Mark Rodriguez

The ferroelectric-to-ferroelectic phase transformation between the high temperature (FERH) and the low temperature (FERL) rhomobohedral phases in lead based perovskite under the dc bias conditions was investigated. Dielectric measurements show that an external electric field stabilizes the FERL phase and moves the phase transformation to a higher temperature. The observation has been further verified by an in situ microfocused x-ray study where an external field can effectively induce the oxygen octahedral tilting in the crystalline lattice and extends the thermal stability region of the FERL phase to a higher temperature. An analysis based on the combination of the Clausius-Clapeyron relationship with lattice dynamic principles suggests that the transformation from FERH to FERL is driven by a short-range interaction in the crystalline lattice. The origin of this short-range interaction is proposed, based on the structural evolution during the phase transformation. Experimental evidence suggests that such interaction driving the structural instability can be exploited by an external electric field near the phase transformation temperature and leads to an unusual, transient field-enhanced deformation near the FERH/FERL phase transformation.

The focus of this paper is to explore the efficacy of screen printing to generate crystalline texture in bismuth titanate through the orientation of highly anisotropic seed crystals. Seed crystals were grown through a molten salt flux technique with aspect ratios of ∼100:1, mixed with equiaxed powder of the same composition and oriented using screen printing, a high shear process. By printing on a flexible polymer substrate and using multiple print/dry cycles, it was possible to create pads with a thickness of several hundred micrometers and to remove the dried pads, creating free-standing samples. Upon sintering, the seed crystals grew at the expense of the matrix powder, a process known as templated grain growth. The degree of texture was analyzed using a variety of techniques including scanning electron microscopy, X-ray diffraction and electron backscatter diffraction.

A new soft chemical route to [Ta6O19]8- has been developed by the dissolution of [Ta(O2)4]3- in conditions alkaline enough to arrest formation of Ta2O5, followed by [VO4]3--catalyzed decomposition of the peroxide ligands and crystallization of the salt. An average of bond lengths and angles from isostructural salts of [Ta6O19]8- and [Nb6O19]8- indicate there is an increase in terminal M(eta=O) bond lengths and M-micro2-O-M angles and a decrease in bridging micro2-O-M bond lengths in [Ta6O19]8-, although the central micro6-O-M bond lengths are identical within experimental error. Two new structures of Na7[HNb6O19].15H2O () and Na8[Ta6O19].15H2O () are exemplary of the fact that protonated micro2-OH are observed exclusively in the niobates. In these structures, the metal-oxide framework, seven sodium atoms, and all fifteen water molecules are located in identical unit cell positions, but in an eighth charge-balancing sodium is located in close proximity to the protonated micro2-OH in . Differences in the basicity of Nb(v)- and Ta(v)-bound oxygen atoms are also manifested at the surfaces of 17O-enriched powders of Nb2O5 and Ta2O5. Oxygen exchange at the surface of these materials readily takes place at both terminal and bridging sites in Nb2O5 but only at terminal sites in Ta2O5.

With use of a variety of structurally diverse “Zn (OR)(Et)(solv)” and “Zn (OR) 2 (solv) 2”(1-13), the effect of nuclearity on the final ZnO nanoparticle morphology and size, using four representative nuclearities, mono-(8), di-(1), tetra-(13), and hepta-(4) nuclear species, was ...

A bismuth-deficient pyrochlore phase has been observed in both powder and film samples fired at 775°C. The estimated stoichiometry of this pyrochlore (based on calculated diffraction patterns) was Sr{sub 0.2}(Sr{sub 0.5}Bi{sub 0.7})TaâO{sub 6.75}. This bismuth-deficient pyrochlore phase may be considered deleterious to the formation of the SrBiâTaâOâ {open_quote}{open_quote}SBT{close_quote}{close_quote} ferroelectric compound since a significant presence of this pyrochlore compound implies a

