关键词: thermoelectromagnetic cooling, thermoelectric, magnetocaloric, composite, chromium telluride

Abstract: Materials with both large magnetocaloric response and high thermoelectric performance are of vital importance for all-solid-state thermoelectromagnetic cooling. These two properties, however, hardly coexist in single phase materials except previously reported hexagonal Cr$_{1-x}$Te half metal where a relatively high magnetic entropy change $(-\Delta S_{\rm M})$ of $\sim 2.4 $ J$\cdot $kg$^{-1}\cdot$K$^{-1}$ @ 5 T and a moderate thermoelectric figure of merit (ZT) of $\sim 1.2\times 10^{-2}$ @ 300 K are simultaneously recorded. Herein we aim to increase the thermoelectric performance of Cr$_{1-x}$Te by compositing with semiconducting Ag$_{2}$Te. It is discovered that the in-situ synthesis of Cr$_{1-x}$Te/Ag$_{2}$Te composites by reacting their constitute elements above melting temperatures is unsuccessful because of strong phase competition. Specifically, at elevated temperatures ($T > 800 $ K), Cr$_{1-x}$Te has a much lower deformation energy than Ag$_{2}$Te and tends to become more Cr-deficient by capturing Te from Ag$_{2}$Te. Therefore, Ag is insufficiently reacted and as a metal it deteriorates ZT. We then rationalize the synthesis of Cr$_{1-x}$Te/Ag$_{2}$Te composites by ex-situ mix of the pre-prepared Cr$_{1-x}$Te and Ag$_{2}$Te binary compounds followed by densification at a low sintering temperature of 573 K under a pressure of 3.5 GPa. We show that by compositing with 7 mol% Ag$_{2}$Te, the Seebeck coefficient of Cr$_{1-x}$Te is largely increased while the lattice thermal conductivity is considerably reduced, leading to 72% improvement of ZT. By comparison, $-\Delta S_{\rm M}$ is only slightly reduced by 10% in the composite. Our work demonstrates the potential of Cr$_{1-x}$Te/Ag$_{2}$Te composites for thermoelectromagnetic cooling.

Key words: thermoelectromagnetic cooling, thermoelectric, magnetocaloric, composite, chromium telluride