1998 MRS Fall Meeting & Exhibit

Chairs

Susan Kauzlarich, Univ of California-Davis
Eugene McCarron, DuPont
Arthur Sleight, Oregon State Univ
Hans-Conrad zur Loye, Univ of South Carolina

Symposium Support 

• CERDEC Corporation
• DuPont, Central Research & Development
• IBM T.J. Watson Research Center
• Inel, Inc.
• National Science Foundation 

1998 Fall Exhibitor 

* Invited paper

TUTORIAL 

Ftd: SYNTHESIS OF INORGANIC MATERIALS 
Sunday, November 29, 1:30-5:00 p.m. 
Salons A/B (Marriott) 

Synthesis of materials is an important component of discovering new phenomena, and is one of the cornerstones in developing new technologies. This tutorial will provide an overview of the fundamentals in synthesis, including materials property design. Structure-property relationships will be discussed, including matching form to function. Various synthetic techniques such as crystal growth and preparation of thin films will be covered. Methods for synthesizing metastable materials will be presented along with specific examples.  Instructor: Don Murphy, Lucent Technologies, Bell Labs Innovations 

SESSION DD1: FRAMEWORK STRUCTURES 
Chairs: Dermot O'Hare and Omar M. Yaghi 
Monday Morning, November 30, 1998 
Backbay Ballroom (S)

8:45 AM DD1.1 
SILICON CLUSTERS IN THE ALPHA-CAGES OF Y ZEOLITE. Jiliang He, Yong Ba, Christopher I. Ratcliffe , John A. Ripmeester, Dennis D. Klug, John S. Tse, Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, CANADA. 

Nanoscale particles of many materials are expected to display novel properties different from bulk material, in particular quantum confinement effects and modified optoelectronic properties. Much effort is being expended to produce such materials using zeolites and other microporous solids as mini-reactors and templates to grow size-restricted clusters and to produce periodic arrays of clusters or nano-wires. Luminescent silicon nanoclusters have been synthesised from Si₂H₆ in the alpha-cages of NAHY zeolite, and a variety of techniques have been applied to characterise the encapsulated species. The synthetic process was monitored by FT-IR, TGA-MS and solid state ¹H and ²⁹Si NMR. The initial step of the synthesis involves anchoring of disilyl groups to the zeolite at 100^oC, together with some chemisorption and trapping of disilane. Multiple quantum ¹H NMR spin-counting shows clusters of these precursors contain 38H atoms, and thus about 14 Si atoms. At 550^oC H² and SiH⁴ are eliminated and Si_n clusters remain. A combination of XPS and Si K-edge XANES results indicate an average 12 Si atoms per alpha-cage. These clusters are capped by up to 5 H atoms and attached to the zeolite framework through SiO linkages. The HOMO-LUMO energy gap in the Si cluster is estimated to be 2.2eV, from a comparison of the band edges of the Si clusters and bulk Si determined by synchrotron photoabsorption (Si K-edge) and photoemission spectroscopies. The material shows room temperature photoluminescence in the yellow-green region with a peak energy at about 2.2 eV. The close correspondence of the latter with the HOMO-LUMO energy gap confirms the origin of luminescence from the Si cluster as a predominantly electron-hole radiative recombination process. 

9:00 AM *DD1.2 
MOLECULAR AND ZEOLITE FRAMEWORKS - NEW PHASES AND DIFFRACTION STUDIES OF SORPTION AND DESORPTION. Cameron J. Kepert, Amelia J. Fowkes, Matthew J. Rosseinsky , University of Oxford, Department of Chemistry, Oxford, U.K.; Richard M. Ibberson, ISIS Facility, Rutherford Appleton Laboratory, Chilton, UK. 

