In order to find the next generation thermoelectric (TE) material, we are focussing on the parameter Nv, the degeneracy of the band extrema in semiconductors near the Fermi energy. We attempt to synthesize ‘multivalley’ semiconductors by incorporating tetrahedral anions to introduce structural complexity while maintaining high crystallographic symmetry.
The synthesis and crystal structures of two new compounds that partially fulfill our requirements for potential TE materials are reported. Pb3(PS4)Br3 is monoclinic, space group P21/m with a=9.1531(1)Å, b=10.9508(3)Å, c=12.7953(1)Å and β=111.024(2)°. Pb3(PS4)I1.75Te0.625 crystallizes in the space group R 3 with a=9.4876(4)Å, c=46.189(3)Å. Both structures are built from alternating layers of lead halide and the thiophosphate ion (PS4)3-.