Ag-Mg antisite defect induced high thermoelectric performance of α-MgAgSb

Abstract

Engineering atomic-scale native point defects has become an attractive strategy to improve the performance of thermoelectric materials. Here, we theoretically predict that Ag-Mg antisite defects as shallow acceptors can be more stable than other intrinsic defects under Mg-poor‒Ag/Sb-rich conditions. Under more Mg-rich conditions, Ag vacancy dominates the intrinsic defects. The p-type conduction behavior of experimentally synthesized α-MgAgSb mainly comes from Ag vacancies and Ag antisites (Ag on Mg sites), which act as shallow acceptors. Ag-Mg antisite defects significantly increase the thermoelectric performance of α-MgAgSb by increasing the number of band valleys near the Fermi level. For Li-doped α-MgAgSb, under more Mg-rich conditions, Li will substitute on Ag sites rather than on Mg sites and may achieve high thermoelectric performance. A secondary valence band is revealed in α-MgAgSb with 14 conducting carrier pockets.

Hf/Sb co-doping induced a high thermoelectric performance of ZrNiSn: First-principles calculation

“…Thermoelectric (TE) materials can perform directly converting waste heat into electricity using in all-solid-state by a temperature difference to induce carriers to flow in a semiconductor, which are helpful to resolving today’s energy crisis 2–4 . Although the TE devices are very reliable and compact, the relatively low efficiency limits their widespread applications.…”

Establishing synthesis–composition–property relationships for enhanced and reproducible thermoelectric properties of MgAgSb

“…As no external dopant was used to adjust the carrier concentration, observed changes of the matrix properties must be related to the intrinsic point defects. If, for simplicity, one assumes that all changes in charge carrier concentration are related to a change in Ag and Sb content (p of MgAgsb is mostly affected by point defects being Ag vacancy (V Ag ), Ag on Mg site (Ag Mg ) in the case of Mg-poor stoichiometry and Sb vacancy (V Sb ) for MgAgSb [36][37][38] ), then one can translate changes in p into changes in the Ag and Sb content and obtain a lower estimate of the size of the single-phase region. Here, a simplied defect chemistry model is used considering only V Sb (produces one electron), V Ag and Ag Mg (each of both produces one hole).…”

“…Indeed, excess of Mg is contributing to the formation of vacancies V Ag . 36,38 For one formula unit of MgAg 1Àx Sb 1Ày , the number of electrons is then given by y and the number of holes by x. a-MgAgSb has a tetragonal crystal structure (a ¼ b s c) with 48 atoms in the lattice, such as Mg 16 Ag (4a,4b,8e) Sb 16 which means that there are 16 formula units per unit cell. 39 We measure the charge carrier concentration as the hole density minus electron density (in a p-type material) which can be rearranged to p ¼ 16ðx À yÞ V , normalized by the unit cell volume.…”

“…[32][33][34][35] For MgAgSb, the main phase properties are likewise governed by intrinsic defects, e.g. Ag vacancies, Ag antisite defects on Mg sites, Sb vacancies [36][37][38] whose concentrations are linked to minimal changes in the composition. With respect to secondary phases the particular challenge for MgAgSb is rst that several of the commonly found secondary phases (such as Ag 3 Sb, Sb or Mg 3 Sb 2 ) possess a high thermal stability and second that during the processing high temperature steps (>360 C) are to be avoided as these would lead to the formation of the metallic g-MgAgSb which shows high thermal stability below 300 C. 39 While the detrimental effect of various secondary phases has been highlighted repeatedly, neither how they can be avoided nor how they impact the TE performance of MgAgSb has been addressed satisfyingly.…”

Metabolic Analysis Reveals Cry1C Gene Transformation Does Not Affect the Sensitivity of Rice to Rice Dwarf Virus

“…The Chinese government has issued the biosafety certificates of two Cry1Ab/Ac rice lines (Huahui1 and Bt -Shanyou 63) [ 5 ]. To date, assessments of Bt rice on non-target organisms and the environment have been conducted thoroughly, and negligible adverse effects have been found [ 4 , 5 , 6 , 7 , 8 , 9 ]. However, Bt rice is not yet commercially produced largely due to the lack of public acceptance.…”