Lattice dynamics and electronic structure of cobalt–titanium spinel Co$_{2}$TiO$_{4}$

The results are presented on phonon excitations and the electronic structure of Co$_{2}$TiO$_{4}$ inverse spinel in which magnetically ordered cobalt ions Co$^{2+}$(3$d^{7}$) are in equal amounts in tetrahedral and octahedral sublattices below $T_{C}$ = 56 K. Single crystals are studied using optical reflection and absorption in a wide spectral range, Raman scattering, and dielectric spectroscopy methods. The dynamics of infrared and Raman-active phonons are studied, and the features associated with disordering in tetrahedral sites are detected. The $d$–$d$ electronic transitions recorded in the regions of 3800 and 6300 cm$^{-1}$ confirm the coordination features of Co$^{2+}$ ions. An increase in the permittivity in the temperature region below 130 K is detected.