The permittivity and the conductivity of Ba-hollandite Ba1.16M2.32Ti5.68O16 (M = Al, Ga) observed by dielectric spectroscopy

Broadband dielectric and resistivity spectra of sintered Ba1.16Al2.32Ti5.68O16 and Ba1.16Ga2.32Ti5.68O16 hollandites were recorded in a frequency range 40–1.1 × 108 Hz at temperatures varying between 320 and 440 K. All the data are presented in the form of complex permittivity and resistivity diagrams in order to obtain respectively the lattice permittivity and the thermal behaviour of the ionic conductivity with respect to the nature and the dielectric polarizabilities of the ionic species in hollandites. A dielectric relaxation was observed depending on the hollandite type and the temperature. A tentative assignment of this relaxation to physical mechanisms is proposed: thermal activated hopping and on-site large amplitude fluctuations of Ba2+ ions.