We present cw and pulsed EPR experiments on ${\mathrm{V}}^{4+}$ in the rutile and anatase phases of ${\mathrm{TiO}}_2$. For the rutile phase, the cw data confirm earlier results, but the relaxation data are different from those previously reported. No earlier results for ${\mathrm{V}}^{4+}$ in the unreduced pure anatase phase exist. We show that a simple point-charge model can be used to interpret the values of the g tensors, but that models considering only nearest neighbors will give erroneous results. We conclude that the observed ${\mathrm{V}}^{4+}$ is substitutional in the rutile, but interstitial in the anatase phase. We propose a relaxation mechanism through phonon-modulated hyperfine coupling to explain our $T_1$ data in the rutile phase.

• Received 21 April 1986

DOI:https://doi.org/10.1103/PhysRevB.34.3060