Evolution of the structural transition in Mo1−xWxTe2

The composition dependence of the structural transition between the monoclinic $1{T}^{\ensuremath{'}}$ and orthorhombic ${T}_d$ phases in the ${\mathrm{Mo}}_{1\ensuremath{-}x}{\mathrm{W}}_x{\mathrm{Te}}₂$ Weyl semimetal was investigated by elastic neutron scattering on single crystals up to $x\ensuremath{\approx}0.54$. First observed in ${\mathrm{MoTe}}₂$, the transition from ${T}_d$ to $1{T}^{\ensuremath{'}}$ is accompanied by an intermediate pseudo-orthorhombic phase, ${T}_d^*$. Upon doping with W, the ${T}_d^*$ phase vanishes by $x\ensuremath{\approx}0.34$. Above this concentration, a phase coexistence behavior with both ${T}_d$ and $1{T}^{\ensuremath{'}}$ is observed instead. The interlayer in-plane positioning parameter $\ensuremath{\delta}$, which relates to the $1{T}^{\ensuremath{'}}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ angle, decreases with temperature as well as with W substitution, likely due to strong anharmonicity in the interlayer interactions. The temperature width of the phase coexistence remains almost constant up to $x\ensuremath{\approx}0.54$, in contrast to the broadening reported under pressure.