Nanostructured BiMnO3+δ obtained at ambient pressure: analysis of its multiferroicity

Abstract

International audienceThe BiMnO3+delta phase has been prepared by mechanosynthesis, at ambient pressure and room temperature, as nanocrystalline powders. This oxide exhibits a metastable character, similar to those prepared by high-pressure and high-temperature methods, remaining stable up to 673 K. Nanostructured ceramic materials (92% densification), maintaining the BiMnO3+delta composition, have been successfully processed by the spark plasma sintering technique, at the very low temperature of 673 K, in a time as short as 6 minutes. Conditions of synthesis and sintering are the key factors that determine the actual delta value, or Mn oxidation state. This parameter plays an important role in their magnetic properties, which vary from ferromagnetic for lower delta values (the case of the mechanosynthesized and SPS processed samples) to spin-glass behavior for higher delta values (thermally annealed samples). Electrical measurements, carried out on the dense BiMnO3+delta ceramic material, show no evidence of ferroelectricity down to 77 K, in good accordance with previous structural studies that indicated their centrosymmetric structures

Nanoscale Ferroelectrics and Multiferroics

“…Ferromagnetic order of the Mn 3+ at the B-site develops at 100 K, while ferroelectric offcenter distortion would be driven by the stereochemically active Bi +3 lone pair at the A-site [44]. However, later detailed structural characterizations, electrical measurements down to 77 K, and studies of the lattice dynamics have shown this oxide not to be ferroelectric [45][46][47]. This is consistent with studies of the xBiMnO 3 -(1 -x)PbTiO 3 solid solution that clearly indicated the disappearance of ferroelectricity for x ≥ 0.5 [48].…”

Perovskite solid solutions with multiferroic morphotropic phase boundaries and property enhancement

“…53 Subsequent additional neutron diffraction experiments confirmed this space group determination, 44 but an independent report using SAED indicated the presence of long-ranged monoclinic C2 order, in coexistence with short ranged P2 or P2 1 distortions, and thus, of a polar state. 54 The length of the short range order seems to increase with the oxygen hyperstoichiometry, 39 but a P2 1 /c space group has been determined for BiMnO 3:08 . 44 Further insight into this issue can only be gained by a sound electrical characterization, which requires the processing of high quality ceramics.…”

“…39 Oxygen hyperstoichiometry was controlled by XPS and magnetic measurements, by comparing the N eel temperature of 80 K to previous reports on the evolution of the magnetism with stoichiometry. 44 A composition of BiMnO 3:04 was estimated, so monoclinic C2/c phase can be assumed.…”

“…44 A composition of BiMnO 3:04 was estimated, so monoclinic C2/c phase can be assumed. 39 A full electrical characterization was carried out. 39 The temperature dependence of the dielectric permittivity is shown in Fig.…”

“…39 A full electrical characterization was carried out. 39 The temperature dependence of the dielectric permittivity is shown in Fig. 7.…”