Research On Phase Diagram And Thermoelectric Properites Of ZrNiSn Based Materials

Thermoelectric materials are considered as one of the promising candidates for renewable applications,which could convert the heat energy to the electricity.The ZrNiSn alloy,as a kind of half-Heusler thermoelectric materials,is favored by the scientific community for its good thermal stability,mechanical properties,and high temperature applications to the industrial waste heat.The excellent band structure and crystal structure indicate the high thermoelectric performance.The reported components for ZrNiSn are fixed to be 1:1:1.There is no clear description the range of single-phase solid solubility.In this research,the isothermal phase diagram was used to study whether there is a continuous solid solution and the solid solubility range of single-phase ZrNiSn.Based on this,the composition of the thermoelectric material was designed and the thermoelectric properties were studied.The isothermal sections phase diagram of the ZrNiSn alloy at 973 K and 1173 K were experimentally determined in the present work by alloy method,respectively.9 single-phase regions,4 two-phase regions and 6 three-phase region were found in1173 K isothermal section and the solid solubility of Ni in one-phase region is1.09¹.130?at.%?.9 single-phase regions,4 two-phase regions and 5 three-phase region were found in 973 K isothermal section phase diagram and the solid solubility of Ni in one-phase region is 0.98-1.07?at.%?.It is shown that ZrNiSn has a continuous solid solubility at both temperatures,and the solid solubility of Ni atoms in the continuous solid solution at 1173 K deviates from the fixed ratio solid solubility of Ni atoms to a large extent.It was found that the continuous solid solubility of the ZrNiSn one-phase region does exist at both temperatures.Compared to the stoichiometric ZrNiSn alloy,the designed alloy Ni_1.09Sn_1.04Zr has lower thermal conductivity and higher electric conductivity.The highest ZT value of Ni_1.09Sn_1.04Zr alloy is 8%higher than that of the stoichiometric ZrNiSn alloy.Another designed Ni_1.07Sn_1.10Zr alloy has better electrical conductivity and Seebeck coefficient compared to the stoichiometric ZrNiSn alloy.Its room-temperature electrical conductivity is 1.22×10⁵ S·m^-1 and the value of the Seebeck coefficient goes up first and then turns down reaching a maximum value-210?V·K^-1 at 723 K,and the highest ZT value reached 0.63.Sb doping adjusts the carrier concentration.After doping with Sb,the electrical conductivity and power factor of the materials are improved,and the Seebeck coefficient is decreased.The Ni_1.09Sn_1.04Zr alloy with the best thermoelectric performance has a large improvement in electrical conductivity and the power factor after doping with Sb.Its room temperature electrical conductivity is 2.9×10⁵ S·m^-1,and the power factor reaches 50?W·cm^-1·K^-2 at 773 K from 16?W·cm^-1·K^-2 of the matrix phase.