However, the studies on the analysis of traits according to the role of Dy are lacking. Here, by introducing two-step calcination, we doped Dy3+ ion on each site of BT (A site, B site and A&B site) and systematically compared the properties according to the Dy doped site. Keywords: MLCCs, dielectric capacitor, BaTiO3, Dysprosium, high reliability dielectrics, TCC, defect engineering. a) Classification of dielectrics, (b) subgroups of dielectrics according to crystallographic point groups.
Frequency dependence of permittivity of dielectric material. a) Circuit diagram with dielectric capacitor, (b) charge and loss current in AC electric field, (c) loss tangent vector expressed as charge and loss current. Temperature dependence of dielectric permittivity of BaTiO3 single crystal in the range - 160ºC and 125ºC. Scheme for donor and acceptor doping of rare earth elements in the BaTiO3 system. Dielectric permittivity and loss of all samples at 10kHz. a) TC and TO-T for all samples (b) Temperature coefficient of capacitance (TCC) and maximum dielectric loss in the range -55°C and 105°C.
Comparison of XRD data between the conventionally synthesized sample and the 2-step calcined sample of (a) Dy-A site and (b) Dy-B site. Nyquist resistivity plots by frequency are compared between the conventionally synthesized sample and the 2-step calcined sample of (a) Dy-A site and (b) Dy-B site.
Introduction
Therefore, in this paper, we controlled the doping site through 2-step calcination and analyzed the dielectric and electrical property systematically according to the doping site. By comparing properties between previous research methods and 2-step calcination, it will also be confirmed whether the site control is possible through previous research methods.
Theoretical background
- Definition of dielectrics
- Classification of dielectrics
- Dielectric property & applications
- Barium Titanate (BaTiO 3 )
The inverse piezoelectric effect shows the strain resulting from an applied electric field and the induced mechanical strain along j is expressed as Eq. Here, 𝐸𝑖𝑗 is an applied electric field. a) Classification of dielectrics, (b) subgroups of dielectrics according to groups of crystallographic points. The pyroelectric material can change the magnitude of the spontaneous polarization according to a change in temperature, and it does not matter if the polarity of the spontaneous polarization can be changed by an external electric field.
Ferroelectric material is a material whose spontaneous polarization is reversed under an external electric field among pyroelectric materials. In the hysteresis loop, when the electric field becomes 0 after increasing, the polarization value does not become 0 due to residual polarization. Also, to change the polarization direction, an electric field greater than the compressive field (Ec) is required (see Fig. 3) [7].
When an electric field is applied to dielectric materials, the dielectric materials are polarized and we can get the polarization that follows by Eq. Dipole (or orientation) polarization is generated when the randomly distributed polar molecules are aligned by electric field. Space charge (or interface) polarization is that the charges accumulate on the interface between two regions or two materials according to electric field.
When an electromagnetic field or an electric field with frequency is applied to the dielectric, meaning that the field changes with time, polarization occurs. Therefore, the polarization vector P will also have the same frequency as the external electric field. Due to leakage current coming from material resistivity, particle inertia and thermal agitation to randomize dipole orientation, the polarization vector P is prevented from having the same frequency as the external electric field.
Complex permittivity function represents the dielectric response to electric field and also includes the dielectric loss term. It also has a fixed polarity, so it must be used according to the direction of polarity. In BaTiO3 system, rare-earth elements act as donor at A site and the reliability can be improved by reducing the concentration of oxygen vacancies (see Eq.
Experimental procedure
Fabrication method
- A-site engineered BaTiO 3
- B-site engineered BaTiO 3
- A&B-site engineered BaTiO 3
- Excessively added Dy on BaTiO 3
- Dy-doped BaTiO 3 from Conventional method
A sample that Dy was excessively added to BaTiO3, referred to as Dy-excess, was prepared using a conventional solid-state reaction. After adding polyvinyl alcohol (PVA) to the dried powder, the powder was sieved with a 150 μm mesh and then uniaxially compressed into 10 mm diameter discs under 120 MPa. These samples were sintered in an alumina crucible at 1350 °C for 2 h in air after burning the PVA at 600 °C for 2 h.
Dy-doped BT at A-site and B-site were weighed according to stoichiometry of Ba0.99Dy0.01TiO3 and BaTi0.99Dy0.01O3, respectively. The raw powders were ground in ethanol for 24 h, dried in an oven and calcined at 1050 ◦C for 4 h in an oven. After adding polyvinyl alcohol (PVA) to dried powder, the powder was sieved with a 150 μm mesh and then uniaxially pressed into 10 mm diameter disks under 120 MPa.
