posted on 2024-03-04, 05:43authored byXin Liu, Shaoqin Wang, Yi Chang, Jiutian Liao, Zirui Dong, Jiye Zhang, Xinyue Zhang, Jun Luo
In comparison with intensively investigated traditional
ternary
half-Heusler compounds, quaternary half-Heusler alloys exhibit inherently
lower lattice thermal conductivities due to their complex crystal
structures. In this work, based on the Slater–Pauling rule,
we successfully design and synthesize single-phase Mg1–xTixNiSb (x = 0.3–0.7) alloys by adjusting the ratio of nominal MgNiSb
and TiNiSb components with, respectively, 17 and 19 valence electrons,
which avoids the use of the costly ScNiSb half-Heusler compound and
provides an economically efficient approach to improve thermoelectric
performance. Due to the strong disorder effect at the Mg/Ti site in
the Mg0.5Ti0.5NiSb sample, the lattice thermal
conductivity of Mg0.5Ti0.5NiSb is significantly
reduced, reaching ∼2.6 W m–1 K–1 at 300 K. By tuning the Mg/Ti ratio, both p-type and n-type Mg1–xTixNiSb
alloys are obtained. The p-type Mg0.55Ti0.45NiSb and n-type Mg0.35Ti0.65NiSb achieve dimensionless
thermoelectric figure of merits zTs of 0.36 at 973
K and 0.40 at 873 K, respectively. Moreover, the electrical and thermal
transport properties of these samples can be further optimized by
doping Cu or Co to reduce the carrier concentration. As a result,
cost-effective and Hf-free p-type Mg0.55Ti0.45Ni0.95Cu0.05Sb and n-type Mg0.35Ti0.65Ni0.95Co0.05Sb with, respectively, zT values of 0.48 at 873 K and 0.52 at 773 K are achieved,
demonstrating the promising potential of developed half-Heusler alloys
with low cost.