CONDUCTIVITY OP BaTiO₃. PURE SINGLE CRYSTALS AND DOPED (Fe, OH) SINGLE CRYSTALS

Abstract
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 W_a and injection energy W_i 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.