Iodometric Determination of Electrons Incorporated into Cages in 12CaO·7Al₂O₃ Crystals

Abstract

The accurate determination of the concentration of electrons incorporated into cages in 12CaO·7Al2O3 (C12A7) has been examined using iodometry. Preliminary experiments confirmed that iodine is reduced in preference to protons by electron-enriched C12A7, even in aqueous solution. The electron concentrations in several C12A7 samples are measured using a procedure where the iodine molecules in an I2−HCl solution are partially reduced by electrons released from the samples, followed by titration of the residual iodine molecules. The accuracy of this procedure is confirmed by the excellent agreement of the results with those from thermogravimetric analysis. The reevaluated maximum electron mobility is nearly twice as high as that reported previously, and the critical electron concentration for the metal−insulator transition is revised slightly because of the accuracy of the iodometry results.

Mayenite-based electride C12A7e−: an innovative synthetic methodviaplasma arc melting

“…By taking information derived from of EPR analysis and thermal analysis for samples (a-d) at maximum qualitative correlations could be concluded. Ne values derived from TG analysis show even for (a) C12A7 an electron concentration of 0.9 · 10 21 cm -3 which would be characteristic to a semiconducting or metallic conducting mayenite electride as reported in the literature studies 42,45,46 . The color of such C12A7eshould be dark green to black, though sample (a) is a white powder, characteristic for an insulating material.…”

“…Matsuishi et al first described using thermogravimetric analysis (TG) to determine the electron concentration in combination with DTA under 80%He/20%O 2 atmosphere 42,45,46 42 . Trofymluk et al report a slightly different behavior, the maximum mass uptake of 1.70 wt.% is not reported, only the uptake of 1.2 wt.% 46 .…”

“…A substitution of oxygen by electrons in the cages thus leads to a larger number of occupied cages -which in turn leads to structural distortions depending on the electron concentration as reviewed by Salasin et al 13 . As the semiconducting stage of C12A7eis characterized by a color change from colorless to green, which is attributed to formation of F-centers comparable to halides, electron paramagnetic resonance (EPR) spectroscopy and diffuse reflectance UV/Vis (DRUV/Vis) spectroscopy are reported to analyze the electron concentration 5,[42][43][44][45] . EPR spectroscopy can show the presence of F-centers regardless of the electron concentration, while a quantitative determination was only possible for N e < 5 · 10 19 cm -3 5 .…”

“…EPR spectroscopy can show the presence of F-centers regardless of the electron concentration, while a quantitative determination was only possible for N e < 5 · 10 19 cm -3 5 . Another method reported for determination of the electron concentration was thermogravimetric (TG) analysis under oxidizing atmosphere 42,45,46 . Furthermore, structural characterization by Rietveld refinement of XRD and NPD data was reported to allow determination of the electron concentration via refinement of the occupancy of the anion position inside the cages 5,42 .…”

“…Only for some special cases Raman spectroscopy, SQUID measurements are reported as ways to investigate the electron concentration 5,43 . Iodometric titration is also used frequently, however the role of metal impurities such as Al or Ca might influence the results as reported by Jiang et al 39,45 . Existing strategies for the synthesis of solid electrides reported in the literature mainly refer to bulk/batch synthesis and are thus limited in their scalability.…”