Structure and Electron-Transport Properties of Anion-Deficient MoTe2: A Combined Experimental and Theoretical Study

We present experimental measurements and first‐principles theoretical analysis of high‐temperature electron‐transport properties of polycrystalline Te‐deficient 2H‐ and 1T′‐MoTe2–x. Electron transport measurements in the temperature range 300–673 K show that polycrystalline 2H‐MoTe2–x exhibits two regimes of activated conduction: hopping of defect‐induced localized carriers at lower temperatures and an extended state conduction at higher temperatures. Its Seebeck coefficient changes from p‐type to n‐type around 497 K peaking near 370 K, which is ascribed to mixed conduction of carriers. In contrast, 1T′‐MoTe2–x exhibits metallic conduction up to 300 K beyond which conductivity slightly increases due to thermal excitation of the minority carriers. 2H‐ and 1T′ forms of MoTe2–x exhibit thermal conductivity with opposite temperature‐dependence due to dominant electronic thermal conductivity in the latter. Using first‐principles calculations based on density functional theory, we determine the nature of defect states associated with Te‐vacancies in 2H‐, 1T′‐ and Td‐MoTe2–x. The defect bands associated with Te vacancies appear within the gap of 2H‐MoTe2 and in the pseudo gap of 1T′‐MoTe2, thereby reducing the bandgap of the former and making the latter more metallic. These defect states are crucial to understanding the observed trends in the temperature‐dependent transport properties of Te‐deficient 2H‐ and 1T′‐MoTe2–x.