Relaxor ferroelectric and photocatalytic behaviour of Ba_(0.785)Bi_(0.127)Y_(0.017)TiO_3 composition

摘要

The composition of Ba_(0.785)Bi_(0.127)Y_(0.017)TiO_3 (BaBiYTiO) belongs to the Ba_(0.785)Bi_(0.127)Y_(0.017)TiO_3 system. A dielectric study on ceramics performed at temperatures in the range (77 K-500 K) and frequency (10~2-2 x 105 Hz) revealed ferroelectric relaxor behaviour with a phase transition close to room temperature. The conductivity of BaBiYTiO obeys to an Arrhenius-type law with activation energy equals to 0.21 eV, in conformity with a small polaron hopping where most electrons are localized. The oxide is lightly doped leading to a wide space charge region (480 nm) in which photoeffect occurs. The presence of domains promotes the separation of the charge carriers through conversion of light into chemical energy. The electrode acquired n-type behaviour, evidenced from the negative thermopower and anodic photocurrent. The fiat band potential V_(ft), (-0.46 V_(SCE)) and the electron density N_D (2.82 × 10~(15)cm~(-3)) were determined in KOH solutions (0.5 M). The Nyquist plot exhibits two well denned time constants characteristic of bulk and grains boundaries contributions and an equivalent electrical circuit has been proposed according to the Randies model. The energy band diagram shows the potentiality of the oxide for the solar-energy conversion. BaBiYTiO has been tested successfully for H_2 production upon visible light when combined to the delafossite CuFeO_2 as sensitizer. An evolution rate of 24 μmol mn~(-1) and a quantum yield of 0.4% under poly chromatic light were obtained.