Decoupling the Electrical Conductivity and Seebeck Coefficient in the RE₂SbO₂ Compounds through Local Structural Perturbations

Abstract

Compromise between the electrical conductivity and Seebeck coefficient limits the efficiency of chemical doping in the thermoelectric research. An alternative strategy, involving the control of a local crystal structure, is demonstrated to improve the thermoelectric performance in the RE(2)SbO(2) system. The RE(2)SbO(2) phases, adopting a disordered anti-ThCr(2)Si(2)-type structure (I4/mmm), were prepared for RE = La, Nd, Sm, Gd, Ho, and Er. By traversing the rare earth series, the lattice parameters of the RE(2)SbO(2) phases are gradually reduced, thus increasing chemical pressure on the Sb environment. As the Sb displacements are perturbed, different charge carrier activation mechanisms dominate the transport properties of these compounds. As a result, the electrical conductivity and Seebeck coefficient are improved simultaneously, while the number of charge carriers in the series remains constant.

Disorder-Controlled Electrical Properties in the Ho2Sb1–xBixO2 Systems

“…Such diminishing, yet detectable, activation energies (values listed in the Supporting Information, Table S3) in the Ho 2 Sb 1−x Bi x O 2 samples (except x = 1) have a profound impact on their charge carrier transport properties. Because the classic band theory cannot explain the semiconducting properties of the RE 2 SbO 2 and RE 2 BiO 2 phases, 8,11 the electrical behaviors observed in the Ho 2 Sb 1−xBi x O 2 system cannot be simply attributed to the conventional band-gap engineering based on elemental substitutions. Instead, the observed physical behaviors can be related to the degree of the atomic disorder within the Sb/Bi layer, which dominates the electronic structure around the Fermi level.…”

“…In the Ho 2 SbO 2 structure, the Sb atoms were shifted from the standard 2a site (0, 0, 0) into the 8i site (x, 0, 0) to properly describe the delocalized Sb electron density, which is in agreement with previous studies. 9,11 In the case of Ho 2 BiO 2 , the Bi atoms were well-described on the 2a site and the refinement for the disordered model (with the 8i site) did not converge. Similarly, the refinement of the Ho 2 Sb 1−x Bi x O 2 crystals proceeded well only when the Sb/Bi atoms were placed into the 2a site.…”

“…As a result, the electrical resistivity of the RE 2 SbO 2 compounds span 3 orders of magnitude without chemical doping, and their thermopower shows distinctly different temperature dependencies with minimal structural modifications. 11 The diversity of the electrical properties in the RE 2 SbO 2 and RE 2 BiO 2 phases stems from their unique atomic arrangement. Their structure can be considered as a natural superlattice 12 of the RE 2 O 2 and Sb/Bi layers, with the RE 2 O 2 slabs dictating the lattice dimensions in the ab plane and the Sb/Bi layers controlling the charge carrier transport.…”

“…The details of the hightemperature reactions in the induction furnace has been reported for the preparation of the Ho 2 SbO 2 sample. 11 X-ray Powder Diffraction. The bulk samples were subjected to Xray powder diffraction analysis on a PANalytical X'Pert Pro diffractometer with an X'Celerator detector and Cu Kα 1 radiation.…”

Electronic Phase Transitions of δ-AgxV2O5 Nanowires: Interplay between Geometric and Electronic Structures

“…1,3 Electronic phase transitions induced in materials as a result of thermal, electrical, mechanical, or magnetic stimuli can be underpinned by a wide range of mechanisms, such as electron−electron correlation (the Mott−Hubbard picture), electron−phonon coupling (such as Peierl's distortion of the atomistic structure), and disorder (Anderson's localization). 3,5 While considerable interest has focused on the canonical metal−insulator transition material VO 2 , the relatively large structural transformation (and concomitant elastic and strain effects), sluggish relaxation dynamics of the metal → insulator transition, and impediments to decoupling the structural progression from the electronic transition in VO 2 have spurred increasing interest in the discovery of other materials exhibiting pronounced electronic phase transitions at relatively high temperatures. Vanadium oxide bronzes, with the general formula M x V 2 O 5 , provide a richly diversified set of compositions and compounds, where strong electron correlation can be systematically (albeit thus far only empirically) tuned.…”