Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XXI. Zum Verständnis des chemischen Transports von Ti4O7, Ti5O9 und Ti6O11 in Gegenwart der Transportmittel HgCl2 und TeCl4

Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XXI. On the Understanding of the Chemical Transport of Ti₄O₇, Ti₅O₉, and Ti₆O₁₁ in the Presence of the Transporting Agents HgCl₂ and TeCl₄ Transport experiments starting with a phase Ti_nO_2n?1 (e.g. Ti₄O₇) and with HgCl₂ as transporting agent show, that in a temperature gradient at the lower temperature T₁ the neighbour phase with a higher oxygen content Ti_n+1O_2n+1 (e.g. Ti₅O₉) is deposited. As we know from previous investigations, results of experiments with TeCl₄ as transporting agent are comparable. Now on the basis of thermodynamical calculations it could be proved that in dry systems Ti/O/HgCl₂ and Ti/O/TeCl₄ (O/Ti < 2,0) a measurable transport of a TiO_x phase resulting in the deposition of a higher phase cannot take place. Observed and calculated results agree, if small amounts of H₂O are present resulting in the formation of HCl from HgCl₂ or TeCl₄ added as transporting agent. The refinement of the model now makes it possible to calculate the composition of the compound deposited at the temperature T₁ also in systems with numerous closely neighbouring phases and for given experimental conditions.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XXVI. Darstellung und elektronenmikroskopische Untersuchung von V16W9O65

Contributions to the Investigation of Inorganic Non-Stoichiometric Compounds. XXVI. Preparation and Electron Optical Investigation of V₁₆W₉O₆₅ The mixed vanadium-tungsten oxide with the composition V₁₆W₉O₆₅ (V_0.64W_0.36O_2.60) was prepared by chemical transport reactions. The dimensions of the tetragonal unit cell are a = 25.074 Å; c = 3,714 Å, determined by the X-ray-Guinier method. The probable space group is 14/mmm. The electron microscopical investigation directly reveals the block structure of the new compound. The blocks are made up of [5 × 5 × ∞] corner sharing M-O-octahedra. Other unusual block sizes are observed as defects. The blocks are connected by common corners like in the related compound (V_0.65W_0.35)₂O₅ with [4 × 4 × ∞] blocks.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XIV. Oxydationsprodukte von orthorhombischem Nb12O29 Elektronenoptische Untersuchung

Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XIV. Oxidation Products of Orthorhombic Nb₁₂O₂₉, Electron Optical Investigation An electron optical investigation shows that the orthorhombic starting material Nb₁₂O₂₉(BII) is well ordered. The oxidation products Nb₂O₅(Ox1BII) and Nb₂O₅(Ox2BII) are different from each other in structures as well as in their reactions. Nb₂O₅(Ox1BII) is unstable in the electron beam and differs from BII by characteristic point-defects. The radiation load can lead to the reduction to BII or to a transition into a defect structure with R-type-tunnels. The not well ordered structure of Nb₂O₅(Ox2BII) is stable in the electron beam. Characteristic is the sequence of [2×5] and [3×4] blocks, the latter in two different orientations. The observed composition O/Nb = 2.500 can be described by the present structural modell assuming vacant niobium tetrahedral sites. The large structural differences between the oxidation products of the orthorhombic and the monoclinic Nb₁₂O₂₉ are remarkable.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XIII. Oxydationsprodukte von monoklinem Nb12O29 Elektronenoptische Untersuchung

Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XIII. Oxidation Products of Monoclinic Nb₁₂O₂₉, Electron Optical Investigation The electron optical investigation shows that the starting material Nb₁₂O₂₉(mon.) is well ordered and that the oxidation products Nb₂O₅(Ox1BI) and Nb₂O₅(Ox2BI) have different structures. Nb₂O₅(Ox1BI) has a similar structure as Nb₁₂O₂₉(mon.), however differs from the latter by characteristic point defects, which in the electron microscope easily disappear by reduction. Nb₂O₅(Ox2BI) has not a well ordered structure; characteristic are rows of [2×n]-blocks which on the average are separated by five [3×n]-blocks. The average block length is n = 4 octahedra. The observed composition O/Nb = 2.500 can be explained by a structure model with unoccupied tetrahedral sites of Nb.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XXXVIII. Quaternäre Nioboxidfluoride des Cadmiums und Mangans mit LiNb6O15F-Struktur

Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XXXVIII. Quaternary Niobium Oxide Fluorides of Cadmium and Manganese with LiNb₆O₁₅F structure For the first time we observed an occupation of the canals in the LiNb₆O₁₅F structure by bivalent metal ions. We obtained wellshaped crystals of M_xNb₆(O, F)₁₆ (M ? Cd, Mn) by heating mixtures of MF₂ and Nb₂O₅. Cd_xNb₆(O, F)₁₆ (Mn_xNb₆(O, F)₁₆) crystallizes in the orthorhombic space group Pmma with a = 16.686 (16.677), b = 3.951 (3.952) and c = 8.907 (8.902) Å. The structure of the cadmium compound was refined to give R = 3.33% and R_w = 2.90%. The resulting formula for the investigated crystal was Cd_0.25Nb₆O_14.5F_1.5.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XLIII. Darstellung und elektronenmikroskopische Untersuchung von (Cr,Nb)12O29

Contributions to the Investigation of Inorganic Non-Stoichiometric Compounds. XLIII. Preparation and Electron Microscopic Investigation of (Cr, Nb)₁₂O₂₉ Transport experiments in the system Cr/Nb/O yielded the compound (Cr, Nb)₁₂O₂₉ as crystalline green needles. The lattice parameters of the monoclinic cell are a = 31.162(8) Å, b = 3.8324(6) Å, c = 20.579(6) Å, β = 113.22(3)°. (Cr, Nb)₁₂O₂₉ is isotypic with monoclinic Nb₁₂O₂₉ as shown by Guinier diagrams and high resolution transmission electron microscopy. Characteristic structural building elements are [3 × 4]-blocks which are columnar sections from the ReO₃ structure. In the real structure one finds numerous defects. Under the influence of the electron beam we observed reversible changes of contrast which indicates that the positions of the M-particles (M = Cr, Nb) have shifted.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XXX. Elektronenmikroskopische Untersuchung in Hochauflösung an metastabilen Niob-Wolfram-Oxiden Vergleich mit der rechnerischen Simultation

Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XXX. High Resolution Electron Microscopy Investigation of Metastable Niobium Tungsten Oxides. Comparison with Computer Simulated Images . Starting with solid solution series (Nb, W)O_x, where WO₃ + NbO₂ was substituted for Nb₂O₅, a gentle oxidation leads from the original block sizes of [3 × 4], [4 × 4], [4 × 5] or [5 × 5] octahedra to a doubling of blocks in the new ternary oxides, e. g. 2 × [5 × 5] → [5 × 10]. As HRTEM of the oxidation products revealed, these new larger blocks are connected in a special way including so-called “L-type-tunnels”. Using a LaB₆-cathode with our electron microscope, we now for the first time can directly see the positions of these tunnels.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XLIV. Neue elektronenmikroskopische Untersuchung zur Realstruktur der metastabilen Nb2O5-Modifikation Ox1C

Contributions to the Investigation of Inorganic Non-Stoichiometric Compounds. XLIV. New Electron Microscopic Investigation of the Metastable Nb₂O₅ Modification Ox1C Oxidation of the blue-black NbO_x phases (2.4 < x < 2.5) in air or a diluted oxygen atmosphere leads all together to 21 metastable colourless (partly yellowish) Nb₂O₅ modifications. These can be described as compounds having block structures like the NbO_x phases themselves. At 200°C the oxidation process to the metastable phases proceeds quite slowly; at higher temperatures all polymorphs are finally transformed to H? Nb₂O₅. Electron diffraction patterns of the polymorph, which can be obtained by heating crystals of Nb₂₂O₅₄ in atmospheric environment at about 200°C (Ox1C), show extra spots in the c* direction compared to Nb₂₂O₅₄. This oxidation product is quite sensitive to the focused electron beam, so the reduction of the crystals back to Nb₂₂O₅₄ can only be avoided by reducing its intensity. Finally HRTEM images of thin crystal areas showing a superstructure were obtained. Comparing those characteristic image contrasts to calculated images of different point defect models one finds, that mainly one point defect is responsible for the superstructure. By migration of one Niobium atom two interstitial oxygen sites are created. So a structure model can be achieved leading to the formula Nb₄₄O₁₁₀.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XXII. Neue metastabile Blockstrukturen im System Nb2O5/WO3 Elektronenoptische Untersuchung

Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XXII. New Metastable Block Structures in the System Nb₂O₅/WO₃, Electron Optical Investigation We succeeded in considerably expanding the region of existence of block structures. By substituting W for Nb, while the ratio O/∑M (M ? Nb, W) is kept constant, and starting from the known phases Nb₂O₅: WO₃ = 6:1, 7:3, 8:5 and 9:8 one obtains series of solid solutions whose metastable products of oxidation have block structures too. In contrast to the solid solutions which have the structures of the starting phases i. e. with socalled blocks of [3 × 4], [4 × 4], [4 × 5] and [5 × 5] M? O-octahedra, the products of the oxidation have structures in which some edge sharing octahedra changed their connections to become octahedra sharing corners thus opening up the possibility for the formation of blocks with twice the number of octahedra as before. Rows of these large blocks with e. g. [4 × 6] or [4 × 8] octahedra alternate nonperiodically with rows of smaller blocks of the initial size. Details of these heavily disordered structures could only be discerned with the help of high resolution electron microscopy.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen XL. Zur Kenntnis der Nioboxidfluoride NiNb14O35F2 und CoNb14O35F2

