Optical Properties and Phenomenological Theory of Ferri-Ferri Phase Transitions in Antiferroelectric Liquid Crystals P. Gisse, M. Sidir, V.L. Lorman, R. Farhi, J. Pavel and H.T. Nguyen J. Phys. II France, 7 12 (1997) 1817-1828 DOI: 10.1051/jp2:1997216