J. Phys. Colloques
Volume 33, Numéro C2, Avril 19722e CONGRÈS EUROPÉEN DE FERROÉLECTRICITÉ
|Page(s)||C2-120 - C2-122|
J. Phys. Colloques 33 (1972) C2-120-C2-122
CONDUCTIVITY OP BaTiO3. PURE SINGLE CRYSTALS AND DOPED (Fe, OH) SINGLE CRYSTALSMme GODEFROY G. and M. COUSON B.
When single crystals of barium titanate are placed under d. c. voltage, they are crossed by a constant and reproducible current after ageing (repeatedly applied voltages followed by earthing). Characteristics i = f (V) obtained with aged crystals are divided into 2 sections : for low voltages, ohmic law ; for high voltages parabolic law. Constants γ and α which are deduced from these laws, increase exponentially with 1/T. Activation energy Wa and injection energy Wi are calculated. A band scheme with two trap-levels may explain our experimental results : a shallow level traps some cathode-injected electrons while a deep level receives electrons from the valence band and ensures a hole-conductivity with low voltage. The shallow levels are more numerous than the deep levels ; both are compensated by ionic impurities which in no way affect conduction. Since the position of the trap-levels depends very little on dopage, the shallow levels are imputed to oxygen vacancies with a trapped electron (F centre) and deep levels to oxygen vacancies without electrons.