Powder EPR study of the Jahn-Teller effect and phase transition in ${\mathrm{Cu}}^{2+}$:${\mathrm{ZnTiF}}_6$⋅${6\mathrm{H}}_2$O

A powder electron-paramagnetic-resonance study of ${\mathrm{Cu}}^{2+}$ in ${\mathrm{ZnTiF}}_6$⋅${6\mathrm{H}}_2$O has been made at 35 GHz in the range 4.2–300 K. The low-temperature structure has been related to four single-crystal Jahn-Teller transitions. The single-line spectrum at high temperature was replaced gradually by a multiline spectrum at temperatures below 165 K, i.e., about 6 K below the single-crystal transition temperature for 0.043 at. % ${\mathrm{Cu}}^{2+}$ concentration. The exponential line broadening with temperature in the high-temperature region (above phase transition) was fitted to an Orbach process, with an excited state at 1350 ${\mathrm{cm}}^{\mathrm{-}1}$. A Jahn-Teller stabilization energy $E_{\mathrm{JT}=1000\mathrm{}}$ ${\mathrm{cm}}^{\mathrm{-}1}$ may be obtained from this fit. The relaxation rate 1/$T_1$ is deduced and compared with that for ${\mathrm{Cu}}^{2+}$:${\mathrm{La}}_3$ ${\mathrm{Mg}}_2$(${\mathrm{NO}}_3$) ${}_{12}{}^{}{}_{}{}^{}\mathrm{O}$.