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The study of the pseudo-binary systems Bi2O3-A2B2O7, with A  Cd2+, Pb2+, Mg2+ and B & Nb5+, Ta5+, reveals two types of solid solutions. The first one with Bi1−2xCdxBxO2−y (y = (1 − x)/2) formulation shows a fluorite-type structure whereas the second type with A2−zB2−zBi2xO7−z/2 formulation is obtained for A2B2O7-rich compositions and possesses structures deriving from the pyrochlore type. The composition dependence of the unit cell parameters has been correlated to possible substitution mechanisms.

The influence of Ba substitution for La and of the fluorination on the thermal conductivity, the electrical resistivity, the thermoelectric power and the specific heat of La2-xBaxCuO4 has been investigated. In the La2-xBaxCuO4 system, either the electron-phonon interactions or phonon-defect interactions may explain the temperature dependence of the thermal conductivity. The intercalation of the fluorine atom into the lattice leads to a superconducting transition with an onset higher than 30 K for all compositions investigated. The effect of fluorine intercalation in these oxides is similar to an increase in barium concentration. Indeed the presence of fluorine leads to an increase of the free carriers concentration and of the lattice disorder. For the particular composition x congruent-to 0.125, the fluorination seems to suppress the low-temperature structural transition (LTO-->LTT) and to eliminate all the anomalies usually observed in the transport properties.

Chlorine gas treatment of La 2 CuO 4 leads to an oxygen-doped material which is superconducting below T c = 32 K. The structural properties of this oxygen-doped La 2 CuO 4+8 have been investigated by Rietveld refinement of the powder neutron diffraction data and analysis of the X-ray absorption spectra obtained in the La L III edge (LaO) region. The extra oxygen atoms occupy the ( 1 4 , 1 4 , y ) positions (O4) with y = 0.2629 at room temperature. Their occupancy factor n = 0.042 leads to the formula La 2 CuO 4.08 . These atoms are located between two successive (LaO) planes of a rock salt layer and are surrounded by four La and four O1 atoms, both groups of atoms forming tetrahedra. The four O1 atoms are located at 2.035 and 2.176 A from the interstitial oxygen. Such short distances have also been found in other oxygen-excess phases, e.g. La 2 CuO 4.048 and La 2 NiO 4.25 . The X-ray absorption spectroscopy results show that the local environment of La atoms is disturbed by the presence of anion excess. The thermal stability of this compound has been compared with that of La 2 Cu(O,F) 4+ y oxyfluoride. Cl 2 − gas treatment has also been used to obtain superconducting phases in the La 2− x Ba x CuO 4 system with x ⩽0.05.

The influence of fluorination on thermal conductivity, specific heat, magnetic susceptibility, electrical resistivity and thermoelectric power of La 1.85−y Sr 0.15 Nd y CuO 4 has been investigated. The temperature variation of the thermal conductivity of the untreated samples with Nd exhibits a change in slope just below the low-temperature structural transition (LTO--->LTT), which could be associated with strong phononelectron interactions. The specific heat of the y = 0.2 unfluorinated sample presents a jump near 50 K confirming the structural transition. Below 10 K, the specific heat of the two y = 0.8 samples (unfluorinated or fluorinated) shows an important increase with decreasing temperature, presumably associated with some type of magnetic ordering in the Nd 3+ ions. In addition to an increase of T c , the fluorination process suppress the anomalies observed in the thermal conductivity.

In the La1.85-xNdxSr0.15CuO4 system, phases deriving from the K2NiF4-type structure are found in the 0 less-than-or-equal-to x less-than-or-equal-to 0.98(5) composition range. Their superconducting properties are strongly influenced by the presence of chemical microinhomogeneities revealed by microprobe analysis and are dependent on the synthesis method, as discussed in more detail for x = 0.6. Electrical and magnetic measurements performed on samples of this system show that bulk superconductivity is observed only for x less-than-or-equal-to 0.4. The occurrence at low temperature of a structural transition explains the disappearance of the superconducting properties. This change induces a peculiar behaviour in the transport properties of these oxides.

