A spectacular pressure-induced electronic transition in KTb(MoO4)(2)

Results of pressure Raman and optical absorption studies are reported for KTb(MoO4)(2). A phase transformation occurs at 27 kbar when the crystal is pressurized at ambient temperature, in a hydrostatic pressure medium, The sample changes to a deep yellow colour at the transition and visibly contracts in the a-axis direction, The colour shifts red on further pressure increase. The Raman spectral features and the X-ray powder pattern change abruptly at the transition indicating a structural change, The colour change is attributed to 4f-5d transition in Tb initiated by the structural transition, and consequent intervalence charge transfer between Tb and Mo.