Pressure-induced structural transitions triggering dimensional crossover in the lithium purple bronze Li_0.9Mo₆O₁₇

At ambient pressure, lithium molybdenum purple bronze (Li0.9Mo6O17) is a quasi-one dimensionalsolid in which the anisotropic crystal structure and the linear dispersion of the underlying bandsproduced by electronic correlations possibly bring about a rare experimental realization of Tomomaga-Luttinger liquid physics. It is also the sole member of the broader purple molybdenum bronzes familywhere a Peierls instability has not been identified at low temperatures. The present study reports apressure-induced series of phase transitions between 0 and 12 GPa. These transitions are stronglyreflected in infrared spectroscopy, Raman spectroscopy, and x-ray diffraction. The most dramaticeffect seen in optical conductivity is the metalization of thec-axis, concomitant to the decrease ofconductivity along theb-axis. This indicates that high pressure drives the material away from itsquasi-one dimensional behavior at ambient pressure. While the first pressure-induced structure ofthe series is resolved, the identification of the underlying mechanisms driving the dimensional changein the physics remains a challenge