Effect of La doping on the structure and cycloidal spin ordering in multiferroic BiFeO3

A series of Bi1 – xLaxFeO3 samples with 0.00 ≤ x ≤ 0.30 was synthesized by the sol – gel method. The effects of lanthanum concentration on the phase formation, microstructure and cycloidal spin ordering were studied using X-ray diffraction, scanning electron microscopy and M ö ssbauer spectroscopy. The crystal structure of the La-doped bismuth ferrite transformed from rhombohedral R3c (x ≤ 0.05) to a mixture of R3c and cubic Pm3m (0.07 ≤ x ≤ 0.15) and finally to a mixture of R3c, Pm3m and orthorhombic Pbam (0.20 ≤ x ≤ 0.30). The Pbam phase, with characteristic porous microstructure shown by microscopy images, was observed in Bi1 – xLaxFeO3 compounds for the first time. Based on the M ö ssbauer spectroscopy, it was found that the cycloidal spin ordering started to disappear at x = 0.07. With increasing La concentration the share of the cycloid decreased from 100% at 0.00 ≤ x ≤ 0.05 to 0% at x = 0.30. At the beginning, for x ≤ 0.02, the anharmonicity parameter, m, of the cycloidal spin ordering was about 0.5, which is typical of a pure BiFeO3 compound. In the range 0.05 ≤ x ≤ 0.25, the m parameter was of the order of 0.1, which indicated the practically harmonic character of the cycloid. The structural transition at x = 0.07 was accompanied by a substantial increase in magnetization.

Source: Acta Crystallographica Section B - July 6, 2023 Category: Chemistry Authors: Pikula, T. Siedliska, K. Szumiata, T. Panek, R. Mitsiuk, V.I. Ruchomski, L. Jartych, E. Tags: bismuth ferrite spin cycloid X-ray diffraction ö ssbauer spectroscopy research papers Source Type: research