I. A. Sluchinskaya, A. I. Lebedev, A. Erko
X-ray diffraction studies showed that the structure of (Sr$_{1-x}$Pr$_x$)TiO$_3$ solid solutions at 300 K changes from cubic $Pm3m$ to tetragonal $I4/mcm$ with increasing $x$. The analysis of XANES and EXAFS spectra of the solid solutions revealed that Pr ions are predominantly in 3+ oxidation state, they substitute for Sr atoms and are on-center regardless of the preparation conditions. Weak dependence of the lattice parameter in (Sr$_{1-x}$Pr$_x$)TiO$_3$ on Pr concentration was explained by competition between relaxation of the Sr--O bond length, which results from the difference in ionic radii of Sr and Pr ions, and repulsion of positively charged Pr$^{3+}$ and Ti$^{4+}$ ions. It was shown that the most important defects which maintain charge neutrality in crystals are charged Sr vacancies and SrO planar faults; Pr does not substitute for Sr sites in the planar faults.
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http://arxiv.org/abs/1203.3066
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