• Corrosion Science and Technology
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• 제22권1호
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• pp.36-43
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• 2023

Single-crystal Ni-rich NCM is a material that has drawn attention in the field of lithium-ion batteries due to its high energy density and long cycle life. In this study, we investigated the properties of single-crystal NCM 811 and its potential for use in lithium-ion batteries. High-quality single crystals of NCM 811 were successfully synthesized by crystal growth via a flux method. The single-crystal nature of the samples was confirmed through detailed characterization techniques, such as scanning electron microscopy and x-ray diffraction with Rietveld refinement. The crystal structure and electrochemical performances of the single-crystal NCM 811 were analyzed and compared to its poly-crystal counterpart. The results indicated that single-crystal NCM 811 had electrochemical performance and thermal stability superior to poly-crystalline NCM 811, making it a suitable candidate for high-performance batteries. The findings of this study contribute to a better understanding of the characteristics and potential of single-crystal NCM 811 for lithium-ion batteries.

• Journal of Electrochemical Science and Technology
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• 제4권3호
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• pp.102-107
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• 2013

The electrochemical properties of Mg-doped $LiFe_{0.48}Mn_{0.48}Mg_{0.04}PO_4$ and pure $LiFe_{0.5}Mn_{0.5}PO_4$ olivine cathodes are examined and the lattice parameters are refined by Rietveld analysis. The calculated atomic parameters from the refinement show that $Mg^{2+}$ doping has a significant effect in the olivine $LiFeMnPO_4$ structure. The unit cell volume is 297.053(2) ${\AA}^3$ for pure $LiFe_{0.5}Mn_{0.5}PO_4$ and is decreased to 296.177(1) ${\AA}^3$ for Mg-doped $LiFe_{0.48}Mn_{0.48}Mg_{0.04}PO_4$ sample. The doping of $Mg^{2+}$ cation with atomic radius smaller than $Mn^{2+}$ and $Fe^{2+}$ ion induces longer Li-O bond length in $LiO_6$ octahedra of the olivine structure. The larger interstitial sites in $LiO_6$ octahedra facilitate the lithium ion migration and also enhance the diffusion kinetics of olivine cathode material. The $LiFe_{0.48}Mn_{0.48}Mg_{0.04}PO_4$ sample with larger Li-O bond length delivers higher discharge capacities and also notably increases the rate capability of the electrode.

• 한국세라믹학회지
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• 제33권1호
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• pp.1-6
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• 1996

A single phase Ba2(Ti8,472Zr0.528)O20 was prepared by the oxalate method from aqueous solution of BaCl2 TiCl4 and ZrOCl2. The structure ananlysis has been carried out by Rietveld analysis method at room temperature. Powder X-ray data of Ba2(Ti8,472Zr0.528)O20 was indexed with the triclinic lattice(a=7.4587 $\AA$ b=14.0672 $\AA$, c=13.3327 $\AA$, $\alpha$=89.87, $\beta$=79.45 ${\gamma}$=84.46) The R (Residual) values of structure refinement were in a range between 10.00 and 8.00 This analysis proved that the added Zr occupied Ti sites in th structure of Ba2Ti9O20. Ba2(Ti8,472Zr0.528)O20 has excellent dielectric properties(dielectric constant K=40.49 at 5.42 GHz Q=4621) so that it can be used as good microwave dielectric materials.

• Korean Chemical Engineering Research
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• 제49권5호
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• pp.657-663
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• 2011

피페리딘 구조가 포함된 구조유도분자가 미치는 알루미노포스페이트 제올라이트 합성과 결정구조에 대한 영향을 조사하였다. 피페리딘 구조가 포함된 구조 유도분자는 피페리딘을 포함하여 2-메틸피페리딘, 2,6-디메틸피페리딘, 2,2,6,6-테트라메틸피페리딘을 사용하였다. 제올라이트 합성은 $1.0Al_2O_3:1.0P_2O_5:0.76SDA:45H_2O$의 조성으로 $170^{\circ}C$에서 7일동안 수열합성을 하였다. 피페리딘을 구조유도분자로 사용한 경우, 층상 구조가 형성되었으며 구조유도분자의 크기가 커질수록 AFI 구조의 AlPO-5가 형성되고 가장 큰 구조 유도분자를 이용한 경우, SAS 구조의 알루미노포스페이트가 형성됨을 리트벨트법으로 확인할 수 있었다. 또한 고체핵자기공명분석법의 결과로부터 미세 다공성 물질인 SAS 골격구조 내에 알루미늄과 인이 위치함을 알 수 있었다.

