Formation of ordered nano-wire microstructures in thermoelectric Pb-Ag-Sb-Te

Regular arrays of nano-wire microstructures containing Ag2Te rods with diameter <400 nm and inter-rod distance <1 μm are formed in a matrix of AgSbTe2 + δ-Sb2Te, which makes an ordered nano-wire composite thermoelectric material. This microstructure is formed during eutectic solidification processing. To understand and guide production of uniform bulk samples of this composite, the liquidus projection of quaternary Pb-Ag-Sb-Te system at 36.0 at.% Te isoplethal section is constructed experimentally, using quenched samples. A three-phase univariant reaction of the quaternary Pb-Ag-Sb-Te system, L → AgSbTe2 + Ag2Te + δ-Sb2Te, is investigated, between a ternary-eutectic melt (Ag-40.0 at.% Sb-36.0 at.% Te) and a quaternary melt (Pb-22.0 at.% Ag-40.0 at.% Sb-36.0 at.% Te), at 496.1 °C and 503.9 °C, respectively. High-resolution transmission electron microscopy confirms that these three phases are simultaneously present at the nanometer scale. Furthermore, unidirectional solidification experiments of the ternary eutectic alloy using the Bridgman method are carried out to examine the alloy's solidification behavior.