The structural and magnetic properties of Na 2 CoMF 7 compounds (M = Al, Cr, Fe), showing a new structure deriving from that of weberite have been investigated. The monoclinic structure, favored by cobalt (II) ions, is intermediate between the orthorhombic type (Na 2 NiFeF 7 ) and the trigonal type (Na 2 MnFeF 7 ). It exhibits (CoF 5 ) n 3n− chains which run along the [110] and [110] directions, forming a sequence of double layers [Co 2 MF 10 ] n 3n− . The influence of the trivalent cation within the layers and between them on the magnetic behavior is demonstrated.

Na3MnF6, Mr = 237.90, monoclinic, P21/n, a = 5.4709 (9), b = 5.6830 (6), c = 8.0734 (12) A,/3 = 88.964 (7) °, V= 250.97 (6) A 3, Z = 2, D x = 3.15 gcm -3, A(Mo Ka) = 0.7107 A., /x = 27.6 cm -1, F(000) = 224, T = 293 K, R = 0.0152, wR = 0.0144 for 550 unique reflections (Fo > 30.(Fo)). The structure is isostructural with that of the cryolite Na3A1F6 and shows the weakest static Jahn-Teller distortion known to date for (MnF6) 3- octahedra (d(Mn--F) axial 2.0176 (8), mean equatorial 1.880 (1) A). The ordering of the elongated octahedra is ferrodis- tortive. Of the Na ions, one third have octahedral and the remainder have bicapped trigonal prismatic eight coordination. Introduction. Single-crystal studies on sodiumhexa- fluorometallates(III) Na3MmF6 (M m = Cr, Fe) revealed cryolite structures closely related to that of NaaA1F6 (Naray-Szabo & Sasvari, 1938; Hawthorne & Ferguson, 1975), space group P21/n. The Cr com- pound crystallizes in the same space group (Brunton, 1969), while for the structure of the iron compound P2~ is assumed (Matvienko, Yakubovich, Simonov, Ivashchenko, Melnikov & Belov, 1981). For several other compounds Na3MF6 (M = Ga, Sc, Ti, V, Mn, Co, Ni, Cu) cryolite-type unit cells were deduced from powder diffraction data (cf. review of Babel & Tressaud, 1985). In the course of studies on the dependence of Jahn-Teller distortion on the struc- ture type, we were interested in the crystal structure of the Mn m compound. Na3MnF6 was mentioned for the first time by Siebert & Hoppe (1971). Lattice parameters have been proposed by Bucovec & Siftar (1975) (a=5.56, b=5.84, c=8.10A, /3=90.7 ° ) which were confirmed roughly by our single-crystal investigation reported here. Experimental. The title compound was prepared by heating a stoichiometric mixture of NaF and MnF3 * To whom correspondence should be addressed.

An X-ray single crystal structure determination (monoclinic, space group P2₁/c, a = 573.6(2), b = 489.2(1), c = 574.8(2) pm, β = 108.07(2), Z = 2; wR = 0.038 for 380 reflections) shows that NaMnF₄ crystallizes in the same layered structure type as LiMnF₄. In the quadratic layers the Mn-F-Mn bridges are strongly asymmetric, due to the Jahn-Teller effect, leading to an antiferrodistortive order of elongated octahedra. The bridging angle is 138.4°. The Na⁺ ions are 6-coordinated as well. The common structural arrangement of both [MnF₆] and [NaF₆] octahedra shows topological relation to the rutile structure. In the magnetic measurements performed on powder samples NaMnF₄ behaves as an antiferromagnet with a weak ferromagnetic component below 13 K. By neutron diffraction on powder (4-70 K) a magnetic cell doubled along the α-axis is found and below a Neel temperature of TN = 13 K the magnetic structure shows colinear antiferromagnetic arrangement of the spins pointing slightly (16) out of the layer plane. The resulting magnetic moment is 3.52 μΒ.

