EPR spectral study and modeling of lithium borovanadate RLi$_{2}$OB$_{2}$O$_{3}$KV$_{2}$O$_{5}$ glasses

Utilizing electron paramagnetic resonance EPR spectroscopy, lithium borovanadate RLi$_{2}$OB$_{2}$O$_{3}$KV$_{2}$O$_{5}$ glasses with R = 0.4 and K ranging from 0.1 to 0.5 were analyzed in order to elucidate the environment of unpaired 3d$^{1}$ electrons. Transitions associated with coupling of such electrons to vanadium nuclear spins were identified and modeled to reveal both g factor and A factor values. For a system with K = 0.3, representative data include: g$_{ll}$ = 1.9242, g$_{\bot }$ = 1.9693, A$_{ll}$ = 184.3768 cm$^{-1}$, A$_{\bot }$ = 64.6568 cm$^{-1}$, $\Delta $g$_{ll}$ = 0.0781, $\Delta $g$_{\bot }$ = 0.0330, and $\Delta $g$_{ll}$/$\Delta $ g$_{\bot }$ = 2.3670. A comparison revealing g$_{ll}<$ g$_{\bot } \quad <$g$_{e}$ is indicative of localized electrons residing in tetragonally-distorted octahedral sites. A slight increase observed in $\Delta $g$_{ll}$/$\Delta $ g$_{\bot }$ values when K = 0.1 to K = 0.3 is further evidence of a possible elongation of the octahedral site associated with increasing K values. This pattern, however, is not present in systems with K values greater than 0.3, suggesting that perhaps no further elongation of the site is possible due to bond constraints. A comprehensive model will be presented to summarize data for the entire family of lithium borovanadates studied here.