The dielectic response of K x Al x Ti8?x O16 and K x Mg x/2 Ti8?x/2 O16

• DOI: 10.1007/bf00549302
• Publication Date: 2004-11-19T09:35:50Z
• Authors: A. K. Jonscher; K. L. Deori; J. -M. Reau; J. Moali
• Keywords: Hollandite; Dielectric response; Exponent

Materials of the hollandite structure with the general formulae Kx Alx Ti8−x O16 and Kx Mgx/2 Ti8−x/2 O16 have been synthesized in the composition range 1.6⩽x⩽2.0 and their dielectric properties have been measured in the temperature range 77 to 800 K and the frequency range 10−3 to 106 Hz. The observed response shows a whole range of features characteristic for both charge carrier and dipolar polarization processes and these are seen as being associated with the one-dimensional transport in channels in the hollandite structure. At low temperatures the dominant response is the “universal” dielectric relation in which the loss follows the law x″(ω) ∢ ωn−1, with the exponent n<1 and equal specifically to approximately 0.7. This is followed at 120 to 180 K by a distinct loss peak superimposed on the above law, and finally at higher temperatures by a region of strong dispersion which is associated with strongly interacting many-body processes between charged carriers restricted by defects to move in limited regions of the channels.