Electron Paramagnetic Resonance of ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Ni}}^{3+}$ in KTa${\mathrm{O}}_3$

The electron paramagnetic resonance of ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Ni}}^{3+}$ in KTa${\mathrm{O}}_3$ is reported. Both impurity ions are substitutional at the two cation sites of the host. For ${\mathrm{Fe}}^{3+}$ the room-temperature $a$ values are 288±5×${10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ for ${\mathrm{Fe}}^{3+}$ on ${\mathrm{Ta}}^{5+}$ site, and 30±1×${10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ for ${\mathrm{Fe}}^{+3\mathrm{}}$ on the ${\mathrm{K}}^{+1\mathrm{}}$ site. The temperature variation of these parameters is discussed. ${\mathrm{Ni}}^{3+}$ at the ${\mathrm{Ta}}^{5+}$ is in a low-spin configuration and undergoes a Jahn-Teller axial distortion. Estimates of $10Dq$ from $g$-shift formulas and axial ground-state splitting from line broadening are given. The resonance of ${\mathrm{Ni}}^{3+}$ at the ${\mathrm{K}}^{+1\mathrm{}}$ site indicates a negative crystal field with a $10Dq$ value of 7400 ${\mathrm{cm}}^{-1\mathrm{}}$ derived from a $g$-shift formula.