Mixed valence states of Cr and Fe in La_(1_x)Sr_xFe_(0.8)Cr_(0.2)O_(3-y)

摘要

The La_(1_x)Sr_xFe_(0.8)Cr_(0.2)O_(3-y) (x = 0.2, 0.4, 0.6 and 0.8) phases were studied by X-ray photoelectron spec-troscopy at room temperature and ~(57)Fe Mossbauer spectroscopy at different temperatures. Mixed valence states were observed both for chromium and iron ions, justifying the complex magnetic behaviour exhibited by these compounds. The Mossbauer results indicate the simultaneous presence of Fe~(3+), Fe~(4+) and Fe~(5+) at 4.2 K and the co-existence of Fe~(3+) and Fe~[(3+n)+] at T = 293 K, with the latter fraction increasing with increasing strontium content. The presence of Cr~(3+/4+) is interpreted as being mainly responsible for the incomplete charge disproportionation reaction of iron at low temperature, as deduced from the Mossbauer results.