Structural origin of recovered ferroelectricity in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>BaTi</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math> nanoparticles
Han Zhang, Shining Liu, Sanjit Ghose, Bruce Ravel, Ighodalo Idehenre, Y. A. Barnakov, S. A. Basun, Dean R. Evans, Trevor A. Tyson
Abstract
Nanoscale $\mathrm{BaTi}{\mathrm{O}}_{3}$ particles $(\ensuremath{\approx}10$ nm) prepared by ball-milling a mixture of oleic acid and heptane have been reported to have an electric polarization several times larger than that for bulk $\mathrm{BaTi}{\mathrm{O}}_{3}$. In this work, detailed local, intermediate, and long-range structural studies are combined with spectroscopic measurements to develop a model structure of these materials. The x-ray spectroscopic measurements reveal large Ti off-centering as the key factor producing the large spontaneous polarization in the nanoparticles. Temperature-dependent lattice parameter changes manifest sharpening of the structural phase transitions in these $\mathrm{BaTi}{\mathrm{O}}_{3}$ nanoparticles compared to the pure nanoparticle systems. Sharp crystalline-type peaks in the barium oleate Raman spectra suggest that this component in the composite core-shell matrix, a product of mechanochemical synthesis, stabilizes an enhanced polar structural phase of the $\mathrm{BaTi}{\mathrm{O}}_{3}$ core nanoparticles.