On the basis of crystal structures and electronic properties, a critical discussion of the nature of chemical bonds in misfit layered chalcogenides is given. It concerns also the various mechanisms of non-stoichiometry that are present in these incommensurate structures. Misfit chalcogenides with a LnY slab opposed to TY2 ones (T = Ti, V, Cr, Nb, Ta) appear as infinite two-dimensional intercalation compounds with an electron donation from LnY to TY2. In case of PbY or SnY slabs a more complex mechanism involving coupled substitutions in both slabs seems to prevail.

The compound BaBiTe3 was prepared by the reaction of Ba/Bi/Te at over 700 °C either in K2TE4 or BaTe3 flux and was recrystallized in Ba/Te3 flux. The black rod-shaped polycrystalline material crystallizes in the orthorhombic space group P212121 with a=4.6077(2) A, b=17.0437(8) Å, c=18.2997(8) Å. Its structure is made of interdigitating columnar anionie [Bi4Te10(Te2)] ∞2+ “herring-bone” shaped segments which arrange into layers with Ba ions between them. The electrical conductivity, thermopower, thermal lattice conductivity, infrared absorption properties of this material suggest it is a narrow gap semiconductor.

The synthesis and structure of four ternary manganese tellurides are reported. All the title compounds form layered structures wherein MnTe4 tetrahedra are the fundamental building blocks. In two compounds MMnTe2 (M = Li, Na), MnTe4 tetrahedra share three corners in the formation of [MnTe3/3Te]1− layers, the fourth Te is bound to only one Mn and formally bears a negative charge. MnTe4 tetrahedra share both corners and edges in the formation of [Mn4Te6]3− and [Mn4.7Te6]3− layers in Na3Mn4Te6 and Na3Mn4.7Te6, respectively. Structural relationships between these ternary tellurides and oxides will be discussed.

Two mercury tellurium compounds [Mn(en)3]2Hg2Te9 and {[Mn(en)3]2Cl2}(Hg2Te4) have been synthesized at 180°C by solvothermal reactions using ethylenediamine as solvent. Single crystal X-ray diffraction analyses show that both compounds crystallize in monoclinic system, space group P21/c (no. 14) with four formula units in the unit cell. The cell dimensions are: a = 12.019(1) Å, b = 28.731(4) Å, c = 18.267(4) Å, β = 98.04(1)°, V = 6246(2) Å3 for [Mn(en)3]2Hg2Te9 and a = 15.720(3) Å, b = 16.812(3) Å, c = 15.224(3) Å, β= 114.31(1)°, V = 3668(1) Å3 for {[Mn(en)3]2Cl2}(Hg2Te4).[Mn(en)3]2Hg2Te9 contains pseudo one-dimensional chains of weakly bound (Hg2Te9)4− Zintl anions. The structure of {[Mn(en)3]2Cl2}(Hg2Te4) contains one-dimensional chains of Zintl anion 1∞ [(Hg2Te4)2−] formed by linking five-membered rings Hg2Te3 through bridging Te atoms. In both structures ethylenediamine incorporates into the manganese complex cation as bidentate ligand.

A new procedure for the synthesis of transition metal sulfosalts in hydrothermal brines is presented. Large, well formed crystals of metal antimony sulfides can be prepared under appropriate conditions in supercritical brines. A new compound prepared by this method, MnSb2S4, is structurally characterized.

LaMnO3 and PbZrO3 perovskites have been synthesized through coprecipitation and sol-gel techniques. After the drying and calcination steps, amorphous mixtures of oxides have been obtained. They are unstable towards phase separation. Therefore, their homogeneity and reactivity strongly depend on the parameters of the calcination, such as the temperature and heating rate. In all cases, the perovskite structure crystallizes around 600°C through nucleation- or diffusion-limited kinetics. The reaction rate depends on the history of the material. A mechanistic interpretation of the reaction, based on the similarity between the structures of PbO, ZrO2, Mn2O3 and La2O3 is proposed.

The reaction of molybdenum trioxide dihydrate, MoO3·2H2O, with methanol produces the title compounds. That these molybdenum oxy-methoxides decompose with liberation of CH2O suggests that they represent exquisite models for selective oxidation of methanol to formaldehyde over molybdate catalysts. While a number of physical techniques have been employed to elucidate certain of their structural aspects, unfortunately, the detailed structures of these materials remain unknown. Problems, both physical and crystallographic, encountered in attempts to determine these structures are discussed. Also discussed is the recent progress made by employing the complimentary nature of electron and powder diffraction techniques.

