Evolution of the structural transition in Mo1-x WxTe2

The composition dependence of the structural transition between the monoclinic 1T′ and orthorhombic Td phases in the Mo1-xWxTe2 Weyl semimetal was investigated by elastic neutron scattering on single crystals up to x≈0.54. First observed in MoTe2, the transition from Td to 1T′ is accompanied by an intermediate pseudo-orthorhombic phase, Td∗. Upon doping with W, the Td∗ phase vanishes by x≈0.34. Above this concentration, a phase coexistence behavior with both Td and 1T′ is observed instead. The interlayer in-plane positioning parameter δ, which relates to the 1T′β 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≈0.54, in contrast to the broadening reported under pressure.