Magnetization, Mossbauer and isothermal dilatometric behavior of oxidized YBa(Co,Fe)(4)O7+delta

authors	Waerenborgh, JC; Tsipis, EV; Pereira, LCJ; Avdeev, M; Naumovich, EN; Kharton, VV
nationality	International
journal	DALTON TRANSACTIONS
keywords	ION MIGRATION; YBACO4O7+DELTA; MECHANISMS; TRANSITION; SIMULATION; CAPABILITY; EXPANSION; PROGRAM; GULP
abstract	Mossbauer spectroscopy and magnetization studies of YBaCo4-xFexO7+delta (x = 0-0.8) oxidized at 0.21 and 100 atm O-2, indicate an increasing role of penta-coordinated Co3+ states when the oxygen content approaches 8-8.5 atoms per formula unit. Strong magnetic correlations are observed in YBaCo(4-x)Fe(x)O8.5 from 2 K up to 55-70 K, whilst the average magnetic moment of Co3+ is lower than that for delta <= 0.2, in correlation with the lower Fe-57(3+) isomer shifts determined from Mossbauer spectra. The hypothesis on dominant five-fold coordination of cobalt cations was validated by molecular dynamics modeling of YBaCo4O8.5. The iron solubility limit in YBaCo4-xFexO7+delta corresponds to approximately x approximate to 0.7. The oxygen intercalation processes in YBaCo4O7+delta at 470-700 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 YBaCo4O7+delta ceramics at 598 K is as high as 0.33%.
publisher	ROYAL SOC CHEMISTRY
issn	1477-9226
year published	2012
volume	41
issue	2
beginning page	667
ending page	678
digital object identifier (doi)	10.1039/c1dt11212k
web of science category	Chemistry, Inorganic & Nuclear
subject category	Chemistry
unique article identifier	WOS:000298000000046