Advanced Materials Research Vol. 412

Abstract: A convenient one-step solvothermal method has been developed to synthesize monodispersed barium titanate nanocrystals with an average size of 5 nm. The key point of this method is the controlling of hydrolysis of Ti (OC₄H₉)₄ with Diethylene glycol (DEG). The as-prepared BaTiO₃ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), FT-IR and TG/DTA analysis. The monodispersed BaTiO₃ nanoparticles obtained by this method have an average size of 5 nm with a narrow size distribution and a lattice tetragonality of 1.0069, which is promising for the ferroelectric science and its industry application.

Abstract: Barium zirconium titanate, Ba (Zr_0.20Ti_0.80)O₃ (BZT) powders were prepared by sol-gel method. These powders were characterized by thermal gravimetric and differential thermal gravimetric analysis (TG-DTA), X-ray diffraction (XRD). The grain size and lattice constant were determined. The decomposition of the precursors was monitored by TG-DTA. XRD patterns reveal that BZT powders heat-treated at 800°C present single phase with perovskite type cubic structure. The average particle size of the BZT powders is about 25 nm.

Abstract: Fine powder of Zn₃Nb₂O₈ was prepared by chemical co-precipitation using KOH, Nb₂O₅ and ZnSO₄·7H₂O as raw materials. Laser particle analyzer was used to investigate the precursor. It showed that the average size (D50) was 3.13μm, and the particle distribution ranged from 1.82µm to 4.47µm. TG-DTA and XRD showed that, the precursor yielded Zn₃Nb₂O₈ ceramics by calcined at 850°C, which was much lower than 1100°C, at which Zn₃Nb₂O₈ ceramics could be obtained by traditional solid state method. The sintering of as-obtained powers with Cuo-Bi₂O₃-V₂O₅ sintering aids results in producing Zn₃Nb₂O₈ ceramics with s density 94.20% of the theoretical, and a product up to 19.83 (at 30MHz) at sintering temperature 950°C.

Abstract: ZnNb₂O₆ powders were prepared by solid phase method and molten salt method. KCl-NaCl-ZnCl₂ was used as molten salt. The mass ratio of molten salt and raw material is 1:1. Pure ZnNb₂O₆ powders were synthesized by molten salt method at 650°C, which was reduced by 200°C relative to solid phase method. ZnNb₂O₆ powders preferably grow along special direction, and appear strip or rod like. ZnNb₂O₆ powders calcined at 650°C have narrow particle size distribution. Median size D50 =5.31μm. With the increase of the calcining temperature grain grows and particle size increases.

Abstract: Crystalline multiferroic BiFeO₃ powders were directly synthesized by sol-gel auto-combustion method. The gels, derived from the solutions of 2-methoxyethane, metal nitrate and citric acid, exhibited the self-propagating combustion behaviors at ambient temperature when it is ignited in air. After auto-combustion, the dried gels transformed into crystalline BiFeO₃ powders and no further calcination was needed. The nature of auto-combustion was ascribed to heat-induced redox between NH₄NO₃ and carboxyl group. The TG-DTA was carried out to study the auto-combustion of dried gels. The synthesized powders were characterized by XRD and SEM techniques.

Abstract: Bi₂Ti₂O₇ nanopowders were prepared using bismuth nitrate and tetrabutyl titanate as starting materials by sol-gel method. The decomposition of precursors, crystal structure and microstructure of the sample was characterized by TG/DTA, XRD and TEM techniques, and the results indicate that the sample is well-crystallized pyrochlore Bi₂Ti₂O₇ phase with spherical shape and an average grain size of 30 nm. Photocatalytic activity of Bi₂Ti₂O₇ powders was evaluated by photodegrading methyl orange solution. The result shows that Bi₂Ti₂O₇ has a higher photocatalytic activity than TiO₂ (mixed with rutile and anatase) with the same concentration, and when concentration of Bi₂Ti₂O₇ increased to 9g/L, half-life period T_1/2 is 0.97h, then methyl orange solution can be completely degraded in more than an hour.

Abstract: Spinel LiMn₂O₄ was synthesized by a solution combustion synthesis using lithium and manganese acetate as raw materials and acetic acid as fuel. The phase composition and micro morphology of the as-prepared products were determined by X-ray diffraction (XRD) and scanning electric microscope (SEM). The electrochemical performance of the products was tested by using a coin-type half battery versus lithium metal foil as anode material. XRD analysis suggested that the main phase of the products was LiMn₂O₄, but there was little impurity Mn₂O₃ in the products. The relative content of Mn₂O₃ was decreased gradually when the molar ratio of Li:Mn: acetic acid increased from 0.5:1:0.5 to 0.5:1:2, but increased again when the molar ratio of Li:Mn: acetic acid was 0.5:1:2.5. The purest product could be prepared when the molar ratio of Li:Mn: acetic acid=0.5:1:2. SEM investigation indicated that the typical crystal structure could not be investigated from the as-prepared products, and the particles were badly agglomerated. Electrochemical performance tests indicated that the specific capacity of the purest product was 108mAh/g. After 30 cycles, the capacity faded only 22% at the current density of 50mA/g, and the average charge/discharge efficiency was ~96%. At the current density of 75mA/g, the initial specific capacity of the purest product was only 72mAh/g, but after 30 cycles, the capacity retention was >92%, exhibiting a good cycling performance.

Abstract: Lithium orthosilicate (Li₄SiO₄) ceramic pebbles was prepared by molten spray process, using lithium carbonate (Li₂CO₃) and silica (SiO₂) as raw material. The XRD experimental investigation results showed that the main crystal phase of the ceramic pebbles is Li₄SiO₄ with small amount of impurity phase, Li₂SiO₃, and some unreacted SiO₂. The average pebbles size is 0.22mm. The sphericity of the pebble is 99%.

Abstract: Pr_1.2Sr_0.8NiO₄ (PSNO) and Sm_0.2Ce_0.8O_1.9 (SCO) powders were synthesized by a glycine-nitrate process and a gel-casting process, respectively. Pr_1.2Sr_0.8NiO₄-x Sm_0.2Ce_0.8O_1.9 (x=0, 25, 50) composite cathode materials were prepared by mechanically mixing the two powders. The particle size of the synthesized PSNO and SCO powders is about 100nm and 50nm, respectively. PSNO and SCO have a good chemical compatibility. Area specific resistance value for the Pr_1.2Sr_0.8NiO₄-x Sm_0.2Ce_0.8O_1.9 (x=25, 50) composite cathode on SCO electrolyte is 0.087 and 0.076Ωcm² at 750°C, which indicates Pr_1.2Sr_0.8NiO₄-Sm_0.2Ce_0.8O_1.9 composite materials may be a promising cathode material for intermediate temperature solid oxide fuel cell (IT-SOFC).

Abstract: Lanthanum molybdate powders were prepared by sol-gel using lanthanum nitrate, ammonium molybdate, citric acid as the main raw materials. The prepared powders were characterized by XRD, SEM, BET and other methods. It is concluded that the best sintering temperature was 550°C, the aging time was 1h and the best ph value was 1.5.