The widespread application of zeolite and aluminophosphate molecular sieves in catalysis and sorption has lead both to an intense study of these materials and a search for analgoues in which the frameworks are assembled from molecular components in a controlled manner. This presentation will address both the preparation and crystal chemistry of transition metal co-ordination polymers and the use of high resolution neutron powder diffraction to study active sites in a Cu-zeolite Y catalyst active for NO decomposition. A driving force for the study of molecular frameworks is the discovery of structural features not displayed by zeolites. The structures of new chiral molecular frameworks based on multiple interpenetration of the (10,3-a) network, and studies of their sorption and desorption chemistry, will be presented: homochirality is rare in existing classical porous solids. The effective mimicking of zeolite behaviour requires that molecular frameworks are robust and retain their structural integrity after removal of the templating species from the extra-framework volume. The structural evolution upon desorption of a polymer framework based on (4,4')-bipyridyl will be described, using single crystal X-ray diffraction. This reveals the framework stability to guest loss and directly demonstrates the porosity of the crystal, which retains structural integrity during desolvation. 
The theme of in-situ diffraction characterisation is continued in a study of the sorption of NO by Cu-exchanged zeolite Y. Copper-exchanged high silica zeolites (ZSM-5 and mordenite) are active catalysts for both decomposition and selective catalytic reduction of NO. The neutron powder diffraction study of the less active, but more heavily copper loaded, Y zeolite under NO pressure reveals the location of two distinct copper sites for sorption. The influence of copper oxidation state on the structures of both the pristine and NO loaded zeolites will be discussed. 

9:30 AM DD1.3 
MICROPOROUS 4-CONNECTED GERMANATE NETWORKS. O.M. Yaghi and Hailian Li, Arizona State University, Department of Chemistry and Biochemistry, Tempe, AZ. 

Although 4-connected nets of zeolitic silicates and aluminosilicates represent a vast, well-established, and useful class of materials, the analogous germanates remain conspicuously absent and largely unexplored. We have developed a synthetic route involving the application of nonaqueous soft chemical methods to the conversion of GeO₂ to previously unknown, microporous germanate 4-connected nets. Two crystalline materials of GeO₂ composition will be reported, namely, [GeO₂]₁₀(DMA)(H₂O), (ASU-7), and [GeO₂]₁₀(DABCO)(H₂0), (ASU-9), with the first possessing a remarkable new zeolite-type net containing 1-D channels, and the second adopting an octadecasil net with large cages. 

9:45 AM DD1.4 
ORGANICALLY-TEMPLATED MIXED-VALENT TITANIUM PHOSPHATE WITH OPEN FRAMEWORK STRUCTURE: SYNTHESIS AND CHARACTERIZATION. Sambandan Ekambaram, Slavi C. Sevov , Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN. 

We have hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction the first mixed-valent Ti(III)/Ti(IV) phosphate with an open-framework structure. The frame of the compound is of the octahedral/tetrahedral type. The template of 1,3-diaminopropane occupies channels running along two directions. The sizes of the channels are comparable to those of many zeolites. The compound has vivid blue-purple color due to Ti(III). Magnetic measurements are consistent with one d-electron per formula unit. TGA/DTA and IR data will be reported as well. This compound is most likely the first member of a larger class of reduced titanium phosphates. An ethylenediamine-templated compound with blue color has been also synthesized hydrothermally and its structure is in process of evaluation. 

10:30 AM DD1.5 
A FIRST PRINCIPLES STUDY OF ALUMINUM SUBSTITUTION IN SODALITE. Kendall T. Thomson , Renata M. Wentzcovitch, Alon V. McCormick, H. Ted Davis, University of Minnesota, Dept of Chemical Engineering and Materials Science, Minneapolis, MN. 

We have conducted a first principles calculation of sodalite (a prototypical zeolite) to explore the structural and chemical properties of aluminum substitution in silicate frameworks. By isolating Al-poor and rich frameworks, with and without extra-framework ions, we show that framework interaction with extra-framework ions has a small but relatively insignificant role in dictating the structure of sodalite. Rather the structural stresses induced by direct Al-substitution are of primary importance. We also explored the full electronic structure of sodalite and offer insight into what determines the equilibrium positions of cations in zeolite frameworks. 

10:45 AM DD1.6 
STUDY OF THE HYDROTHERMAL SYNTHESIS OF GALLIUM PHOSPHATES USING IN SITU TIME-RESOLVED X-RAY DIFFRACTION. Robin J. Francis, Richard Walton, Dermot O'Hare , Inorganic Chemistry Laboratory, University of Oxford, Oxford, UK; Thierry Loiseau, Gerard Férey, Institut Lavoisier, IREM UMR C173, Université de Versailles, Versailles, FRANCE. 