Polyoxoniobate chemistry, both in the solid state and in solution is dominated by [Nb6O19]8−, the Lindquist ion. Recently, we have expanded this chemistry through use of hydrothermal synthesis. The current publication illustrates how use of heteroatoms is another means of diversifying polyoxoniobate chemistry. Here we report the synthesis of Na8[Nb8Ti2O28]·34H2O and its structural characterization from single-crystal X-ray data. This salt crystallizes in the P-1 space group (a=11.829(4) Å, b=12.205(4) Å, c=12.532(4) Å, α=97.666(5)°, β=113.840(4)°, γ=110.809(4)°), and the decameric anionic cluster [Nb8Ti2O28]8− has the same cluster geometry as the previously reported [Nb10O28]6− and [V10O28]6−. Molecular modeling studies of [Nb10O28]6− and all possible isomers of [Nb8Ti2O28]8− suggest that this cluster geometry is stabilized by incorporating the Ti4+ into cluster positions in which edge-sharing is maximized. In this manner, the overall repulsion between edge-sharing octahedra within the cluster is minimized, as Ti4+ is both slightly smaller and of lower charge than Nb5+. Synthetic studies also show that while the [Nb10O28]6− cluster is difficult to obtain, the [Nb8Ti2O28]8− cluster can be synthesized reproducibly and is stable in neutral to basic solutions, as well.

... David Ingersoll, Thomas J. Headley, Scott D. Bunge, Dawn M. Pedrotty, Sacha M. De'Angeli,Sara C. Vick, and Hongyou Fan. Sandia National Laboratories, Advanced Materials Laboratory, 1001 University Boulevard, SE, Albuquerque, New Mexico 87106. Chem. Mater. ...

organic compounds. Volume 59 Part 8 Pages o1123-o1125 August 2003. Received 17 June 2003 Accepted 2 July 2003 Online 17 July 2003. [ac6047sup1] [3d view] [Cited in] © International Union of Crystallography 2003. Key indicators. Single-crystal X-ray study. T = 168 K. ...

Embedded resistor circuits have been generated with the use of a Micropen system, Ag conductor paste (DuPont 6142D), a new experimental resistor ink from DuPont (E84005-140), and Low Temperature Co-fired Ceramic (LTCC) green tape (DuPont A951). Sample circuits were processed under varying peak temperature ranges (835°C–875°C) and peak soak times (10 min–720 min). Resistors were characterized by SEM, TEM, EDS, and high-temperature XRD. Results indicate that devitrification of resistor glass phase to Celcian, Hexacelcian, and a Zinc-silicate phase occurred in the firing ranges used (835–875°C) but kinetics of divitrification vary substantially over this temperature range. The resistor material appears structurally and chemically compatible with the LTCC. RuO2 grains do not significantly react with the devitrifying matrix material during processing. RuO2 grains coarsen significantly with extended time and temperature and the electrical properties appear to be strongly affected by the change in RuO2 grain size.

