The phonon dispersions of graphene and graphene layers are theoretically investigated within fifth-nearest-neighbor forceconstant approach. Based on their symmetry groups, the number of Raman-and infrared-active modes at the point is given. Interatomic force constants are recalculated by fitting them to experimental phonon energy dispersion curves. Wavenumbers of optically active modes are presented as a function of number of layers (n). Our calculated results reproduce well the experimental data of G peak for graphene (1587 cm −1 ) and graphite (1581.6 cm −1 ) and clearly give the relation that ω G = 1581.6 + 11/(1 + n 1.6 ).

Raman spectra of ordinary and extraordinary phonons in LiNbO, and LiTaO, are recorded under a set of angles between wave vector and optic axis with the same backward scattering geometry, which makes all of the extraordinary phonons to appear in one directional-dispersion spectra series, and the directional dispersion is reliably determined. The symmetry and the number of polar phonons in both the crystals are found to be the same, 4AlrThe directional dispersion of extraordinary phonons has thirteen branches with similar coupling in LiNbO, and LiTaO,. C oc060B reoMeTpmeB paccemm ~a a a~ mccnenosaHbI cnewpbi KOM6HHaUMOHHO~O paCCeRHllR 06bIKHOBeHHbIX H HeO6bIKHOBeHHbIX @OHOHOB B LiNbO, II LiTaO, KpllCTaJIJIaX IlpH Cepllll YTJIOB MelKHy BOJIHOBbIM BeKTOPOM II OIITllqeCHOg OCbH). B OHHOfi CepHll CIIeK-TPOB YrJIOBOfi AIICIlepCIIll IlORBHJIllCb BCe IIOJIOCbI HeO6bIKHOBeHHbIX @OHOHOB , II YrJIOBaR ~EiClIepCllR gaCTOT 6bma OIlpeAeJIeHa HaAeWHO. CHMMeTPIIR II YllCJIO IIOJlRpHbIX QOHOHOB B 06011~ xpkicTannax opmaKoBb1, T.e. 4 A 1~ + 4 A 1~ + ~E T + EL. YrnoBa, Hmnep-CIIH HeO6bIKHOBeHHbIX @OHOHOB IIMeeT BeTBbI c n o~o 6~o H CBRBbH) B LiNbO, II LiTaO,. l) Weijin Road 94, Tianjun, The People's Republic of China.

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Infrared reflectance and Raman spectra of LBO crystals were recorded at room temperature and liquid nitrogen temperature. The vibrational modes are classified by the factor group analysis method and the spectral bands are assigned to vibrations of the (B306)3-ring and BO, tetrahedra.

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