Low-Temperature Structural Transitions in the Phonon-Glass Thermoelectric Material β-Zn₄Sb₃:  Ordering of Zn Interstitials and Defects

Abstract

The low-temperature phase transitions of thermoelectric Zn 4 Sb 3 have been characterized using singlecrystal X-ray diffraction, electrical resistance, and thermal conductivity measurements. Room-temperature stable, disordered β-Zn 4 Sb 3 undergoes a phase transition at 254 K to ordered R-Zn 4 Sb 3 , which has an ideal composition Zn 13 Sb 10 . Below 235 K, a second low-temperature phase (R′-Zn 4 Sb 3 ) can be detected. The sequence of phase transitions β-R-R′ is reversible. The R-R′ transformation originates from a slight Zn deficiency with respect to Zn 13 Sb 10 . The actual composition of Zn 4 Sb 3 is Zn 13-δ Sb 10 .

Entropic stabilization and retrograde solubility in Zn4Sb3

“…Yet Zn 4 Sb 3 is observed below 700K. Furthermore, at low temperature, a reversible transition to a low symmetry, meta-stable, ordered 'α' (and α ) phase is observed 8,9 . Synthetically, Zn 4 Sb 3 is usually prepared with excess Zn: Zn 13.3 Sb 10 .…”

Cd13−xInySb10 (x≈2.7, y≈1.5): An Interstitial‐Free Variant of Thermoelectric β‐Zn4Sb3

“…[9,24] The ideal crystallographic composition of both a-phases is M 13 Sb 10 ; however, a-Zn 4 Sb 3 is known to be Zn deficient (Zn 13Àd Sb 10 ). [25] The reversible a-b order-disorder transition occurs at 254 and 373 K for Zn 4 Sb 3 and Cd 4 Sb 3 , respectively, and can be monitored in single-crystal diffraction experiments. [9,15,24] With respect to the crystallographic composition of aCd 4 [23] Only by modeling the high-temperature b-phase structure with five extra, partially occupied Cd positions of interstitials can the R values and residual densities be brought down to the same level as for Cd 13Àx In y Sb 10 .…”

“…The phenomenon of low thermal conductivity is usually attributed to the presence of interstitial M atoms and vacancies in the b-phases, [5,6] and the formation of complex, large unit cell structures in the ordered aphases. [9,25] How do the properties of interstitial-free Cd 13Àx In y Sb 10 compare to those of Cd 4 Sb 3 ?…”

Predicted Electronic and Thermodynamic Properties of a Newly Discovered Zn8Sb7 Phase

“…Atomic positions were allowed to relax to a local minimum and were verified to not have settled into identical configurations. While this method is by no means exhaustive in gauging the configurational disorder in Zn 8 Sb 7 , it does provide a basis for making certain assumptions, to follow in the Results and Discussion.…”

“…Thus, Zn 8 Sb 7 would be slightly favored over ZnSb and Zn 4 Sb 3 . At the pressure required to adjust the calculated Zn 8 Sb 7 lattice parameter to the experimental value (À3.4 GPa), the energy correction is 3 meV/atom in favor of Zn 8 Sb 7 . We suggest that through some combination of surface energy and lattice strain, Zn 8 …”