Using either an ammoniacal route, the reaction between DyCl3, Na0, and HOR in liquid ammonia, or preferentially reacting Dy(N(SiMe3)2)3 with HOR in a solvent, we isolated a family of dysprosium alkoxides as [Dy(mu-ONep)2(ONep)]4 (1), (ONep)2Dy[(mu3-ONep)(mu-ONep)Dy(ONep)(THF)]2(mu-ONep) (2), (ONep)2Dy[(mu3-ONep)(mu-ONep)Dy(ONep)(py)]2(mu-ONep) (3), [Dy3(mu3-OBut)2(mu-OBut3(OBut)4(HOBut)2] (4), [Dy3(mu3-OBut)2(mu-OBut)3(OBut)4(THF)2] (5), [Dy3(mu3-OBut)2(mu-OBut)3(OBut)4(py)2] (6), (DMP)Dy(mu-DMP)4[Dy(DMP)2(NH3)]2 (7), [Dy(eta6-DMP)(DMP)2]2 (8), Dy(DMP)3(THF)3 (9), Dy(DMP)3(py)3 (10), Dy(DIP)3(NH3)2 (11), [Dy(eta6-DIP)(DIP)2]2 (12), Dy(DIP)3(THF)2 (13), Dy(DIP)3(py)3 (14), Dy(DBP)3(NH3) (15), Dy(DBP)3 (16), Dy(DBP)3(THF) (17), Dy(DBP)3(py)2 (18), [Dy(mu-TPS)(TPS2]2 (19), Dy(TPS)3(THF)3 (20), and Dy(TPS)3(py)3 (21), where OBut) = OCMe3, DMP = OC6H3(Me)(2)-2,6, DIP = OC6H3(CHMe2)(2)-2,6, DBP = OC6H3(CMe3)(2)-2,6, TPS = OSi(C6H5)3, tol = toluene, THF = tetrahydrofuran, and py = pyridine. We were not able to obtain X-ray quality crystals of compounds 2, 8, and 9. The structures observed and data collected for the Dy compounds are consistent with those reported for its other congeners. A number of these precursors were used as Dy dopants in Pb(Zr0.3Ti0.7)O3 (PZT 30/70) thin films, with compound 12 yielding the highest-quality films. The resulting Pb0.94Dy0.04(Zr0.3Ti0.7)O3 [PDyZT (4/30/70)] had similar properties to PZT (30/70), but showed substantial resistance to polarization reversal fatigue.

The hexaniobate Lindqvist ion $[\hbox{Nb}_{6}\hbox{O}_{19}]^{8-}$ has long been known as the dominant specie in alkaline niobium oxide solutions. Recent advances in heteropolyniobate chemistry continue to be greatly aided by use of $[\hbox{Nb}_{6}\hbox{O}_{19}]^{8-}$ alkali salts as soluble precursors; in particular, potassium, sodium and lithium hexaniobate salts. We report here the solid-state characterization and solution behavior of Li, K, Rb and Cs Lindqvist $[\hbox{Nb}_{6}\hbox{O}_{19}]^{8-}$ salts. Synthesis and single-crystal X-ray diffraction data is reported for nine new hexaniobate salts. These structures differ in the number of charge-balancing alkali cations, protonation of the clusters, relative arrangement of the clusters and alkali metal cations, amount of lattice water and its mode of interaction with other lattice species. Trends of alkali-cluster bonding are observed as a function of alkali radius. Protonation of the clusters in the solid-state is influenced by the method of crystallization of the $[\hbox{Nb}_{6}\hbox{O}_{19}]^{8-}$ salt. Lability of the cluster oxygens is observed by solution 17O NMR experiments. Rates of isotopic enrichment of the bridging oxygen, terminal oxygen and bridging hydroxyl cluster sites are compared for aqueous solutions of Li, K, Rb and Cs hexaniobate salts. Parameters influencing the oxo-ligand exchange rates of the salts are discussed relative to their use as heteropolyniobate precursors.

Abstract The Sr-Bi-Ta-O system is of interest for thin-film non-volatile ferroelectric memories. A better understanding of the process by which the perovskite phase forms can provide insight for improved processing of this ferroelectric compound. We have prepared thin-...

Abstract Non-traditional precursor solutions for production of ferroelectric thin films have been developed for PXZT (X= L, N, S), SBT, and PMN systems. For PXZT and SBT, pyridine is a key solvent, wherein, it both solubilizes and reduces the reactivity of the individual ...

A series of K (OAr)(solv) compounds have been synthesized from K [N (SiMe3) 2] and 1 equiv of a substituted aryl alcohol (oMP, 2-methyl; oPP, 2-iso-propyl; oBP, 2-tert-butyl; DMP, 2, 6-dimethyl; DIP, 2, 6-di-iso-propyl; DBP, 2, 6-di-tert-butyl) in tetrahydrofuran or pyridine. ...

