Structural, Spectroscopic, Electric and Magnetic Properties of New Trigonal K 5 FeHf(MoO 4 ) 6 Orthomolybdate.

A new multicationic structurally disordered KFeHf(MoO) crystal belonging to the molybdate family is synthesized by the two-stage solid state reaction method. The characterization of the electronic and vibrational properties of the KFeHf(MoO) was performed using density functional theory calculations, group theory, Raman and infrared spectroscopy. The vibrational spectra are dominated by vibrations of the MoO tetrahedra, while the lattice modes are observed in a low-wavenumber part of the spectra. The experimental gap in the phonon spectra between 450 and 700 cm is in a good agreement with the simulated phonon density of the states. KFeHf(MoO) is a paramagnetic down to 4.2 K. The negative Curie-Weiss temperature of -6.7 K indicates dominant antiferromagnetic interactions in the compound. The direct and indirect optical bandgaps of KFeHf(MoO) are 2.97 and 3.21 eV, respectively. The KFeHf(MoO) bandgap narrowing, with respect to the variety of known molybdates and the ab initio calculations, is explained by the presence of Mott-Hubbard optical excitation in the system of Fe ions.