Raman spectra of Bi4-xLaxTi3O12 have been investigated. For an increasing degree of La doping, we find a substantial hardening of the vibration involving Bi atoms at the perovskite A site, whereas the Bi mode at the Bi2O2 layer is negligibly changed. From a comparison with a simple mass consideration, we identify a precise cation distribution, which indicates a pronounced site selectivity of La ions for the A site for x < ∼ 1. At room temperature, the lowest mode at 28 cm-1 shows a significant softening with La doping. This behaviour resembles the temperature dependence in the nondoped material (at constant composition). A remarkable correlation is found between the soft-mode frequency and TC for Bi4-xLaxTi3O12. We suggest that this correlation, as well as the soft-mode frequency for substituted materials, offers useful guidelines for designing materials in a controlled manner.
|Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers
|Published - 2001 9月
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