Structural characterization of A-site nonstoichiometric (1 − x)Bi0.5Na0.5TiO3–xBaTiO3 ceramics
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Lead-free 1 − x(Bi0.5Na0.5TiO3)–xBaTiO3, x = 0.055, 0.06 and 0.07, ceramics [i.e., near the morphotropic phase boundary (MPB)] were modified by varying the A-site cation stoichiometry to induce acceptor and donor doping through the addition of excess Na and Bi, respectively. The role of A-site nonstoichiometry on the crystal structure was investigated by using Raman spectroscopy and high-energy X-ray diffraction (XRD) techniques. The Raman spectra were analyzed via spectral deconvolution, and the resultant fitted data demonstrated deviations in the dominant bands (at 200–400 cm−1 and 400–600 cm−1) which indicated a shift toward tetragonal distortions in all Na-excess samples. High-energy XRD data showed that all the characteristic peaks corresponding to tetragonal P4bm structure became more prominent in Na-excess sample. Rietveld refinement data confirmed the coexistence of rhombohedral (R3c) and tetragonal (P4bm) phases with a significant increase in P4bm phase fraction in Na-excess composition. The clear agreements between Raman spectroscopy and high-energy XRD data suggest that Bi-excess samples (i.e., donor doping) had little or no effect on crystal structure, whereas Na-excess samples (i.e., acceptor doping) had a significant influence on the structure near the MPB such that tetragonal distortions were induced in both the local structure and the long-range average structure.
This work was financial supported by faculty of science, Naresuan University. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
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The authors declare that they have no conflict of interest.
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