Ion Coordination and Transport in Magnesium Polymer Electrolytes Based on Polyester-co-Polycarbonate

Magnesium-ion-conducting solid polymer electrolytes have been studied for rechargeable Mg metal batteries, one of the beyond-Li-ion systems. In this paper, magnesium polymer electrolytes with magnesium bis(trifluoromethane)sulfonimide (Mg(TFSI)2) salt in poly(ε-caprolactone-co-trimethylene carbonate) (PCL-PTMC) were investigated and compared with the poly(ethylene oxide) (PEO) analogs. Both thermal properties and vibrational spectroscopy indicated that the total ion conduction in the PEO electrolytes was dominated by the anion conduction due to strong polymer coordination with fully dissociated Mg2+. On the other hand, in PCL-PTMC electrolytes, there is relatively weaker polymer–cation coordination and increased anion–cation coordination. Sporadic Mg- and F-rich particles were observed on the Cu electrodes after polarization tests in Cu|Mg cells with PCL-PTMC electrolyte, suggesting that Mg was conducted in the ion complex form (MgxTFSIy) to the copper working electrode to be reduced which resulted in anion decomposition. However, the Mg metal deposition/stripping was not favorable with either Mg(TFSI)2 in PCL-PTMC or Mg(TFSI)2 in PEO, which inhibited quantitative analysis of magnesium conduction. A remaining challenge is thus to accurately assess transport numbers in these systems.

Unusual cation coordination in nanostructured mullites

Nanocrystalline mullite-type bismuth-bearing complex oxides Bi2(M0.5Al0.5)4O9 (M=Fe3+, Ga3+) are prepared by high-energy ball milling of the corresponding microcrystalline counterparts. An unusual five-fold coordination of metal cations is revealed in nanostructured Bi2(M0.5Al0.5)4O9 by means of 27Al magic angle spinning nuclear magnetic resonance and 57Fe Mössbauer spectroscopies. The concentration of five-fold coordinated cations increases with decreasing crystallite size of a material at the expense of octahedrally coordinated ones. In addition to the nuclear spectroscopic methods, Rietveld analyses of the X-ray diffraction data of the as-prepared nanooxides show that the constituent tetrahedra, octahedra, and the newly formed structural units with five-fold cation coordination are strongly distorted. With decreasing crystallite size of mullites, the average volume of their octahedra increases whereas this parameter decreases for tetrahedra. The macroscopic behaviour of the non-equilibrium nanomullites is characterised by SQUID magnetometry. The Fe-containing mullites exhibit a superposition of a dominant antiferromagnetism and a weak ferromagnetism. The increase in both the remanent magnetization and the coercive field with decreasing crystallite size is attributed to the effect of spin canting. The latter is confined to the interfacial and surface regions of the nanomaterials, and arises due to both the mechanically induced deformation of constituent structural units and the formation of cation sites with the unusual five-fold coordination.

Empirical Electronic Polarizabilities for Use in Refractive Index Measurements III. Structures with Short [5]Ti–O and Vanadyl Bonds

ABSTRACT The electronic polarizabilities of most cations, such as Na+, Ca2+, Fe2+, Fe3+, and Zr4+, show a monotonic decrease as the cation coordination increases. However, polarizabilities of the ions [5]Ti4+, [5]V5+, and [6]V5+ show strong deviations from a regular decrease. In this paper we characterize the [5]Ti and vanadyl compounds by infrared frequencies, by the short [5]Ti4+– O, [5]V4+–O, [6]V4+–O, [5]V5+–O, and [6]V5+–O bonds and the polarizabilities of [5]Ti4+, [5]V4+, [6]V4+, [5]V5+, and [6]V5+ determined from refractive index measurements. Analysis of the structures of 18 compounds containing short [5]Ti–O bonds supports the concept of the short Ti–O bond being associated with the bond valence sum (omitting Ti) around the oxygen atom O*. The short Ti–O* bond occurs to satisfy the bond valence requirement of (O2–) of ∼2.0 vu. Plotting the [5]Ti–O* distances of 18 minerals versus the bond valence sum (BVS) around O* shows an approximately linear relationship. Extrapolation to BVS = 0 yields a minimum distance of 1.65 Å. The mean value is 1.693 Å. The mean short distances in V4+ vanadyl minerals are 1.597 Å (CN = 5) and 1.590 Å (CN = 6), whereas the mean short distance in five V5+ minerals is 1.647 Å (CN = 5) and in 14 V5+ minerals is 1.644 Å (CN = 6). We compare the polarizabilities of [5]Ti and [5,6]V4+ and [5,6]V5+ ions with the polarizabilities of [4]-coordinated Ti4+ ([4]Ti4+ ) and [6]-coordinated Ti4+ ([6]Ti4+ ) and of [4]-, [5]-, and [6]-coordinated V4+ and V5+ ([n]V4+ and [n]V5+) and hypothesize that the reduced polarizability of [5]Ti4+, [5]V5+, and [6]V5+ ions is caused by the short Ti–O* and V=O bonds.

Adsorption of Pharmaceuticals onto Smectite Clay Minerals: A Combined Experimental and Theoretical Study

The adsorption of two pharmaceuticals, carbamazepine and paracetamol, onto the expandable clay mineral saponite has been studied through the combination of kinetic experiments, X-ray diffraction, and theoretical modeling. Kinetic experiments indicate low adsorption for carbamazepine and paracetamol on expandable smectite clay. Accordingly, X-ray diffraction experiments show that neither compound enters smectite interlayer space. Molecular dynamics simulations were carried out to understand the interactions between the two pharmaceuticals and the saponite basal surface in the presence of Na+ cations. Calculations reveal that paracetamol almost does not coordinate solution cations, whereas a rather low coordination to cation is observed for carbamazepine. As a result, the adsorption onto the clay surface results mainly from van der Waals interactions for both pharmaceuticals. Carbamazepine does adsorb the surface via two configurations, one involving cation coordination, which corresponds to a rather stable adsorption compared to paracetamol. This is confirmed by structural analyses completed with desorption free energy profile.