Relaxor ferroelectric and photo-electrochemical properties of lead-free Ba1−xEu2x/3(Ti0.75Zr0.25)O3 ceramics. Application to chromate reduction

• Chromate photoreduction is performed on lead free relaxor Ba1−xEu2x/3(Ti0.75Zr0.25).
• The dielectric relaxation rate follows the Vogel–Fulcher law.
• The capacitance plot shows n-type conduction with flat band potential of −0.60 VSCE.
• 95% of chromate (10−4 M) is reduced after 6 h of exposition to solar light (AM1).

The perovskite Ba1−xEu2x/3Ti0.75Zr0.25O3 (x = 0.025, 0.05) have been prepared by solid state reaction. A dielectric study on ceramics performed in the ranges of temperature (77–500 K) and frequency (102–2 × 105 Hz) reveal typical relaxor behavior and diffuse phase transition. The relaxor parameters (Tm, ΔTm, Δεr′/εr′) decrease slightly with the increase of Eu-dopant concentration. The dielectric relaxation rate follows the Vogel–Fulcher relation with activation energy of 21 meV, an attempt frequency fo = 1.1 × 108 Hz and a static freezing temperature Tf = 95 K for x = 0.025. An optical gap of 2.25 eV is obtained from the diffuse reflectance spectrum. The photo-electrochemistry throws light on the nature of the electronic bands. The Mott-Schottky plot is characteristic of n-type conduction from which a flat band potential of −0.60 VSCE and an electrons density of 1.2 × 1018 cm−3 are determined for the composition x = 0.025. The upper valence band located at 6.4 eV below vacuum is made up of O2−: 2p orbital whereas the conduction band consists of empty 3d levels (4.13 eV) with a high reducing ability. The energetic diagram clearly assesses the photoactivity of the perovskite. The performance is improved when the crystallite size becomes comparable with the length of the nanodomains. As application, 95% of chromate (10−4 M) is reduced after 6 h of exposition to sunlight (AM1).