Induced modifications in structural, microstructural, and ferroelectric properties of bismuth ferrite ceramics doped with lanthanum and europium

The series of ten ceramic samples with the composition Bi1-xLaxFeO3 (x = 0.05; 0.10; 0.15), Bi1-yEuyFeO3 (y = 0.05; 0.10; 0.15) and Bi1-(x+y)LaxEuyFeO3 (x = y = 0; 0.025; 0.05; 0.075), obtained by sintering at 835 °C of the as-prepared powders synthesized via the hydro-evaporation method, were examined in this work. The influence of their structural and microstructural properties on the ferroelectric behavior of bismuth ferrite was investigated, considering the specificities of both dopant ions (La3+, Eu3+). XRD analysis revealed that lanthanum and europium doped bismuth ferrite ceramics had the rhombohedral (R3c) structure as the dominant one, while the samples doped with 15 mol% of dopant ions contained the orthorhombic phases as well. The partial substitution of Bi3+ ions with 10 mol% of La3+ or Eu3+ and 15 mol% of La3+ ions generated significantly enhanced ferroelectric responses (the large remnant polarizations and high coercive fields) and an almost square form of the hysteresis curves in comparison with undoped and the other doped samples. The bismuth ferrite ceramic sample doped with 15 mol% of La3+ ions exhibited the highest remnant electric polarization (Pr = 24 °C/cm2 in electric field equal to 160 kV/cm), nearly saturated hysteresis curves in high electric fields, and the lowest leakage currents, which are consequences of its unique structural and microstructural properties. The samples doped with 15 mol% europium and co-doped with 7.5 mol% lanthanum and 7.5 mol% europium exhibited a poor ferroelectric response due to the non-polar orthorhombic structures. The leakage current densities of La and Eu-doped bismuth ferrite samples were reduced due to the decrease in the concentration of oxygen vacancies, which were the primary cause of the electric conductivity in the undoped bismuth ferrite ceramics. The decrease in the grain size of the doped samples also affected the reduction of their leakage currents