A temperature-dependent Raman scattering and X-ray diffraction study of K2Mo2O7·H2O and ab initio calculations of K2Mo2O7

• Temperature dependence on the vibrational properties of the K 2 Mo 2 O 7 ·H 2 O. • Temperature-induced phase transformation in the K 2 Mo 2 O 7 ·H 2 O. • Electronic properties of the K 2 Mo 2 O 7 ·H 2 O semiconductor material. • Lattice dynamic calculations based on the density-functional theory (DFT). This study reports a temperature-dependent Raman scattering and X-ray diffraction study of K 2 Mo 2 O 7 ·H 2 O. The high-temperature Raman scattering analysis shows that the material remains structurally stable, with triclinic symmetry, in a temperature range from 300 to 413 K and undergoes a structural phase transition between 413 and 418 K. This phase transition is most likely connected with the dehydration process of K 2 Mo 2 O 7 ·H 2 O. The temperature-dependent X-ray diffraction patterns are measured from 30 to 573 K. The results show that the discovered phase transition occurs between 419 and 433 K, in good agreement with the Raman scattering results. According to the Raman data, with increasing temperature, the dehydrated crystal of K 2 Mo 2 O 7 undergoes a new phase transformation at 603 K and melts at ~843 K. Principal component and hierarchical cluster analyses are performed based on the treatment of the raw spectral data to infer the phase transformations occurring in the material. Assignments of the Raman modes for the K 2 Mo 2 O 7 system at ambient conditions are studied through first-principles calculations based on density functional perturbation theory. These calculations are applied to understand the electronic properties, including the band structure and the associated projected density of states, of K 2 Mo 2 O 7 under the local density approximation.