研究目的
Investigating the structure, valence states, conduction mechanism, and dielectric properties of Cu and Nb co-doped BaTiO3 ceramic, specifically focusing on variable-range-hopping conduction and polaron dielectric relaxation.
研究成果
The research confirms VRH conduction and polaron dielectric relaxation in Cu and Nb co-doped BaTiO3, attributed to a highly distorted and disordered structure with mixed-valent Cu ions. This provides insights into the mechanisms behind colossal dielectric constants and suggests potential applications in electronics, with recommendations for further studies on other compositions and detailed local structure analyses.
研究不足
The study is limited to one specific composition (BaTi0.7(Cu0.1Nb0.2)O3) and may not generalize to other doping levels or materials. The fine-grained microstructure and high disorder could affect reproducibility. Techniques like XRD may not detect very local distortions, and EPR signals were broad without hyperfine structure, limiting detailed analysis of Cu ions.
1：Experimental Design and Method Selection:
The study used a solid-state reaction method to prepare BaTi0.7(Cu0.1Nb0.2)O3 ceramic. Techniques included XRD, SEM, Raman spectroscopy, XPS, broadband dielectric spectroscopy, and EPR to analyze structure, microstructure, valence states, dielectric properties, and magnetic properties. Theoretical models like Mott's VRH and UDR were applied for data analysis.
2：7(Cu1Nb2)O3 ceramic. Techniques included XRD, SEM, Raman spectroscopy, XPS, broadband dielectric spectroscopy, and EPR to analyze structure, microstructure, valence states, dielectric properties, and magnetic properties. Theoretical models like Mott's VRH and UDR were applied for data analysis. Sample Selection and Data Sources:
2. Sample Selection and Data Sources: The sample was synthesized from high-purity BaCO3, TiO2, CuO, and Nb2O5 powders. Data were collected from laboratory measurements across temperature ranges (e.g., 173-473 K) and frequency ranges (e.g., 1 Hz–10 MHz).
3：List of Experimental Equipment and Materials:
Equipment included XRD (DX-2700, Dandong, China), SEM (EVO MA10, Zeiss, Germany), Raman spectrometer (XploRA, Horiba Jobin Yvon, France), XPS (Thermo ESCALAB 250Xi), dielectric spectrometer (Concept 41, Novocontrol Technologies, Germany), and EPR spectrometer (A300, Bruker, Germany). Materials were high-purity reagents from Sinopharm Chemical Reagent Co., Ltd.
4：Experimental Procedures and Operational Workflow:
Powders were calcined, milled, pressed into pellets, and sintered. Electrodes (Ag paste or sputtered Au) were applied. Measurements were conducted at various temperatures and frequencies, with data analyzed using software like GSAS-EXPGUI and ZView.
5：Data Analysis Methods:
Data were analyzed using Rietveld refinement for XRD, fitting functions for XPS, UDR and VRH models for conductivity and dielectric relaxation, and equivalent circuit modeling for impedance data.
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SEM
EVO MA10
Zeiss
Examining morphology and microstructure
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XPS Spectrometer
Thermo ESCALAB 250Xi
Thermo
Studying valence states of cations
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EPR Spectrometer
A300
Bruker
Electron paramagnetic resonance measurements
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XRD
DX-2700
Dandong
Identifying crystal structure and phase analysis
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Raman Spectrometer
XploRA
Horiba Jobin Yvon
Recording Raman spectra at different temperatures
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Dielectric Spectrometer
Concept 41
Novocontrol Technologies
Measuring dielectric properties
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