A method is described for the low‐temperature preparation of amorphous vanadates of general formula RVO4 (R = In, Cr, Fe, Al, Y), and their electrochemical properties vs. Li are reported. A dissolution‐reprecipitation process from a mixed solution of NH4VO3 and Rfalse(NO3)3 was used to prepare these compounds. By appropriate annealing of the amorphous precursors, several crystallized vanadates were obtained as well. Among all of these vanadates, either amorphous or crystallized, only those with R = In and Fe are of potential interest as negative electrodes in lithium‐ion rechargeable batteries since they display reversible capacities as large as 900 mAh/g. This different electrochemical behavior depending on the nature of the metallic element implies that R is not just a spectator with respect to the Li uptake into these materials. From both electrochemical and in situ x‐ray diffraction data, a mechanism of Li uptake/removal different from the usual Li insertion/deinsertion process is proposed.

Sodium may be topotactically inserted into the perovskite layers (under thermodynamic control) or the rock-salt layers (under kinetic control) of the cation-deficient n = 2 Ruddlesden-Popper oxysulfides Ln2Ti2O5S2 with concomitant reduction of TiIV.

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Lithium intercalation into the oxide slabs of the cation-deficient n = 2 Ruddlesden-Popper oxysulfide Y(2)Ti(2)O(5)S(2) to produce Li(x)Y(2)Ti(2)O(5)S(2) (0 < x < 2) is described. Neutron powder diffraction measurements reveal that at low levels of lithium intercalation into Y(2)Ti(2)O(5)S(2), the tetragonal symmetry of the host is retained: Li(0.30(5))Y(2)Ti(2)O(5)S(2), I4/mmm, a = 3.80002(2) A, c = 22.6396(2) A, Z = 2. The lithium ion occupies a site coordinated by four oxide ions in an approximately square planar geometry in the perovskite-like oxide slabs of the structure. At higher levels of lithium intercalation, the symmetry of the cell is lowered to orthorhombic: Li(0.99(5))Y(2)Ti(2)O(5)S(2), Immm, a = 3.82697(3) A, b = 3.91378(3) A, c = 22.2718(2) A, Z = 2, with ordering of Li(+) ions over two inequivalent sites. At still higher levels of lithium intercalation, tetragonal symmetry is regained: Li(1.52(5))Y(2)Ti(2)O(5)S(2), I4/mmm, a = 3.91443(4) A, c = 22.0669(3) A, Z = 2. A phase gap exists close to the transition from the tetragonal to orthorhombic structures (0.6 < x < 0.8). The changes in symmetry of the system with electron count may be considered analogous to a cooperative electronically driven Jahn-Teller type distortion. Magnetic susceptibility and resistivity measurements are consistent with metallic properties for x > 1, and the two-phase region is identified as coincident with an insulator to metal transition.

The electrochemical reaction of lithium with triclinic FeVO4 (a = 6.714(1) Å, b = 8.060(2) Å, c = 9.352(2) Å, α = 96.678(1)°, β = 106.641(1)°, and γ = 101.523(1)°, P-1) has been investigated by means of 57Fe Mössbauer spectroscopy in order to complement the previous X-ray diffraction and X-ray absorption near edge structure studies on the same system. A complex FeIII → FeII → Fe0 or FeIII → FeII, Fe0 reduction process has been detected upon the first discharge of the battery down to 0.02 V, with in addition the iron reoxidation during the next charge step. A mechanism based on “lithium adsorption” is proposed in order to explain this unexpected behavior.

A chimie douce method has been used to prepare vanadates ( V5+) of various elements, trivalent (Al, Cr, Fe, In, Y, Bi), divalent (Co, Ni), monovalent (Li, Tl ), and a combination of nickel and lithium. By varying several parameters, especially the pH during the synthesis, several types of vanadates have been obtained ranging from orthovanadates ( VO 4 3−) to decavanadates ( V 10 O 28 6−). The pH conditions required to prepare the various vanadates fall nicely within the expectations of the previously reported cation charge-pH diagram.

Sodium intercalation into the oxide slabs of the cation-deficient n ) 2 Ruddlesden-Popper oxysulfide Y 2 Ti 2 O 5 S 2 to produce R-Na x Y 2 Ti 2 O 5 S 2 (0 < x e 1.0) is reported. These materials have been probed as a function of the amount of intercalated sodium using high-resolution neutron powder diffraction. At all levels of sodium intercalation the tetragonal symmetry of the host is retained, for example: NaThe sodium ion occupies a site coordinated by twelve oxide ions which corresponds to the "A"-site in the perovskite-like oxide slabs of the structure. At levels of sodium intercalation up to the maximum R-Na 1.0 Y 2 Ti 2 O 5 S 2 the cell volume increases approximately linearly with x as electrons enter bands which are antibonding with respect to the Ti-O framework. The effects on the structural details of electrostatic repulsion between the yttrium and intercalated sodium ions is discussed, and these materials are compared with the analogous lithium intercalates. Magnetic susceptibility and electrical resistivity measurements are consistent with delocalization of the intercalated electrons especially for large x. The insertion of lithium into R-Na 0.5 Y 2 Ti 2 O 5 S 2 and of magnesium into Y 2 Ti 2 O 5 S 2 are also reported.

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