Session P20 - Structural Phase Transitions.
MIXED session, Wednesday afternoon, March 22
208A, MCC
We have observed the evolution of structural transition in Y hydrides (YHx, x=0-3) using time-resolved x-ray diffraction. Y films capped with thin Pd layers were prepared under UHV. The chamber was then back filled with hydrogen to stimulate the transition. Pressure was carefully controlled to allow observation of intermediate stages. Upon H loading the films transformed from alpha-phase (Y-hcp) to beta-phase (dihydride-fcc), then to gamma-phase (trihydride-hex). The lattice expansion in alpha-phase and contraction in beta-phase were clearly observed. Gamma-phase films could be transformed back to beta-phase reversibly by annealing to 130C. Optical transmission was measured simultaneously and to monitor the metal-insulator transition between beta- and gamma-phase. Our results are to be compared with earlier results on transmission [1] and x-ray. [2] [1] J.N. Huiberts et al., Nature 380, 231 (1996). [2] A. Remholf et al., Phys. Rev. B 56, R1 (1997).