Pressure-induced symmetry breaking and robust Mo₃ clusters (S = 0) in kagome compounds M₂Mo₃O₈ (M = Zn, Fe)

This study explores the high-pressure behavior of Zn₂Mo₃O₈ and Fe₂Mo₃O₈, both composed of Mo₃O₁₃ clusters, through synchrotron X-ray diffraction, high-pressure Raman spectroscopy, and electrical transport measurements. The results reveal that both compounds undergo similar structural phase transitions from the hexagonal P6₃mc phase to the monoclinic P2₁ phase at elevated pressures. High-pressure Raman spectroscopy further shows the emergence of new vibrational modes and a gradual softening of the A₁ mode, both of which are closely associated with the structural phase transition and potential breathing behavior of the Mo₃ clusters. Thermal activation model analysis of resistivity measurements reveals pressure-dependent activation energy trends, including an anomalous trend reversal. Comparative experiments demonstrate that the presence or absence of magnetism in interlayer transition metal atoms does not affect the structural evolution, but seems to have an impact on transport properties under applied pressure. This suggests that the pressure-induced changes are primarily associated with the behavior of the Mo₃ clusters in these compounds.