EPR in a barium borosilicate glass containing titanium ions

EPR spectra were studied in an equimolar barium borosilicate glass containing 0 to 12 mol% titanium ions. The valence concentration ratio, defined as the ratio of the concentration of the lower valence state transition metal ion Ti³⁺ to the total concentration of the transition metal ion Ti³⁺ + Ti⁴⁺, was varied between 0.15 and 0.85 at each concentration. The spectra were studied as a function of temperature down to 15 K. A broad asymmetric absorption peak is observed with effectiveg ~ 1.938 at room temperature. This absorption is attributed to a tetragonally distorted octahedral ligand field around Ti³⁺ ion. Theg value decreases as the temperature decreases, with a distinct transition between 60 and 100 K. Accompanied by this decrease ing is a distinct broadening of the curves with a transition in the same transition range. These and other observations are explained in terms of a lengthening of the spin-lattice relaxation time in this transition range and this transition is analogous to the NMR motional narrowing phenomena in solids. Many observations at low temperatures suggest a non-random distribution of titanium ions in these glasses.