Chlorine gas treatment of La 2 CuO 4 leads to an oxygen-doped material which is superconducting below T c = 32 K. The structural properties of this oxygen-doped La 2 CuO 4+8 have been investigated by Rietveld refinement of the powder neutron diffraction data and analysis of the X-ray absorption spectra obtained in the La L III edge (LaO) region. The extra oxygen atoms occupy the ( 1 4 , 1 4 , y ) positions (O4) with y = 0.2629 at room temperature. Their occupancy factor n = 0.042 leads to the formula La 2 CuO 4.08 . These atoms are located between two successive (LaO) planes of a rock salt layer and are surrounded by four La and four O1 atoms, both groups of atoms forming tetrahedra. The four O1 atoms are located at 2.035 and 2.176 A from the interstitial oxygen. Such short distances have also been found in other oxygen-excess phases, e.g. La 2 CuO 4.048 and La 2 NiO 4.25 . The X-ray absorption spectroscopy results show that the local environment of La atoms is disturbed by the presence of anion excess. The thermal stability of this compound has been compared with that of La 2 Cu(O,F) 4+ y oxyfluoride. Cl 2 − gas treatment has also been used to obtain superconducting phases in the La 2− x Ba x CuO 4 system with x ⩽0.05.

In the La1.85-xNdxSr0.15CuO4 system, phases deriving from the K2NiF4-type structure are found in the 0 less-than-or-equal-to x less-than-or-equal-to 0.98(5) composition range. Their superconducting properties are strongly influenced by the presence of chemical microinhomogeneities revealed by microprobe analysis and are dependent on the synthesis method, as discussed in more detail for x = 0.6. Electrical and magnetic measurements performed on samples of this system show that bulk superconductivity is observed only for x less-than-or-equal-to 0.4. The occurrence at low temperature of a structural transition explains the disappearance of the superconducting properties. This change induces a peculiar behaviour in the transport properties of these oxides.

The peculiar reactivity of fluorine with graphite can be related to some characteristic parameters of this element. The competition between strong C-F bonds in covalent graphite fluorides and weak semi-ionic bonds in graphite intercalation compounds is pointed out. The different experimental routes for the intercalation of fluorine and metal fluorides into graphite are reviewed. The oxidation state, the environment of the metal and the nature of the bonding between the intercalated species and carbon can be approached by various techniques, including XANES, EXAFS, and XPS spectroscopies. The structural relationships between the graphene sublattice and the intercalate sublattice can be pointed out on the basis of single crystal data. Concerning the transport properties, acceptor-GICs have proved to be very appropriate to investigate the effects of disorder and reduced dimensionality. The charge transfer which accompanies the insertion of fluorinated species between the graphene layers can be evalu...

