Raman Spectra and Directional Dispersion in LiNbO₃ and LiTaO₃

Abstract

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.

Ferroelectric phase transition of stoichiometric lithium tantalate studied by Raman, Brillouin, and neutron scattering

“…The phonon frequency exhibits only a small dependence on the lithium composition of a crystal, while the phonon damping is very sensitive to it, the same as the case of LN. 26,29 In the present study, the damping of A 1 ͑TO 1 ͒ mode is 15 cm −1 for SLT, while for CLT it is 25 cm −1 . The Raman spectra at RT are noteworthy from the two aspects in comparison with those previously reported.…”

Raman studies of ferroelectric domain walls in lithium tantalate and niobate

“…The E(TO6) phonon mode was not shifted at all. These shifts are not correlated with the shifts that are caused by the directional dispersion of the polar Raman modes [13] which we have measured under crystal rotation. This excludes a tilt of the ferroelectric axis in the domain wall vicinity as the origin of the effect.…”

Influence of ferroelectric domain walls on the Raman scattering process in lithium tantalate and niobate

“…In both polarization measurement geometries, the spectral regions that increase in intensity overlap with the directional dispersion curves [10] due to phonons propagating in directions not parallel to the laser axis. For instance, there is evidence for the presence of the ATO 3 (356 cm −1 ) and ATO 4 (597 cm −1 ) modes in the zxx z geometry.…”

“…Instrumental to our study is the fact that, in LiTaO 3 and LiNbO 3 , phonon modes that propagate in different directions have slightly different frequencies. By comparing the frequency of the Raman peak with this directional dispersion effect [10][11][12], it is possible to identify the phonon mode and its propagation direction.The Raman modes expected in a particular experimental geometry can be determined from conservation of momentum, which limits the propagation directions of the phonon, in combination with the Raman scattering efficiency equation for uniaxial crystals given by Loudon [13]. In the backscattering geometry, the Raman modes present in the spectra from the bulk crystal correspond to phonons that propagate parallel to the laser axis.…”

“…Instrumental to our study is the fact that, in LiTaO 3 and LiNbO 3 , phonon modes that propagate in different directions have slightly different frequencies. By comparing the frequency of the Raman peak with this directional dispersion effect [10][11][12], it is possible to identify the phonon mode and its propagation direction.…”