Electrical and magnetic properties of hexagonal BaTiO$_{3-\delta}$
T. Kolodiazhnyi, A. A. Belik, S. C. Wimbush, and H. Haneda

The electrical resistivity, Hall coefficient and magnetic susceptibility of n-type hexagonal \btd\ (hex-\btd) 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 ca.\ 43 meV separating the localized electron ground state from the conduction band. Magnetic measurements reveal a strong magnetic anomaly in hex-\btd\ 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-\btd\ 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-\btd.

© 2008 The American Physical Society.