"Phase transformation pathways of ultrafast-laser-irradiated Ln2O3 (Ln=Er-Lu)"

Dylan R. Rittman: Cameron L. Tracy, Chien-Hung Chen, Jonathan M. Solomon, Mark Asta, Wendy L. Mao, Steven M. Yalisove, and Rodney C. Ewing; Physical Review B, 01/10/18.

Additional Authors: Cameron L. Tracy, Chien-Hung Chen, Jonathan M. Solomon, Mark Asta, Wendy L. Mao, Steven M. Yalisove, and Rodney C. Ewing

Abstract:

Ultrafast laser irradiation causes intense electronic excitations in materials, leading to transient high temperatures and pressures. Here, we show that ultrafast laser irradiation drives an irreversible cubic-to-monoclinic phase transformation in Ln2O3(Ln=Er–Lu), and explore the mechanism by which the phase transformation occurs. A combination of grazing incidence x-ray diffraction and transmission electron microscopy are used to determine the magnitude and depth-dependence of the phase transformation, respectively. Although all compositions undergo the same transformation, their transformation mechanisms differ. The transformation is pressure-driven for Ln=Tm–Lu, consistent with the material’s phase behavior under equilibrium conditions. However, the transformation is thermally driven for Ln=Er, revealing that the nonequilibrium conditions of ultrafast laser irradiation can lead to novel transformation pathways. Ab initio molecular-dynamics simulations are used to examine the atomic-scale effects of electronic excitation, showing the production of oxygen Frenkel pairs and the migration of interstitial oxygen to tetrahedrally coordinated constitutional vacancy sites, the first step in a defect-driven phase transformation.