We have been investigating the kinetics and the mechanism of the crystallisation of microporous phosphates under hydrothermal conditions using time-resolved in-situ energy-dispersive X-ray powder diffraction. In particular we have studied the crystallisation of open-framework oxyfluorophosphates of aluminium and gallium belonging to the ULM-n family. Our recent work has shown that the microporous oxyfluorinated gallium phosphate ULM-5, Ga₁₆(PO₄)₁₄(HPO₄)₂(OH)₂F₇4H₃N(CH₂)₆NH₃,

is formed via previously unobserved crystalline intermediates when P₂O₅ is used as the phosphorus source in its synthesis, but not when H₃PO₄ is used. We have also extended these studies to other members of the ULM-n family, for both the aluminium and gallium analogues. The ULM-3 structure is formed from a gallophosphate gel in the presence of 1,3 diaminopropane (DAP) when the pH is between 5 and 10, and ULM-4 is formed at lower pH from a gel made of the same components. A crystalline intermediate is always observed during the crystallisation of ULM-3 whereas no intermediate phases are observed during the crystallisation of ULM-4. 

11:00 AM DD1.7 
INVESTIGATIONS OF CATION LOCATION IN TWO ONE-DIMENSIONAL PORE LOW-SILICA ZEOLITES USING NEUTRON DIFFRACTION AND NMR SPECTROSCOPY. Allen Burton , Matthias Feuerstein, Raul F. Lobo, University of Delaware, Department of Chemical Engineering, Newark, DE. 

To explain the catalytic and adsorption properties of zeolites, it is vital to understand the structure-property relationships of these materials. Framework topology, cation content, cation identity, and cation location strongly determine the interactions that guest molecules have with zeolites. Here we investigate cancrinite, a low silica (Si/Al = 1) zeolite with unidimensional 12-membered ring pores. However, its use in industry has been precluded by the fact that all other conventional syntheses yield a cancrinite with pores blocked by polyatomic anions. This motivated our study of a cancrinite synthesized by Liu et al.[1]who have reported that the material is free of pore blockage. 
The cancrinite sample is prepared in a nitrogen-filled glove box using sodium metal to make sodium hydroxide free of carbonate. FTIR, NMR, and pore volume measurements of calcined cancrinite have been made to check for the presence of carbonate ions. The sample is dehydrated by heating in vacuum at 400^oC for 24 hours. Neutron diffraction measurements are performed on the sample at the National Institute of Standards and Technology (NIST). The dehydrated sample is also studied by solid state ²3Na MAS NMR. The refinement shows cations postioned inside the cancrinite cages and above the six-rings which line the cancrinite pore. 
In the second part of our work, we examine a series of G-L zeolites.[2] These are low silica zeolites that have the same framework topology as zeolite L, another zeolite with unidimensional 12-membered ring pores. These zeolites are characterized by high thermal stability (>600^oC), an unusual characteristic of highly aluminous zeolites. A higher silica analog of this zeolite, Pt/Ba-L (Si/Al = 3), is used industrially for the aromatization of alkanes. [3] 
Neutron diffraction data are collected on dehydrated samples of as made (Ba, K)-G,L and (Ba, Li)-G,L and on lithium-exchanged (Ba, K)-G,L. A series of syntheses of (Ba,K)-G,L have been carried out in which the the barium content of the synthesis mixture is varied. The results of the synthesis experiments and the diffraction experiments indicate that only a threshold amount of barium is required in the gel to fill the cation sites inside and between the cancrinite cages of zeolite L. 

11:15 AM DD1.8 
PROCESSES IN POLYNARY COPPER OXIDES AND COPPER OXIDE/MESOPOROUS SILICA COMPOSITES. Stefan Ebbinghaus, Michael Fröba, Armin Reller , Institute of Inorganic and Applied Chemistry, University of Hamburg, GERMANY; Pino Fortunato, Institute of Inorganic Chemistry, University of Zürich, Zürich, SWITZERLAND. 

