Pressure-induced symmetry breaking and robust Mo clusters ( = 0) in kagome compounds MMoO (M = Zn, Fe).

This study explores the high-pressure behavior of ZnMoO and FeMoO, both composed of MoO 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 6 phase to the monoclinic 2 phase at elevated pressures. High-pressure Raman spectroscopy further shows the emergence of new vibrational modes and a gradual softening of the A mode, both of which are closely associated with the structural phase transition and potential breathing behavior of the Mo 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 Mo clusters in these compounds.