Terahertz-induced Martensitic Transformation in Partially Stabilized Zirconia

Martensitic crystal structures are usually obtained by rapid thermal quenching of certain alloys, as this induces local shear deformation. This paper reveals that the latter, and hence a martensitic structural transformation, can also be achieved by exciting a suitable transverse phonon mode, as is demonstrated in partially stabilized zirconia by using intense terahertz pulses. Martensitic crystal structures are usually obtained by rapid thermal quenching of certain alloys, which induces stress and subsequent shear deformation. Here, we demonstrate that it is also possible to intentionally excite a suitable transverse acoustic phonon mode to induce a local shear deformation. We irradiate the surface of a partially stabilized zirconia plate with intense terahertz pulses and verify martensitic transformation from the tetragonal to the monoclinic phases by Raman spectroscopy and the observed destructive spallation of the zirconia microcrystals. We calculate the phonon modes in tetragonal zirconia and determine the decay channel that triggers the transformation. The phonon mode required for the martensitic transformation can be excited via the Klemens process. Since terahertz pulses can induce a specific local shear deformation beyond thermal equilibrium, they can be used to elucidate phase transformation mechanisms with approaches based on nonlinear phononics.