Dielectric properties of Bi-substituted LDHs synthesized by co-precipitation and sol-gel methods

Magnesium-aluminum-bismuth layered double hydroxides (Mg₃Al_1−xBi_x; LDHs) were prepared using both coprecipitation and sol-gel methods. For the preparation of Mg/Al/Bi LDH by the co-precipitation method, the appropriate amounts of dissolved starting materials (Al(NO₃)₃ · 9H₂O, Mg(NO₃)₂ · 6H₂O and Bi(NO₃)₃ · 5H₂O) were mixed with a solution of NaHCO₃:NaOH. In the sol-gel processing, the precursor Mg–Al–Bi–O gels were synthesized using the same starting materials and ethylene glycol as complexing agent. The mixed-metal oxides obtained by subsequent heating of Mg–Al–Bi–O gels at 650 °C were reconstructed to Mg₃Al_1−xBi_x LDHs in water at 80 °C. All the synthesized products were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and dielectric measurements.