T${}_d$ to 1T${}^{\mathrm{\prime }}$ structural phase transition in WTe${}_2$ Weyl semimetal

Elastic neutron scattering on a single crystal and powder X-ray diffraction measurements were carried out to investigate how the crystal structure evolves as a function of temperature in the Weyl semimetal WTe${}_2$. A sharp transition from the low-temperature orthorhombic phase (T${}_d$) to the high-temperature monoclinic phase (1T${}^{\mathrm{\prime }}$) was observed at ambient pressure in the single crystal near $\sim$565 K. Unlike in MoTe${}_2$, the solid-solid transition from T${}_d$ to 1T${}^{\mathrm{\prime }}$ occurs without the cell doubling of the intermediate T${}_d^{\ast }$ phase with AABB (or ABBA) layer stacking. In powders however, the thermal transition from the T${}_d$ to the 1T${}^{\mathrm{\prime }}$ phase is broadened and a two phase coexistence was observed until 700K, well above the structural transition.