We have developed an ambient-pressure sol-gel synthetic route to superconducting borate-doped Sr2CuO2(CO3) using polyether alkoxide precursors. In our sol-gel preparation, the starting solutions contain strontium and copper alkoxide complexes in 2-(2-methoxy-ethoxy)ethanol. Boron is incorporated into the solution by using an aqueous boric acid solution for hydrolysis. Dried gels were examined by x-ray diffraction and thermal gravimetric analysis. By experimenting with various firing sequences and atmospheres we have established a successful route for reproducibly preparing relatively pure Sr2CuO2CO3 and boron-doped phases. Final products were characterized by x-ray diffraction, elemental analysis and magnetic susceptibility. Samples of nominal composition Sr2CuO2(CO3)0.85(BO2)0.15 are superconducting with a Tc(onset) of ∼25K. Subsequent treatment at 1100°C and 3 GPa for one hour increased Tc(onset) to ∼35K.

The insertion of alkali metals in W18O49 is governed by size of the cations. In this way, lithium insertion ( rVI = 0.76 Å ) seems to be optimal and a maximum of 23.5 lithium per formula can be reached before the irreversible reduction of W18O49. On the other hand, when sodium is inserted ( rVI = 1.02 Å ) an order of magnitude decrease in the amount inserted is observed and a maximum of only 1.8 sodium per formula can be intercalated. On the basis of the different phases that we have previously detected by electrochemical methods in the Li / W18O49 and Na / W18O49 systems, we have started a structural characterization by electron diffraction techniques. These studies have revealed some lithium and sodium ordering states for certain compositions; this can be explained taking into account the different types of tunnels present in W18O49.

Acid leaching chrysotile asbestos results in a stepwise loss of magnesium which reduces the strain locally. This results in a partial unwiding of the structural sheets which makes possible further leaching. Strong acids are used for a coarse brutal attack of the chrysotile structure, whereas weak acids allow a fine control of the magnesium leaching degree required to have the adequate properties of the partially leached asbestos which is used for the preparation of zeolites with enhanced catalytic properties. The final material is not carcinogenic. The leached materials were characterized by atomic absorption spectrometry, bulk density and BET specific surface area measurements, and X-ray diffraction.

Thin films of V2O5 and β-CuxV2O5 have been grown by MOCVD using VO(OiPr)3 and Cu(tmhd)2 (tmhd = tetramethylheptanedionato) as precursor molecules. Films were grown on chips of Si3N4 coated silicon wafers in a cold wall reactor using a H.F. heater. A mixture of helium and oxygen was used as a reactive carrier gas, and depositions were performed at low pressure. The films were examined by SEM, characterized by XRD, and analyzed by EDS and EMPA techniques. All the films proved to be carbon free.

For V2O5, the substrate temperature was varied from 450 to 630°C. The films are highly caxis oriented for both ends of the temperature range, and less oriented for intermediate temperatures. For 630°C, the XRD pattern consists almost entirely of reflections (001) and (002).

For β-CuxV2O5, the substrate temperature was varied from 450°C to 650°C. Pure β-phase films with x varying from 0.25 to 0.55 have been obtained above 500°C, by using well chosen gas phase composition. Morphology and texture depend dramatically on the temperature. The most oriented films exhibit a strong anisotropy of electrical surface conductivity.

Oriented films of layered Se-carbon compounds are grown on Ni substrates in evacuated sealed quartz tubes. Results of X-ray diffraction, Raman scattering and the c-axis electrical transport studies are reported. A discussion of possible models for the carbon -Se interaction is presented.

The influence of hydrogen incorporation and oxygen removal on superconducting YBa2Cu3O7-δ is discussed in comparison with their respective effects. Both hydrogen incorporation and oxygen removal induce the orthorhombic (O)-to-tetragonal (T) transition and antiferromagnetic ordering as well. However, there exist no consistent changes in the c-axis for the O-to-T transition and the superconducting transition temperature Tc upon hydrogen incorporation in YBa2Cu3O7-δ on the other hand, the c-axis certainly increases in the corresponding transition driven by oxygen nonstoichiometry and Tc decreases with increasing δ in YBa2Cu3O7-δ. Plots of Tc vs. the lattice parameter c reveal no significant suppression in Tc upon hydrogenation than oxygen removal. It is concluded that the Cu-O bond distances or the Cu-Cu plane spacings along the c-axis change somewhat differently in two cases; it is believed that the charge-carrier concentration is reduced less significantly upon hydrogenation than oxygen removal in YBa2Cu3O7-δ, giving rise to the aforementioned finding.

