Appearance of a Td∗ phase across the Td-1T′ phase boundary in the Weyl semimetal MoTe2

Using elastic neutron scattering on single crystals of MoTe2 and Mo1-xWxTe2 (x-0.01), the temperature dependence of the recently discovered Td∗ phase, present between the lowerature orthorhombic Td phase and higherature monoclinic 1T′ phase, is explored. The Td∗ phase appears only on warming from Td and is observed in the hysteresis region prior to the 1T′ transition. This phase consists of four layers in its unit cell, and is constructed by an "AABB" sequence of layer stacking operations rather than the "AB" and "AA" sequences of the 1T′ and Td phases, respectively. Though the Td∗ phase emerges without disorder on warming from Td, on cooling from 1T′ diffuse scattering is observed that suggests a frustrated tendency toward the "AABB" stacking.