研究目的
To synthesize and investigate the structure of the pyrochlores with the general formula Bi1.5Mg1?xLixNb1.5O7?δ, to analyze the effect of the Li+ cation doping on dielectric properties and conductivity, to study of protonic transport.
研究成果
The Bi1.5Mg1?xLixNb1.5O7?δ samples with the pyrochlore structure were successfully synthesized. Lithium cations distribute in the bismuth sites and are not mobile up to 120°C. The ceramics exhibit increased dielectric permittivity with lithium content, making them potential materials for high-frequency ceramic capacitors. The materials are mixed conductors with electronic (p-type) conductivity below 360°C, proton conductivity up to 500°C, and oxygen ionic conductivity above 400°C.
研究不足
The study is limited to specific compositions (x up to 0.75) and temperature ranges (up to 750°C). The unambiguous determination of lithium content in phases is challenging, and impurity phases are present in some samples, which may affect results. The proton conductivity is inferred but not fully quantified.
1：Experimental Design and Method Selection:
The study involves synthesis of Li- and Mg-codoped bismuth niobates using organic-inorganic precursors combustion method, structural characterization via XRD and NMR spectroscopy, and electrical property investigation using impedance spectroscopy. Theoretical models include Rietveld refinement for XRD patterns and Arrhenius behavior analysis for conductivity.
2：Sample Selection and Data Sources:
Samples with compositions Bi1.5Mg1?xLixNb1.5O7?δ (0 ≤ x ≤ 0.75) were synthesized from reagents including Bi(NO3)3·5H2O, Mg(NO3)2·6H2O, LiNO3·3H2O, Nb2O5, and citric acid. Data were collected from synthesized ceramic pellets.
3：5Mg1?xLixNb5O7?δ (0 ≤ x ≤ 75) were synthesized from reagents including Bi(NO3)3·5H2O, Mg(NO3)2·6H2O, LiNO3·3H2O, Nb2O5, and citric acid. Data were collected from synthesized ceramic pellets.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes SHIMADZU XRD-6000 diffractometer, TESCAN VEGA 3SBU scanning electron microscope with X-ACT EDS microanalyzer, Agilent VNMR 400 WB pulsed spectrometer, and Immittance Meters E7-28. Materials include the listed reagents and silver paste for electrode coating.
4：Materials include the listed reagents and silver paste for electrode coating.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Synthesis involved heating stoichiometric mixtures, combustion, pressing into pellets, and calcination at various temperatures. XRD analysis was performed at 25°C, NMR spectra recorded from 25 to 120°C, and impedance measurements from 25 to 750°C in different atmospheres. Data were analyzed using FullProf and ZView 2 software.
5：Data Analysis Methods:
XRD patterns were fitted using Rietveld method with FullProf software. NMR spectra were analyzed for chemical shifts and dynamics. Impedance data were fitted with equivalent circuits using ZView 2, and conductivity was analyzed using Arrhenius plots.
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