Magnetization, Mssbauer and isothermal dilatometric behavior of oxidized YBa(Co,Fe)4O7+Electronic supplementary information (ESI) available: Selected Mssbauer spectra of YBaCo3.9657Fe0.04O8.5 in the vicinity of TMF and typical distribution of the cobaltoxygen polyhedra fractions in consecutive layers parallel to the ab plane of simulated YBaCo4O8.5, extracted from the MD results at 150 K. See DOI: 10.1039/c1dt11212k

• Main Authors: Waerenborgh, Joo C, Tsipis, Ekaterina V, Pereira, Laura C. J, Avdeev, Maxim, Naumovich, Eugene N, Kharton, Vladislav V
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c1dt11212k

Mssbauer spectroscopy and magnetization studies of YBaCo 4- x Fe x O 7+ ( x = 00.8) oxidized at 0.21 and 100 atm O 2 , indicate an increasing role of penta-coordinated Co 3+ states when the oxygen content approaches 88.5 atoms per formula unit. Strong magnetic correlations are observed in YBaCo 4- x Fe x O 8.5 from 2 K up to 5570 K, whilst the average magnetic moment of Co 3+ is lower than that for 0.2, in correlation with the lower 57 Fe 3+ isomer shifts determined from Mssbauer spectra. The hypothesis on dominant five-fold coordination of cobalt cations was validated by molecular dynamics modeling of YBaCo 4 O 8.5 . The iron solubility limit in YBaCo 4- x Fe x O 7+ corresponds to approximately x 0.7. The oxygen intercalation processes in YBaCo 4 O 7+ at 470700 K, analyzed by X-ray diffraction, thermogravimetry and controlled-atmosphere dilatometry, lead to unusual volume expansion opposing to the cobalt cation radius variations. This behavior is associated with increasing cobalt coordination numbers and with rising local distortions and disorder in the crystal lattice on oxidation, predicted by the computer simulations. When the oxygen partial pressure increases from 4 10 5 to 1 atm, the linear strain in YBaCo 4 O 7+ ceramics at 598 K is as high as 0.33%. Mssbauer spectroscopy, magnetization, X-ray diffraction, computer simulations, controlled-atmosphere dilatometry and thermogravimetry were used to study oxidation mechanisms in YBaCo 4- x Fe x O 7+ ( x = 00.8, = 01.5), a family of promising oxygen-storage and electrode materials.