Parameters of the potential well of an off-center Ge atom in a GeTe-SnTe solid solution
An method is proposed for determining the shape of the three-dimensional multiwell potential of an off-center atom from EXAFS data. The parameters of the potential well of a Ge atom in GeTe and Sn1−xGexTe (x ≥ 0.4) are determined in the classical and quantum-mechanical approximations. The potential-well depth is varied in the interval 20–40 meV depending on the Ge content, which indicates that the phase transition in these crystals is intermediate in character between the displacement and order-disorder transitions. From analyzing the conditions for the applicability of the classical approximation, it follows that quantum effects must be taken into account in determining the parameters of the potential well of an off-center Ge atom in Sn1−xGexTe. Quantum-mechanical calculations show that the energy of the lower level in the vibration spectrum of the Ge atom coincides with the maximum energy in the potential well to within several millielectronvolts. The high probability of tunneling or an over-barrier transition of the off-center atom between the potential-well minima prevents dipole reorientations from being frozen at low temperatures.
PACS numbers61.10.Ht 61.72.-y 77.84.Bw
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