Structural and chemical analysis of colossal magnetoresistance manganites by Raman spectrometry - art. no. 104430

Colossal magnetoresistance manganites in a wide composition range can be sy stematically characterized by Raman spectrometry with respect to the cation substitution in the A sublattice of the perovskite structure, oxygen isoto pe exchange, and variations of the Mn3+/Mn4+ ratio. The effects can be clea rly separated by analysis of the experimental band shifts of the A(g)(2) so ft mode as a function of the tolerance factor t and a parameter V(1/3)t, wh ere V is the perovskite cell volume. This allows us to structurally and che mically analyze mixed-valence manganites in the series (La1-xPrx)(0.7)(Ca0. 3MnO3)-O-16 (La1-xPrx)(0.7)(Ca0.3MnO3)-O-18 (x =0-1), (La0.25Pr0.75)(1-x)Ca xMnO3 (x=0.2-0.5), R1-xSrxMnO3 (x=0.33, 0.45, R=Nd, Nd0.5Sm0.5 Sm, Eu, Gd), La0.7Sr0.3MnO3, La0.35Pr0.35Sr0.3MnO3, La0.5Ca0.5MnO3, LaMnO3. The band sh ift indicates in particular the existence of doped holes on Mn sites but no t on the oxygen sites, thus providing validation for the basic assumptions of the Zener double exchange model. The mechanism of lattice strain in thin films of the compounds was tested; variations of the Jahn-Teller distortio n and valence angle perturbations can in this case be separated by Raman sp ectrometry.