Investigation of lattice-dynamical effects and hyperfine interactions in ZnO byZn67Mössbauer spectroscopy

Using the high-resolution 93.3-keV transition in ${}_{}{}^{67}{}_{}{}^{}\mathrm{Zn}$ we studied the temperature dependence of the Lamb-Mössbauer factor (LMF), the center shift, and the quadrupole interaction in ZnO single crystals. The temperature range for this high-energy Mössbauer resonance could be extended up to liquid-nitrogen temperature (77.3 K). The mean-square atomic displacements show very little anisotropy. The results on the LMF can well be described by the Debye model with ${\mathrm{FTHETA}}_D^{\mathrm{LMF}\mathrm{\sim }317}$ K. The quadrupole interaction is $e^2$qQ/h=2.401±0.004 MHz at 4.2 K and it is independent of temperature within 1%. At 77.3 K the center shift has changed by 9.0 μm/s compared to its value at 4.2 K. Already at low temperatures, phonon-induced electron transfer from zinc to oxygen is observed. The shift caused by charge transfer shows a $T^4$ dependence at low temperatures, in agreement with theoretical calculations.