The composition dependence of the structural transition between the monoclinic 1T$^{ \prime}$ and orthorhombic T$_{ d}$ phases in the Mo$_{ 1-x}$W$_{ x}$Te$_{ 2}$ Weyl semimetal was investigated by elastic neutron scattering on single crystals up to $x \approx 0.54$. First observed in MoTe$_{ 2}$, the transition from T$_{ d}$ to 1T$^{ \prime}$ is accompanied by an intermediate pseudo-orthorhombic phase, T$_{ d}^{ *}$. Upon doping with W, the T$_{ d}^{ *}$ phase vanishes by $x \approx 0.34$. Above this concentration, a phase coexistence behavior with both T$_{ d}$ and 1T$^{ \prime}$ is observed instead. The interlayer in-plane positioning parameter $\delta$, which relates to the 1T$^{ \prime}$ $\beta$ 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 $x \approx 0.54$, in contrast to the broadening reported under pressure.
Categories: cond-mat.mtrl-sci