Search

Magnetic refrigeration materials containing rare-earth ions are promising for hydrogen liquefaction and energy storage applications. Here, the role of crystal-field level splitting on magnetic entropy change is systematically investigated, comparing mean-field calculations with neutron scattering experiments in HoB2.

Stimulated by a recent report of a giant magnetocaloric effect in HoB2 found via machine-learning predictions, we have explored the magnetocaloric properties of a related compound ErB2 that has remained the last ferromagnetic material among the rare-earth diboride (REB2) family with unreported magnetic entropy change $|{\rm \Delta} {S_M}|$. The evaluated $|{\rm \Delta} {S_M}|$ at field change of 5 T in ErB2 turned out to be as high as 26.1 J kg−1 K−1 around the ferromagnetic transition (${T_C}$) of 14 K. In this series, HoB2 is found to be the material with the largest $|{\rm \Delta} {S_M}|$ as the model predicted, while the predicted values showed a deviation with a systematic error compared to the experimental values. Through a coalition analysis using SHAP, we explore how this rare-earth dependence and the deviation in the prediction are deduced in the model. We further discuss how SHAP analysis can be useful in clarifying favorable combinations of constituent atoms through the machine-learned model with compositional descriptors. This analysis helps us to perform materials design with aid of machine learning of materials data.

Recently, a massive magnetocaloric effect near the liquefaction temperature of hydrogen has been reported in the ferromagnetic material HoB2. Here we investigate the effects of Dy substitution in the magnetocaloric properties of Ho1-xDyxB2 alloys (x = 0, 0.3, 0.5, 0.7, 1.0). We find that the Curie temperature (TC) gradually increases upon Dy substitution, while the magnitude of the magnetic entropy change |ΔSM| and adiabatic temperature change ΔTad showed a gradual decrease. On the other hand, due to the presence of successive transitions in these alloys, the peak height of the above magnetocaloric properties tends to be kept in a wide temperature range, leading to a relatively robust figure of merit in a wide temperature span. These alloys could be interesting candidates for magnetic refrigeration in the temperature range of 10–60 K.

Candidate compounds for new thermoelectric and superconducting materials, which have narrow band gap and flat bands near band edges, were exhaustively searched by the high-throughput first-principles calculation from an inorganic materials database named AtomWork. We focused on PbBi2Te4 which has the similar electronic band structure and the same crystal structure with those of a pressure-induced superconductor SnBi2Se4 explored by the same data-driven approach. The PbBi2Te4 was successfully synthesized as single crystals using a melt and slow cooling method. The core level X-ray photoelectron spectroscopy analysis revealed Pb2+, Bi3+ and Te2- valence states in PbBi2Te4. The thermoelectric properties of the PbBi2Te4 sample were measured at ambient pressure and the electrical resistance was also evaluated under high pressure using a diamond anvil cell with boron-doped diamond electrodes. The resistance decreased with increasing of the pressure, and pressure-induced superconducting transitions were discovered at 2.5 K under 10 GPa. The maximum superconducting transition temperature increased up to 8.4 K at 21.7 GPa. The data-driven approach shows promising power to accelerate the discovery of new thermoelectric and superconducting materials.

We have developed the rapid growth method for HgBa _2 Ca _2 Cu _3 O _8+ _δ (Hg-1223) by using a sealed quartz tube technique with a small amount of cesium chloride (CsCl). Our results suggested that a small amount of CsCl works as a flux during the crystal growth of Hg-1223. The developed method achieved the growth of the Hg-1223 single crystal pieces in 4 h. Furthermore, the grown single crystals showed high purity. The developed method is useful for application purposes such as high transition-temperature ( T _c ) superconducting cable.

We synthesized superconducting fullerene nanowhiskers (C60NWs) by potassium (K) intercalation. They showed large superconducting volume fractions, as high as 80%. The superconducting transition temperature at 17 K was independent of the K content (x) in the range between 1.6 and 6.0 in K-doped C60 nanowhiskers (KxC60NWs), while the superconducting volume fractions changed with x. The highest shielding fraction of a full shielding volume was observed in the material of K3.3C60NW by heating at 200 °C. On the other hand, that of a K-doped fullerene (K-C60) crystal was less than 1%. We report the superconducting behaviors of our newly synthesized KxC60NWs in comparison to those of KxC60 crystals, which show superconductivity at 19 K in K3C60. The lattice structures are also discussed, based on the x-ray diffraction (XRD) analyses.

This study focused on operational procedure of water allocation across a public irrigation system in Indonesia. The objective is at achieving goals of water distribution in the attempt to gain both equity and efficiency. Methodology of this study is conducted through a series observation on the field that have implemented Pasten, Faktor-K, Faktor Palawija Relative (FPR) and Golongan methods as the step of water allocation procedures. Results of the study showed that these methods were carried out harmonically amongst the irrigated area according to the characteristic of its land and availability of water. There are no overlapping or varying of the methods using in each block. However, it was found some violations of operational rules due to lack of irrigation inspectors, malfunction of measurement structure, miss in assessing areas by crop type and planting date, and many tertiary blocks across more than one village.

We follow the evolution of the electronic properties of the titled homologous series when n as well as the atomic type of A and M are varied where for n = 1, A = Ca, Sr and M = Rh, Ir while for n = 3, A = Ca, Sr and M = Rh. The crystal structure of n = 1 members is known to be CaRh2B2-type (Fddd), while that of n = 3 is Ca3Rh8B6-type (Fmmm); the latter can be visualized as a stacking of structural fragments from AM3B2 (P6/mmm) and AM2B2. The metallic properties of the n = 1 and 3 members are distinctly different: on the one hand, the n = 1 members are characterized by a linear coefficient of the electronic specific heat γ ≈ 3 mJ mol−1 K−2, a Debye temperature θD ≈ 300 K, a normal conductivity down to 2 K and a relatively strong linear magnetoresistivity for fields up to 150 kOe. The n = 3 family, on the other hand, exhibits γ ≈ 18 mJ mol−1 K−2, θD ≈ 330 K, a weak linear magnetoresistivity and an onset of superconductivity (for Ca3Rh8B6, Tc = 4.0 K and Hc2 = 14.5 kOe, while for Sr3Rh8 B6, Tc = 3.4 K and Hc2 ≈ 4.0 kOe). These remarkable differences are consistent with the findings of the electronic band structures and density of state (DOS) calculations. In particular, satisfactory agreement between the measured and calculated γ was obtained. Furthermore, the Fermi level, EF, of Ca3Rh8B6 lies at almost the top of a pronounced local DOS peak, while that of CaRh2B2 lies at a local valley: this is the main reason behind the differences between the, e.g., superconducting properties. Finally, although all atoms contribute to the DOS at EF, the contribution of the Rh atoms is the strongest.