RESUMEN
Crystallization from glass can lead to the stabilization of metastable crystalline phases, which offers an interesting way to unveil novel compounds and control the optical properties of resulting glass-ceramics. Here, we report on a crystallization study of the ZrF4-TeO2 glass system and show that under specific synthesis conditions, a previously unreported Te0.47Zr0.53OxFy zirconium oxyfluorotellurite antiglass phase can be selectively crystallized at the nanometric scale within the 65TeO2-35ZrF4 amorphous matrix. This leads to highly transparent glass-ceramics in both the visible and near-infrared ranges. Under longer heat treatment, the stable cubic ZrTe3O8 phase crystallizes in addition to the previous unreported antiglass phase. The structure, microstructure, and optical properties of 65TeO2-35ZrF4Tm3+-doped glass-ceramics, were investigated in detail by means of X-ray diffraction, scanning and transmission electron microscopies, and 19F, 91Zr, and 125Te NMR, Raman, and photoluminescence spectroscopies. The crystal chemistry study of several single crystals samples by X-ray diffraction evidence that the novel phase, derived from α-UO3 type, corresponds in terms of long-range ordering inside this basic hexagonal/trigonal disordered phase (antiglass) to a complex series of modulated microphases rather than a stoichiometric compound with various superstructures analogous to those observed in the UO3-U3O8 subsystem. These results highlight the peculiar disorder-order phenomenon occurring in tellurite materials.
RESUMEN
The first ternary BaF2-Ln(Y)F3-ZrF4 phases crystallizing near the composition range of fluoride glasses, namely Ba4YZr3F23 (barium yttrium fluoridozirconate) and isotypic Ba4LnZr3F23 (Ln = Yb, Er and Nd), have been synthesized. The crystal structure of Ba4YZr3F23 cannot be correctly determined in the centrosymmetric space group Pnma (R1 = 0.09); it is preferably described in the noncentrosymmetric space group Pn21a (R1 = 0.028). All cations are located at y = 0.25-0.29 and 0.75-0.79. This new structure type is formed by infinite {[YZr3F23]8-}n columns associating, along [001], YF9 tricapped trigonal prisms, ZrF8 dodecahedra and ZrF7 polyhedra. These columns are interconnected via BaF10+1 and BaF12 irregular polyhedra.
RESUMEN
The low-temperature triclinic variety α-BaZr2F10 constitutes a new structure type, less symmetrical than the higher-temperature ß-variety. It is based on the stacking of double sheets of Zr polyhedra, connecting three different kinds of ZrF7 polyhedra and one ZrF8 polyhedron via vertices and edges, separated by corrugated Ba2+ layers. It is compared to the high-temperature ß-variety, directly recrystallizing from barium fluoridozirconate glass, and also to BaTe2F10 and KTe2F9.
RESUMEN
The structure of the high-temperature monoclinic variety α-SrHfF6 (strontium hafnium hexafluoride) [and of isostructural α-SrZrF6 (strontium zirconium hexafluoride)] associates Hf2F12 bipolyhedra and SrF8 snub disphenoids, forming zigzag twisted [SrF6]n layers. The distribution of the Hf and Sr polyhedra forms a three-dimensional framework which can be related to the family of anion-excess ReO3-related superstructures. α-SrHfF6 corresponds to a new ABX6 type and is compared to the other main families already described. A partial amorphization of this structure is observed in samples quenched from the melt.
RESUMEN
The crystal structure of the high-pressure (4-8â GPa) form of zirconium tetrafluoride, γ-ZrF4, is based on the association by corner- and edge-sharing of ZrF8 triangulated dodecahedra, forming a three-dimensional framework. It presents some analogies with high-temperature α-ZrF4 but clearly constitutes a new MX4 structure type. The main MX4 ionic structure types, and especially those deriving from the `anion-excess ReO3-type', are compared and it is shown that the TeF4 structure can also be included in this family.
RESUMEN
A new oxyfluorotellurate(IV), indium fluoridopentaoxidotellurate(IV), InTe2O5F, has been synthesized by solid-state reaction and structurally characterized. The crystal structure consists of a three-dimensional framework formed by InO4F2 octahedra and Te2O5 units. The InO4F2 octahedra are linked through the F atoms, which lie on twofold axes, giving rise to helical chains. These helical chains are connected via the Te2O5 units. The helical chains of indium octahedra surround cavities, into which the lone pairs of electrons of the Te atoms point.