The structure of CsPd2F5 has been confirmed from neutron diffraction data on powdered sample. CsPd2F5 crystallizes in the orthorhombic Imma space group. At 100 K, the unit-cell constants are a = 6.473(2) A, b = 7.853(5) A, c = 10.718(3) A and the calculation carried out using the Rietveld method leads to R1 = 0.020. The network is formed of PdF6 octahedra chains containing half of Pd in high-spin configuration, connected one to each other by square planes containing the other half of Pd in low-spin configuration. CsPd2F5 orders antiferromagnetically below TN = 38 K. In the ordered state a weak ferromagnetic component occurs (σ0 = 0.098 μB at 2 K). The magnetic structure determined at 4 K is consistent with the magnetization data and can be described in the Im′m′a′ magnetic group without any doubling of the unit-cell parameters. Within the chains, Pd2+ are coupled antiparallel. The magnetic moments are located in the (x0z) plane, the angle between the moments and the z axis being 18°. Magnetische Struktur von CsPd2F5 Die Struktur von CsPd2F5 wird durch Neutronenbeugungsdaten an Pulverproben bestatigt. CsPd2F5 kristallisiert in der orthorhombischen Raumgruppe Imma. Die Gitterkonstanten bei 100 K sind a = 6,473(2), b = 7,853(5), c = 10,718(3) A, und mit der Rietveld-Methode wird ein R1 = 0,020 erhalten. Die Struktur wird aus Ketten von PdF6-Oktaedern gebildet, die die eine Halfte des Palladiums in high-spin-Konfiguration enthalten und miteinander uber Quadrate verbunden sind, in denen die andere Halfte des Palladiums in low-spin-Konfiguration vorliegt. CsPd2F5 ist unter TN = 38 K antiferromagnetisch. Im geordneten Zustand zeigt sich eine schwache ferromagnetische Komponente (σ0 = 0,098 μB bei 2 K). Die bei 4 K bestimmte magnetische Struktur ist mit den magnetischen Daten vereinbar und kann in der magnetischen Gruppe Im′m′a′ ohne eine Verdoppelung der Gitterparameter beschrieben werden. In den Ketten sind die Pd2+ antiparallel gepaart. Die magnetischen Momente sind in der (x0z)-Ebene lokalisiert, der Winkel zwischen den Momenten und der z-Achse betragt 18°.

Supercritical fluids exhibit a range of unusual properties that can be exploited for new reactions which are qualitatively different from those involving classical solid state chemistry. After giving a brief introduction to these fluids we describe their use in inorganic chemistry and related fields. We then present two examples concerning different areas of solid state chemistry: (i) the formation of novel inorganic nanoparticles; (ii) the preparation of new open-structure oxy(hydroxy)fluorides, thus showing the advantages of this supercritical fluid processing that can be seen as an alternative method to regular solution chemistry or solid-gas reactions.

Cs2NH4GaF6 prepared by solid-state reaction exhibits at room temperature a cubic Fm 3 m elpasolite structure with a0=9.167 A. Calorimetric measurements have shown the presence of a first order phase transition at T0=161 K. Pressure dependence of the phase transition temperature has been studied by DTA under pressure. The data are analyzed in the framework of orientational disordering of [NH4]+ and [GaF6]3− ions.

Surface modification of graphite powder has been performed by elemental fluorine and radiofrequency (rf) plasma fluorination. Both methods give rise to an enlargement of the surface areas of graphite samples and a change of the pore volume distribution. The capacities of surface-fluorinated graphite samples are higher than those of original samples and even more than the theoretical capacity of graphite, 372 mAh g−1, without any reduction of the first colombic efficiencies. The increments of the capacities are ∼5, 10, and 15% for graphite samples with average particle diameters of 7, 25 and 40 μm, respectively.

Structural phase transition temperatures are determined for some elpasolite-type fluorides Rb2KMF6 (M = Ga, Cr, Fe) through electron spin resonance. The results are compared with low temperature X-ray diffraction and calorimetric results. For the new elpasolite Rb2KGaF6 a transition temperature of T ≈ 120 K is detected using Cr3+ and Fe3+ as paramagnetic probes. In the case of Rb2KGaF6:Fe3+ the isotropic superhyperfine constant As is well resolved in the powder spectrum. An analysis of experimental As values found for Fe3+ in different fluoride lattices is reported. In the case of paramagnetic elpasolites, the variation of the linewidth of the ESR spectra of Rb2KCrF6 and Rb2KFeF6 with temperature confirms the occurrence of a phase transition at T(Cr) ≈ 150 K and T(Fe) ≈ 170 K. The Cr3+ or Fe3+ doped K2NaGaF6 elpasolite which remains cubic down to very low temperatures is also checked. As expected no change in the ESR spectra occurs in this case. Fur einige Elpasolit-Fluoride Rb2KMF6 (M = Ga, Cr and Fe) wird mittels ESR die Temperatur des strukturellen Phasenuberganges ermittelt. Die Ergebnisse werden mit Rontgenbeugungsergebnissen bei tiefen Temperaturen und kalorimetrischen Datan verglichen. Fur Rb2KGaF6 wird die Ubergangstemperatur T ≈ 120 K gefunden, wobei Cr3+ und Fe3+ als paramagnetische Ionen dienen. Im Fall des Rb2KGaF6:Fe3+ ist die isotrope Hyperfeinkonstante As im Pulverspektrum gut aufgelost. Die experimentellen As-Werte fur Fe3+ in verschiedenen Fluoriten werden analysiert. Fur die paramagnetischen Elpasolite Rb2KCrF6 und Rb2KFeF6 bestatigt die Temperaturabhangigkeit der ESR-Linienbreite das Auftreten eines Phasenuberganges bei T(Cr) ≈ 150 K und T(Fe) ≈ 170 K. Cr3+- und Fe3+ -haltiges K2NaGaF6 bleibt bis zu sehr tiefen Temperaturen kubisch und, wie erwartet, tritt hier keine Anderung in den ESR-Spektren auf.

