# Time-domain Brillouin scattering: Application to elasticity measurement in cubic solids compressed in a diamond anvil cell

Feng Xu, Andreas Zerr, Laurent Belliard, P. Djemia, Chen-Hui Li, Xinze

Zhang, Haijun Huang

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## To cite this version:

Feng Xu, Andreas Zerr, Laurent Belliard, P. Djemia, Chen-Hui Li, et al., Time-domain Brillouin scattering: Application to elasticity measurement in cubic solids compressed in a diamond anvil cell. 2023 International Congress on Ultrasonics (ICU 2023), Xiuming Wang, Sep 2023, Beijing, China. pp.520-521. hal-04750937

HAL Id: hal-04750937

https://hal.science/hal-04750937v1

Submitted on 24 Oct 2024

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Time-domain Brillouin scattering: Application to elasticity measurement in cubic solids compressed in a diamond anvil cell

Feng Xu¹, Andreas Zerr², Laurent Belliard³, Philippe Djemia², Chenhui Li⁴, Xinze Zhang¹,
Haijun Huang¹

¹School of Science, Wuhan University of Technology, 430070 Wuhan, China

²Laboratoire des Sciences des Procédés et des Matériaux, CNRS UPR 3407, Université Sorbonne Paris Nord, F-93430 Villetaneuse, France

³Institut des NanoSciences de Paris, CNRS UMR 7588, Sorbonne Université, 75005 Paris, France

⁴State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, 100083 Beijing, China

Time-domain Brillouin scattering (TDBS) is based on the technique of picosecond laser ultrasonics, which permits measurement of sound velocities in transparent samples compressed a diamond anvil cell (DAC) with a very high temporal/spatial resolution. We present here our recent works on two minerals, both crystallizing in the cubic B1-structure, using the TDBS+DAC technique. Knowledge of their elastic behaviour at high pressures permits a better understanding of the seismic observations in the Earth's interior and thus to conclude about its dynamics. Here, elastic anisotropy of MgO, the end-member of the second most abundant mineral of the lower mantle, namely ferropericlase (Mg₁-xFex)O, is of particular importance. Using the TDBS+DAC technique, we measured pressure dependences of the longitudinal sound velocities (vL) in single crystals of MgO along two different directions (100) and (111). All three independent members of the elastic tensor Cij, as well as its elastic anisotropy at high pressures were derived applying reliable experimental equation of state. Our measurements revealed a continuous enhancement of the elastic anisotropy of MgO at pressures of the upper part of the lower mantle [1], in contrast to the only earlier experimental data. However, our results agree with all theoretical predictions and the measurements on ferropericlase with a moderate Fe-content. Also, we demonstrated that the TDBS technique permits access to the Cij(P) dependences of cubic solids via a very different approach: Thanks to a very high spatial resolution (typically two or three hundreds of nm) of the technique, we measured the vL distributions in polycrystalline NaCl samples and derived the extreme vL values, which are vL100 and vL111 in any cubic crystal, using the envelope method [2,3,4]. This advantage of the TDBS technique permitted us the measurement of Cij(P) of the high-pressure B2-phase of NaCl having cubic CsCl-type structure which is not accessible as single crystals. The latter result, together with the earlier reports on the Cij(P) of CaO, permitted us to propose a mechanism of the B1-B2 phase transition [5]. Furthermore, we applied this finding to predict pressure of the B1-B2 phase transition of MgO. The above presented results demonstrated the potential of the TDBS technique in examination of the elastic behaviour and phase transition of cubic minerals compressed in a DAC to high pressures, also in excess of 100 GPa.
References:

1. Zhang X., et al., (submitted 2023)

2. Kuriakose M., et al., *Phys. Rev. B* **96**, 134122 (2017)

3. Raetz S., et al., *Phys. Rev. B* **99**, 224102 (2019)

4. Xu F., et al., *J. Appl. Phys.* **130**, 035903 (2021)

5. Xu F., et al., *arXiv*, 2209.10899 (2022)