Heterometallic Precursors Research Articles

Geometrical Molecular Structure Design Concept in Approach to Homo- and Heterometallic Precursors of Advanced Materials in Sol?Gel Technology

The article describes the principles of the Single Source Precursor approach to inorganic materials and introduces the Geometrical Molecular Structure Design Concept (MSDC) based on the choice of a proper molecular structure type for the desired precursor and completing it with ligands providing both the necessary number of donor atoms and the sterical protection of the chosen core. Application of MSDC is illustrated with examples taken from development of new approaches in the synthesis of oxide and sulfide catalysts and ferroelectric oxide materials.

Electrical characterization of SrTiO 3 thin films deposited on Si(0 0 1) substrate by liquid injection MOCVD

The electrical properties of SrTiO 3 thin films grown on Si substrates by liquid injection MOCVD have been investigated as a function of films thickness (from 4 to 200 nm). Using an heterometallic precursor and optimised low pressure conditions, highly textured SrTiO 3 films were obtained in a 30–150 nm thickness range. A continuous increase of the SrTiO 3 dielectric permittivity with increasing films thickness is deduced, and an interface state density minimum value, lower than 1×10 11 cm −2 eV −1, is observed for 30 nm films. The lowest gate current is obtained for 30–50 nm films; in those samples, the conduction is identified as a Schottky emission type mechanism. For thinner films, the gate current increases when the thickness decreases as classically observed for amorphous oxides. For thicker samples, the leakage current is enhanced by the polycrystalline microstructure of the SrTiO 3 films.

Synthesis of multifunctional photonic crystals

A method for the synthesis of three-dimensionally ordered macroporous crystals from materials that exhibit additional functionality using a hetero-metallic precursor is reported.

Autostoichiometric Mocvd Of Multicomponent Thin Films LiTaO3, LiNbO3 and SrxBa1-xNbO6

AbstractA novel stoichiometric vapor deposition process, Autostoichiometric MOCVD, was developed in this study to prepare stoichiometric thin films. Heterometallic alkoxides were used as single precursor for two different metal components in Autostoichiometric MOCVD. The molecular ratios of the metals were conserved through the precursor evaporation and the deposition reactions based on the chemical nature of precursors and the deposition reaction mechanisms. A non-stoichiometric factor K was defined to study the evaporation process of precursors. A precursor evaluation method using the K factor and the thermal decomposition analysis was introduced to quantitatively analyze the stoichiometric evaporation characteristic of a heterometallic alkoxide precursor. Single phase LiTaO3, LiNbO3, SrNb2O6 and BaNb2O6 films were successfully obtained using precursor LiTa(n-OBut)6 or LiTa(i-OBut)6, LiNb(n-OBut)6, SrNb2(n-OBut)12 and BaNb2(n-OBut)12, respectively. Solid solution Sr1-x.BaxNb2O6(SBN) films were also successfully obtained by a two-step Autostoichiometric MOCVD.

A study of amorphous precursors for PbZrO 3 −PbTiO 3 based ceramic materials

Amorphous precursors for PbZrO3 and PbTiO3 ceramics were prepared from lead acetate and the transition metal n -propoxide in n-propanol or n-butoxide in n-butanol and hydrolysed with an excess of water. According to GLC and TGA/EGA analyses, the type of alkoxide group influences distinctly the structure of heterometallic precursors, i.e., oxo or acetate bridging, and the amounts of hydroxyl and organic groups bound to the metal network. The local environments of metal atoms in the amorphous precursors were also studied by EXAFS. The analysis reveals that in Pb-Zr precursors alkoxide groups modify the coordination spheres of the zirconium atoms. Conversely, local environments of both lead and titanium atoms within the analysed range of 3.4 A depend weakly on the type of alkoxide used.

Autostoichiometric Vapor Deposition of Multicomponent Oxides

ABSTRACTThe theoretical basis of an autostoichiometric vapor deposition method is discussed. We try to define and analyze through the stagnant film model for vapor deposition, the mechanism through which the stoichiometry of a multicomponent oxide film can be precisely controlled. It is found that the utilization of a thermally stable, heterometallic molecular precursor, and a chemical reaction scheme which partially protects the integrity of the precursor molecule during deposition are essential for autostoichiometric vapor deposition. An ideal deposition reaction is the vapor phase hydrolysis, substrate surface polycondensation of volatile double alkoxides. A simple low pressure apparatus can be used to realize autostoichiometric vapor deposition.

Low-temperature synthesis of YBa2Cu3O7 –xfilms by the solution process using Y–Ba–Cu heterometallic alkoxide

Superconducting YBa2Cu3O7 –x films have been synthesized successfully at a low temperature of 600 °C by the solution process using the Y–Ba–Cu heterometallic alkoxide. The heterometallic alkoxide was synthesized by chemical modification and partial hydrolysis of component alkoxides. In gel films prepared from a heterometallic alkoxide solution, YBa2Cu3O7 –x was obtained as a single phase at 600 °C under an argon atmosphere, whereas YBa2Cu3O7 –x together with other crystalline phases was obtained from mixed alkoxide solutions. The heterometallic alkoxide precursor and the firing process under argon both proved effective for the low-temperature synthesis of single-phase YBa2Cu3O7 –x films. The film fired at 800 °C for 6 h under argon followed by annealing at 450 °C for 24 h under oxygen, showed zero resistance at 74 K.