Thermoelectric Properties of p-and n-type Eu5Sn2As6

Eu5Sn2As6 is a Zintl phase crystalizing in the orthorhombic space group Pbam with one-dimensional chains of corner-shared SnAs4 tetrahedra running in the c-direction. Eu5Sn2As6 has an impressive room temperature Seebeck of 100 mu V/K and < - 100 mu V/K at 600 K crossing from p- to n-type at 650 K. The maximum thermoelectric figure of merit, zT, for Eu5Sn2As6 is small (0.075), comparable to that of the Zintl phase Ca5Al2Sb6 whose thermoelectric performance was improved by doping Na onto the Ca sites. In this study, we show that the thermoelectric properties of Eu5Sn2As6 can be improved by substituting with K or La. The series Eu5-xKxSn2As6 provides an increase in maximum zT of 0.22 for x-0.15 due to a decrease resistivity while the onset of bipolar conduction systematically increases in temperature. Upon La substitution, Eu5-xLaxSn2As6 results in a new n-type Zintl phase across the temperature range of 300-800 K.