1 A 5 B 6 C 7 Ferroelectrics as Novel Materials for Phononic Crystals Selami Palaz 1 , O. Oltulu 1 , A.M. Mamedov* 2,3 , E. Ozbay 2 1 Department of Physics, Harran University, Sanliurfa, Turkey 2 Nanotechnology Research Center (NANOTAM), Bilkent University, Ankara, Turkey 3 International Scientific Center, Baku State University, Baku, Azerbaijan * Corresponding e-mail: mamedov@bilkent.edu.tr Abstract: In the present work the acoustic band structure of a two-dimensional (2D) phononic crystal (PC) containing an semiconducting ferroelectrics - A 5 B 6 C 7 (A=Sb, Bi; B=S, Se, Te; C=I, Br, and Cl) were investigated theoretically and numerically by the plane-wave- expansion (PWE) method. Two-dimensional PC with square lattices composed of semiconducting ferroelectric cylindrical rods embedded in the organic/inorganic matrix are studied to find the existence of stop bands for the waves of certain energy. This phononic bandgap - forbidden frequency range - allows sound to be controlled in many useful ways in structures that can act as sonic filters, waveguides or resonant cavities. Phononic band diagram ω=ω(k) for a 2D PC was plotted versus the wavevector k along the Г-X-M-Г path in the square Brillouin zone (BZ) show four stop bands in the wide frequency range . The unusual properties of matrix and ferroelectric properties of A 5 B 6 C 7 give us ability to control the wave propagation through the PC in over a wide frequency range. We study the 2D composites by solving the basic acoustic wave equation and use Bloch wave analysis to identify the band gaps. Keywords: Phononic crystals, band gaps, metamaterials.