RESUMEN
The structure of an already evidenced but still uncharacterized GeTe(2)O(6) phase consists of isolated GeO(6) octahedra connected via isolated TeO(3) units. The germanium cations occupy a site with 1 symmetry. The Te and O atoms are in general positions of the P2(1)/n space group. This structure corresponds to a new type of tetravalent tellurate and is different from other AB(2)X(6) structures in which the B cation presents a stereochemically active electronic lone pair. It derives from the pseudo-hexagonal MI(2)O(6) (M = Mg, Mn, Co and Fe) type by a strong monoclinic distortion caused by the much smaller size of Ge(4+) compared with the divalent M cations.
RESUMEN
As part of a continuing study of oxyfluorotellurates(IV), materials likely to present interesting nonlinear optical properties, two new phases, titanium(IV) tellurium(IV) trioxide difluoride, TiTeO(3)F(2), and divanadium(IV) ditellurium(IV) heptaoxide difluoride, V(2)Te(2)O(7)F(2), have been characterized and present, respectively, titanium and vanadium in the tetravalent state. The TiTeO(3)F(2) structure is based on linear double rows of TiO(3)F(3) polyhedra sharing vertices. These rows are connected to adjacent rows via two vertices of Te(2)O(5) bipolyhedra. The Te, Ti, one F and two O atoms are on general positions, with one O and F statistically occupying the same site with half-occupancy for each anion. One O and one F occupy sites with .m. symmetry. The V(2)Te(2)O(7)F(2) structure consists of zigzag chains of VO(4)F(2) octahedra alternately sharing O-O and F-F edges. These chains are connected via Te(2)O(5) bipolyhedra, forming independent mixed layers. The Te, V, one F and three O atoms are on general positions while one O atom occupies a site of \overline{1} symmetry. In both phases, the electronic lone pair E of the Te(IV) atom is stereochemically active. A full O/F anionic ordering is observed in V(2)Te(2)O(7)F(2), but in TiTeO(3)F(2) one of the six anionic sites is occupied by half oxygen and half fluorine, all the others being strictly ordered. These compounds represent new members of a growing family of oxyfluorotellurates(IV), including the recently characterized members of formula MTeO(3)F, M being a trivalent cation. As was true for the previous members, they are characterized by an unusually high thermal and chemical stability in relation to the absence of direct Te-F bonds.
RESUMEN
As an extension of a general structural study concerning fluorides and oxyfluorides of cations presenting a stereochemically active electronic lone pair, until now limited to tellurium(IV) phases, the previously unknown structure of NaIO(2)F(2) corresponds to a new structure type based on isolated IO(2)F(2)(-) polyhedra forming sheets separated by Na(+) layers. The sodium ion is octahedrally coordinated with 2/m site symmetry, while the I(V) atom has m2m symmetry with a stereochemically active lone electron pair. The O and F atoms (both with m symmetry) are bonded to the I(V) atoms in a fully ordered manner. A comparison with the structure of ferroelastic KIO(2)F(2) and with structures based on hexagonal close packing of anions, mainly rutile-type and FeTeO(3)F-type, reveals differences that are attributed to the smaller ionic radius of Na(+) and the ordering of the Na and I cations.
RESUMEN
In the course of a general study of oxyfluorotellurates(IV), materials likely to exhibit interesting nonlinear optical properties, the crystal structures of the new phases scandium tellurium trioxide fluoride, ScTeO(3)F, and indium tellurium trioxide fluoride, InTeO(3)F, belonging to two different structural types and also differing from that of the recently published MTeO(3)F (M = Fe, Ga and Cr) series, have been determined. The ScTeO(3)F structure can be described as an intergrowth of two different layers of scandium octahedra connected via isolated TeO(3) groups. The scandium ions occupy two different sites with ..2 and 2.. site symmetry. The Te, F and O atoms are on general positions of the Pnna space group. The InTeO(3)F structure consists of zigzag sheets of InO(5)F octahedra. The In, Te, O and F atoms are all located on general positions of the P2(1)/a space group. TeO(3)F polyhedra are inserted between the zigzag sheets of InO(5)F octahedra and with them form double (InTeO(3)F)(n) layers. Therefore, InTeO(3)F is a true layer structure, unlike the previous types. In all these phases, the electronic lone pair of the Te(IV) atom is stereochemically active and a full O/F anionic ordering is observed.
RESUMEN
The crystal structures of the new isomorphous compounds iron(III) oxyfluorotellurate(IV), FeTeO(3)F, gallium(III) oxyfluorotellurate(IV), GaTeO(3)F, and chromium(III) oxyfluorotellurate(IV), CrTeO(3)F, consist of zigzag chains of MO(4)F(2) distorted octahedra alternately sharing O-O and F-F edges and connected via TeO(3) trigonal pyramids. A full O/F anionic ordering is observed and the electronic lone pair of the Te(IV) cation is stereochemically active.