Lattice vibrations of ABi2Nb2O9 crystals (A = Ca, Sr, Ba)

A normal coordinate analysis has been made to investigate the Raman and the infrared wavenumbers in ABi2Nb2O9 crystals (A = Ca, Sr, Ba) (ABN) having space group A21am   (No. 36, C2v12). The calculation of zone center phonons incorporates nine stretching and nine bending force constants. The Raman and the infrared frequencies for ABN crystals (A = Ca, Sr, Ba) have been assigned for the first time in A21am phase. The calculated Raman and infrared wavenumbers are in very good agreement with the observed ones. The potential energy distribution has also been investigated for determining the significance of contribution from each force constant toward the Raman and the infrared wavenumbers.