Effect of Cr on the Structure and Property of Mo_1–xCr_xSe₂ (0 ≤ x ≤ 0.2) and Cr₂Se₃

Layered Mo1–xCrxSe2 (0 ≤ x ≤ 0.2) and Cr2Se3 single crystals are grown by a chemical vapor transport method using I2 as a transport agent. X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses show that the Cr-doped MoSe2 is maintained in a two-layer hexagonal (2H) structure like that of undoped MoSe2, whereas Cr2Se3 is crystallized in the rhombohedral (hexagonal) phase. Lattice constants of the layered Mo1–xCrxSe2 (0 ≤ x ≤ 0.2) series are increased as the Cr content is increased. The direct and indirect bandgaps are also decreased with increasing Cr composition in Mo1–xCrxSe2 (0 ≤ x ≤ 0.2). X-ray photoemission spectroscopy (XPS) revealed the Mo site (valence Mo4+) substituted by Cr in the Mo1–xCrxSe2 (0 < x ≤ 0.2) series mainly causes a Cr6+ valence state and produces n-type conductivity. For Cr2Se3, the main state is Cr3+. Resistivity, Hall, and hot-probe measurements show high p-type conductivity of Cr2Se3. Temperature variations of magnetic susceptibility show that an antiferromagnetic transition occurred in Cr2Se3 below and close to 50 K. The photocatalytic behavior of the layered Mo1–xCrxSe2 (0 ≤ x ≤ 0.2) series has also been assessed by methylene-blue (MB) degradation. The degradation efficiency increases as the Cr content is increased. The photocatalysis enhancement (with increasing Cr) is due to bandgap reduction and ionic contribution from the largely Cr6+ state. The Cr2Se3 and Cr-doped MoSe2 can be applied to magnetic and photocatalytic materials.