Polyanionic materials have been intensively studied as promising active materials for positive electrodes in Na-ion batteries thanks to their excellent stability upon cycling and the fast ionic mobility in their structural framework. Among them, Na3V2(PO4)2F3 and Na3(VO)2(PO4)2F are two of the most promising ones due to their high voltages for Na +-ion extraction and their high energy densities: 500 Wh.kg-1 and 495 Wh.kg-1 , respectively. Here, we study the formation mechanism as well as the stability of these phases in aqueous media and the possible use of a washing step in water in order to remove undesirable impurities formed during the synthesis. Furthermore, the origin of the extra capacity observed in the high voltage region for Na3V2(PO4)2F3 and Na3V2(PO4)2F1.5O1.5 was studied by operando X-ray absorption spectroscopy.

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The hydrothermal reactions of uranyl nitrate and metallic copper with aromatic polycarboxylic acids gave rise to the formation of five heterometallic UO(2)(2+)-Cu(2+) coordination polymers: (UO(2))Cu(H(2)O)(2)(1,2-bdc)(2) (1; 1,2-bdc = phthalate), (UO(2))Cu(H(2)O)(2)(btec)⋅4 H(2)O (2) and (UO(2))Cu(btec) (2'; btec = pyromellitate), (UO(2))(2)Cu(H(2)O)(4)(mel) (3; mel = mellitate), and (UO(2))(2)O(OH)(2)Cu(H(2)O)(2)(1,3-bdc)⋅H(2)O (4; 1,3-bdc = isophthlalate). Single-crystal X-ray diffraction (XRD) analysis of compound 1 revealed 2D layers of chains of UO(8) and CuO(4)(H(2)O)(2) units that were connected through the phthalate ligands. In compound 2, these sheets were connected to each other through the two additional carboxylate arms of the pyromellitate, thus resulting in a 3D open-framework with 1D channels that trapped water molecules. Upon heating, free and bonded water species (from Cu-OH(2)) were evacuated from the structure. This thermal transition was followed by in situ XRD and IR spectroscopy. Heating induced a solid-state topotactic transformation with the formation of a new set of Cu-O interactions in the crystalline anhydrous structure (2'), in order to keep the square-planar environment around the copper centers. The structure of compound 3 was built up from trinuclear motifs, in which one copper center, CuO(4)(OH(2))(2), was linked to two uranium units, UO(5)(H(2)O)(2). The assembly of this trimer, "U(2)Cu", with the mellitate generated a 3D network. Complex 4 contained a tetranuclear uranyl core of UO(5)(OH)(2) and UO(6)(OH) units that were linked to two copper centers, CuO(OH)(2)(H(2)O)(2), which were then connected to each other through isophthalate ligands and U=O-Cu interactions to create a 3D structure. The common structural feature of these different compounds is a bridging oxo group of U=O-Cu type, which is reflected by apical Cu-O distances in the range 2.350(3)-2.745(5) Å. In the case of a shorter Cu-O distance, a slight lengthening of the uranyl bond (U=O) is observed (e.g., 1.805(3) Å in complex 4).

Investigation of the effects of Al substitution for V on the structural properties and electrochemical performances for two of the most promising positive electrode materials for Na-ion batteries, Na3V2(PO4)2F3 and Na3V2(PO4)2FO2.

In this Communication, nanoparticles of the fluoridosilicates A2SiF6 (A=Li, Na, K, Rb, Cs), which are extremely promising host lattices for future LEDs, are presented for the first time. The preparation method we introduce here is a very simple and energy and time saving one, moreover the usage of toxic HF or elemental fluorine is avoided. In detail, the ionic liquid [Bmim]PF6 was used both as solvent and fluoride source in an ionothermally assisted microwave synthesis. The small size of the so‐obtained nanoparticles is of huge relevance for their applications as thin films or for the coverage of surfaces, for example in next‐generation white LEDs upon doping with Mn4+.

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Four new mixed lead-bismuth oxychloride compounds have been prepared and characterized by single crystal X-ray diffraction. Their crystal structures are described on the basis of the association of distinct building units found in parent Pb or Bi oxychlorides. The new compound PbBi4O6Cl2 is formed of the stacking of 2D positive [Bi2O2](2+) layers and neutral [PbBi2O4](0) double layers separated by Cl(-) anions. Similar motifs with finite lengths are combined together in the new series [Pb(n)Bi(10-n)O13][Bi2O2](n)Cl(4+n). From the structural viewpoint, it is striking that this family of homologous phases is strongly related to Bi24O31Cl10 well-known as Arppe's compound in which the fluorite-like [Bi2O2]n subunit was increased from n = 1 (mixed Bi/Pb Arppe's compound) to n = 2, 3, and 4 new members. The preparation of the respective powders shows the predominant stability of the n = 2 term which was prepared as a single-phase, while other terms have not been obtained in absence of secondary phases. For n = 2, the impedance spectroscopy shows a conductivity value σ ∼ 10(-3) S cm(-1) at 650 °C and suggests a contribution of Cl(-) in the diffusion process. Most remarkable, PbBi4O6Cl2 as well as [Pb2Bi8O13][Bi2O2]2Cl6 show very bright red emission at low temperature, which could be assigned to Bi(3+) transitions by comparison to BaBi4O6Cl2. The different shapes of the excitation spectra lead to the assumption of a complete Pb-Bi energy transfer.

The Sillen X1 series of Bi(3+)A(2+)O2X (A = Cd, Ca, Sr, Ba, Pb; X = Cl, Br, I) compounds is composed of three main crystallographic types, namely, the tetragonal form (space group (S.G.) I4/mmm), the orthorhombic form (S.G. Cmcm), and the monoclinic form (S.G. P21/m). Because of Bi(3+)/A(2+) disorder the Bi(3+) based photoluminescence (PL) of the tetragonal polytypes is quenched at room temperature (RT). In the two other ordered forms, the Bi-O-Bi connectivity is different but limited, such that bluish/greenish emission occurs at RT in the monoclinic CdBiO2Cl and CaBiO2Cl and orthorhombic SrBiO2Cl and BaBiO2Cl phases. The crystal structure of BaBiO2Br was refined in the orthorhombic Cmcm space group and also shows RT emission. Focusing on the RT luminescent activity as a key parameter, the PL active compounds were investigated by means of density functional theory calculations and UV-visible reflectance spectroscopy. The influence of A and X ions on the excitation energy is discussed by analyzing the A-O-Bi and Bi-X bonding schemes and gives some insights for rational tuning of both the excitation and emission energies.