Characterization method
- X-ray Diffraction
- Scanning Electron Microscopy
- Dielectric Spectroscopy
- Impedance Analyzer
Energy dispersive spectroscopy (EDS, AMETEK-EDAX, Mahwah, USA) was also used for qualitative chemical characterization and elemental analysis.
Results & Discussion
- Crystal structure & Microstructure analysis
- Dielectric property
- Electrical & Ferroelectric property
- Comparison between site controlled and uncontrolled samples
- Crystal structure & Microstructure analysis
- Dielectric property
- Electrical property
19, the Dy-doped sample has no secondary phase, indicating that all Dy is well doped in the BaTiO3 lattice. Furthermore, all double-doped specimens show reduced grain sizes compared to pristine BT, which is because energy is required to incorporate the dopant into the lattice and thus the energy required for grain growth is reduced [ 4]. Furthermore, while site Dy-A and site Dy-B show reduced resistivity compared to pristine, excess Dy data also show enhanced resistivity value as site A&B.
This result indicates that Dy is doped in excess of Dy on both A-site and B-site, with self-compensation. The reason why there is a difference in resistance value between Dy-A&B site and Dy-Excess is because the amount of Dy occupying each A site and B site is not controlled in Dy-Excess sample and thus the ratio of Dy doped on the A site and the B site will not be same with Dy-A&B site. All samples show hysteresis loop indicating ferroelectric property but in Dy-B site distortion of hysteresis loop is observed due to leakage current.
Therefore, the properties between the conventionally synthesized sample and the samples calcined in two steps will be compared here to confirm whether site control is possible with the conventional method. There is no secondary phase in all the XRD data and Dy is also well doped at the target site and shows a peak shift in all the normal (labeled C.S.) and stepped patterns. Therefore, in terms of crystal structure and microstructure, there is no noticeable difference between the normal pattern and the stepped pattern at Dy-A site and Dy-B site.
The difference between conventionally synthesized sample and 2-step calcined sample is noticeable in dielectric properties. This means that in the conventional method, Dy is also doped at not only the B site but also the A site due to self-compensation, and so the amount of formed oxygen vacancies is quite reduced compared to the B site with steps. Therefore, we can conclude that the sample could not be completely doped at the target site by conventional method. a) Temperature dependent dielectric permittivity and loss, (b) TO-T and TC, and (c) TCC and maximum dielectric loss in the range of −55°C and 105°C for the Dy-A site. a) Temperature-dependent dielectric permittivity and loss, (b) TO-T and TC, and (c) TCC and maximum dielectric loss in the −55°C and 105°C region of the Dy-B site.
The difference between the conventionally synthesized sample and the 2-step calcined sample was also shown in the impedance data. In Fig. 28, Conventional samples (C.S.) at both Dy-A and Dy-B sites have larger semicircles than gap samples, indicating improved insulation resistance in conventional samples. This results because, in the conventional method, charge carrier formation is suppressed because Dy is also doped at an unspecified site, self-compensation occurring.
Conclusion
다층 세라믹용 BaTiO3 기반 세라믹의 유전 특성 및 신뢰성에 대한 희토류 원소의 시너지 효과. 연구 진행이 잘 안 될 때에도 항상 격려와 지지를 해주시고, 때로는 부족함을 일깨워 주시고, 사랑스러운 조언으로 지도해 주셔서 감사하다는 말씀을 전하고 싶습니다. 바쁜 일정에도 불구하고 논문을 심사해주신 손재성 교수님, 차채영 교수님에게도 감사드립니다.
제 논문에 대해 교수님께서 해주신 좋은 말씀과 조언이 큰 도움이 되었습니다. 아무것도 모르는 나를 배려하는 마음으로 보살펴준 츤데레 우석이. 혜림은 따뜻하고 포근한 마음을 갖고 있어요.
내 옆에 앉아 사랑을 위해 늘 노력하지만 실패하는 신사 준용이 이번에는 성공하길 바란다. 대학원을 졸업하고 더욱 멋져진 정우는 박사학위를 취득하면 연예인이 될 예정이다. 민서에게 더 가까이 다가가지 못해서 아쉽다.
그리고 제가 많이 부족할 때 지도해주시고 때로는 친한 언니처럼 인생 조언도 해주시던 주현 선생님 덕분에 저는 대학원에서도 성장하고 행복한 삶을 살 수 있었습니다. 교수님 옆에서 존경하고 너무 감사드립니다. 마지막으로, 멀리서도 늘 곁에 있어준 가족들.
앞으로도 사회에 나가서 안주하지 않고 계속 성장하는 자랑스러운 SFC 졸업생이 되겠습니다.
