Cerium is regarded as one of the few metals that exhibit a first-order liquid-liquid phase transition (LLPT)[1, 2]. However, despite the theoretical attribution of the LLPT to the localized-itinerant transition of f-electrons, there is still a lack of compelling experimental evidence to support this important scientific inquiry. We investigate the evolution of sound velocity in molten cerium along the isothermal and isobaric paths under static compression, conclusively showing the existence of a LLPT and an associated mechanism predominating liquids' compressibility. Also, the continuous viscosity derived from shear wave attenuation are also show the anomaly in molten Ce. Finally, by designing shock-release experiments in shock-driven molten Ce, we observe a first-order LLPT along the release path. The volume change associated with the transition is less than 6%, much smaller than the one (14%) obtained in static compression experiments, indicating that the LLPT in molten Ce is strongly rate dependent[3].

[1] A. Cadien, Q.Y. Hu, Y. Meng, Y.Q. Cheng, M.W. Chen, J.F. Shu, H.K. Mao, H.W. Sheng, First-Order Liquid-Liquid Phase Transition in Cerium, Phys. Rev. Lett., 110, 125503 (2013).
[2] M.J. Lipp, Z. Jenei, D. Ruddle, C. Aracne-Ruddle, H. Cynn, W.J. Evans, Y. Kono, C. Kenney-Benson, C. Park, Equation of state measurements by radiography provide evidence for a liquid-liquid phase transition in cerium, J. Phys.: Conf. Ser., 500, 032011 (2014).
[3] L. Xu, Z. Wang, Z. Li, X. Li, S. Yao, J. Li, X. Zhou, Y. Yu, J. Hu, Q. Wu, Liquid–liquid phase transition in molten cerium during shock release, Appl. Phys. Lett. , 118, 074102 (2021).
 

phase transition, molten cerium