Xuechen Huang,Hanxing Liu,Zhe Song,Hua Hao,Wenqin Zhang,Qi Xu,Chuyu Peng,Ling Huang,Minghe Cao
Dense (1 − x )BaTiO 3− x (Na 1/4 Bi 3/4 )(Mg 1/4 Ti 3/4 )O 3 [(1 − x )BT– x NBMT] polycrystalline ceramics were prepared by solid-state reaction method. The detailed structure analysis was performed by X-ray diffraction (XRD) and Raman spectroscopy , confirming that the Ba and Ti sites were partially replaced by Na + /Bi 3+ and Mg 2+ ions, respectively. An obvious structural variation from tetragonal to pseudocubic was observed for sample with x = 0.08–0.12. The lattice parameter for sample with x ≥ 0.12 decreased linearly with x value. Three changing modes in frequency, width and intensity were observed with x value in the Raman spectra, indicating intense changes of local structure, accounting for evolved dielectric and ferroelectric macroscopic properties. The subgrain microstructures were observed by conventional transmission electron microscopy (TEM) imaging with an energy-dispersive X-ray spectroscopy (EDS) attachment. A large number of core–shell grains were detected by TEM dark field, for x = 0.20, which were attributed to the dissolution–precipitation mechanism. In this present study, (1 − x )BT– x NBMT ceramics are considered promising for high temperature capacitor applications.
Nb 2 O 5 doped 0.8BaTiO 3 –0.2(Na 1/4 Bi 3/4 )(Mg 1/4 Ti 3/4 )O 3 (0.8BT–0.2NBMT) polycrystalline ceramics were prepared by solid state reaction method. 0.8BT–0.2NBMT samples were observed to possess two dielectric peaks, which were attributed to the formation of core–shell structure (Huang et al. in J Eur Ceram Soc 36:533–540, 2015 ). Longer sintering induced uniform distributions of the additives. The introduction of Nb 2 O 5 into 0.8BT–0.2NBMT could obviously bring about the improvement of the dielectric temperature stability, the degradation of the dielectric loss at room temperature and the decrease of the sintering temperature. The 0.8BT–0.2NBMT ceramics doped with 2.0 at% Nb 2 O 5 could satisfy the temperature range of the X9R (−55 to 200 °C, △C/C 25°C = ±15% or less) characteristics, with a moderate dielectric constant of 1130, low dielectric loss of 0.7%, low sintering temperature of 1050 °C and insulation resistivity of 5 × 10 12 Ω cm at room temperature, which might be promising for practical use in multilayer ceramic capacitors. The inhomogeneous distribution and the existence of the secondary phases were responsible for this excellent dielectric temperature characteristic. The complex impedance analysis was introduced to elaborate the conduction mechanism.
Huang Xuechen,Liu Bang,Wang Shuanghu,Liu Yuxi,Wu Gang
Bi 2 O 3 - and MgO-doped BaTiO 3 –(Na 1/4 Bi 3/4 )(Mg 1/4 Ti 3/4 )O 3 (BT–NBMT) ceramics were synthesized from a solid-state approach, and then the impacts of Bi 2 O 3 and MgO dosages on the structures and dielectric characteristics were studied. Obvious dual peaks were observed with Bi 2 O 3 dosage to 0.04 and MgO dosage to 0.02. The low-temperature dielectric stability and grain size of the Bi 2 O 3 dopant were improved, while those of the MgO dopant hardly changed with MgO dosage to 0.02, indicating the core/shell microstructure of BT–NBMT was formed following the dissolving-precipitating mechanism of BT systems doped with low-melting-point substances. The low-temperature dielectric stability of the Bi 2 O 3 - or MgO-doped BT–NBMT ceramics first improved and then deteriorated with the increase of doping concentrations. High-temperature stability and diffuse-state transition were found in the optimal ceramics. The second phases of Bi 2 O 3 and MgO, magnesium titanium compounds were observed in Bi 2 O 3 and MgO dopants, respectively. Bi 2 O 3 -doped and MgO-doped ceramics exhibited a fine-grained microstructure and significant grain growth, respectively, and the core/shell microstructure was responsible for the dielectric temperature stability for Bi 2 O 3 dopants and collapsed to a homogeneous one with remarkable grain growth and the second phases for MgO dopants.
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