The influence of fluorination on the thermal conductivity, the electrical resistivity and the thermoelectric power of YBa2Cu3O7-delta has been investigated. It was found that the presence of fluorine does not drastically modify the thermal conductivity of the YBa2Cu3O7-delta compounds. The sip of the thermoelectric power was found to be negative between 92 and approximately 200 K for the sample without fluorine and positive above 92 K for the YBa2Cu3O7-delta compound treated in fluorine atmosphere. Also, a small increase of the electrical resistivity was found after treatment with fluorine. These results are consistent with the fact that the fluorine treatment generates passivation layers around the ceramic grains without affecting the inner structure of the grains.

The influence of a low temperature fluorine gas treatment on structural, superconducting and transport properties of oxides with the K2NiF4 structure has been studied. When materials with the composition La2-xBaxCuO4 where 0 less-than-or-equal-to x less-than-or-equal-to 0.04 are treated under 1 bar of F2 gas at 200-degrees-C, an increase in the orthorhombic distortion (b - a) is observed and the materials become superconductors. The insertion of anionic species in the lattice is confirmed by the observation of an increase in weight and in the c-parameter and by the elemental analysis. After annealing at 200-250-degrees-C under vacuum or argon atmosphere, La2-xBaxCu(O,F)4+delta oxyfluorides lose their superconducting properties. This change is accompanied by a structural orthorhombic-to-orthorhombic transition for values of x up to 0.02 and by an orthorhombic-tetragonal-orthorhombic sequence where x = 0.04. Similar behaviour is also observed in the T/O solid solution in the La2-xNdxCuO4 SYStem (0 less-than-or-equal-to x less-than-or-equal-to 0. 3).

The influence of a fluorine-gas treatment on both structural and superconducting properties of the La 2− x Sr x CuO 4 (0≤ x ≤0.1 5) solid solution has been studied. This treatment leads to the occurence of superconductivity at 40 K and 36 K for x =0 and x =0.02, respectively. In contrast, only a small change of the critical temperature is observed for x =0.10 and x =0.15 after fluorination of the compounds. Such a behaviour is consistent with the increase of the hole concentration arising from the incorporation of anionic species into the lattice. The study of the F 2 -treated La 2 CuO 4 by neutron diffraction reveals that the occupancy rate of the anionic interstitial site O(4))( 1 4 , 1 4 , 0.2646) is n =0.089(6), corresponding to the formula La 2 Cu(O,F) 4, 18 for the resulting oxyfluoride. The analysis of the EXAFS spectra recorded at the La L III -edge shows an increment of the anionic species around lanthanum ions.

