The fluorination of La(2)CuO(4) was achieved for the first time under normal conditions of pressure and temperature (1 MPa and 298 K) via electrochemical insertion in organic fluorinated electrolytes and led to lanthanum oxyfluorides of general formula La(2)CuO(4)F(x). Analyses showed that, underneath a very thin layer of LaF(3) (a few atomic layers), fluorine is effectively inserted in the material's structure. The fluorination strongly modifies the lanthanum environment, whereas very little modification is observed on copper, suggesting an insertion in the La(2)O(2) blocks of the structure. In all cases, fluorine insertion breaks the translation symmetry and introduces a long-distance disorder, as shown by electron spin resonance. These results highlight the efficiency of electrochemistry as a new "chimie douce" type fluorination technique for solid-state materials. Performed at room temperature, it additionally does not require any specific experimental care. The choice of the electrolytic medium is crucial with regard to the fluorine insertion rate as well as the material deterioration. Successful application of this technique to the well-known La(2)CuO(4) material provides a basis for further syntheses from other oxides.
The electrochemical intercalation of oxygen into La 2 CuO 4 has been studied in various anhydrous organic media. Several combinations between an organic solvent and a supporting electrolyte have been examined. The addition of an oxygen source such as KO 2 or H 2 O has been found to be unnecessary. Experiments have shown that the electrochemical oxygen insertion mainly implies the decomposition of the solvent leading to the formation of oxygen species able to oxidize the starting material. La 2 CuO 4.10 has been prepared in the DMSO associated with nBu 4 NClO 4 . A superconducting behavior is observed below 44 K and the physical characterizations of the material before and after controlled anodic polarization are reported. It has also been shown that this intercalation reaction is reversible. The mechanism of the oxygen intercalation is tentatively proposed with respect to the organic media. Fluorine has also been intercalated for the first time in such media.Oxides showing high oxidation states of metal cations are usually prepared at high temperatures under high oxygen pressures, which gives the thermodynamically stable form of the compound. Preparing such oxides at lower temperatures ͑20-300°C͒ requires reactions of ''Chimie Douce''-type, 1 often leading to metastable compounds. Besides the use of highly oxidizing reagents, 2,3 electrochemical processes have been used and many studies have shown that the use of the electric field as the driving force for redox reactions can be very beneficial in solid-state chemistry for preparing new materials at about room temperature, as for instance in the field of batteries. Initiated for the first time in 1989, the electrochemical oxidation appeared as an efficient ''Chimie Douce'' technique for intercalating oxygen into oxide host networks. 4 It is carried out in air, at room temperature, in alkaline media, and allows preparing noteworthy materials, some having never been obtained with classic synthesis routes used in solid-state chemistry.In alkaline solution, in the vicinity of the oxygen evolution, under anodic potentials, a very high oxygen activity can be obtained at the electrode surface according toOn metallic electrodes, such a reaction competes with the formation of oxide thin films ͑i.e., Al 2 O 3 , ZnO, CuO, TiO 2 ,...) 5 whereas on appropriate oxide electrodes such as A x M m O y 1 not only the surface is affected but also the bulk. When analyzed in electrochemistry, these materials present (i, E) curves which exhibit a typical plateau at potentials lower than that corresponding to oxygen evolution, which is the signature of an oxidation process according towhere A is an alkaline-earth or a lanthanide ion and M a 3d transition metal and 2␦ ϭ the number of exchanged electrons corresponding to the amount of oxidized metal cations (Cu 3ϩ for La 2 CuO 4 ). 6 Various oxides have thus been prepared and characterized, 1 some of them exhibiting quite original properties such as superconductivity for La 2 CuO 4.09 , 7 charge density ordering in La 2 NiO 4.25 , 8 ferro...
The electrochemical intercalation of oxygen into La 2 CuO 4 has been carried out for the ®rst time in anhydrous organic±inorganic media such as dimethyl sulfoxide (DMSO)/0.1 M NaClO 4 or nBu 4 NBF 4 . The electrochemical reaction needs the presence of an oxygen source (KO 2 ) even with potential oxidising supporting electrolytes (NaClO 4 ). The anodic polarisation is performed at room temperature, with the aim of replacing the usual ef®cient but sometimes aggressive alkaline media. This so-called chimie douce reaction gave rise to noteworthy materials having compositions up to La 2 CuO 4.08 for which superconducting behaviour was observed below 42 K. The physical characteristics of the material (XRD, chemical composition, electronic properties) before and after controlled anodic polarisation are reported. The processes are time dependent and the oxygen stoichiometry could be controlled through reaction times.
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