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Low-temperature anomalies of cuprite observed by Raman spectroscopy and x-ray powder diffraction

✍ Scribed by M. Ivanda; D. Waasmaier; A. Endriss; J. Ihringer; A. Kirfel; W. Kiefer

Publisher
John Wiley and Sons
Year
1997
Tongue
English
Weight
417 KB
Volume
28
Category
Article
ISSN
0377-0486

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✦ Synopsis

Anomalous low-temperature behaviour of is observed by both Raman-spectroscopy using laser excitation Cu 2 O frequencies near the resonance of the 1S "blue excitonÏ and x-ray powder di †ractometry using a high-resolution Guinier Ðlm camera. Changes in frequency of the Raman-allowed phonon band, and also of intensities of C 25 ' (LO) other Raman-forbidden bands, indicate anomalies at temperatures of 90 and 190 K, respectively. The anomaly at 90 K is qualitatively interpreted by an order-disorder phase transition and that at 190 K by a discontinuous change of excitonic states. Close to these temperatures, the powder di †raction diagrams also revealed anomalous behaviour of the lattice constant. Upon cooling and heating, the thermal expansion coefficient becomes signiÐcantly negative at 200 K, and at about 80 K a small reproducible contraction/expansion of the cubic lattice is observed. Both e †ects add evidence for hitherto unknown instabilities of the structure at low temperatures. 1997 Cu 2

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