On the basis of infra-red spectra and protonic conductivity measurements, a model was proposed for H ion migration in K1-yLiyTa1-xNbxO3 doped crystals, and was used to make an estimate of the pre-exponential factor. It was supposed that the H ions were generally bounded along a line which connected the 2 second-nearest O ions. However, jumping occurred only between the 2 nearest O ions. Besides the vibration, the [OH] bands also exhibited a librational motion which could be described by an harmonic oscillator potential. The model showed that the transition energy of the second, and higher, overtone of the [OH] vibration could be higher than the activation energy for H ion migration. The expected value of the pre-exponential factor (2.07 x 10-9m2/s) was in agreement with experimental results.

X.Tong, M.Zhang, A.Yariv, A.Agranat: Applied Physics Letters, 1996, 69[22], 3345-7