H. Aroui

Ca doping in BaTiO3 crystal: Effect on the Raman spectra and vibrational modes

Polarized Raman measurements were carried out in a 3% Ca- doped BaTiO3 (BCT) single crystal and compared with those in undoped BaTiO3 (BT) in order to study the effect of Ca2+ incorporation into the BT lattice. Spectra recorded at room temperature in BCT show peaks unexpected by the Raman selection rules in BT, proving an off-centering of Ca with respect to the Ba site in BT. Main phonon lines A1 polarized along the ferroelectric c axis are notably shifted to lower frequency by Ca doping, while the phonons E in the plane normal to c are nearly unaffected. In addition, the modes A1 are highly anharmonic, even more than in BT, as revealed by the temperature dependences of their frequency and damping which are analyzed in terms of 3rd and 4th order anharmonic potential.

Semi-classical calculations of self-broadening coefficients of OCS and HCN at temperatures between 200 K and 298 K

Graphical abstract Comparison between measured [9] and theoretical (present work) self-broadening coefficients of the ν2 band of HCN. The experimental values at temperatures 267 K, 232 K and 212 K were deduced using Eq. (16) and measured values of n exponent of Ref. [9].