Averaging of electron spin resonance spectra of Cu2+ ions in SrO crystals due to motion near a paramagnetic center

The second less intensive spectrum (spectrum-2) of EPR Cu2+ ions is studied for SrO single crystals. The investigation is carried out for the temperature range 4.2 - 500 K. At 77 K spectrum -2 of Cu2+ ions has a rhombic symmetry with parameters gsub(z)=2.361, gsub(x)=2.082, gsub(y)=2.050. Axes X, Y, Z are parallel to the axes <100> of the crystal. With temperature increasing the lines corresponding to gsub(z) are slowly broadening, and the lines corresponding to gsub(x) and gsub(y) are broadening much faster and at 160 K vanish. At further increase in temperature instead of two groups of lines (gsub(x) and gsub(y)) there appears one group with gsub(tr) = 1/2(gsub(x) + gsub(y)) and the spectrum acquires a tetragonal symmetry. In the range of 170 - 270 K the line corresponding to gsub(tr) is narrowing. With T = 300 K all the lines are broadening and above 500 K are not detected. The effect of an one-side pressure upon spectrum-2 is studied experimentally. Possible mechanisms of reorientation and averaging of X and Y components of the crystal field affecting copper ions are proposed