Synthesis of Neodymium-Doped Yttrium Aluminum Garnet (Nd∶YAG) Nano-Sized Powders by Low Temperature Combustion

The homogeneously dispersed, less agglomerated (Nd0.01Y0.99)3Al5O12 nano-sized powders were synthesized by the low temperature combustion (LCS), using Nd2O3, Y2O3, Al(NO3)3·9H2O, ammonia water and citric acid as starting materials. This method effectively solves the problems caused by solid-state reaction at high temperature and hard agglomerates brought by the chemical precipitation method. The powders were characterized by TG-DTA, XRD, FT-IR, TEM respectively and the photoluminescence (PL) spectra of (Nd0.01Y0.99)3Al5O12 green and sintered ceramic disks were measured. The results show that the forming temperature of YAG crystal phase is 850 ℃ and YAP crystal phase appearing during the calcinations transforms to pure YAG at 1050 ℃. The particle size of the powders synthesized by the LCS is in a range of 20～50 nm depending on the thermal treatment temperatures. The effectively induced cross section (σin) with the value 4.03×10-19 cm2 of (Nd0.01Y0.99)3Al5O12 ceramics is about 44% higher than that of single crystal.

Low Temperature Direct Synthesis of Strontium Titanate Powder

Low temperature direct synthesis (LTDS) involves the preparation of a base solution of Sr^(2+),and the mixing of base solution with tetrabutyl titanate solution.LTDS is an advantageous method because it does not require the complex hydrothermal facilities and it can prevent the agglomeration in calcinations of other liquid methods.In our work,we adopted LTDS method to prepare the nano strontium titanate powders,and characterize them by XRD,FT-IR and TGA.The influences of preparation temperature and solvents on grain size and lattice parameters were investigated.The results show that preparation temperature can slightly change the lattice parameters of grain,while solvents also play important roles in the preparation.

A Novel Nanocrystalline TiO_2 Thin Film Electrodes Prepared at Low Temperature

Nanocrystalline TiO2 thin films were successfully prepared by a new “water-cooked” method on both conductive glass substrates and flexible substrates at low temperature. Dye-sensitized solar cells based on these films have exhibited high overall light-to-electricity conversion efficiencies of 4.67 % and 1.94 % on conductive glass substrate and flexible substrate, respectively, under the illumination at 100 mW/cm2.

Low-Temperature Synthesis of Crystalline Inorganic/Metallic Nanocrystal-Halloysite Composite Nanotubes

We have demonstrated a facile approach for the low-temperature synthesis of crystalline inorganic/metallic nanocrystal-halloysite composite nanotubes by employing the bulk controlled synthesis of inorganic/metallic nanocrystals on halloysite nanotubes.The halloysite clay nanotubes can adsorb the target precursor and induce inorganic/metallic nanocrystals to grow in situ.The crystalline phase and morphology of the composite clay nanotubes is tunable.By simply tuning the acidity of the titania sol,the crystalline titania-clay nanotubes with tunable crystalline phases of anatase,a mixture of anatase and rutile or rutile are achieved.The approach is general and has been extended to synthesize the representative perovskite oxide(barium and strontium titanate)-halloysite composite nanotubes.Metallic nickel nanocrystal can also be grown on the surface of halloysite nanotubes at low temperature.The traditional thermal treatment for crystallite transformation is not required,thus intact contour of halloysite nanotubes and the crystallinity structure of halloysite nanotubes can be guaranteed.The combined properties from inorganic/metallic nanocrystal(high refractive index,high dielectric constant and catalytic ability)and the halloysite clay nanotubes are promising for applications such as photonic crystals,high-k-gate dielectrics,photocatalysis and purification.

