New developments in Energy Havesting: US-China collaboration on Magnetocaloric Effect Materials Joseph H. Ross Jr., Texas A&M University Main Campus, DMR Figure 1: Micrograph of Ni 43 Mn 42 Co 4 Sn 11 polycrystalline annealed ribbon. Magnetocaloric response is a function of microstructure. Figure 2: Magnetocaloric response of annealed ribbon showing large response at relatively low fields Materials exhibiting the magnetocaloric effect (MCE) have been a focus of great interest due to harmful emissions in traditional vapor compression refrigeration. Effective MCE materials exhibit magnetic transitions coupled to a crystal structure distortion. Heat transfer capabilities can be measured via the entropy change, and potentially useful materials have been discovered among rare earth compounds. Unfortunately, such materials are cost prohibitive and subject to increasing demand worldwide. On the other hand, Heusler-type can be inexpensive and have recently been demonstrated to yield MCE transitions similar to the highest values previously reported. “Microstructural Design for Enhance Efficiency in Solid State Energy Conversion”, funded by the NSF Materials World Network program, couples a US team including PI J. Ross and I. Karaman at Texas A&M University with a Shanghai team led by Jianguo Li, the latter funded by NSF-China. With Ph.D. student Nick Bruno, the US team recently demonstrated that ribbons of NiCoMnSn-based Heusler material not only produce a similar MCE compared to rare earths, but the operating temperature, refrigeration capacity, and efficiency can be optimized by modifying the microstructure and stoichiometry. Fig. 2 shows the large extracted entropy change covering a wide temperature range. In further work to optimize these materials for applications, the team of Prof. Li has performed a compositional optimization, identifying a NiMnIn- based composition with potentially improved properties. Additional magnetic measurements are now underway in the US labs. In terms of elasto-caloric effect (ECE), US student Bruno has studied the effect of crystallographic orientation on the ECE in NiFeGa single crystalline shape memory alloys. He has demonstrated that the orientation with the highest change in critical stress for martensitic transformation with the change in temperature (dsigma/dT) demonstrates the highest ECE effect. However, transformation hysteresis should also be taken into account to evaluate the conversion efficiency.

The “Microstructural Design for Enhance Efficiency in Solid State Energy Conversion” project includes educational and cultural, as well as research, exchanges between Texas A&M University (TAMU) and Shanghai Jiaotong University (SJTU). Currently 3 Ph.D. students at TAMU, and 2 students at SJTU, are working directly on this collaborative project, as part of larger research teams at both institutions. A planning meeting and joint seminar took place in Shanghai in August Prof. Li will visit TAMU laboratories in December 2012, and TAMU students will visit SJTU laboratories starting in May 2013, to learn advanced fabrication techniques at the Shanghai facility. This allows students to learn techniques not available in the counterpart laboratories, while also conveying improved cross-cultural and interdisciplinary understanding. Team members have also participated in a number of activities to encourage interest in materials science among younger students. Among these, in April project students Nick Bruno and James Monroe along with PI J. Ross assembled a display of shape memory alloy thermal effects and applications at the Physics and Engineering Fair at TAMU, attended by thousands of children, families, and future students. Broader Impacts of US-China collaboration on Magnetocaloric Effect Materials Joseph H. Ross Jr., Texas A&M University Main Campus, DMR Collaboration team members at joint seminar in Shanghai: Ph.D. student Huang, Prof. Li (SJTU), Prof. Karaman and Prof. Ross (TAMU), with additional Ph.D. student Chen from Li’s group (SJTU). Physics and Engineering Festival and practical demonstration of Shape Memory Alloy applications for students and parents.