Makoto Nagasako

Using a chloride-based flux, single-phase layered perovskite Gd _{2−4 x} Y _x Sm _x Tb _x Ho _x Ti ₂ O ₅ S ₂ ( x = 0.10–0.33) single crystals were grown, representing the first successful synthesis of high-entropy ceramics in the perovskite-type oxysulfide system.

In advanced applications such as aerospace and space exploration, materials must balance lightness, functionality and extreme thermal fluctuation resistance^1,2. Shape-memory alloys show promise with strength, toughness and substantial strain recovery due to superelasticity, but maintaining low mass and effective operation at cryogenic temperatures is challenging^3–6. We hereby introduce a new shape-memory alloy that adheres to these stringent criteria. Predominantly composed of Ti and Al with a chemical composition of Ti_75.25Al₂₀Cr_4.75, this alloy is characterized by a low density (4.36 × 10³ kg m^{− 3}) and a high specific strength (185 × 10³ Pa m³ per kg) at room temperature, while showing excellent superelasticity. The superelasticity, owing to a reversible stress-induced phase transformation from an ordered body-centred cubic parent phase to an ordered orthorhombic martensite, allows for a recoverable strain exceeding 7%. This functionality persists across a broad range of temperatures, from deep cryogenic 4.2 K to above room temperature, arising from an unconventional temperature dependence of transformation stresses. Below a certain threshold during cooling, the critical transformation stress inversely correlates with temperature. We interpret this behaviour from the perspective of a temperature-dependent anomalous lattice instability of the parent phase. This alloy holds potential in everyday appliances requiring flexible strain accommodation, as well as components designed for extreme environmental conditions such as deep space and liquefied gases.

The identification of internal α-alumina (α-Al2O3) scales is crucial because α-Al2O3 determines the performance of heat-resistant alloys. A non-destructive method was recently developed to rapidly identify internal α-Al2O3 scales on the Ni–Cr–Al and Ni–Al alloys by obtaining their surface cathodoluminescence (CL) spectra. However, the peak intensities at 695 nm originating from α-Al2O3 considerably deviated from those estimated from the attenuation rates of overlaid scales (Cr2O3, NiO, and NiAl2O4) and the CL peak intensity at 695 nm for the α-Al2O3 scale on the Fe–Cr–Al alloy surface. In this study, factors causing the deviations in the CL peak intensity at 695 nm for the internal α-Al2O3 scales were investigated by obtaining images of the scales and their CL spectra. The surface Cr2O3 scale on the Ni–25Cr–5Al alloy exhibited a surface the roughness of ~1 μm, causing the CL peak intensity at 695 nm to be one order of magnitude higher than the estimated value. The CL spectrum and scanning transmission electron microscopy observation revealed that θ-Al2O3 overlaid on α-Al2O3 in the internal Al2O3 scale on the Ni–14Al alloy reduced the CL peak intensity at 695 nm by two orders of magnitude.

Metamagnetic shape memory alloys (MMSMAs) are attractive functional materials owing to their unique properties such as magnetostrain, magnetoresistance, and the magnetocaloric effect caused by magnetic‐field‐induced transitions. However, the energy loss during the martensitic transformation, that is, the dissipation energy, E_dis, is sometimes large for these alloys, which limits their applications. In this paper, a new Pd₂MnGa Heusler‐type MMSMA with an extremely small E_dis and hysteresis is reported. The microstructures, crystal structures, magnetic properties, martensitic transformations, and magnetic‐field‐induced strain of aged Pd₂MnGa alloys are investigated. A martensitic transformation from L2₁ to 10M structures is seen at 127.4 K with a small thermal hysteresis of 1.3 K. The reverse martensitic transformation is induced by applying a magnetic field with a small E_dis (= 0.3 J mol⁻¹ only) and a small magnetic‐field hysteresis (= 7 kOe) at 120 K. The low values of E_dis and the hysteresis may be attributed to good lattice compatibility in the martensitic transformation. A large magnetic‐field‐induced strain of 0.26% is recorded, indicating the proposed MMSMA's potential as an actuator. The Pd₂MnGa alloy with low values of E_dis and hysteresis may enable new possibilities for high‐efficiency MMSMAs.

Temperature-stable superelasticity: Shape memory alloys are superelastic, which means that they can recover their original shape after a large amount of strain. However, in most alloys, this behavior tends to only work well for a small range of temperatures. Xia et al. identified an iron-manganese-aluminum-chromium-nickel alloy for which superelasticity is virtually temperature independent (see the Perspective by La Roca and Sade). This distinctive property is attractive for a variety of applications in which large temperature variations are normal, such as in space exploration. Science , this issue p. 855 ; see also p. 773

A Ce ³⁺ -based layered perovskite compound, Dion–Jacobson type RbCeTa ₂ O ₇ , has been discovered for the first time by introducing only a trivalent cerium ion to form [CeTa ₂ O ₇ ] ⁻ layers.

We report the martensitic transformation behavior in Co-V-Ga Heusler alloys. Thermoanalysis and thermomagnetization measurements were conducted to observe the martensitic transformation. By using a transmission electron microscope and an in situ X-ray diffractometer, martensitic transformation was found to occur from the L2₁ Heusler parent phase to the D0₂₂ martensite phase. Phase diagrams were determined for two pseudo-binary sections where martensitic transformation was detected. Magnetic properties, including the Curie temperatures and spontaneous magnetization of the parent phase, were also investigated. The magnetic properties showing behaviors different from those of NiMn-based alloys were found.