New sustainable ternary copper phosphide thermoelectrics

Abstract

The thermoelectric performance of ACuP (A = Mg and Ca) with abundant elements and low gravimetric density is reported. Both systems are p-type doped by intrinsic Cu vacancy defects, have...

Recent progress in phosphide materials for thermoelectric conversion

“…Following on from CaAgP, we reported the thermoelectric properties of MgCuP and CaCuP, based on sustainable elements and with low gravimetric densities. 50 These compositions each have different crystal structures (shown in Fig. 8c-d) and are different from CaAgP, again highlighting the structural diversity of the phosphides.…”

“…A notable exception is CaCuP with S 2 σ = 1.75 mW.m -1 .K -2 , possibly linked to its simple crystal structure. 50 Low values are found for Zn 0.75 Cu 2 P 8 , 59,63 rich in P-P bonds and the clathrate Ba 8 Cu 14 Ge 6 P 26 , 57 which are both limited to S 2 σ < 0.4-0.6 mW.m -1 .K -2 . In all cases, the reported S 2 σ are much smaller than state-of-theart materials, that typically achieve power factors >4 mW.m -1 .K -2 and up to 10 mW m -1 K -2 for some low-defect half-Heusler phases.…”

“…Notable exceptions are the high zT phase Cd 3 P 2 and the topological material TaP. [53][54][55][56] MgCuP, 50 YbCuZnP 2 , 47 CaAg0 .9 P, 60 EuIn 2 PAs, 61 ErCuZnP 2 . 49 ).…”

“…55 The best performance amongst the larger group of p-type materials is zT ~ 0.7 at 750 K for the tetrahedrite Ag 6 Ge 10 P 12 , benefitting from several optimisation studies 58,69 since the original report in 2017. 48 Clathrates based on Ba 8 Cu 16 P 30 have been reported with zT ~ 0.6 at 800 K. 57,76 The A(CuZn)P 2 122-phases reach zT = 0.6 at 800-1000 K, 47,49 whilst 111 phases, including CaCuP reach zT = 0.5 at 800 K. 50…”

“…46 However, red phosphorus, effectively consisting of (P 4 ) n oligomers, has much better stability and is commonly used for synthesis. 46 Once formed, metal phosphides can exhibit excellent stability, [47][48][49][50] in particular if more electropositive alkali and alkaline earth elements are avoided. This review will start with an overview of the reported thermoelectric properties from the recent literature, and it will discuss some of the underlying electronic and thermal parameters.…”