The Na (+) and [Cu(en) 2(H 2O) 2] (2+) (en = ethylenediamine) salt of a pseudosandwich-type heteropolyniobate forms upon prolonged heating of Cu(NO 3) 2 and hydrated Na 14[(SiOH) 2Si 2Nb 16O 54] in a mixed water-en solution. The structure [ a = 14.992(2) A, b = 25.426(4) A, c = 30.046(4) A, orthorhombic, Pnn2, R1 = 6.04%, based on 25869 unique reflections] consists of two [Na(SiOH) 2Si 2Nb 16O 54] (13-) units linked by six sodium cations, and this sandwich is charge-balanced by five [Cu(en) 2(H 2O) 2] (2+) complexes, seven protons, and three additional sodium atoms (all per a sandwich-type cluster). Diffuse-reflectance UV-vis indicates that there is a lambda max at 383 nm for the Cu (II) d-d transition and the (29)Si MAS NMR spectrum has two peaks at -78.2 ppm (151 Hz) and -75.5 ppm (257 Hz) for the two pairs of symmetry-equivalent internal [SiO 4] (4-) and external [SiO 3(OH)] (3-) tetrahedra, respectively. Unlike tungsten-based sandwich-type complexes, the [Na(SiOH) 2Si 2Nb 16O 54] (13-) units are linked exclusively by Na (+) instead of one or more d-electron metals.

A nonaqueous coprecipitation process has been developed to prepare controlled stoichiometry lithium cobalt oxide precipitates. The process involved mixing a methanolic LiCo-(NOâ)â solution with a methanolic solution containing tetramethylammonium oxalate as a precipitating agent. The resulting oxalates were readily converted to phase-pure lithium cobalt oxide at 800 C under an oxygen atmosphere. The various starting solutions, oxalate precipitates, and the

A novel Sr-Ta-O perovskite phase has been synthesized by a chemical preparation route and crystallized on Pt-coated SiO2/Si substrates at ∼800°C. The phase was isolated as a thin film only (not as a polycrystalline powder) and is likely metastable. SEM, EDS, XRD, EPR, and Raman analyses suggest this phase is cation-deficient, having the formula SrxTaxO3 (x∼ 0.85). X-ray Rietveld analysis indicates the structure to be a simple-cubic perovskite-type lattice; Pm3m space group, a= 3.955(2) Å, V= 61.86 Å3, Z= 1. Electrical property measurements recorded a dielectric constant k of ∼16 with a tan delta of 0.04.

The reaction of [Sn(NMe(2))(2)](2) (1) with 4 equiv of HOCH(2)CMe(3) (HONep) leads to the isolation of [Sn(ONep)(2)](infinity) (2). Each Sn atom is four coordinated with mu-ONep ligands bridging the metal centers; however, if the free electrons of the Sn(II) metal center are considered, each Sn center adopts a distorted trigonal bipyramidal (TBP) geometry. Through (119)Sn NMR experiments, the polymeric compound 2 was found to be disrupted into smaller oligomers in solution. Titration of 2 with H(2)O led to the identification of two unique hydrolysis products characterized by single-crystal X-ray diffraction as Sn(5)(mu(3)-O)(2)(mu-ONep)(6) (3) and Sn(6)(mu(3)-O)(4)(mu-ONep)(4) (4). Compound 3 consists of an asymmetrical molecule that has five Sn atoms arranged in a square-based pyramidal geometry linked by four basal mu-ONep ligands, two facial mu(3)-O, and two facial mu-ONep ligands. Compound 4 was solved in a novel octahedral arrangement of six Sn cations with an asymmetric arrangement of mu(3)-O and mu-ONep ligands that yields two square base pyramidal and four pyramidal coordinated Sn cations. These compounds were further identified by multinuclear ((1)H, (13)C, (17)O, and (119)Sn) solid-state MAS and high resolution, solution NMR experiments. Because of the complexity of the compounds and the accessibility of the various nuclei, 2D NMR experiments were also undertaken to elucidate the solution behavior of these compounds. On the basis of these studies, it was determined that while the central core of the solid-state structures of 3 and 4 is retained, dynamic ligand exchange leads to more symmetrical molecules in solution. Novel products 3 and 4 lend structural insight into the stepwise hydrolysis of Sn(II) alkoxides.