Electrical and magnetic properties of hexagonal BaTiO3-δ

The electrical resistivity, Hall coefficient, and magnetic susceptibility of n-type hexagonal BaTiO(3-delta) (hex-BaTiO(3-delta)) have been measured in the 5-400 K temperature range. Above 200 K this compound undergoes a transition from an insulating to a semiconducting state. Below 140 K Hall effect data indicate the existence of an energy gap of approximately 43 meV separating the localized electron ground state from the conduction band. Magnetic measurements reveal a strong magnetic anomaly in hex-BaTiO(3-delta) with a maximum in the susceptibility at around 160-200 K. This anomaly is quite similar to that of the hexagonal BaMg(1/3)Ru(2/3)O(3) which may indicate that the electron ground state in hex-BaTiO(3-delta) is comprised of spin singlet Ti(3+)-Ti(3+) dimers. We further propose that the thermal dissociation of these dimers is responsible for the change in the electron transport mechanism in hex-BaTiO(3-delta).