1. For some recent reviews see Ferraro, J.R., Maroni, V.A.: Preprint. Appl. Spectrosc. (submitted for publication), Thomsen, C., Cardona, M.: In: Physical properties of high-temperature superconductors. Ginsberg, D.M. (ed.), p. 409. Singapore: World Scientific 1989
2. Timusk, T., Reedyk, M., Hughes, R., Bonn, D.A., Garrett, J.D., Greedan, J.E., Stager, C.V., Tanner, D.B., Feng, G.Å., Herr, S.L., Kamaras, K., Thomas, G.A., Cooper, S.L., Orenstein, J., Schneemeyer, L.F., Mills, A.J.: Physica C162?164, 841 (1989)
3. See for example the articles in the Series: Vibrational spectra and structure. Durig, J.R. (ed.) Amsterdam: Elsevier as well as articles in Spectrochim. Acta, A35 (1979)
4. For a recent discussion on the vibrational spectra of layered materials see Nakashima, S., Hangyo, M., Mitsuishi, A.: In: Vibrational spectra and structure. Durig, J.R. (ed.), Vol. 14, p. 305. Amsterdam: Elsevier 1981
5. Kress, W., Schroder, U., Prade, J., Kulkarni, A.D., De Wette, F.W.: Phys. Rev. B38, 2906 (1988)