Eberhard Zirngiebl

Characterization of the intergrain properties of YBa2Cu3O7−x by Raman spectroscopy

Abstract The identification of the oxygen vibrations of YBa 2 Cu 3 O 7− x by Raman spectroscopy may be affected by impurity phases. The latter gave rise to the puzzle that Raman scattering of fractured polycrystalline samples exhibited up to 10% BaCuO 2 (deduced from the 640- cm −1 peak intensity), whereas 1% was deduced from X-ray and magnetic susceptibility measurements. We found that the BaCuO 2 contribution in the Raman spectrum is strongly reduced by measuring on mechanically cut and polished surfaces of polycrystalline samples. This reveals that the grains are coated by BaCuO 2 , possibly due to an eutectic melt of BaCuO 2 and CuO. Annealing BaCuO 2 in argon proves that the 640-cm −1 peak intensity is a measure of the oxygen content of the BaCuO 2 and is not due to the oxygen vibration along the Cu-O chains of the YBa 2 Cu 3 O 7− x .

Chapter 95 Light scattering in intermetallic compounds

Publisher Summary This chapter presents a status report on the progress that has been made in applying light scattering to various rare-earth (R) intermetallic compounds with the emphasis on Kondo- and intermediate valence-type materials. In this field of research, light scattering provides detailed information about localized electronic excitations—such as crystalline electric field (CEF) excitations, spin–orbit-split multiplet excitations—and phononic and elastic properties. An overview of the rather diverse features observed by Raman scattering in metallic R compounds ranging from purely electronic excitations to phonons and strongly coupled electron–phonon excitations is presented in the chapter. The primary interest in investigating mixed-valence materials using Raman scattering arose from the estimate that the inverse timescale of the 4f-charge fluctuations inducing volume changes of up to 15% may be of the order of the phonon frequencies. Hence, early Raman scattering experiments in intermediate-valence materials is concerned with the investigation of phonon anomalies and their relation to the electron–phonon interaction. Polarized Raman scattering has provided an experimental test of the relative importance of the different charge deformabilities introduced in the lattice dynamical model calculations.