Td to 1T′ structural phase transition in the WTe2 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 WTe2. A sharp transition from the low-temperature orthorhombic phase (Td) to the high-temperature monoclinic phase (1T′) was observed at ambient pressure in the single crystal near ∼565 K. Unlike in MoTe2, the solid-solid transition from Td to 1T′ 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 Td to the 1T′ phase was broadened and a two-phase coexistence was observed until 700 K, well above the structural transition.