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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

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Journal of Advanced Ceramics 2022年第10期11卷 1613-1625页

作者： Yuan ZHANG Longfei ZHAO Zhupeng YE Yanwei ZENG College of Materials Science and Engineering Nanjing Tech UniversityNanjing 211816China

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.

关键词： melilite La_(2)Ga_(3)O_(7.5) low temperature synthesis gel-precursor meta-stability kinetic mechanism

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low temperature synthesis and Characterization of Li1.2-y NayV3O8(0≤y≤1.2) from V2O5 Gel

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Chinese Journal of Chemistry 2003年第3期21卷 232-237页

作者：谢静刚肖婕等 DepartmentofChemistry WuhanUniversityWuhanHubei430072China

Without overnight heating and stirring, Li 1.2 V 3 O 8 and its analogs Li 1.2‐y Na y V 3 O 8 (0 ≤ y ≤ 1.2) were successfully synthesized by adding mixed solution of LiOH and NaVO 3 to V 2 O 5 gel and dehydrating the prepared gel in 150–350°C. The simplicity awards this synthesis process superiority over other low temperature synthesis routes when mass production is concerned. TG‐DTA, XRD and TEM experiments were carried out for physical characterization. By galvanostatic charge‐discharge and cyclic voltammetry tests, these products showed better electrochemical performance than high temperature products as cathode active materials in secondary lithium batteries. After treatment of Li 1.2 V 3 O 8 at 250°C, it exhibited a capacity of 350 mAh/g when cycled at current rate of about 60 mA/g over the voltage range of 3.8–1.7 V vs. Li + /Li. The influence of partial substitution of Li by Na was also extensively studied.

关键词： low temperature synthesis V2O5 gel Li1.2‐yNayV3O8 cathode material

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low-temperature synthesis of Crystalline Inorganic/Metallic Nanocrystal-Halloysite Composite Nanotubes

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Chinese Journal of Chemistry 2014年第7期32卷 599-606页

作者： Cuiping Li Jiaqiang Wang Siquan Feng Zan Liu Department of Applied Chemistry Key Laboratory of Medicinal Chemistry for Natural ResourceMinistry of EducationSchool of Chemical Science and TechnologyYunnan UniversityKunmingYunnan 650091China Kunming Cable Co. LtdKunmingYunnan 650100China

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.

关键词： composite nanotubes halloysite inorganic nanocrystal perovskite oxide low temperature synthesis

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Carbon gel assisted low temperature liquid phase synthesis of nano LiFePO4 with high rate and cycle performances

Carbon gel assisted low temperature liquid phase synthesis o...

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河南省化学会2016年学术年会

作者： Hongwei Tang Yanli Si Zhaorong Chang School of Chemistry and Chemical Engineering Henan Normal University

Single-phase nano-scale LiFePO has been successfully synthesized via a carbon gel assisted low temperature liquid-phase method. This is achieved by adding a certain amount of glucose in the solution mixed with LiOH and dimethyl sulfoxide(DMSO), which acts as Li source and crystal growth inhibitor.The product, Li Fe PO, is obtained after reacting with Fe SO and H3PO in water/DMSO solution.LiFePO/C composites are then produced by mixing a certain amount of glucose with Li Fe PO and sintering over a short time under an inert atmosphere. Scanning electron microscopy and transmission electron microscopy show that Li Fe PO and LiFePO/C are well distributed with sizes ranging from 50-80 nm. For LiFePO/C, LiFePO is uniformly coated with a carbon layer. LiFePO/C material exhibits excellent discharge capacities of 160.0, 117. and 106.8 m Ah g(-1) at rates of 0.2, 5 and 10C,respectively. At a rate of 10C, the capacity retention ratio of the Li Fe PO/C electrode after 100 cycles is 99.%, showing excellent high-rate discharge capability and cycle performance compared with commercial Li Fe PO.

关键词： solution-phase method low temperature synthesis lithium ion battery LiFePO4/C dimethyl sulfoxide

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

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Journal of Materials Science & Technology 2022年第26期121卷 181-189页

作者： Juntao Song Guiqing Chen Huimin Xiang Fuzhi Dai Shun Dong Wenbo Han Xinghong Zhang Yanchun Zhou Science and Technology on Advanced Composite in Special Environments Laboratory Harbin Institute of TechnologyHarbin150080China Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials&Processing TechnologyBeijing100076China

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.

关键词： Carbon stoichiometry High-entropy ceramics Transition metal carbide low temperature synthesis Tunable mechanical properties

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A Novel Nanocrystalline TiO_2 Thin Film Electrodes Prepared at low temperature

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Chinese Chemical Letters 2005年第7期16卷 967-970页

作者： ChengYuLI XuePingLI YuTaoMA ZhengPingWANG XiaoWenZHOU YuanLIN ShuJingFENG XuRuiXIAO ChemicalCollegeofHarbinEngineeringUniversity Harbin150001 KeyLaboratoryofPhotochemistry CenterforMolecularScienceInstituteofChemistryChineseAcademyofSciencesBeijing100080

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.

关键词： Tetrabutyl titanate low temperature synthesis nanocrystalline TiO2 dye-sensitized solar cells flexible solar cells.

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Phase Transformation and Mechanism of Cordierite Ceramic Powders Prepared by Gangue

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China's Refractories 2012年第4期21卷 32-37页

作者： WANG Xiao YANG Liushuan LIU Yiran ZHENG Donglai Department of Materials & Civil Engineering Henan University of Urban Construction School of Materials Science & Engineering Henan University of Science and Technology Sinosteel Luoyang Institute of Refractories Research Co. Ltd.

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.

关键词： gangue cordierite low temperature synthesis phase transformation mechanism

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