Contributions to the Investigation of Inorganic Non-Stoichiometric Compounds. XL. On the Nibium Oxide Flurides NiNb₁₄O₃₅F₂ and CoNb₁₄O₃₅F₂ Crystals of NiNb₁₄O₃₅F₂ and CoNb₁₄O₃₅F₂ were prepared from mixtures M²⁺F₂/Nb₂O₅ = 1:7 (M²⁺ = Ni, Co) by migration in a gradient of temperature (for example 1200 → 1100°C). In accordance with the isostructural compound MgNb₁₄O₃₅F₂ they have a block structure consisting of edge-sharing building elements (blocks) of [3 × 5] M–X-octahedra (X = O, F) in a monoclinic arrangement. The data for the unit cells of NiNb₁₄O₃₅F₂ (CoNb₁₄O₃₅F₂) resulting from the evaluation of the Guinier diagrams are a = 20.62 (20.65), b = 3.83 (3.83), c = 19.25 (19.27) Å, β = 108.41 (108.35)°. The images obtained from HRTEM investigations show only few faults of the ideal structure.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XXXIV. Fehlgeordnete Strukturen mit Großen Blöcken im System Nb2O5/WO3 — Elektronenmikroskopische Untersuchung

Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XXXIV. Disordered Structures Consisting of Large Blocks in the System Nb₂O₅/WO₃. An Electronmicroscopical Investigation The real structures of samples which have been prepared by quenching procedures using the composition Nb₂O₅: WO₃ = 10:11 are in most cases heavily disordered; some areas show extremly large blocks. The electron microscopic investigation revealed that the blocks consist of [n × m] M? O octahedra and have edge lengths of n = 5 to 14 and of m = 5 to 13 and in one case we even found [n × m] = [5 × 32]. In comparison, samples that were heated below the melting point for a longer time, showed a less disordered structure. Block sizes of [5 × 6] to [5 × 9] in a matrix of [5 × 5] blocks could be observed.     

Zum chemischen Transport von ZrO2 und HfO2 mit den Transportmitteln Cl2 und TeCl4

On the Chemical Transport of ZrO₂ and HfO₂ with the Transport Agents Cl₂ and TeCl₄ ZrO₂ und HfO₂ migrate in a temperature gradient (1100 → 1000°C) with the transport agent either Cl₂ or TeCl₄ by endothermic transport reaction. At experiments in silica glass tubes with TeCl₄ well developed crystals of ZrO₂ could be obtained. From HfO₂, as from both oxides using Cl₂, only powdery products are formed. The transport rates with TeCl₄ were higher than with Cl₂. The influence of different pressures was examined for the transport of ZrO₂ with TeCl₂ with thermochemical model calculations the expected transport rates could be investigated. The large correspondence between calculated and experimental received values speaks for a true interpretation of the transport observations.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XLII. Darstellung und elektronenmikroskopische Untersuchung von α-MNb24O62 und MNb52O132 (M = Zr,Hf)

Contributions to the Investigation of Inorganic Non-Stoichiometric Compounds. XLII. Preparation and Electron Microscopic Investigation of α-MNb₂₄O₆₂ and MNb₅₂O₁₃₂ (M = Zr, Hf) The new ternary oxides α-HfNb₂₄O₆₂ and HfNb₅₂O₁₃₂ were obtained by oxidizing corresponding mixtures of HfO₂/NbO₂ and subsequent heating at 1150°C, a temperature which is unusually low for reactions in this system. In contrast, α-ZrNb₂₄O₆₂ could not be obtained in this way. Instead, samples with a certain amount of this compound were synthesized in a manner described previously, but they always contained considerable amounts of the β-Modification, too. HRTEM-investigations showed all compounds, mentioned above, to have block structures. The ideal structure of HfNb₅₂O₁₃₂ corresponds to the wellknown NbO_x?phase Nb₅₃O₁₃₂; α-ZrNb₂₄O₆₂ and α-HfNb₂₄O₆₂ are isostructural to Nb₂₅O₆₂. Additionally, there exist corresponding relationships to TiNb₅₂O₁₃₂ and TiNb₂₄O₆₂. Samples with a starting composition of ZrO₂/NbO₂ = 1:24 were microheterogenous and contained large amounts of the hybrid phase ZrNb₃₈O₉₇.