Appearance of a Td* phase across the Td−1T′ phase boundary in the Weyl semimetal MoTe2

Using elastic neutron scattering on single crystals of ${\mathrm{MoTe}}_{2}$ and ${\mathrm{Mo}}_{1\ensuremath{-}x}{\mathrm{W}}_{x}{\mathrm{Te}}_{2}$ ($x\ensuremath{\lesssim}0.01$), the temperature dependence of the recently discovered ${T}_{d}^{*}$ phase, present between the low-temperature orthorhombic ${T}_{d}$ phase and high-temperature monoclinic $1{T}^{\ensuremath{'}}$ phase, is explored. The ${T}_{d}^{*}$ phase appears only on warming from ${T}_{d}$ and is observed in the hysteresis region prior to the $1{T}^{\ensuremath{'}}$ 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 $1{T}^{\ensuremath{'}}$ and ${T}_{d}$ phases, respectively. Though the ${T}_{d}^{*}$ phase emerges without disorder on warming from ${T}_{d}$, on cooling from $1{T}^{\ensuremath{'}}$ diffuse scattering is observed that suggests a frustrated tendency toward the ``AABB'' stacking.