Phase Boundary Mapping in ZrNiSn Half-Heusler for Enhanced Thermoelectric Performance
Xiaofang Li, Pengbo Yang, Yumei Wang, Zongwei Zhang, Dandan Qin, Wenhua Xue, Chen Chen, Yi-Fang Huang, Xiaodong Xie, Xinyu Wang, Mujin Yang, Cuiping Wang, Feng Cao, Jiehe Sui, Xingjun Liu, Qian Zhang
Abstract
The solubility range of interstitial Ni in the ZrNi <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>+</mml:mo> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> </mml:math> Sn half-Heusler phase is a controversial issue, but it has an impact on the thermoelectric properties. In this study, two isothermal section phase diagrams of the Zr-Ni-Sn ternary system at 973 K and 1173 K were experimentally constructed based on the binary phase diagrams of Zr-Ni, Zr-Sn, and Ni-Sn. The thermodynamic equilibrium phases were obtained after a long time of heating treatment on the raw alloys prepared by levitation melting. Solubilities of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>x</mml:mi> <mml:mo><</mml:mo> <mml:mn>0.07</mml:mn> </mml:math> at 973 K and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>x</mml:mi> <mml:mo><</mml:mo> <mml:mn>0.13</mml:mn> </mml:math> at 1173 K were clearly indicated. An intermediate-Heusler phase with a partly filled Ni void was observed, which is believed to be beneficial to the lowered lattice thermal conductivity. The highest <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mtext>ZT</mml:mtext> <mml:mtext> </mml:mtext> <mml:mtext>value</mml:mtext> <mml:mtext>~</mml:mtext> <mml:mn>0.71</mml:mn> </mml:math> at 973 K was obtained for ZrNi 1.11 Sn 1.04 . The phase boundary mapping provides an important instruction for the further optimization of ZrNiSn-based materials and other systems.