Revisiting the Role of Vacancies in Manganese Related Perovskites

Abstract

Abstract:Oxygen engineering is an important tool for on-demand tailoring of manganese related perovskites into optimized performances. Anionic vacancies can be induced in both doped and undoped manganites by means of topotactic reduction processes under oxygen controlled atmosphere. This has given rise to the stabilization of new phases as a consequence of ordering of oxygen vacancies in which Mn 2+ appears due to the reducing process. Different reduction pathways are proposed for LaMnO 3 and doped systems. FM interactions remain at the octahedral layers when vacancies are longrange ordered. The peculiar magnetic behaviour of new layered perovskite superstructures is discussed.

Magnetic Structure and Electronic Study of Complex Oxygen‐Deficient Manganites

“…Although all of them exhibit AFM ordering with Neel temperature (T N ) around 150 K, La 0.5 Sr 0.5 MnO 2.5 also exhibits ferromagnetic (FM) interactions. [13,14] This behaviour resembles that observed on the full oxidized precursor perovskites and it seems to remain in the topotactic reducing processes. The existence of FM interactions in the La 0.5 Sr 0.5 MnO 3 perovskite is related to double exchange interactions through Mn 3 + -O-Mn 4 + angles of 1808.…”

“…[12][13][14] From these results, the crystal structures of La 0.5 Sr 0.5 MnO 2.5 and Nd 0.5 Sr 0.5 MnO 2.5 have been refined from ND data using the space group Ibm2 as starting model. Pnma and Icmm space groups were also considered but the best results were gathered for Ibm2.…”

“…This result is in agreement with previous magnetometry measurements. [13,14] However, differences are found for La 0.5 Sr 0.5 MnO 2.5 since FM interactions have been detected by magnetization measurements. Actually, there are very few examples of brownmillerite-related compounds with FM interactions and in most cases they comprise an A 2 MBO 5 composition, M being a magnetic cation, such as Mn or Co, and B a non-magnetic cation.…”

“…Further details of topotactic reduction have been reported elsewhere. [12][13][14] Neutron powder diffraction data were collected at the Institut Laue-Langevin (ILL). The data were acquired on the high-resolution powder diffractometer D2B at 5 and 300 K, with neutrons of wavelength 1.594 .…”

“…However, under strict oxygen control, it is possible to stabilize ordered La 1Àx A x MnO 3Àd oxygen-deficient phases by topotactic reduction of the parent perovskite. Following this procedure, we have obtained the La 0.5 Ca 0.5 MnO 2.5 , [12] La 0.5 Sr 0.5 MnO 2.5 [13] and Nd 0.5 Sr 0.5 MnO 2.5 [14] brownmillerite compounds as well as the La 4 Mn 4 O 11 [15] n = 4 term of the A n B n O 3nÀ1 homologous series.…”