Jahn-Teller Effects in the Electron Paramagnetic Resonance of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">Cu</mml:mi></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math>in Ca<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mn/><mml:mo>(</mml:mo><mml:mi mathvariant="normal">OH</mml:mi><mml:mo>)</mml:mo><mml:mn/></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

The EPR spectra of ${\mathrm{Cu}}^{++}$ present as an impurity in haxagonal Ca${(\mathrm{OH})}_{2}$ has been investigated in the temperature range 85-380\ifmmode^\circ\else\textdegree\fi{}K. Below 145\ifmmode^\circ\else\textdegree\fi{}K, the EPR spectra, I, show a "static" Jahn-Teller effect (JTE) with ${g}_{\mathrm{II}}=2.421$, ${g}_{\ensuremath{\perp}}=2.079$, $^{65}A=142\ifmmode\pm\else\textpm\fi{}1$ G, $^{63}A=132\ifmmode\pm\else\textpm\fi{}1$ G, $^{65}B=^{63}B=0\ifmmode\pm\else\textpm\fi{}3$ G. Above 145\ifmmode^\circ\else\textdegree\fi{}K, the spectrum, III, is due to the "dynamic" JTE with ${g}_{\mathrm{II}}=2.241$, ${g}_{\ensuremath{\perp}}=2.172$, $A=48$ G and $B=37$ G. These values for III are almost exact averages of the corresponding values for I when the latter executes hindered rotation about the hexagonal $c$ axis. Further support for this interpretation is provided by the studies of peak-height dependence on temperature for both the static and dynamic spectra.

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