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Dynamic crystallography reveals spontaneous anisotropy in cubic GeTe

Journal Article · · Nature Materials
 [1];  [2];  [3];  [4];  [5];  [2];  [2];  [6];  [7];  [7];  [8];  [2];  [9]
  1. Université de Bourgogne, Dijon (France)
  2. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
  3. University of Chicago, IL (United States)
  4. Universidad de Costa Rica, San José (Costa Rica)
  5. University of Chicago, IL (United States); Argonne National Laboratory (ANL), Argonne, IL (United States)
  6. European Synchrotron, Grenoble (France)
  7. Northwestern University, Evanston, IL (United States)
  8. Institut Laue-Langevin, Grenoble (France)
  9. Brookhaven National Laboratory (BNL), Upton, NY (United States). Condensed Matter Physics; Columbia University, New York, NY (United States)

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.

Research Organization:
Brookhaven National Laboratory (BNL), Upton, NY (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division; USDOE Laboratory Directed Research and Development (LDRD) Program; National Science Foundation (NSF); University of Costa Rica; ISITE-BFC
Grant/Contract Number:
SC0012704; AC05-00OR22725; AC02-06CH11357; SC0014520
OSTI ID:
1963580
Alternate ID(s):
OSTI ID: 1969333
OSTI ID: 1976009
Report Number(s):
BNL-224181-2023-JAAM
Journal Information:
Nature Materials, Journal Name: Nature Materials Journal Issue: 3 Vol. 22; ISSN 1476-1122
Publisher:
Springer NatureCopyright Statement
Country of Publication:
United States
Language:
English

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