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首页> 外文期刊>Physica, C. Superconductivity and its applications >Raman study of phonons and crystal-field excitations in NdBa2Cu3-xGaxO7-delta
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Raman study of phonons and crystal-field excitations in NdBa2Cu3-xGaxO7-delta

机译：NdBa2Cu3-xGaxO7-δ中声子和晶体场激发的拉曼研究

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摘要

We have performed Raman measurements on a series of NdBa2Cu3-xGaxO7-delta ceramics (0 < x < 0.08) in order to monitor the influence of Ga doping on the properties of these materials. While the O(4) apex-oxygen phonon exhibits a considerable softening of (14 +/- 2) cm(-1) with increasing Ga content between x = 0.00 and 0.08, the O(2)+O(3) in-phase phonon frequency is much less influenced. At low temperature, the O(2)-O(3) out-of-phase vibration is split into two peaks by interaction with a Nd3+ crystal-field (CF) excitation of similar energy. Using a two-level model, we derive from the spectra the energies of the uncoupled phonon and the CF excitation, as well as the coupling constant of the CF-excitation-phonon interaction. The coupling constant and the phonon frequency are almost independent of Ga doping, while the energy of the CF excitation is (5.6 +/- 1.6) cm(-1) lower in NdBa2Cu2.92Ga0.08O7-delta than in NdBa2Cu3O7-delta. This decrease is attributed to changes in the positions and charges of the oxygen ions in the CuO2 planes. Using structural data obtained by neutron diffraction, we perform a point-charge-model calculation to separate structural and charge-transfer contributions to the observed change in the CF level energy. We find that the negative oxygen charge in the CuO, planes is increased by about 1% in NdBa2Cu2.92Ga0.08O7-delta as compared to the Ga-free sample. (C) 1998 Elsevier Science B.V. All rights reserved. [References: 28]
机译：我们已经对一系列NdBa2Cu3-xGaxO7-delta陶瓷（0

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