Spectroscopic study of the electric field induced valence change of Fe-defect centers in SrTiO3

Abstract

The electrochemical changes induced by an electric field in Fe-doped SrTiO 3 have been investigated by X-ray absorption spectroscopy (XANES and EXAFS), electron paramagnetic resonance (EPR) and Raman spectroscopy. A detailed study of the Fe dopant in the regions around the anode and cathode reveals new insights into the local structure and valence state of Fe in SrTiO 3 single crystals. The ab initio full multiple-scattering XANES calculations give an evidence of the oxygen vacancy presence in the first coordination shell of iron. Differences in the length and disorder of the Fe-O bonds as extracted from EXAFS are correlated to the unequivocal identification of the defect type by complementary spectroscopical techniques to identify the valence state of the Fe-dopant and the presence of the Fe À V Ö complexes. Through this combinatorial approach, novel structural information on Fe À V Ö complexes is provided by X-ray absorption spectroscopy, and the relation of Fe-O bond length, doping level and oxidation state in SrTi 1Àx Fe x O 3 is briefly discussed.

Defect mechanisms of coloration in Fe-doped SrTiO3 from first principles

“…13 Experimental measurements of Fe:STO have found that resistance degradation is accompanied by the formation of a color front that transitions from dark brown at the anode (þ external potential) to transparent at the cathode (-external potential). 7,14,15 Similar absorption peaks to those found in electrocoloration have been observed in Fe:STO annealed at different oxygen pressures. Combined electron paramagnetic resonance (EPR) and absorption measurements provided indirect evidence that neutral iron substituting on the titanium site (Fe 0 Ti ) is likely associated with the brown coloration in oxidized Fe:STO.…”

Probing the oxygen vacancy distribution in resistive switching Fe-SrTiO3 metal-insulator-metal-structures by micro-x ray absorption near-edge structure

“…The presence of oxygen vacancies in the first coordination shell of transition-metal (TM) dopants can be traced by x-ray absorption near-edge structure (XANES) through a characteristic increase of intensity in the pre-edge region of the TM K-edge. 8,9 This approach was used to interpret the spatial distribution of TM-V O defect associates in the material, and extended channels of oxygen vacancies have been demonstrated by micro-XANES (lXANES) in Cr-doped SrTiO 3 single crystals. 8,10 In this letter, we examine lm-sized thin-film memristor devices with lXANES and utilize the sensitivity of the TM K-edge to obtain information about the local changes around the TM-dopant induced by resistive switching and their spatial distribution in the MIM-structure.…”

“…9 As a reference, we will use a Fe-doped SrTiO 3 single crystal that has been subjected to a long-term dc voltage at moderately elevated temperature. Such treatment induces an ion concentration polarization and a corresponding oxidation and reduction near the anode and cathode, respectively, which leads to pronounced coloration at the anode (called electrocoloration) because of the Fe doping.…”

“…3(b)). While the homogeneous reduction of the electrode can be interpreted as a simple increase of the Fe-V O -concentration, the spectral changes at the location of the filament are further examined through selfconsistent, real-space full-multiple-scattering (FMS) XANES calculations 9 by the FDMNES code, 12 performed within the quadrupole and non-muffin-tin approximation using the finite difference method (FDM). Figure 4 elucidates the influence of oxygen vacancies on the shape of the Fe K-edge XANES, demonstrating that the decrease of the white line intensity (peak E) and an increase of the shoulder S intensity (corresponding to the peaks C and D in the calculated XANES), as observed at the location of the filament, can be explained by the presence of an additional oxygen vacancy in the first coordination shell of the Fe atoms.…”

A comparison study of solving diffusion equations with different algorithm methods

“…The breakdown and degradation of devices have limited widespread implementation of these applications for extreme environments. [9][10][11][12][13] The point defect play a significant role in the breakdown and degradation of materials, therefore the defect evolution becomes a major concern in the applications of dielectric and ferroelectric materials. [14][15][16] The defect transports of breakdown and degradation processes have been widely investigated experimentally.…”