3.1. Fabrication method
3.1.1. A-site engineered BaTiO
3Sample where Dy is doped on the A site of BaTiO3, which is named as Dy-A, was prepared using a conventional solid-state reaction method. To surely incorporate Dy3+ on A site, first Ba0.99Dy0.01CO3
(BD) was prepared. Dried powders for 24 h, TiO2 (Sigma Aldrich, 99%) and Dy2O3 (Solvay, 99.9%) were weighted according to the formula of BD, followed by ball milling for 24 h in ethanol. The mixed powders were dried in an oven and calcinated at 700 ◦C for 2 h in a furnace. The calcinated BD and TiO2 (Sigma Aldrich, 99%) were weighted as Ba0.99Dy0.01TiO3. The mixed powders were conducted second ball-milling for 24 h in ethanol, dried in an oven and calcinated at 1050°C for 4 h in a furnace.
After adding polyvinyl alcohol (PVA) on calcinated powder, the powder was sieved with a 150 μm mesh and then uniaxially pressed into disc-shape of 10mm-diameter under 120 MPa. These samples were sintered in an alumina crucible at 1350°C for 2 h in air after burning out PVA at 600°C for 2 h.
3.1.2. B-site engineered BaTiO
3Sample where Dy is doped on the B site of BaTiO3, which is named as Dy-B, prepared using a conventional solid-state reaction method. To surely incorporate Dy3+ on B site, first we prepared Ti0.99Dy0.01O2 (TD). Dried powders for 24 h, TiO2 (Sigma Aldrich, 99%) and Dy2O3 (Solvay, 99.9%) were weighted according to the formula of TD, followed by ball milling for 24 h in ethanol. The mixed powders were dried in an oven and calcinated at 800°C for 2 h in a furnace. The calcinated TD and BaCO3 (Sigma Aldrich, 99%) were weighted as BaTi0.99Dy0.01O3. All the following processes including calcination molding were carried out in the same way as A-site engineered BaTiO3. These B-site engineered BaTiO3samples were sintered in an alumina crucible at 1375°C for 2 h in air after burning out PVA at 600°C for 2 h.
3.1.3. A&B-site engineered BaTiO
3Sample where Dy is doped on both A site and B site of BaTiO3, which is named as Dy-A&B, was prepared using a conventional solid-state reaction method, too. To surely incorporate Dy3+ on both A and B site, we prepared Ba0.995Dy0.005CO3 (BD-A&B) calcinated at 700°C for 2 h and Ti0.995Dy0.005O2
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(TD-A&B) calcinated at 800°C for 2 h. The BD5 and TD5 were weighted according to the formula of Ba0.995Dy0.005Ti0.995Dy0.005O3. All the following processes including calcination and sintering were carried out in the same way as A-site engineered BaTiO3.
3.1.4. Excessively added Dy on BaTiO
3Sample that Dy was excessively added in BaTiO3, which is named as Dy-excess, was prepared using a conventional solid-state reaction method. The raw powders, BaCO3 and TiO2, were ball-milled for 24 h in ethanol, dried in an oven and calcinated at 1050°C for 4 h in a furnace. The calcinated powder were mixed with 1 mol.% Dy by second ball-milling step. The mixed powder was dried. After adding polyvinyl alcohol (PVA) on dried powder, the powder was sieved with a 150 μm mesh and then uni- axially pressed into discs of 10mm-diameter under 120 MPa. These samples were sintered in an alumina crucible at 1350°C for 2 h in air after burning out PVA at 600°C for 2 h.
3.1.5.
Dy-doped BaTiO3 from Conventional methodThe samples were prepared using a conventional solid-state reaction method. These samples synthesized with conventional method was named as ‘C.S.’. Dy doped BT on A-site and B-site was weighted according to stoichiometry of Ba0.99Dy0.01TiO3 and BaTi0.99Dy0.01O3, respectively. The raw powders were ball-milled for 24 h in ethanol, dried in an oven and calcinated at 1050 ◦C for 4 h in a furnace. The mixed powder was dried. After adding polyvinyl alcohol (PVA) on dried powder, the powder was sieved with a 150 μm mesh and then uni-axially pressed into discs of 10mm-diameter under 120 MPa. These samples were sintered in an alumina crucible at 1350 ◦C and 1375◦C for 2 h in air after burning out PVA at 600 ◦C for 2 h.
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Fig. 13. Basic process of solid-solution synthesis method.
Fig. 14. Scheme of experiment strategy for dopant site control. The 2-step calcination is introduced.
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3.2. Characterization method
3.2.1. X-ray diffraction
X-ray diffraction was conducted to analyze the crystal structure, crystallinity and existence of secondary phase by measuring the angles and intensities of diffracted beam. In this experiment, X-ray diffractometer (D/MAX2500 V/PC, Tokyo, Japan) with Cu-Kα (λ = 1.5406 Å ) radiation was used over the two theta range of 20◦-80◦. Lattice parameters can be calculated through bragg’s law and d- spacing for 7 crystal systems (see Fig. 15).
(a)
(b)
Fig. 15. (a) Bragg’s Law for X-ray diffraction, (b) d-spacing from XRD data to obtain lattice parameter
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3.2.2. Scanning Electron Microscopy
Scanning electron microscopy (SEM, Quanta 200 FEG, FEI Company) was used to observe the microstructure. Also energy dispersive spectroscopy (EDS, AMETEK-EDAX, Mahwah, USA) was used for qualitatively chemical characterization and elemental analysis. All samples for SEM image were polished and thermally etched at 1200 ◦C for 30 min and Pt electrode was coated on the surface of samples.
3.2.3. Dielectric Spectroscopy
The temperature dependent dielectric permittivity and loss curves were obtained by dielectric spectroscopy (Concept-40, Novocontrol Technologies, Germany) with 0.1 Vrms in the frequency range 0.1kHz to 1MHz. The temperature measurement range was between -55°C and 150°C with a heating rate of 3 ◦C/ min.
3.2.4. Impedance Analyzer
The complex impedance spectra were measured by impedance analyzer (HP 4192A, Hewlett- Packard Company, Palo Alto, CA), connected to a furnace with sample holder, over temperature range 30°C to 600°C. Impedance analysis was conducted 10Hz to 10MHz.
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