Sol-gel approach to low-temperature synthesis of single-phase metastable La_(2)Ga_(3)O_(7.5) melilite with enhanced grain-boundary oxide ionic conductivity via a kinetically favorable mechanism

Starting with the stoichiometric and highly homogeneous gel-precursor,single-phase metastable melilite La_(2)Ga_(3)O_(7.5),as the end-member of solid solution La_(1+x)Sr_(1−x)Ga_(3)O_(7+x/2)(0≤x≤1),has been synthesized by solid-state reaction at 700℃ for 2 h via a kinetically favorable mechanism and characterized by X-ray diffraction(XRD),Raman,X-ray photoelectron spectroscopy(XPS),field emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),AC impedance spectroscopy,etc.It has been revealed that the as-synthesized melilite La_(2)Ga_(3)O_(7.5) shows an orthorhombic symmetry with crystal cell parameters a=11.4690(1)A,b=11.2825(4)A,and c=10.3735(4)A,while has more Raman active modes than LaSrGa_(3)O_(7) with a tetragonal structure,which was also synthesized under the same conditions for comparison,but tends to slowly decompose into perovskite LaGaO_(3) and Ga2O_(3) when annealed at 700℃ for over 20 h driven by its meta-stability.Moreover,the metastable La2Ga3O7.5 shows a higher XPS binding energy for the excess oxide ions in the crystal structure than those at normal lattice sites.Its intrinsic grain oxide ion conductivity can reach as high as 0.04 and 0.51 mS·cm^(-1) at 550 and 700℃,respectively,characterized by a simple Arrhenius relationship ln(σT)-1/T with invariable activation energy,E_(a)=1.22 eV,over the temperature range from 300 to 700℃,along with an apparent grain boundary conductivity that is about double that from the grains thanks to the clean grain boundaries.This paper provides a new strategic approach to the synthesis of complex oxides that may be of high performance but are difficultly achieved by the conventional ceramic method at high temperatures.

Phase Transformation and Mechanism of Cordierite Ceramic Powders Prepared by Gangue

Cordierite ceramic powders were prepared by solid reaction at low temperatures using gangue as main starting material and adjusting component oxides in formulations. The powders were characterized by XRD, SEM and EDS. The emphasis was placed on the reaction mechanism and phase transformation of synthesized powders. The results show that cordierite ceramic powders can be synthesized at 1 150 - 1 250 % for 3 - 5 h and its morphology is irregularly granular. The synthesis temperature has an important effect on the phase transformations of powders but the reaction time only has a little effect. The impurities in gangue result in the detected secondary magnesium aluminate spinel and the decreased synthesis temperature.

Preparation of Neodymium-Doped Yttrium Aluminum Garnet Transparent Ceramics by Homogeneous Precipitation Method

substitutes tion, high loosely dis Neodymium doped-yttrium aluminum garnet （Nd ： YAG） transparent polycrystalline ceramics already become of single crystals because they are provided with easy fabrication, low cost, large size, highly doped concentraheat conductivity, mass fabrication, multi-layers and multi-filnctions. The Nd：YAG precursor powders with persed , slightly agglomerated, super fine and YAG cubic crystal phase were synthesized at 1100 ℃ by the homogeneous precipitation method, using Nd2O3, Y2O3, Al（NO3）3·9H2O and urea as raw materials, （NH4）2SO4 as electrical stabilizer, TEOS as sintering additive. The Nd：YAG transparent ceramics were prepared after being vacuum sintered at 1700 ℃ for 5 h. The Nd：YAG ceramic materials were characterized by the TG-DTA, XRD, FT-IR, TEM, FEG-ESEM and FT-PL. The results show that the crystallization temperature of YAG is 850 ℃ and the intermediate crystal phase YAP forming during the heat treatment transforms to YAG cubic crystal phase at 1050 ℃. The lasing wavelength of （Nd0.01 Y0.99）3Al5O12 transparent ceramics is 1.065 μm and there exists a slight red-shift compared to the single crystal with the same chemical composition. The optical transmittance is 45 % in the visible light and 58 % in the near infrared light and the optical transmittance descends with the decreasing the wavelength.

