Spin glass formation in La0.9Sr0.1CoO3 catalyst for flameless combustion of methane

Microstructure of LaCoO3 prepared by freeze-drying of metal–citrate precursors revealed by EPR

“…The low-field magnetic absorption is more pronounced for La 0.9 Sr 0.1 CoO 3 . In accordance with the EPR studies on La 1Àx Sr x CoO 3 [22,26,37], the broad signal and the low-field magnetic absorption can be assigned to ferromagnetic Co 3+ -Co 4+ clusters and spin glass behaviours, respectively.…”

“…We have to mention that at T4300 K two overlapping EPR signals with g % 2:3 have been detected for La 0.9 Sr 0.1 CoO 3 obtained by the sol-gel method at 1000 1C [22]. These signals have been attributed to paramagnetic oxygen species and to species involving cobalt (such as Co 3+ /O 2 À pairs) [22]. These signals are not detected for pure and Sr-doped LaCoO 3 samples studied by us.…”

“…The appearance of Co 4+ ions together with Co 3+ ions in ex-citrate LaCoO 3 is concordant with the slightly higher values of the mean oxidation state of the Co ions in these samples. We have to mention that at T4300 K two overlapping EPR signals with g % 2:3 have been detected for La 0.9 Sr 0.1 CoO 3 obtained by the sol-gel method at 1000 1C [22]. These signals have been attributed to paramagnetic oxygen species and to species involving cobalt (such as Co 3+ /O 2 À pairs) [22].…”

“…These ions are coupled to Co 3+ ions by double-exchange interactions, forming ferromagnetic clusters with T C E 240 K [16,26]. For La 0.9 Sr 0.1 CoO 3 , low-field magnetic absorption due to the formation of a spin glass has been detected in the low-temperature EPR spectrum (TE100 K) [22]. By increasing the Sr content, the competition between alien ferromagnetic Co 3+ -Co 4+ couples and allied antiferromagnetic Co 3+ -Co 3+ and Co 4+ -Co 4+ couples causes a magnetic frustration.…”

“…Electron paramagnetic resonance spectroscopy (EPR) has been shown to be an effective experimental tool for studying the defect structure of cobaltites with layered [17,18], spinel [19][20][21] and perovskite structure [22][23][24][25][26]. Concerning LaCoO 3 , an EPR signal from the excited triplet state of Co 3+ in LaCoO 3 has been detected using high-frequency EPR spectroscopy only (n4400 GHz) [24].…”