31 research outputs found
Absence of Tc-Pinning Phenomenon Under High Pressure in High-Entropy REO0.5F0.5BiS2 Layered Superconductor
Recently, robustness of superconductivity (transition temperature, Tc) under
high pressures has been observed in high-entropy alloy (HEA), bcc-type
Ti-Zr-Hf-Nb-Ta, and HEA-type compounds (Ag,In,Sn,Pb,Bi)Te with a NaCl-type
structure. Since those materials have three-dimensional crystal structure,
investigation on the pressure dependence of Tc of low-dimensional materials is
needed to understand the phenomena. Here, we investigated the superconducting
properties and the crystal structure of BiS2-based layered system
REO0.5F0.5BiS2. Although the robustness of Tc was induced in MTe with
increasing M-site configurational entropy, the increase in RE-site
configurational entropy does not induce robustness of Tc under high pressures
in REO0.5F0.5BiS2. The crystal structure of HEA-type REO0.5F0.5BiS2 was
confirmed as monoclinic P21/m, which is the same space group as the
zero-entropy counterpart LaO0.5F0.5BiS2. The results suggest that an increase
in configurational entropy at blocking layers do not affect crystal structure
and superconducting properties under high pressures in the BiS2-based layered
system.Comment: 9 pages, 4 figure
Lattice Anharmonicity in BiS2-Based Layered Superconductor RE(O,F)BiS2 (RE = La, Ce, Pr, Nd)
We studied Gr\"uneisen parameter ({\gamma}G) to investigate lattice
anharmonicity in a layered BiS2-based superconductor system REO1-xFxBiS2 (RE =
La, Ce, Pr, Nd), where in-plane chemical pressure was tuned by substituting the
RE elements. With increasing in-plane chemical pressure, bulk modulus
remarkably increases, and a high {\gamma}G is observed for RE = Nd. The
dependence of {\gamma}G on in-plane chemical pressure exhibits a good
correlation with Tc, and a higher Tc is achieved when {\gamma}G is large for RE
= Nd. In addition, {\gamma}G shows a slight decrease by a decrease of F
concentration (x) in REO1-xFxBiS2. Our results show that the anharmonic
vibration of Bi along the c-axis is present in REO1-xFxBiS2, and the
enhancement of the anharmonicity is positively linked to superconducting Tc and
pairing mechanisms.Comment: 15 pages, 5 figure
Stability and Metastability of Li3YCl6 and Li3HoCl6
[EN] Metastable solid electrolytes exhibit superior conductivity compared to stable ones, making them a subject of considerable interest. However, synthesis of the metastable phase is affected by multiple thermodynamic and kinetic parameters, leading to ambiguity in the organization of stability and metastability. In this study, we organized remnant and intermediate metastability based on temperature. The intermediate metastable phase, which is less stable than the temperature-independent stable phase, typically transforms into the stable phase(s) at high temperatures. In contrast, the remnant metastable phase is formed by first obtaining most stable phase at specific temperatures and then “trapping” it by rapidly changing the temperature. By investigating Li+ conducting chlorides, Li3MCl6 (M = Y and Ho), we demonstrated that heating starting materials to approximately 600 K produced low-temperature Li3MCl6 phase with one formula unit while further heating resulted in high-temperature Li3MCl6 phase with three formula units. Annealing quenched Li3MCl6 at 573 K resulted in a phase transition from the high-temperature to low-temperature phase, indicating that the high-temperature phase was remnant metastable at low temperatures.This research was partially supported by KAKENHI (Grant No. JP20KK0124), JST PRESTO (Grant Nos. JPMJPR21Q2 and JPMJPR21Q8), and Grant-in-Aid for JSPS Fellows (21J11152).N
放射光X線回折によるバリウムアルミネートとカルシウムストロンチウムサルホアルミネートの結晶構造と相転移に関する研究
内容の要約広島大学(Hiroshima University)博士(理学)Doctor of Sciencedoctora