Structural and Thermoelectric Properties of Al$_{1+x}$Fe$_{2-y}$M$_y$B$_2$ (M=Ag, Ni, Sb, Ga, and Ge) Intermetallic Borides

D. Sivaprahasam; R. Preyadarshini; Ashutosh Kumar

doi:10.1007/s00339-025-08440-y

paper

Structural and Thermoelectric Properties of Al $_{1 + x}$ Fe $_{2 - y}$ M $_{y}$ B $_{2}$ (M=Ag, Ni, Sb, Ga, and Ge) Intermetallic Borides

arXiv:2410.12314 · doi:10.1007/s00339-025-08440-y

Abstract

AlFe $_{2}$ B $_{2}$ , a ternary transition metal boride doped with Ag, Ni, Sb, Ga, and Ge was investigated for the phase constituents, microstructure, and thermoelectric properties. The parent compound with 20\% excess Al (Al $_{1.2}$ Fe $_{2}$ B $_{2}$ ) prepared by vacuum arc melting contains orthorhombic AlFe $_{2}$ B $_{2}$ and FeB upon doping form additional phases such as Ag $_{5}$ Al, AlNi $_{3}$ , Al $_{3}$ Ni $_{2}$ , AlSb, and AlB $_{2}$ . The structural parameters of the AlFe $_{2}$ B $_{2}$ phase in Ag, Ni, and Sb-doped samples are nearly the same as the un-doped one. The lattice parameters and cell volume increase noticeably in Ga and Ge-doped compounds. The Ga-doped sample shows only FeB as a secondary phase; however, the AlB $_{2}$ phase is observed in Ge-doped AlFe $_{2}$ B $_{2}$ . The microstructure investigated in FEG-SEM with EDS shows the AlFe $_{2}$ B $_{2}$ matrix is chemically homogenous in all samples, except the Ga-doped one, with uniformly distributed single or multiple secondary phases. The DSC-TG results show that all the dopants decrease the AlFe $_{2}$ B $_{2}$ phase peritectic decomposition reaction temperature, indicating the structure destabilizes. The thermoelectric properties measured show that AlFe $_{2}$ B $_{2}$ is an n-type compound with electrical conductivity in the range of 0.35-0.46 $\times$ 10 $^{6}$ S/m. The addition of Ag, Ni, Ga, and Ge marginally alters the Seebeck and electrical conductivity. The noticeable improvement in Seebeck coefficient and with negligible change in electrical conductivity resulted in a highest power factor of 0.4 mW/mK $^{2}$ for Sb-doped sample. The thermal conductivity of AlFe $_{2}$ B $_{2}$ , which is in the range of 6.4-9.1 W/m-K between 300 to 773\,K, decreases with Sb doping to 5.2-8.5 W/m-K resulting in a maximum zT of 0.04 at 773K.

11 pages, 9 images, 2 tables

Structural and Thermoelectric Properties of Al1+x​Fe2−y​My​B2​ (M=Ag, Ni, Sb, Ga, and Ge) Intermetallic Borides

Abstract

Structural and Thermoelectric Properties of Al $_{1 + x}$ Fe $_{2 - y}$ M $_{y}$ B $_{2}$ (M=Ag, Ni, Sb, Ga, and Ge) Intermetallic Borides