Comparison of the energy loss of the current Pd-based alloy against previous alloys.
Newswise — Shape memory alloys (SMA) retain their initial form and revert to it upon heating. Analogous to the transition of a liquid into a vapor through boiling, SMAs undergo a phase change when exposed to heat or cold. This phase alteration involves atomic motion, imperceptible to the unaided eye.
Shape memory alloys (SMAs) find utility in a wide range of uses, such as actuators and sensors. Nonetheless, the requirement to thermally manipulate SMAs causes a temporal lag in their phase transition.
A newly developed variant of SMA, known as metamagnetic shape memory alloys (MMSMAs), circumvent this inherent constraint by leveraging their capacity to undergo phase transition upon exposure to an external magnetic field. However, MMSMAs have thus far been unsuccessful in addressing another prevalent issue encountered by conventional SMAs—the significant energy loss during phase transformation, which exacerbates notably under low-temperature conditions.
A notable breakthrough has been achieved by a research team at Tohoku University, who successfully developed a palladium-based (Pd) metamagnetic shape memory alloy (MMSMA) that showcases remarkable mitigation of energy loss. This advancement is particularly pronounced at low temperatures, with the energy loss reduced to a mere 1/100th when compared to existing MMSMAs, even at approximately 100 K.
Xiao Xu, the corresponding author of the paper and assistant professor at Tohoku University's Graduate School of Engineering, expressed their astonishment at the minimal energy loss observed in their newly developed Pd-based alloy. Consequently, their study aimed to address two key inquiries: Firstly, how does the energy loss behave when the temperature decreases even further, such as at the extremely low temperature of liquid helium (4.2 K)? And secondly, why did their material demonstrate such a significant reduction in energy loss?
In order to investigate these questions, Xiao Xu and the team at Tohoku University's Institute for Materials Research (IMR) collaborated with researchers from the University of Tokyo's Institute for Solid State Physics (ISSP). They commenced their research by conducting magnetization measurements using pulsed high magnetic fields at the ultra-low temperature of liquid helium. The results indicated that, similar to conventional shape memory alloys (SMAs), the newly developed Pd-based SMA exhibited an escalation in energy loss as the temperature decreased. However, even under these conditions, the energy loss remained considerably smaller compared to existing SMAs.
Further investigations were conducted by the research group, including X-ray diffraction measurements carried out at low temperatures and under the influence of strong magnetic fields. These measurements unveiled a crucial finding: the newly developed Pd-based alloy exhibited superior lattice compatibility for phase transformation. This means that the crystals within the alloy's structure could undergo changes more easily, providing an explanation for its reduced energy loss when compared to existing SMAs. The improved lattice compatibility accounted for the alloy's enhanced performance in mitigating energy loss.
"We are equally amazed by the substantial magnetostriction exhibited by our Pd-based alloy, akin to that of rare-earth materials under chilly conditions. This advancement holds extensive advantages for fostering a sustainable tomorrow," Xu remarks. "Hydrogen energy is gaining notable prominence as an eco-friendly power reservoir. As hydrogen transportation frequently entails conversion to liquefied helium, the demand for low-temperature-compatible technology is on the rise. Our Pd-based alloy operates with minimal energy dissipation even at low temperatures and holds potential for implementation as magnetic sensors and actuators."
Details of the group’s research were published in the journal Advanced Science on June 13, 2023.
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