TY - JOUR
T1 - Iron valence in double-perovskite (Ba,Sr,Ca)2FeMoO6
T2 - Isovalent substitution effect
AU - Yasukawa, Y.
AU - Lindén, J.
AU - Chan, T. S.
AU - Liu, R. S.
AU - Yamauchi, H.
AU - Karppinen, M.
PY - 2004/8
Y1 - 2004/8
N2 - In the Fe-Mo based B-site ordered double-perovskite, A2FeMoO6.0, with iron in the mixed-valence II/III state, the valence value of Fe is not precisely fixed at 2.5 but may be fine-tuned by means of applying chemical pressure at the A-cation site. This is shown through a systematic 57Fe Mössbauer spectroscopy study using a series of A2FeMoO6.0 [A=(Ba,Sr) or (Sr,Ca)] samples with high degree of Fe/Mo order, the same stoichiometric oxygen content and also almost the same grain size. The isomer shift values and other hyperfine parameters obtained from the Mössbauer spectra confirm that Fe remains in the mixed-valence state within the whole range of A constituents. However, upon increasing the average cation size at the A site the precise valence of Fe is found to decrease such that within the A=(Ba,Sr) regime the valence of Fe is closer to II, while within the A=(Sr,Ca) regime it is closer to the actual mixed-valence II/III state. As the valence of Fe approaches II, the difference in charges between Fe and Mo increases, and parallel with this the degree of Fe/Mo order increases. Additionally, for the less-ordered samples an increased tendency of clustering of the antisite Fe atoms is deduced from the Mössbauer data.
AB - In the Fe-Mo based B-site ordered double-perovskite, A2FeMoO6.0, with iron in the mixed-valence II/III state, the valence value of Fe is not precisely fixed at 2.5 but may be fine-tuned by means of applying chemical pressure at the A-cation site. This is shown through a systematic 57Fe Mössbauer spectroscopy study using a series of A2FeMoO6.0 [A=(Ba,Sr) or (Sr,Ca)] samples with high degree of Fe/Mo order, the same stoichiometric oxygen content and also almost the same grain size. The isomer shift values and other hyperfine parameters obtained from the Mössbauer spectra confirm that Fe remains in the mixed-valence state within the whole range of A constituents. However, upon increasing the average cation size at the A site the precise valence of Fe is found to decrease such that within the A=(Ba,Sr) regime the valence of Fe is closer to II, while within the A=(Sr,Ca) regime it is closer to the actual mixed-valence II/III state. As the valence of Fe approaches II, the difference in charges between Fe and Mo increases, and parallel with this the degree of Fe/Mo order increases. Additionally, for the less-ordered samples an increased tendency of clustering of the antisite Fe atoms is deduced from the Mössbauer data.
KW - Fe Mössbauer spectroscopy
KW - Double perovskite
KW - Halfmetal
KW - Isovalent substitution
KW - Valence mixing
UR - http://www.scopus.com/inward/record.url?scp=3342898268&partnerID=8YFLogxK
U2 - 10.1016/j.jssc.2004.04.031
DO - 10.1016/j.jssc.2004.04.031
M3 - Article
AN - SCOPUS:3342898268
SN - 0022-4596
VL - 177
SP - 2655
EP - 2662
JO - Journal of Solid State Chemistry
JF - Journal of Solid State Chemistry
IS - 8
ER -