Two group IV precursors, titanium(IV) neo-pentoxide, [Ti(m-ONep) (ONep) 3 ] 2 (1, where ONep = OCH 2 C(CH 3 ) 3 ), and zirconium(IV) neo-pentoxide, [Zr(m-ONep)(ONep) 3 ] 2 (2), were found to possess relatively high volatility at low temperatures. These compounds were therefore investigated as metal±organic CVD (MOCVD) precursors using a lamp-heated cold-wall CVD reactor by direct vaporization without a carrier gas. The ONep derivatives proved to be competitive precursors for the production of thin films of the appropriate MO 2 (M = Ti or Zr) materials in comparison to other metallo-organic precursors. Compound 1 was found to vaporize at 120 C with a deposition rate of~0.350 mm/min onto a substrate at 330 C forming the anatase phase with <1 % residual C found in the final film. Compound 2 was found to vaporize at 160 C and deposited a crystalline material at 300 C with <1 % residual C found in the final film. A comparison with standard alkoxide and b-diketonates is presented where appropriate.
A nonaqueous coprecipitation process has been developed to prepare controlled stoichiometry lithium manganese oxalate precipitates. The process involved mixing a methanolic Li-Mn nitrate solution with a methanolic solution containing tetramethylammonium oxalate as the precipitating agent. The resulting oxalates were readily converted to a variety of phase pure lithium manganese oxides at moderate temperatures (1600°C), where the phase formed was determined by the initial L i m n ratio in the starting solution. Metal cation dopants have been incorporated into the oxalate precipitate by dissolving the appropriate metal nitrate in the Li-Mn precursor solution The various starting solutions, oxalate precipitates, and calcined oxides have been extensively characterized using a variety of techniques, including 7Li NMR, TGAIDTA, SEM, and XRD. Results indicate that a strong interaction occurs between Li and Mn in the nitrate solution which carries over into the oxalate phase during precipitation. The morphology and the crystallite size of the oxide powders were shown to be controlled by the morphology of the oxalate precursor and the oxalate calcination temperature, respectively, The results of initial cathode performance tests with respect to dopant type (Al, Ni, Co) and concentration for LiMn204 are also reported.
In the sol-gel processing of ceramic thin films it has been frequently noted that the processing behavior, microstructure and properties of the films are dependent on the nature of the coating solution. In an attempt to understand such thin film processing-property relationships, we have systematically investigated the effects of varying the precursor nature on thin film densification and crystallization for 23-02 and Ti02 films. Metal alkoxide starting compounds, e.g., zirconium n-butoxideen-butanol and titanium i-propoxide, were reacted with acetic acid and 2,4-pentanedione to prepare coating solutions for thin film deposition. The use of these chelating ligands resulted in solution oligomeric species of different nature. Studies of thin film processing indicated that film processing characteristics, i.e., consolidation, densification and crystallization, were strongly dependent on solution precursor nature. Ligand steric size, pyrolysis behavior, extent of chelation, and precursor reactivity were found to be key variables in controlling film processing characteristics.
---We describe Chemical Solution Deposition (CSD) processes by which Strontmm~= B Tantdate (SBT) thin films can be prepared at temperatures as low as 550°C. In this paper, we will present strategies used to optimize the properties of the films including solution chemistry, film composition, the nature of the substrate (or bottom electrode) used, and the thermal processing cycle. Under suitable conditions, -1700i& films can be prepared which have a large switchable polarization (2P, > 10p.C/cm2), and an operating voltage, defined as the voltage at which 0.80 x 2Prmax is switched, 2.OV. We also describe an all-alkoxide route to SBT films from which SBT can be crystallized at 550"C.
Theoretical calculations based on time-dependent density functional theory are used to characterize the electronic absorption spectrum of a heteroleptic Ti-alkoxide molecule, (OPy)(2)Ti(TAP)(2) [OPy = pyridine carbinoxide, TAP = 2,4,6 tris(dimethylamino)phenoxide] under investigation as a photosensitive precursor for use in optically initiated solution synthesis of the metal oxide. Computational results support the assignment of UV absorption features observed in solid-state precursor films to key intrinsic ground-state transitions that involve ligand-to-metal charge transfer and pi-pi* transitions within the cyclic ligand moieties present. The nature of electron density redistribution associated with these transitions provides early insight into the excitation wavelength dependence of photostructural modification previously observed in this precursor system.
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