Atomic‐Scale Observation of Off‐Centering Rattlers in Filled Skutterudites

Abstract

As one of the most fundamental order parameters, the coordinate order of atoms is a cornerstone in determining the physical and chemical properties of materials. Off‐centering shifts of atoms from their centrosymmetric positions, a phenomenon that is closely related to symmetry breaking and structural transitions in crystals, is of key importance in modifying a broad range of fundamental properties, such as ferroelectricity, antiferroelectricity, and piezoelectricity. In thermoelectric materials, which can be used to directly interconvert heat to electricity, off‐centering has been proposed in, e.g., lead tellurides, halide perovskites, type I and II clathrates, and filled skutterudites, to be the physical origin of the experimentally measured exceptionally low thermal conductivity, but only indirectly supported from structural refinements and experimental/theoretical vibration mode analyses. In this work, Yb partially filled and Ce fully filled skutterudite is taken as a model system for directly measuring the off‐centering shifts of filler atoms, i.e., rattlers, with picometer precision in real space, by means of atomic‐resolution negative spherical aberration imaging transmission electron microscopy. This finding allows an in‐depth understanding of the relationship between the off‐centering and the thermoelectric performance, and the presented methodology here is also applicable to investigate the off‐centering phenomena in other functional materials, e.g., ferroelectrics and solar cells.

Understanding Structural Incorporation of Oxygen Vacancies in Perovskite Cobaltite Films and Potential Consequences for Electrocatalysis

“…In order to understand the image contrast shown in Figure , and more importantly to evaluate the concentration of oxygen, image simulations were performed and the resulting images were compared quantitatively with experiments on the absolute contrast level − ,− using an iterative approach. Since it is more meaningful to know the average information of oxygen content, which is expected to be highly correlated with the conductivity and band structures of PBCO and thus affects the catalytic properties, we further divided Figure b into eight successive patches and obtained the mean experimental image by averaging the intensity distribution of all of the patches, as shown in Figure a, for subsequent investigations.…”

“…The precision of determining an atomic column using NCSI is better than 6 pm, as evaluated by the standard deviation of lattice parameters in both STO and PBCO, and will not be shown individually in the following text. Details on the measurement precision can be found elsewhere. , The camera modulation transfer function was measured using the knife-edge method for image quantification. Multislice NCSI image simulations were carried out using Dr. Probe software .…”

“…Details on the measurement precision can be found elsewhere. 39,40 The camera modulation transfer function was measured using the knife-edge method 41 for image quantification.…”

Contrasting roles of Bi-doping and Bi2Te3 alloying on the thermoelectric performance of SnTe

“…However, the intrinsic coupling nature among these thermoelectric parameters implies that it is hard to obtain an enhanced ZT value via independent modulation of a single parameter. 4 To date, among the numerous thermoelectric materials at intermediate temperatures, including skutterudites, 5,6 GeTe, 7,8 SnSe, 9,10 PbTe 11,12 and its analogues PbSe 13,14 and PbS, 15,16 etc., PbTe has been regarded as a promising candidate for its good thermal stability, superior mechanical property, and outstanding performance. However, abuse of lead might induce growing worldwide concerns about environmental issues.…”

“…To date, among the numerous thermoelectric materials at intermediate temperatures, including skutterudites, 5,6 GeTe, 7,8 SnSe, 9,10 PbTe 11,12 and its analogues PbSe 13,14 and PbS, 15,16 etc. , PbTe has been regarded as a promising candidate for its good thermal stability, superior mechanical property, and outstanding performance.…”