Structural inhomogeneities in fast ion conducting glasses

Abstract

The structures of the ion conducting glasses ${\mathrm{L}\mathrm{i}\mathrm{C}\mathrm{l}\ensuremath{-}\mathrm{L}\mathrm{i}}_{2}{\mathrm{O}\ensuremath{-}2\mathrm{B}}_{2}{\mathrm{O}}_{3},$ $({\mathrm{A}\mathrm{g}\mathrm{I})}_{0.6}{\ensuremath{-}(\mathrm{A}\mathrm{g}}_{2}{\mathrm{O}\ensuremath{-}\mathrm{B}}_{2}{\mathrm{O}}_{3}{)}_{0.4},$ ${\mathrm{C}\mathrm{s}\mathrm{I}\ensuremath{-}4\mathrm{AgPO}}_{3},$ and ${\mathrm{PbI}}_{2}{\ensuremath{-}9\mathrm{AgPO}}_{3}$ have been investigated using small- and wide-angle neutron diffraction experiments. We have applied the reverse Monte Carlo modeling method to the experimental data with the aim to reveal the intermediate-range structure on a length scale of 5\char21{}50 \AA{}. The $({\mathrm{A}\mathrm{g}\mathrm{I})}_{0.6}{\ensuremath{-}(\mathrm{A}\mathrm{g}}_{2}{\mathrm{O}\ensuremath{-}\mathrm{B}}_{2}{\mathrm{O}}_{3}{)}_{0.4}$ glass shows exceptionally high scattering intensity at low Q values (0.5 ${\mathrm{\AA{}}}^{\mathrm{\ensuremath{-}}1}$) due to the existence of chemical inhomogeneities on length scales up to at least 50 \AA{}. Both the salt ions and the network atoms are inhomogeneously distributed. The first diffraction peak, located at 0.46 ${\mathrm{\AA{}}}^{\mathrm{\ensuremath{-}}1}$ in the total structure factor, is caused by a characteristic distance between B-O segments separated by salt ions. The ${\mathrm{L}\mathrm{i}\mathrm{C}\mathrm{l}\ensuremath{-}\mathrm{L}\mathrm{i}}_{2}{\mathrm{O}\ensuremath{-}2\mathrm{B}}_{2}{\mathrm{O}}_{3}$ glass shows inhomogeneities only in the distribution of salt ions, where particularly the chlorine ions are very inhomogeneously distributed. The ion concentration fluctuations occur on a wide range of length scales. In contrast to the investigated borate glasses, the two phosphate glasses show only minor structural inhomogeneities on length scales above 10 \AA{}.