Abstract
A layered Zintl antimonide NaZnSb (PbClF or Cu2Sb structure type; P4/nmm) was synthesized using the reactive sodium hydride NaH precursor. This method provides comprehensive compositional control and facilitates the fast preparation of high-purity samples in large quantities. NaZnSb is highly reactive to humidity/air and hydrolyzes to NaOH, ZnO, and Sb in aerobic conditions. On the other hand, NaZnSb is thermally stable up to 873 K in vacuum, as no structural changes were observed from high-temperature synchrotron powder X-ray diffraction data in the 300–873 K temperature range. The unit cell expansion upon heating is isotropic; however, interatomic distance elongation is not isotropic, consistent with the layered structure. Low- and high-temperature thermoelectric properties were measured on pellets densified by spark plasma sintering. The resistivity of NaZnSb ranges from 11 mΩ∙cm to 31 mΩ∙cm within the 2–676 K range, consistent with heavily doped semiconductor behavior, with a narrow band gap of 0.23 eV. NaZnSb has a large positive Seebeck coefficient (244 μV∙K−1 at 476 K), leading to the maximum of zT of 0.23 at 675 K. The measured thermoelectric properties are in good agreement with those predicted by theoretical calculations.
Highlights
IntroductionClassical Zintl compounds consist of cationic entities (electropositive alkali or alkali earth metals) and anionic fragments composed of p-elements from Group 13 to 16
Zintl phases represent a special class of intermetallic compounds [1,2]
The structure is composed of three crystallographic positions, NaZnSb was first the reported by Schuster et al.Zn back in and
Summary
Classical Zintl compounds consist of cationic entities (electropositive alkali or alkali earth metals) and anionic fragments composed of p-elements from Group 13 to 16. The p-elements within the anionic fragments satisfy an octet through formation of covalent bonds and lone pair localization. Such bonding patterns often lead to complex structures and electron-balanced compositions. Zintl antimonides [4] stand out as a promising class of thermoelectric materials, often exhibiting low thermal conductivities and amenability for doping. Several other Zintl antimonides exhibit good thermoelectric performance at high temperatures: Ca9 Zn4+x Sb9 , EuZn2 Sb2 , Yb9 Mn4.2 Sb9 , YbCd2 Sb2 , and AeZn2 Sb2
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