Effect of Heat Treatment on Crystallization of Nd:YAG Ceramics

（Nd0.01Y0.99）3Al5O12 nano-sized powders were synthesized by low temperature combustion （LCS）, using Nd2O3, Y2O3, Al（NO3）3.9H2O, ammonia water and citric acid as starting materials. The powders were characterized by TG-DTA, XRD, FT-IR, ICP and TEM, respectively. The grain sizes were calculated by the Scherrer＇s formula using the full width at half maximum （FWHM） of YAG （420） crystal plane diffraction lines. The study focused on crystallization of ceramics at different heat treatment temperatures. The experimental results show that crystallizing temperature of YAG is 850 ℃, and the intermediate crystal phase YAP, appearing during heat treatment, transforms to YAG cubic crystal phase at the temperature of 1 050℃. The particle size of the powders synthesized by LCS is nano-sized. With the temperature increasing, the mean grain sizes raise, the stand deviations keep almost at the value of 2.0 and the lattice parameters decrease. The grains mainly grow by grain boundary diffusion. The lattice parameter expansion is caused by an increase of the repulsive dipolar interactions on surfaces of crystallites,

Cathode catalysis performance of SmBaCuMO_(5+δ) (M=Fe, Co, Ni) in ammonia synthesis

The SmBaCuMO5+δ (M=Fe, Co, Ni) (SBCM) powders were synthesized by the citrate sol-gel method and the powders were sintered to ceramic pellets. The powders and sintered ceramic pellets were characterized with XRD, TEM and SEM measurements. The cathode catalytic performances of SBCM ceramic pellets for ammonia synthesis were studied from wet hydrogen and dry nitrogen at atmospheric pressure and low temperature, using SBCM ceramic pellets as cathode, Nafion proton exchange membrane as electrolyte, Ni-Ce0.8Sm0....

Regulating the formation ability and mechanical properties of high-entropy transition metal carbides by carbon stoichiometry

Tremendous efforts have been dedicated to promote the formation ability of high-entropy transition metal carbides.However,the majority of methods for the synthesis of high-entropy transition metal carbides still face the challenges of high temperature,low efficiency,additional longtime post-treatment and uncontrollable properties.To cope with these challenges,high-entropy transition metal carbides with regulatable carbon stoichiometry(HE TMC)were designed and synthesized,achieving improved ability for single phase solid solutions formation,promoting of sintering and controllable mechanical properties.Two typical composition series,i.e.,easily synthesized(ZrHfTaNb)C(ZHTNC)and difficultly synthesized(Zr_(0.25)Hf_(0.25)Ta_(0.25)Ti_(0.25))C(ZHTTC)are selected to demonstrate the promoting formation ability of single phase solid solutions from carbon stoichiometry deviations.Single phase high-entropy ZHTTC,which has been proven difficult in forming a single phase solid solution,can be prepared with the decrease of C/TM ratio under 2000℃;while the high-entropy ZHTNC,which has been proven easy in forming a single phase solid solution,can be synthesized at lower temperatures with the decrease of C/TM ratio.The synergistic effect of entropy stabilization and reduced chemical bond strength gaining from carbon stoichiometry deviations is responsible for the formation of single phase solid solutions and the promoted sintering of HE TMC.For example,the relative density of bulk(ZrHfTaNb)C(SPS-ZHTNC)increases from 90.98%to 94.25%with decreasing the C/TM atomic ratio from 0.9 to 0.74.More importantly,the room temperature flexural strength,fracture toughness and brittleness index of SPS-ZHTNCcan be tuned in the range of 384 MPa–419 MPa,4.41 MPam–4.73 MPamand 3.679μm–4.083μm,respectively.Thus,the HE TMCprepared by adjusting the ratio of carbon to refractory transition metal oxides have great potential for achieving low temperature synthesis,promoted sintering and tunable properties.