Haizheng Song

Aerosol-assisted MOCVD growth of Gd2O3-doped CeO2 thin SOFC electrolyte film on anode substrate

Abstract Aerosol-assisted metal-organic chemical vapor deposition (AA-MOCVD) with β-diketonate precursors was employed in depositing thin films of solid oxide fuel cells (SOFCs) electrolyte material, gadolinia-doped ceria (GDC), on anode (NiO+YSZ) substrates. The films have been successfully synthesized in a wide temperature range (300–600 °C) and characterized by X-ray powder diffraction, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The sheet resistance measurements were carried out between 350 and 850 °C to study the effects of adsorbed oxygen on film ionic conductivity.

Synthesis and characterization of volatile metal β-diketonate chelates of M(DPM)n (M=Ce, Gd, Y, Zr, n=3,4) used as precursors for MOCVD

Abstract High pure Ce(DPM) 4 , Gd(DPM) 3 , Y(DPM) 3 and Zr(DPM) 4 (DPM=dipivaloylmethanate=2,2,6,6-tetramethyl-3,5-heptanedionato) powders were successfully synthesized from inorganic salts and HDPM in ethanol/aqueous solution followed by recrystallization from toluene. Freshly prepared samples have been characterized by elemental analysis, X-ray diffraction, thermogravimetry-differential thermal analysis, nuclear magnetic resonance spectroscopy and fourier transform infrared spectroscopy. Aged samples, obtained by exposing fresh ones into air for 30 days, were also represented. Various structures, stabilities and volatilities result from different metal atoms and coordination numbers. Those metal β-diketonate chelates are served as precursors of metalorganic chemical vapor deposition for single and multi-component oxide thin films.

Aerosol-assisted MOCVD deposition of YDC thin films on (NiO + YDC) substrates

Abstract Aerosol-assisted metallo-organic CVD (MOCVD) method (spray pyrolysis) has been employed to deposit thin films of solid electrolyte onto dense (NiO + YDC) substrates in our laboratory. The β-diketonate precursors Ce(tmhd) 4 and Y(tmhd) 3 were chosen as the source materials for deposition of yttria-doped ceria (YDC) thin films in the temperature range 500–700°C. Scanning electron microscopy (SEM) observation revealed the YDC films to have uniform and nanometric grains, with thickness ranging from 0.18 to 1.2 μm with different deposition times. X-ray diffraction (XRD) analyses showed that the films possessed a single phase with a fluorite cubic structure. X-ray photoelectron spectroscopy (XPS) showed that the elemental ratio Y/Ce of the film was close to that of the mixed solution precursor at a deposition temperature 600°C. After being reduced in an H 2 atmosphere at 600°C for 10 h, the (NiO + YDC) substrate was converted into Ni + YDC. The YDC thin film was found to be N 2 leak tight up to the pressure of 0.65 MPa. AC impedance analyses showed that the ionic conductivity of YDC thin film on (Ni + YDC) substrate was slightly less than that of YDC prepared by sintering, but higher than that of yttria-stabilized zirconia (YSZ). These results suggest that the YDC thin film obtained by aerosol-assisted MOCVD is a potential solid electrolyte alternative to YSZ, at intermediate operating temperatures, for solid oxide fuel cell (SOFC) applications.

Progress in ion-transport inorganic membranes by novel chemical vapor deposition (CVD) techniques

Abstract Novel metal–organic chemical vapor deposition (MOCVD) techniques using metal β-diketonate chelates as volatile precursors and some technical modifications, have been developed in the last decade in order to prepare thin films or layers of functional materials, particularly the multi-component ion-transport inorganic membranes. This article gives an overview on the progress in these aspects, mainly based on the research activities at the authors laboratory.

Properties characterization of Ce(DPM)4 served as precursor for MOCVD

Abstract High purity Ce(DPM) 4 (DPM=2,2,6,6-tetramethyl-3,5-heptanedionato) powder was successfully synthesized from Ce(NO) 3 and HDPM followed by reduced pressure distillation and recrystallization from toluene. This metal β-diketonate complex used as precursor for metal–organic chemical vapor deposition (MOCVD) of CeO 2 film has been characterized by elemental analyses, X-ray diffraction (XRD), thermogravimetry–differential thermal analysis (TG–DTA) analysis, 1 H -NMR spectroscopy, and infrared spectroscopy. The structure of this complex is monocline and the sublimation temperature is 145°C. This product was sufficiently stable after it was exposed to air for 30 days, as only a few impurities such as Ce 2 (CO 3 ) 3 ·8H 2 O, Ce(OH) 3 , and H 2 O can be identified. Ce(DPM) 4 decomposes during evaporation, the chemical bonds dissociate in the sequence of CC(CH 3 ) 3 >CH>CO and CC by heating. At 280°C this complex thoroughly decomposes to CeO 2 .

Formation and Rate Processes of Y2O3 Stabilized ZrO2 Thin Films from Zr ( DPM ) 4 and Y ( DPM ) 3 by Cold-Wall Aerosol-Assisted MOCVD

Yttria-stabilized zirconia (YSZ) thin films on polycrystalline substrates were grown by cold-wall aerosol-assisted metallorganic chemical vapor deposition (MOCVD) at the temperatures of 673-1233 K using metal β-diketonatechelates as precursors. Thin uniform films with amorphous structure were obtained below 673 K; when the deposition temperature increases to 773-1023 K, YSZ films appear to be a mixture of cubic and monoclinic phases; single cubic YSZ phase can be obtained at deposition temperature above 1023 K. The Y/Zr atom ratio estimated from the corresponding X-ray photoelectron spectroscopy peaks is less than the feed ratio, which can be interpreted by different transfer resistance of Y and Zr intermediates diffusing to the substrate surface. The films obtained at 673-1023 K possess a layer structure originated from low mobility of the absorbed species. Along with the increase of the deposition temperature, the grains become mature and larger, and then unite with each other to form a continuous columnar film. Mass transport dominates the growth process within lower temperatures, and homogeneous reaction will interrupt the growth at increasingly high temperatures. Growth rate expression with respect to temperature, pressure, gas flow rate, and metal concentration of precursor solutions was deduced assuming deposition of mass-transport limited mechanism, which is consistent with the experimental results.

Deposition of Y2O3 stabilized ZrO2 thin films from Zr(DPM)4 and Y(DPM)3 by aerosol-assisted MOCVD

Abstract A novel aerosol-assisted metalorganic chemical vapor deposition (AA-MOCVD) technology was developed to prepare of Y2O3-stabilized ZrO2 (YSZ) thin films on polycrystalline substrates at the temperatures of 350–700 °C from metal β-diketonate chelates precursors. Thin films with rather uniform and amorphous microstructure were obtained at the substrate temperatures below 600 °C and changed into full cubic microstructure after annealing treatment at 1100 °C for 3 h. A detailed deposition mechanism has described the AA-MOCVD process. The resistance measurement of electrochemical cell Pt/Ni-YDC/YSZ film/Pt showed that conductivity activation energy (Ea) changed at 610 °C with 85.8 kJ/mol at 610–850 °C and 136 kJ/mol at 350–610 °C.