Abstract

We have studied the behavior of the Raman phonons through the transition from a static to dynamic Jahn–Teller order in stoichiometric RMnO₃ samples, (in particular, LaMnO₃ single crystal and PrMnO₃ and YMnO₃ polycrystalline pellets). Thermal expansion effects on the phonon frequencies are not relevant above 300 K in La and Pr samples. The intensity of the spectrum decreases drastically as the temperature increases but is still observable in the pseudo-cubic phase. The remaining spectral weight, above the Jahn–Teller transition, can be explained by the presence of dynamic Jahn–Teller distortions that lower the symmetry of the cubic perovskite. The Raman spectra of LaMnO₃ and PrMnO₃, which presents a similar structural transition temperature, shows the same behavior while that of YMnO₃ is clearly different. This is explained by the fact that this compound presents a stronger cooperative Jahn–Teller distortion. Anharmonic scattering of the phonons are the origin of the phonon softening and partially that of the strong width increase as temperature reaches that of the Jahn–Teller transition.

Author Keywords: Magnetically ordered materials; Electron–phonon interactions; Exchange and superexchange; Phonons; Inelastic light scattering

PACS classification codes: 63.20-e; 75.30 Vn; 63.20 Kr

Article Outline

1. Introduction

2. Experimental details

3. Results and discussion

4. Conclusions

Acknowledgements

References