1. B. Lüthi, Physical Acoustics in the Solid State, 2nd edn. (Springer, Berlin, 2005), pp. 119–146
2. M.D. Sturge, in The Jahn-Teller Effect in Solids, ed. by S. Frederick, D. Turnbull, H. Ehrenreich. Solid State Physics, vol 20 (Academic, New York, 1967), p. 89
3. V.V. Gudkov, A.T. Lonchakov, V.I. Sokolov, I.V. Zhevstovskikh, V.T. Surikov, Phys. Rev. B 77 155210 (2008)
4. L.D. Landau, E.M. Lifshitz, Theoretical Physics: Theory of Elastisity, vol.7 (Nauka, Moscow, 1987) (in English: Addson-Wesley, Reading, MA, 1959)
5. R.N. Thurston, in Physical Acoustics: Priciples and Methods, ed. by W.P. Mason, vol 1A (Academic, New York, 1964)