Observation of electronic and structural transitions in two-dimensional ferroelastic semiconductor of Nb2GeTe4 via pressure manipulation

Nb2GeTe4, a two-dimensional ferroelastic semiconductor, has garnered intense research interest due to its nontrivial physicochemical characteristics of high carrier mobility as well as extraordinary ferroelasticity and optical absorbance along with potential applications in electronic and optoelectronic devices. In this work, the high-pressure structural, vibrational, and electrical transport properties of Nb2GeTe4 up to 60.0 GPa under different hydrostatic environments were systematically studied by Raman spectroscopy, electrical conductivity, and first-principles theoretical calculations. Under non-hydrostatic compression, Nb2GeTe4 experienced a metallization at 11.8 GPa originating from the closure of bandgap due to the considerable compression of interlayer distance and sequential an isostructural phase transition (IPT) at 26.5 GPa. The comparable metallization pressure and the pronounced delay of IPT by ∼4.0 GPa under hydrostatic condition can be reasonably interpreted by the influence of deviatoric stress. Upon decompression, the phase transition of Nb2GeTe4 was demonstrated to be reversible with the possible structural destruction under different hydrostatic environments. Moreover, Nb2GeTe4 underwent a Ohmic-to-super-Ohmic conversion at 1000 mV under high pressure, which was presumably caused by the higher sinusoidal voltage than its thermal voltage. These findings enrich our foundational comprehension on high-pressure physicochemical properties of Nb2GeTe4, thereby fostering its potential applications in electronic and optoelectronic devices.