Synthesis, Crystal and Electronic Structures of New Narrow-Band-Gap Semiconducting Antimonide Oxides RE₃SbO₃and RE₈Sb_3−δO₈, with RE = La, Sm, Gd, and Ho

Abstract

In the search for high-temperature thermoelectric materials, two families of novel, narrow-band-gap semiconducting antimonide oxides with the compositions RE(3)SbO(3) and RE(8)Sb(3-delta)O(8) (RE = La, Sm, Gd, Ho) have been discovered. Their synthesis was motivated by attempts to open a band gap in the semimetallic RESb binaries through a chemical fusion of RESb and corresponding insulating RE(2)O(3). Temperatures of 1350 degrees C or higher are required to obtain these phases. Both RE(3)SbO(3) and RE(8)Sb(3-delta)O(8) adopt new monoclinic structures with the C2/m space group and feature similar REO frameworks composed of "RE(4)O" tetrahedral units. In both structures, the Sb atoms occupy the empty channels within the REO sublattice. High-purity bulk Sm and Ho samples were prepared and subjected to electrical resistivity measurements. Both the RE(3)SbO(3) and RE(8)Sb(3-delta)O(8) (RE = Sm, Ho) phases exhibit a semiconductor-type electrical behavior. While a small band gap in RE(3)SbO(3) results from the separation of the valence and conduction bands, a band gap in RE(8)Sb(3-delta)O(8) appears to result from the Anderson localization of electrons. The relationship among the composition, crystal structures, and electrical resistivity is analyzed using electronic structure calculations.

Modulated crystal structure of Pr2SbO2

“…Combinations of rare earth metals (RE), Sb and O form stuffed variants of the PbFCl type, such as RE 9 Sb 5 O 5 Nuss & Jansen, 2007;Wang et al, 2011), RE 8 Sb 3 O 8 (Wang et al, 2010) or RE 3 SbO 3 (Wang et al, 2010;Forbes et al, 2013). They can be regarded as chemically fused semimetallic RESb and insulating RE 2 O 3 .…”

Thermoelectric Properties of New Thallium Tellurides

“…The decrease of S with rising temperature is in par with the carrier concentration increase, and the positive values of S are indicative of p-type conduction. For Tl 4 ZrTe 4 , S drops from +330 μVK -1 to +50 μVK -1 , and for Tl 4 HfTe 4 from +370 μVK -1 to +80 μVK -1 from 320 K to 560 K. The nonstoichiometric compound Tl 4 Zr 1.1 Te 4 , however, exhibited a comparable, thus non-metallic, dependence, which was unexpected from the theoretical calculations, probably due to a disorder induced localization of carriers as suggested for Ln 8 Sb 3-O 8 (where Ln is a lanthanide element) [41].…”

New Ternary La2Sb‐Type Compounds, ScRESb (RE = La, Ce, Pr, Nd, Sm, Tb), and the Oxygen Stuffed Variant Sc4Yb4Sb4O

“…Further increase of the oxygen content in this class of materials leads to RE 9 Sb 5 O 5 ‐type compounds,23–25 which represent oxygen stuffed shear variants of La 2 Sb, including an ordered defect in the rare‐earth metal sub‐lattice,8,23 or to the RE 2 Pn O 2 family ( Pn = Sb, Bi), of anti ‐ThCr 2 Si 2 ‐type of structure 26–31. All are regarded as potential thermoelectric materials since they show diverse patterns of structural disorder 29–32…”