Rational design and synthesis of Cr1–xTe/Ag₂Te composites for solid-state thermoelectromagnetic cooling near room temperature

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 (−Δ S M ) of ∼2.4 J⋅kg −1 ⋅K −1 @ 5 T and a moderate thermoelectric figure of merit ( ZT ) of ∼1.2 × 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, −Δ S 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.