Dynamic redox processes are described for different metal oxides and metal oxide/mesoporous silica composites containing copper in different oxidation states and different moieties: For the spinel-type Cu_1+xMn_2-xO₄ the atomic and electronic structures are spezified with respect to the reversible process Cu²+ + Mn³⁺ = Cu¹⁺ + Mn⁴⁺, i.e. the crucial equilibrium allowing the catalytic oxidation of CO to CO₂ at ambient temperature. A comparison with perovskite-type LaCu_1-xMn_xO is presented. For the K₂NiF₄-type compound La_2-xSr_xCu_1-yRu_yO_4- for the first time [6]. The products were characterized with XRD, TEM, TG/DTA/MS and X-ray absorption spectroscopy. Analyses of the XANES and EXAFS of the respective Re L1 and Re L3 edges could identify the Re/O species as rhenium dioxide. 

11:45 AM DD1.10 
SYNTHESIS AND PROPERTIES OF OCTAHEDRAL MOLECULAR SIEVES OF MANGANESE OXIDE WITH TUNNELS COMPOSED OF 2 X 4 MnO_6/3 OCTAHDRA. Elaine N. Tolentino, GuanGuang Xia, Mimi Nguyen-Vu, NianGao Duan, Stephanie L. Brock , University of Connecticut, Department of Chemistry, Storrs, CT; Steven L. Suib, University of Connecticut, Department of Chemistry, Chemical Engineering, and Institute of Materials Science, Storrs, CT. 

The family of mixed valent manganese oxides consists of a wealth of tunnel, layered, and intergrowth structures and display a remarkable range of useful properties, from the oxidation of organic compounds, to the electrochemical insertion of lithium and magnetoresistive effects. Recently, a new manganese oxide material with the formula Rb₁₆Mn₂₄O₄₈ was reported with a structure consisting of tunnels bordered by 2 MnO_6/3 edge sharing octahedra on one side, corner shared to 4 MnO_6/3 edge sharing octahedra on the adjoining side, with Rb⁺ cations within the tunnels (Rziha, Gies, & Rius; Eur. J. Mineral. 1996, 8, 675). The material was prepared in milligram quantities from hydrothermal treatment of octahedral layered manganese oxides (birnessites) with RbOH at 350 C and 2 kBar in a gold ampoule. This synthesis produced enough material for a structure solution via a combination of single crystal and powder (Rietveld refinement) techniques, but the scale is insufficient for the application of extensive characterization techniques or for any potential applications in battery or catalytic reactions. Additionally, the material as prepared is contaminated with other manganese oxide phases. 
We have developed a new synthetic strategy for the bulk (gram quantity) preparation of these 2 x 4 materials using both Rb⁺ and Na⁺ as structure directors. These materials are synthesized hydrothermally from the Na or Rb octahedral layered (birnessite) phases at 210 C under autogeneous pressure. They have been characterized by X-ray powder diffraction with Rietveld refinement, thermal gravimetric analysis and differential scanning calorimetry, average oxidation state measurement, BET surface area analysis and scanning and tunneling electron microscopies. The synthesis, detailed structure, and properties will be discussed and compared to other octahedral molecular sieve materials.

SESSION DD2: ELECTRONIC & MAGNETIC MATERIALS 
Chairs: John E. Greedan and J. M. Honig 
Monday Afternoon, November 30, 1998 
Backbay Ballroom (S)

1:30 PM *DD2.1 
TRANSPARENT CONDUCTING OXIDES: SYNTHESIS, DOPING, AND CHARACTERIZATION. G.B. Palmer, A. Ambrosini, and K.R. Poeppelmeier, Northwestern University, Department of Chemistry, Evanston, IL; D.R. Kammler and T.O. Mason , Northwestern University, Department of Materials Science and Engineering and Materials Research Center, Evanston, IL. 