The superconductivity properties previously described for La 2 CuO 4 -derived materials under reactive atmosphere (F 2 or Cl 2 gas) and for fluorinated La 2− x Ba x CuO 4 (0 x ⩽0.15) have been monitored by electron spin resonance (ESR). The intensity of the zero magnetic field microwave absorption depends on the halogenation temperature and pressure. This absorption in characteristic of the superconducting volume fraction. In addition to the zero field resonance, the Cu 2+ ESR signal gives information on localized copper species belonging to non-superconducting phases or decomposition products obtained by halogenation at high temperature or pressure.

A new NaBa 2 Mn 3 F 11 fluoride has been prepared by solid-state reaction. The crystal structure has been determined from X-ray diffraction measurements on a single crystal ( R =0.0317, wR =0.0295). The crystal symmetry is rhombohedral, space group R3¯c with the unit cell constants of a =7.003 A and c =35.466 A. The most important feature of the structure is the unusual environment of Mn 2+ , which is located in a pentagonal bipyramid (CN=7). To our knowledge this is the second example of such a surrounding for Mn 2+ in fluoride compounds. These bipyramids are linked by edge sharing and constitute [Mn 3 F 11 ] layers which are perpendicular to the c -axis and separated by the Na + and Ba 2+ cations. The surrounding of the Ba 2+ ions is a tricapped trigonal prism. Along the c -axis these prisms form [Ba 2 F 15 ] pairs by edge sharing. The Na atoms exhibit a distorted cubic environment. Above 40 K the magnetic susceptibility follows a Curie-Weiss law with Θ p = − 31.5 K and C =4.1. The broad maximum observed around T =15 K can result from the low dimensionality of the magnetic arrangement (2D).

Disorder-induced phenomena are evidenced in both electrical and thermal transport properties of various graphite host materials with transition metal fluoride (C/sub x/MF/sub y/ with M=Cr, Rh, Au and Ir). The electrical resistivity results are analyzed in the framework of weak-localization and carrier-carrier interaction models for two-dimensional disordered electron systems. Compared to other acceptor compounds, these fluoride GICs exhibit essentially two new features. First, for some highly resistive compounds, the logarithmic increase in resistivity with decreasing temperature starts already at room temperature and is dominant down to the lowest temperature investigated (1.5 K). Second, the effect of disorder is also observable in the temperature dependence of the thermal conductivity and thermoelectric power.

The indium weberite Na2NiInF7 has been synthesized in the form of single crystals. The symmetry of the unit cell is orthorhombic: a = 7.356(1)A, b = 10.334(2)A, and c = 7.5231(1)A, with space group Pmnb, Z = 4. The structure has been determined using 831 independent reflections (R = 0.026, Rw = 0.017). It is isostructural with Na2CuCrF7 and Na2CuInF7. Parallel [NiF5]3n−n octahedra chains run along the [100] axis separated by In atoms with octahedral coordination (InF = 2.083 A) with a seventh further atom at 2.730 A. The sodium atoms are 7- and 8-coordinated. The expected one-dimensional magnetic behavior has been confirmed, with a 3D-ordering temperature TN = 9 K. Below this temperature, a weak ferromagnetic component is observed.

The intercalation process of some d-transition metal fluorides in graphite has been investigated using anhydrous liquid HF. C(x)MF(y) GICs have been obtained for M = Cr, Rh, Ir and Au. The charge transfer has been evaluated from optical reflectivity measurements. Comparison has been carried out between electrical conductivity obtained from optical data and from a contactless method. Results on the in-plane electrical resistivity and thermal conductivity are reported. All compounds exhibit a logarithmic resistivity divergence in the low-temperature range due to weak localization and carrier-carrier interaction effects for 2D metals.

