Combined First-Principles Calculations and Experimental Study of the Phonon Modes in the Multiferroic Compound GeV4S8

详细信息    查看全文

• 作者：Elena Cannuccia ; Vinh Ta Phuoc ; Benjamin Brière ; Laurent Cario ; Etienne Janod ; Benoît Corraze ; Marie Bernadette Lepetit
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：February 16, 2017
• 年：2017
• 卷：121
• 期：6
• 页码：3522-3529
• 全文大小：454K
• ISSN：1932-7455

文摘

The lattice dynamics of the GeV₄S₈ compound has been investigated using both density functional calculations and Raman/infrared (IR) measurements. While the accordance between the computed and the experimental data is very good in the low-temperature, ferroelectric phase (25K, Imm2), this is not the case for the high-temperature, paraelectric one within the F4̅3m group. Using group theory and first-principles calculations, we show that the IR/Raman phonon modes are, however, compatible with the I4̅m2 space group. Analysis of the different modes at the ferroelectric transition shows that simultaneous weakening/strengthening of two symmetry-related bonds within the V₄S₄ cluster is a direct consequence of the orbital-order instability driving the ferroelectric transition. The softening of modes associated with such distortions call for strong orbital occupation fluctuations above T_c. These fluctuations, associated with the discrepancy between the X-ray scattering F4̅3m group and the lattice dynamics I4̅m2 group, can be interpreted within a dynamical Jahn–Teller distortion model for the paraelectric phase.