The nature of the collapsed structural transition in valence-fluctuating EuT2P2 (T = Fe, Ru, Co)

The aim of the proposed experiment is to elucidate the nature of the structural transition into the collapsed tetragonal phase of EuT2P2 (T = Fe, Ru, Co) under pressure at 10, 50 and 300 K. This proposal is motivated by the possibility of a strong coupling of electronic and structural degrees of freedom around the valence transition of Eu-based pnictides. If the valence transition of europium is intertwined with the structural transition into the collapsed tetragonal phase, this would open the way to a new materials class with intriguing coupled electronic and elastic phenomena. To this end, we will study high-quality crystals and follow the large change (~20%) of the c/a ratio of the lattice parameters as function of pressure up to 10 GPa.