Phase transitions and Raman spectra correlations in La2-xSrxCuO4(0.0 <= x <= 0.45)

The doping (x) and temperature dependence of the structural parameters and Raman spectra of high-quality La2-xSrxCuO4 polycrystalline compounds with x = 0.0-0.45 have been investigated. For x = 0 the squared frequency and the linewidth of the soft mode attributed to the tilting vibrations of the CuO 6 octahedra about the (110) axis vary linearly with the laser-induced tempe rature rise. A similar behavior is observed at low temperatures for x great er than or equal to 0 that correlates the softening of this mode with the t etragonal-to-orthorhombic transition for the Sr-doped compounds. Changes in the apex oxygen phonon characteristics are correlated with the tetragonal- to-orthorhombic phase transition. At room temperature the relative intensit y of the La/Sr mode and another mode at similar to 150 cm(-1) when compared to the apex one follows very closely the variation of the superconducting transition temperature with Sr content. This correlation is attributed to a charge redistribution at room temperature that affects the transition temp erature and the bonding orbitals of the La/Sr, the apex, and the similar to 150 cm(-1) phonons.