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Distortion-Dependent Raman Spectra and Mode Mixing in RMnO3 Perovskites

M. N. Iliev·M. V. Abrashev·J. Laverdiere·S. Jandl·M. M. Gospodinov·Y. -Q. Wang·Y. -Y. Sun
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Abstract

The polarized Raman spectra of orthorhombic RMnO3 series (R=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Y) were studied at room temperature. The variation of phonon frequencies with R ionic radius rR as a whole confirms the commonly accepted Raman line assignments with two noticeable exceptions: (1) with decreasing rR the stretching Ag(1) and bending Ag(3) modes strongly mix for R=Sm to Tb, while for further decrease or rR (R=Dy,Ho,Y) the Ag(3) mode is observed at higher frequency than Ag(1) mode; (2) similar distortion-dependent mode mixing takes place for the rotational Ag(2) and O1(x) [Ag(7)] modes. The mode mixing is particularly strong for the RMnO3 compounds with rR values close to the transition from A-type to incommensurate sinusoidal antiferromagnetic ordering at low temperatures. The frequency of rotational Ag(2) and Ag(4) modes scales to the angles of MnO6 [101] and [010] rotations, respectively, and could be used as a measure of their value.

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M. N. Iliev, M. V. Abrashev, J. Laverdiere, S. Jandl, M. M. Gospodinov, Y. -Q. Wang, Y. -Y. Sun. 2005-10-07. Distortion-Dependent Raman Spectra and Mode Mixing in RMnO3 Perovskites. https://arxiv.org/abs/cond-mat/0510198

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