An Assessment of Thermally Driven Local Structural Phase Changes in 1$T$$'$- MoTe$_2$

Abstract

The role of layer disorder is important in establishing the topological phases of MoTe${_2}$. A rich tapestry of atomic ordering influences the structural phase transitions (SPTs), but there is little understanding of the mechanistic details of the phase transition. An atomistic level study was conducted to investigate the local structure of the 1$T$$'$ and $T_d$ phases of MoTe${_2}$ by using the Pair Distribution Function (PDF) technique. While the average structure exhibits an SPT and co-existence of phases as a function of temperature, the local structure shows the suppression of SPT at short-range ordering, and the sample remains in the monoclinic (1$T$$'$) phase at all measured temperatures. A sharp PDF peak observed at short distances indicated a strong atom-atom correlation between the Mo and Te atoms within the Mo-octahedra. In addition, a large box modeling of the PDF data indicated a preferential motion of Te atoms towards $c$-axis at all temperatures. The structural defects, such as stacking faults, likely result in the co-existence of phases in the average structure and suppress the local SPT of MoTe$_2$. These results are stepping stones in understanding the long-debated origins of structural, vibrational, and electronic properties of MoTe$_2$ and similar transition metal dichalcogenides.