T d to 1 T ′ structural phase transition in the WTe 2 Weyl semimetal

Elastic neutron scattering on a single crystal combined with powder x-ray diffraction measurements were carried out to investigate how the crystal structure evolves as a function of temperature in the Weyl semimetal $\mathrm{W}{\mathrm{Te}}_{2}$. A sharp transition from the low-temperature orthorhombic phase (${T}_{d}$) to the high-temperature monoclinic phase ($1{T}^{\ensuremath{'}}$) was observed at ambient pressure in the single crystal near $\ensuremath{\sim}565$ K. Unlike in ${\mathrm{MoTe}}_{2}$, the solid-solid transition from ${T}_{d}$ to $1{T}^{\ensuremath{'}}$ occurs without the cell doubling of the intermediate ${T}_{d}^{*}$ phase with AABB (or ABBA) layer stacking. In powders, however, the thermal transition from the ${T}_{d}$ to the $1{T}^{\ensuremath{'}}$ phase was broadened and a two-phase coexistence was observed until 700 K, well above the structural transition.