Thermoelectric properties of ternary Zintl-phase XAgP (X= Sr, Ag) compounds

Rising need for inexhaustible energy sources has been a pressing factor for seeking effective thermoelectric (TE) materials. In this work, we examine the ABC-type compounds resulting from the combination of elements belonging to groups 2, 11, and 15 of the periodic table. Since semiconductors are usually good TE materials, we investigated the band structure of these compounds for existence of a band gap. Thus, we shortlisted two ternary Zintl compounds XAgP (X= Sr and Ba), which crystallize in the hexagonal structure with space group P6₃/mmc, and investigated these thoroughly. The TE performance was studied within the Boltzmann transport theory. At room temperature, SrAgP exhibits (mainly due to a large phonon group-velocity) slightly higher lattice thermal conductivity than for BaAgP. However, balanced values of other transport coefficients for SrAgP help raise its power factor and

thermoelectric figure-of-merit (ZT) far beyond those for BaAgP. In particular, we show that the room-temperature ZT value of p-type SrAgP is 1.5 times larger than for BaAgP. Hence, these Zintl compounds, with low thermal conductivity and significantly large transport coefficients, open new pathways in search of energy-efficient TE materials.