oxygen permeation stability of OTMs, and further promotes the application of OTMs in oxy-fuel combustion technologies aimed at improving CO2 capture and storage efficiency.

cond-mat.mtrl-sci↗

arXiv2025

Strongly correlated electronic superconductivity in the noncentrosymmetric Re-Os-based high/medium-entropy alloys

The class of unconventional superconductors, particularly noncentrosymmetric superconductors, has been highly considered as potential materials for understanding the complex properties of quantum materials. Here, five previously unreported Re3.5Os3.5Ta0.5Hf0.5Nb3, Re3Os3Ta0.5Hf0.5Nb3, Re3.5Os3.5Mo0.5Hf0.5Nb3, Re3.5Os3.5Mo0.5W0.5Nb3, and Re3Os3Mo0.5Hf0.5Nb3 Re-Os-based high/medium-entropy alloys (MEAs-HEAs) with valence electron count ranging from 6.45 to 6.81 were synthesized and investigated using x-ray diffraction, transport, magnetization, and specific heat measurements. Our analyses confirm that all five compounds crystallize in a noncentrosymmetric {\alpha}-Mn-type structure and exhibit type-II superconductivity with Tc values from 4.20 K to 5.11 K, respectively. Unexpectedly, despite being immersed in an acidic environment for one month, the structures and superconducting properties of HEAs remain stable. Our findings indicate that the Tc increases with an increasing valence electron count in MEAs-HEAs. Furthermore, these noncentrosymmetric {\alpha}-Mn-type HEA superconductors have large Kadowaki-Woods ratios (KWR), implying the presence of strong electronic correlations.

cond-mat.supr-con↗

arXiv2025

Strong correlation behavior and Strong coupling superconductivity in (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix with the rich magnetic element Ni

Searching for new superconductors, especially unconventional superconductors, has been studied extensively for decades but remains one of the major outstanding challenges in condensed matter physics. Medium/high-entropy alloys (MEAs-HEAs) are new fertile soils of unconventional superconductors and generate widespread interest and questions on the existence of superconductivity in highly disordered materials. Here, we report on the effect of Ni-doped on the crystal structure and superconductivity properties of strongly coupled TiHfNbTa MEA. XRD results indicate that the maximum solid solution of (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix is about 7.7%. Resistivity, magnetic susceptibility, and specific heat measurements demonstrated that (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix HEAs are all bulk type-II superconductors and follow the trend of the increase of Tc with the increase of Ni-doped contents. The specific heat jump of all (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix are much larger than the BCS value of 1.43, suggesting all these HEAs are strongly coupled superconductors. Additionally, large Kadawaki-Woods ratio values suggest that there is a strong electron correlation effect in this system. The (Ti1/4Hf1/4Nb1/4Ta1/4)1-xNix HEA system is a new ideal material platform for the study of strong correlation behavior and strongly coupled superconductivity, which provides an insight into the physics of high-temperature superconductors or other unconventional superconductors.

cond-mat.supr-con↗