The results of studies of Y₂Ti₂O₇ single crystals doped with Er³⁺ and Yb³⁺ ions by means of electron paramagnetic resonance (EPR) and dc-magnetometry are reported. EPR signals of the trigonal centers with the characteristic hyperfine structure of Er³⁺ or Yb³⁺ ions were observed. Field dependences of magnetization of single crystals for magnetic fields directed along the crystallographic axes and temperature dependences of magnetic susceptibilities were measured. Spin Hamiltonian parameters (g-factors and parameters of the hyperfine interaction) for Er³⁺ and Yb³⁺ ions were obtained from analysis of experimental data. The registered EPR spectra and magnetization curves were successfully reproduced by simulations in framework of the crystal-field approach, in particular, with an account for hybridization of ground 4f¹³ configuration of Yb³⁺ ions with the charge transfer states.

The Li diffusion in Li_1-xCuSbO₄ with lithium deficiency x = 0.02, 0.05, 0.07 and 0.1 was studied by investigation of motional narrowing of the central ⁷ NMR line in the temperature range from 290 K to 470 K. The activation energy of hopping of lithium ions was determined from the temperature dependence of the NMR linewidth. The dependence of the obtained activation energy on the lithium content indicates the opening of motion channels in the crystals at x close to 0.1 due to the formation of free vacancies at the lithium position, which favors the thermally activated hopping of ions.