Nonlinear elastic behaviour of crystals in the quantum paraelectric regimeA. V. Kityk, W. Schranz, P. Sondergeld, D. Havlik, E. K. H. Salje and J. F. ScottEurophys. Lett., 50 1 (2000) 41-47DOI: https://doi.org/10.1209/epl/i2000-00232-4