There are currently four families of transparent conductors, based upon semiconducting oxides of indium, tin, zinc, and copper. The first three are n-type oxides with substantial conductivities. The newly reported copper oxides have quite low conductivities in comparison, but have nevertheless generated considerable excitement in the TCO field. We have investigated a number of combination (solid solution, binary cation, and ternary cation) TCOs, including previously unreported phases and/or compositions. A number of strategies appear to be promising, including structural layering, isovalent co-substitution of cations, and hybridization of cation-related electronic states. The most important factor in the figure-of-merit for TCOs is the electron (or hole) mobility. The challenge is how to accomplish carrier doping without perturbing the periodic potential of the conduction band-forming metal-oxide array. TCO optimization requires a careful combination of extrinsic, aliovalent doping and intrinsic, oxygen defect production. Little attention has been paid to the kinetics of post-process oxidation/reduction annealing to optimize TCO properties via control of oxygen defects. The underlying defect structures of TCO materials are only now beginning to be understood. In this talk we report our work on the synthesis, doping, and characterization of indium-based TCO phases in the Zn-In-O, Zn-In-Sn-O, and Ga-In-Sn-O systems. We also discuss ramifications for the discovery of novel TCOs in related Sn-based and Cu-based systems. 

2:00 PM *DD2.2 
CHARACTERIZATION OF TRANSPARENT CONDUCTOR PULSED LASER DEPOSITED FILMS IN THE INDIUM ZINC OXIDE SYSTEM. Negar Naghavi, Aline Rougier , Claude Guéry, Corinne Marcel, and Franáois Portemer, Laboratoire de Reactivite et de Chimie des Solides, Universite de Picardie Jules Verne, FRANCE. 

In recent years, there has been a growing interest in the development of new transparent conducting oxides (TCO), with similar optical and electrical properties as the well-known indium tin oxide (ITO), but at a lower cost. Such materials offer a wide range of applications (displays, solar cells and electrochromics). Equilibrium phase relationships in the ZnO-In₂O₃system were determined using solid-state reaction techniques. Pure compounds with the Zn_kIn₂O_k+3 (k3) formula were obtained [1]. Thin films of Zn_kIn₂O_k+3 (k=3,4 and 5) phases were deposited on glass substrate by pulsed laser deposition. Their composition (i.e. In/Zn ratio value), deduced from EDX measurements, and their structural features are strongly dependent on the conditions of deposition (oxygen pressure, temperature of deposition, distance film-substrate...). The X-ray diffraction study shows that the films prepared at room temperature are amorphous, whereas for higher temperature of deposition (T300C) broad X-ray diffraction peaks appear. The electrical and optical properties of the so-called IZO films will be discussed in relation to the conditions of deposition and the In/Zn ratio values. [1] G. Palmer, K.R. Poeppelmeier, Abstract B9, MRS Spring Meeting, San Francisco 1998. 

3:00 PM *DD2.3 
TUNING OF MAGNETISM IN A 3D CUPRATE: Se_1-xTe_xCuO₃ PEROVSKITES. M.A. Subramanian , DuPont Central Research & Development, Experimental Station, Wilmington, DE; A.P. Ramirez, Bell Laboratories, Lucent Technologies, Murray Hill, NJ. 

The distorted-perovskite oxides of the formula, Se₁-xTe_xCuO₃ (0  x  1) with all the copper in +2 oxidation state (^9) have been prepared. The compounds are characterized by single-crystal x-ray diffraction structure refinements, magnetizationand specific heat. A continuous evolution in both structural and bulk properties is observed between the ferromagnetic ground state for x = 0 and the antiferromagnetic state for x = 1. It is observed that the transition between ferromagnetic and antiferromagnetic nearest-neighbor coupling occurs at a Cu-O-Cu bond angle close to 128^. The value of this critical angle lies significantly below the trend in the main sequence formed by the lighter 3dTi₃O_12-x. Tsuyoshi Kijima , Shigeki Kimura, Yohmi Kawahara, Kaoru Ohe, Mitsunori Yada, Machida Machida, Miyazaki Univ, Dept of Materials Science, Miyazaki, JAPAN. 

