TY - JOUR
T1 - Dynamic crystallography reveals spontaneous anisotropy in cubic GeTe
AU - Kimber, Simon A.J.
AU - Zhang, Jiayong
AU - Liang, Charles H.
AU - Guzmán-Verri, Gian G.
AU - Littlewood, Peter B.
AU - Cheng, Yongqiang
AU - Abernathy, Douglas L.
AU - Hudspeth, Jessica M.
AU - Luo, Zhong Zhen
AU - Kanatzidis, Mercouri G.
AU - Chatterji, Tapan
AU - Ramirez-Cuesta, Anibal J.
AU - Billinge, Simon J. L.
N1 - Funding: The authors thank the European Synchrotron Radiation Facility for the provision of beamline time on ID15B and ID31. This research used resources at the Spallation Neutron Source, a US Department of Energy (DOE), Office of Science User Facility, operated by the Oak Ridge National Laboratory. The computing and software resources were made available through the VirtuES and the ICEMAN projects, funded by the Laboratory Directed Research and Development program (LDRDs 7739, 8237,10447) and Compute and Data Environment for Science (CADES) at the Oak Ridge National Laboratory, which is supported by the Office of Science of the DOE under Contract DE-AC05-00OR22725. S.J.L.B. acknowledges support from the US DOE, Office of Science, Office of Basic Energy Sciences, under contract no. DE- SC0012704. C.H.L. acknowledges support from NSF GRFP DGE-1746045. G.G.G.-V. acknowledges support from the Vice-Rector for Research at the University of Costa Rica (project no. 816-C1-601). Work at Argonne (P.B.L.) is supported by the US DOE, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering, under contract no. DE-AC02-06CH11357. At Northwestern University (M.G.K.), work on thermoelectric materials is primarily supported by the US DOE, Office of Science, Office of Basic Energy Sciences, under award no. DE-SC0014520. This work was supported by the Programme of Investments for the Future, an ISITE-BFC project (contract no. ANR-15-IDEX-0003) (S.A.J.K.).
PY - 2023/3/1
Y1 - 2023/3/1
N2 - Cubic energy materials such as thermoelectrics or hybrid perovskite materials are often understood to be highly disordered. In GeTe and related IV–VI compounds, this is thought to provide the low thermal conductivities needed for thermoelectric applications. Since conventional crystallography cannot distinguish between static disorder and atomic motions, we develop the energy-resolved variable-shutter pair distribution function technique. This collects structural snapshots with varying exposure times, on timescales relevant for atomic motions. In disagreement with previous interpretations, we find the time-averaged structure of GeTe to be crystalline at all temperatures, but with anisotropic anharmonic dynamics at higher temperatures that resemble static disorder at fast shutter speeds, with correlated ferroelectric fluctuations along the <100>c direction. We show that this anisotropy naturally emerges from a Ginzburg–Landau model that couples polarization fluctuations through long-range elastic interactions. By accessing time-dependent atomic correlations in energy materials, we resolve the long-standing disagreement between local and average structure probes and show that spontaneous anisotropy is ubiquitous in cubic IV–VI materials.
AB - Cubic energy materials such as thermoelectrics or hybrid perovskite materials are often understood to be highly disordered. In GeTe and related IV–VI compounds, this is thought to provide the low thermal conductivities needed for thermoelectric applications. Since conventional crystallography cannot distinguish between static disorder and atomic motions, we develop the energy-resolved variable-shutter pair distribution function technique. This collects structural snapshots with varying exposure times, on timescales relevant for atomic motions. In disagreement with previous interpretations, we find the time-averaged structure of GeTe to be crystalline at all temperatures, but with anisotropic anharmonic dynamics at higher temperatures that resemble static disorder at fast shutter speeds, with correlated ferroelectric fluctuations along the <100>c direction. We show that this anisotropy naturally emerges from a Ginzburg–Landau model that couples polarization fluctuations through long-range elastic interactions. By accessing time-dependent atomic correlations in energy materials, we resolve the long-standing disagreement between local and average structure probes and show that spontaneous anisotropy is ubiquitous in cubic IV–VI materials.
U2 - 10.1038/s41563-023-01483-7
DO - 10.1038/s41563-023-01483-7
M3 - Letter
C2 - 36804639
AN - SCOPUS:85148475934
SN - 1476-1122
VL - 22
SP - 311
EP - 315
JO - Nature Materials
JF - Nature Materials
IS - 3
ER -