Abstract:
Half Heusler(hH) compounds have demonstrated exceptional capability in a wide range of functional ap plications as semiconductors. Although there are theoretical predictions about newer compounds and their
thermodynamic stability, experimental validation is often missing. In this study, we report two quaternary
multicomponent Zr-based hH alloy systems, namely ZrNi0.5Fe0.5Sb and ZrNiIn0.5Sb0.5, designed by com bining 19 and 17 VEC (valence electron count) alloy systems. The structural features, including the crystal
structures and compositions, were established using multiple techniques like X-ray diffraction, scanning
and transmission electron microscopy. Both these systems crystallized in signature hH cubic structure
(F4
3
m) having lattice parameters 0.6091 nm and 0.6104 nm, respectively. The measurement of Seebeck
coefficients over a wide temperature range showed p-to n-type semiconductor transition in ZrNi0.5Fe0.5Sb at
around 888 K due to bipolar conduction. Subsequently, the partial substitution of Co for Fe sites
(ZnNi0.5Fe0.3Co0.2Sb) completely suppressed the bipolar conductivity, making it a n-type semiconductor and
increased the absolute value of Seebeck coefficient, by an order of magnitude, to − 133μV/K. The alloy
ZrNiIn0.5Sb0.5 showed n-type semiconductor behavior throughout the measurement temperature range.
This study conducts an in-depth examination of the microstructural phase evolution, chemical environment
of the elements forming the novel hH phase and demonstrates the tunability of electronic properties
through aliovalent substitutions at various lattice sites.
