Eels Study of Valence State and Oxygen Vacancies In Magnetoresistive Oxides

Colossal magnetoresistive (CMR) has been observed in a class of oxides, La1-xAxMnO3(A = Ca, Sr, or Ba). Transition and rare earth metal elements with mixed valences are usually present in these materials for stimulating structural and chemical evolutions, leading to specific functionality. The partial substitution of trivalent La3+by divalent element A2+is balanced by the conversion of Mn valence states between Mn3+and Mn4+and the creation of oxygen vacancies as well, since the ionic structure of La1-xAxMnO3-yis proposed to bein which the valence conversion is the key for determining the material's properties. In practice, quantifying of oxygen vacancies is a challenge to existing microscopy techniques particularly for thin film specimens because of the strong effect from the defects at the substrate-film interface and the surface disordering.