Local structure study of Mn and V in spinel Mn(2-x)V(1 + x)O4 series by high-resolution Kb Emission Spectroscopy

CEPPI, S.; TIRAO, G .A.; POMIRO, F.; CARBONIO, R. E.; PANNUNZIO MINER, E.V.

campinas

Encuentro; Reunion Anual de Usuarios LNLS 2011; 2011

LNLS

Since the magnetoresistance effect (MR) was discovered in spinel-type compounds [1] these have been the subject of renewed studies in the field of material sciences. Although their MR is not as marked as that of some perovskites, spinel-type materials are attractive candidates for MR materials because a great number of spinels have ferrimagnetic properties and display some kind of electrical conductivity. The general formula for the cationic distribution is (A1¡gBg)T (B2¡gAg)OO4 where g is the degree of inversion (0 · g · 1) and T (O) indicate tetrahedral (octahedral) site. A knowledge of the cation distribution between O and T sites and cation charge is crucial, since it determines the magnetic and electrical properties of the spinels. As we were interested in ferrimagnetic spinels which potentially could display some MR effects, we prepared and characterized the structural and magnetic properties of spinel-type oxides Mn(2¡x)V(1+x)O4 (with x=0, 1/3, 1) in previous work [2]. X-ray and neutron diffraction weremade in order to determinate the crystal structure, but in this experiments unable to univocally assign oxidation states [2].Technical developments have allowed X-ray emission spectroscopy (XES) to become a powerful tool to study the chemical environment and the electronic structure of materials [3]. The XES experiments are based on measurements of X-ray energy shifts, satellite lines, variation of line shapes and relative intensities, related not only with oxidation state but also with chemical bonding for the same oxidation state. Particularly, in the first row transition metal compounds, Kb Xray emission spectra can provide information about oxidation state, ligand type, metal-ligand bonding length and metal coordination [3-6]. High-resolution Kb emission spectra of Manganese and Vanadium compounds were measured using a non-conventional spectrometer [7] at the D12A-XRD1 LNLS beamline. Using spectral parameters and comparing with known standards, the oxidation state of Mn and V of spineltype oxides Mn(2¡x)V(1+x)O4 was determined.