The crystal structures of two new copper weberites Na2CuGaF7 and Na2CuInF7 have been determined. Na2CuGaF7 has the monoclinic space group C2/c: a = 1232.5(5) pm, b = 731.8(1) pm, c = 1278.0(5) pm, β = 109.29(2)° and Z = 8. Na2CuInF7 crystallizes in the orthorhombic space group Pmnb: a = 731.8(1) pm, b = 1060.2(2) pm, c = 771.2(1) pm and Z = 4. The structures have been refined from 1175 reflections to R = 0.043 (wR = 0.035) for Na2CuGaF7, and from 1917 reflections to R = 0.034 (wR = 0.025) for Na2CuInF7. The structures consist of [CuF5]n3n− chains which are parallel the a-axis in Na2CuInF7 and oriented in two alternating directions in Na2CuGaF7. Sodium atoms exhibit either seven-fold or eight-fold coordination. Although strong antiferromagnetic interactions are observed inside the chains, there is no evidence for three-dimensional ordering.

The crystal structure of a new liner chain compound Tl 2 MnF 5 .H 2 O has been determined by X-ray diffraction. The structure has been refined down to R=0.034 [Cmcm space group (Z=4); unit cell constants a=9.688 (2) A, b=8.002 (1) A, and c=8.339 (1) A]. Manganese is located within elongated fluorine octahedra sharing two opposite corners to form infinite (MnF 5 ) n 2n- chains along the c-axis separated by Tl atoms and water molecules

Intercalation into graphite of CrF 4 containing some amounts of CrF 5 has been investigated using anhydrous HF solutions. Stage-2 GICs are generally obtained with repeat distance I c =11.45 A, whatever the pristine graphite material. The I c value corresponds to CrF 6 octahedra with two faces lying parallel to the graphene layers. The fitting of the intensities of the (00 l ) powder diffraction lines and the relationships between the unit cells of the graphite and of the intercalate sublattices leads to a theoretical C 18 CrF 4.5 formulation which is in good agreement with the observed composition, i.e., C x CrF 4.5 with 17≤ x ≤21. XANES. ESR, and magnetic measurements have confirmed the (+IV) oxidation state of the intercalated chromium and have corroborated the charge transfer evaluation from reflectivity data.

The heat capacity and the pressure dependence of the phase transition temperature of CoZrF6 are measured. The first order phase transition Fm3m R3 is characterized by large values of both, the entropy change ΔS = (5.8 ± 0.8) J mol−1 K−1 and the rate of increase of the transition temperature T0 with applied hydrostatic pressure, dT0/dp = (340 ± 40) K GPa−1. An analysis of the results is performed in terms of the Landau theory. The parameters of the thermodynamic potential are determined. [Russian Text Ignored].

The microwave-assisted route allows the synthesis of a new Ti hydroxyfluoride adopting a derived form of a ReO3-type network. Combined techniques such as (i) powder X-ray and neutron diffraction coupled with electron microscopy; (ii) chemical analysis and density measurements; and (iii) FTIR and TGA analyses support the occurrence of Ti vacancies and the stabilization of hydroxyl groups in the vicinity of Ti4+ cations. A superstructure of the ReO3 network has been proposed with two Ti sites and two anionic (OH/F) positions. This original compound exhibits UV-shielding properties with an optical band gap around 3.2 eV and could be considered for potential applications as protective UV absorbers.The O(2p)−Ti(3d) charge transfer band, responsible for this absorption, implies the OH groups and the nonbonding character of the 2p valence band. By changing the synthesis conditions which become reducing, Ti3+ can be stabilized in this network in an elongated octahedral site as revealed by ESR experiments and UV−v...

The results of single crystal X-ray structure determinations are reported for Ba2CaCuV2F14 (a = 1383.6(3), b = 540.89(8), c = 1493.1(3) pm, β = 91.65(3)°) and Ba2CaCuCr2F14 (a = 1381.1(5), b = 535.5(1), c = 1481.4(6) pm, β = 91,50(4)°), both isotypic with usovite (space group C2/c, Z = 4). The resulting average distances are V-F: 193.8 pm, Cr-F: 190.7 pm, and Cu-F: 209.2 resp. 207.1 pm for the Jahn-Teller elongated [CuF6] octahedra. Within the cross-linked double chains of octahedra F-bridged trimers M-Cu-M, magnetically studied earlier, are confirmed and discussed.