It is well known that the bismuth-based layered cuprate high Tc superconductor, Bi₂Sr₂CaCu₂O₈ (Bi2212), intercalates iodine and/or silver (or mercury) to form modified superconductors with the guest species located between the double Bi-O sheets. A similar example was demonstrated by the recent observation of iodine intercalation in the layered bismuth oxide-ion conductor BaBi₈O₁₃. Such an intercalation process is available for modifying or controlling the physical properties of layered metal oxides through the host-guest electronic interaction. No studies, however, have been reported concerning the intercalation of metal iodides into any other class of metal oxides. This paper reports for the first time the intercalation of lithium and iodide ions into the ferroelectric layered bismuth titanate Bi₄Ti₃O_12-x. In contrast to Bi2212, the structure of the host titanate is chara-cterized by the existence of an additional oxide anion layer interleaved with any two adjacent BiO sheets. The reaction of Bi₄Ti₃O_12-x with lithium iodide under an atmosphere of iodine at 350C afforded an intercalation compound LiI₃Bi₄Ti₃O_11-x in its high yield. The new bismuth titanate is brownish red in color, and formed in an orthorhombic cell with the lattice parameters of a=0.5912(1), b=0.5256(1), and c=3.6889(8) nm. The pathway to the new intercalation compound is proposed on the basis of X-ray, XPS, SEM and compositional observations. The present result would open a route to a large family of metal-iodine intercalated compounds since the titanate is representative of a great number of bismuth-based layered ferroelectrics given by the general formula of Bi₂M_n-1R_nO_3n+3 (n=1-5). 

3:45 PM DD2.5 
ELECTRICAL AND MAGNETIC PROPERTIES OF ALKALINE EARTH SUBSTITUTED LANTHANUM MANGANATE CRYSTALS PREPARED BY FUSED SALT ELECTROLYSIS. William H. McCarroll , Rider University, Chemistry Department, Lawrenceville, NJ; K. V. Ramanujachary, Chemistry Dept., Rowan University, Glassboro, NJ; Ian D. Fawcett, Martha Greenblatt, Chemistry Dept., Rutgers University, Piscataway, NJ. 

Fused salt electrolysis has been used at 975-1000 C to successfully prepare small single crystals (up to 2 mm on edge) of strontium and calcium substituted lanthanum manganese perovskite oxides. Crystals can be prepared containing up to 33 mole percent strontium which have Curie temperatures and insulator-metal transitions around 380 K which are remarkably sharp. Crystals with as little as 11 mole percent strontium show similar transitions in the neighborhood of 320-340 K with a magnetoresistance of approximately 30% at 310 K. This remarkable behavior at such a low strontium content may be ascribed to a relatively high level of vacancies on the A cation sites. The magnetic and electrical properties of these phases, including magnetoresistance, will be presented and compared with the properties previously reported for polycrystalline samples and arc image floating zone crystals of similar composition. Prliminary data regarding calcium substituted crystals will also be given. 

4:00 PM DD2.6 
CYANIDE-, DICYANAMIDE-, AND TRICYANOMETHANIDE-BASED 3-D NETWORK STRUCTURED MAGNETS. Joel S. Miller , Jamie L. Manson, University of Utah, Dept. of Chemistry, Salt Lake City, UT. 

Magnetically ordered materials based upon the tetrahedral [Mn(II)(CN)₄]^2- (S = 5/2) building block have been prepared and structurally characterized. M(II)[Mn(II)(CN)₄] has an interpenetrating sphalerite (diamond) structure. In contrast, M(II){Mn(II)[C(CN)₃]₂} possesses an interpenetrating rutile structure with stronger internetwork than intranetwork spin coupling. The tricoordinate nature of [C(CN)₃]^- leads to spin frustration. In contrast to CN bonding to two metal sites, dicyanamide, [N(CN)₂]-, can bind via the central N providing a shorter pathway for spin coupling and stronger magnetic coupling. -[Co[N(CN)₂]₂] and Ni[N(CN)₂]₂] order ferromagnetically at 9.2 and 20.6 K, respectively, while -[Co[N(CN)₂]₂] is a canted antiferromagnet at 8.9 K, and Mn[N(CN)₂]₂] is an antiferromagnet at 16 K. The structure/ magnetic behavior relationship for this class of magnetic materials will be discussed.