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Average and local atomic-scale structure in BaZrxTi1−xO3 (x D0:10, 0.20, 0.40) ceramics by high-energy x-ray diffraction and Raman spectroscopy

Highresolution xray diffraction (XRD), Raman spectroscopy and total scattering XRD coupled to atomic pair distribution function (PDF) analysis studies of the atomicscale structure of archetypal BaZrxTi1−xO3 (x D0:10, 0.20, 0.40) ceramics are presented over a wide temperature range (100–450 K). For x D0:1 and 0.2 the results reveal, well above the Curie temperature, the presence of Tirich polar clusters which are precursors of a longrange ferroelectric order observed below TC. Polar nanoregions (PNRs) and relaxor behaviour are observed over the whole temperature range for x D0:4. Irrespective of ceramic composition, the polar clusters are due to locally correlated offcentre displacement of Zr=Ti cations compatible with local rhombohedral symmetry. Formation of Zrrich clusters is indicated by Raman spectroscopy for all compositions. Considering the isovalent substitution of Ti with Zr in BaZrxTi1−xO3, the mechanism of formation and growth of the PNRs is not due to charge ordering and random fields, but rather to a reduction of the local strain promoted by the large difference in ion size between Zr4C and Ti4C. As a result, nonpolar or weakly polar Zrrich clusters and polar Tirich clusters are randomly distributed in a paraelectric lattice and the longrange ferroelectric order is disrupted with increasing Zr concentration.

relaxors; BaTiO3; Raman spectroscopy; highenergy

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