Single crystals and powders of vermiculite are dehydrated and then intercalated with alkali metals (K and Rb) using a two-temperature-zone furnace. The samples, originally transparent, exhibit metallic silver color upon intercalation. Our x-ray diffraction experiments indicate that the c-axis lattice constant becomes smaller after the intercalation process. A SQUID magnetometer is used to measure the magnetization of the samples as functions of temperature and magnetic field. Evidence for Pauli paramagnetism and enhancement of ferromagnetism are found in the Rb- and K-intercalated compounds, in addition to Curie paramagnetism due to iron impurities in the original vermiculite.

Hydrothermal titration (HTT) techniques represent a new synthetic strategy for the production of open frameworks. As an example, initial digestion of amorphous GeS2 in the presence of tetraethyl ammonium hydroxide (TEAOH) at 100°C is followed by injection of Ag+ into this mixture to condense the [Ge4S10]4− clusters and form a framework consisting of 8-ring channels bounded by alternating GeS-clusters and Ag+. The rational use of this apparatus depends upon determining the timing of injection. Insight into the changes occurring during reactant digestion is provided by real time synchrotron X-ray powder diffraction. Changes in the the system dimethylamine-Sb-S have been followed in real time at different temperatures. The transformation from mixtures of DMA, Sb and S to the known open phase DMA-SbS-SB8 was followed by observing monochromatic X-ray scattering detected on an imaging plates over a 8 hr period with one continuous exposure.

Extending our prior work on tungsten and molybdenum oxides, we have found that a wide variety of vanadium oxides can be prepared using hydrothermal methods. These include a number of layer compounds as well as cluster complexes. The starting reaction medium usually contained vanadium pentoxide, an alkali containing compound such as LiOH, an organic template such as tetramethylammonium, and the pH of the whole was controlled by the addition of acid. Reaction temperature was 150°C to 200°C, and time was up to 3 days. A new lithium vanadium oxide, which has the simplest structure of any layered vanadium oxide, was formed. The lithium could be readily removed leading to a new form of vanadium dioxide. This vanadium oxide was also capable of intercalating a variety of other ionic and molecular species. Several other new vanadium oxides containing the TMA cation were also formed; one of these TMAV3O7 readily absorbed oxygen to form TMAV3O8. Addition of zinc or iron to the reaction medium caused the formation of layer structures containing double V2O5 layers; for iron the TMA was retained in the structure whereas for zinc the TMA was excluded. Changing the organic entity resulted in other new structures, for example methylamine and dimethylamine gave tetragonal structures.

Several low temperature tungsten-containing oxynitride phases were isolated and stabilized by doping with Fe, Co, and Ni. These Phases have the rocksalt structure and form around 420 °C by reacting MWO4 (M=Fe, Co, Ni) with dry ammonia. They served as intermediates in the formation of the hexagonal ternary nitrides (MWN2). X-ray powder diffraction analyses of these phases indicate that W0.62(NO) could be the parent structure type in each case. The incorporation of group VIIIB elements in the W0.62(NO) structure may play an important role in the formation and stabilization of these low temperature phases.

Reaction of silver(I) nitrate and hexamethylenetetramine (HMTA) gives crystals of Ag2(HMTA)(NO3)2, which was formulated by elemental microanalysis and a single crystal x-ray study. Its Ag2(HMTA) open-framework is the first example of a decorated CdSO4net. The relative orientation of the tetrahedral HMTA building blocks in this structure point to numerous opportunities toward constructing novel chiral and polar porous frameworks.

The pH of the reaction media is a critical factor in the formation of new vanadium oxides with the tetramethylammonium (TMA) ion via the conventional hydrothermal method. New vanadium oxides; TMAV3O7, Li0.6V2−δO4−δ·H2O and Li0.6V2−δO4−δ, TMAV4O10, and two more new vanadium phases with d spacings of 11.5Å and 19.1Å are formed as the pH is varied with acetic acid. The synthesis and characterization of TMAV3O7, a new vanadium oxide with tetramethylammonium ions residing between its layers is discussed. The intercalation of alkylamines, DMSO, and water into Li0.6V2−δO4−δ·H2O is described. Microwave hydrothermal synthesis is a new and alternate soft chemistry technique used to accelerate the synthesis of TMAV4O10. This method also aided in the formation of a new cluster compound, [Li(H2O)4]2TMA(V10O28)·4H2O.

Within the ASU MRSEC, we are using a combination of high pressure synthesis techniques (multi-anvil, piston cylinder), combined with in situ studies in diamond anvil cells, and ab initio calculations, to prepare a range of new materials at high pressure, and to study their physical properties under extreme conditions of pressure and temperature. Work in progress includes experiments on nitrides, particularly glasses and crystalline materials based in the P3N5-HPN2-PON system, silicate and germanate perovskites and related vanadates and niobates, and high hardness materials in the B-C-N-0 system. Some of our recent results are presented.