• 한국재료학회지
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• 제33권11호
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• pp.465-474
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• 2023

The effects of La³⁺ substitution for Sr²⁺-site on the crystal structure and the dielectric properties of (Ba_0.7Sr_0.3-3x/2La_x) (Ti_0.9Zr_0.1)O₃ (BSLTZ) (0.005 ≤ x ≤ 0.02) ceramics were investigated. The structural characteristics of the BSLTZ ceramics were quantitatively evaluated using the Rietveld refinement method from X-ray diffraction (XRD) data. For the specimens sintered at 1,550 ℃ for 6 h, a single phase with a perovskite structure and homogeneous microstructure were observed for the entire range of compositions. With increasing La³⁺ substitution (x), the unit cell volume decreased because the ionic size of La³⁺ (1.36 Å) ions is smaller than that of Sr²⁺ (1.44 Å) ions. With increasing La³⁺ substitution (x), the tetragonal phase fraction increased due to the A-site cation size mismatch effect. Dielectric constant (ε_r) increased with the La³⁺ substitution (x) due to the increase in tetragonality (c/a) and the average B-site bond valence of the ABO₃ perovskite. The BSLTZ ceramics showed a higher dielectric loss due to the smaller grain size than that of (Ba_0.7Sr_0.3)(Ti_0.9Zr_0.1)O₃ ceramics. BSLTZ (x = 0.02) ceramics met the X7R specification proposed by the Electronic Industries Association (EIA).

• 한국결정성장학회지
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• 제33권5호
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• pp.174-180
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• 2023

본 연구는 백자와 청자 소지에 철/코발트 황하물의 안료를 시유하여 1250℃에서 소성한 도자기 표면의 상형성을 연구하였다. 시편의 특성은 X-선 회절분석기, 전계방사형 주사전자현미경, 에너지 분산형 엑스선분석기 및 UV-vis 분광계를 이용하였다. X-선 리트벨트 정밀화 분석으로 백자소지는 석영과 뮬라이트가, 청자소지는 뮬라이트와 plagioclase가 주 결정상이다. 백자와 청자소지에 철/코발트 황하물의 안료를 시유한 경우 백자는 스피넬상이 청자는 andradite 상의 이차상이 형성되었다. 시편 소지의 색상은 밝기인 L^* 값은 백자와 청자소지가 72.01, 60.92이고 백자가 청자소지 보다는 백색도가 높다. 철/코발트 황하물의 안료를 도포한 시편에서 백자와 청자 시편의 경우, L^* 값은 44.89, 52.27, a^* 값은 2.12, 1.40, b^* 값은 1.4 5, 13.79를 각각 보이고 있다. L^* 값은 백자소지에 안료를 도포한 시편에서 큰 변화가 있으며, b^* 값은 소지에 따라 크게 차이가 나는 것을 알 수가 있다. 이는 표면층에 생성되는 Fe₂O₃ 상과 andradite 결정상 생성과 밀접한 관련이 있다.

• Bulletin of the Korean Chemical Society
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• 제33권6호
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• pp.1845-1850
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• 2012

Layered metal hydroxides (LMHs) containing calcium were synthesized by coprecipitation in solution having two different trivalent metal ions, iron and aluminum. Two mixed metal solutions ($Ca^{2+}/Al^{3+}$ and $Ca^{2+}/Fe^{3+}$ = 2/1) were added to sodium hydroxide solution and the final pH was adjusted to ~11.5 and ~13 for CaAl-and CaFe-LMHs. Powder X-ray diffraction (XRD) for the two LMH samples showed well developed ($00l$) diffractions indicating 2-dimensional crystal structure of the synthesized LMHs. Rietveld refinement of the X-ray diffraction pattern, the local structure analysis through X-ray absorption spectroscopy, and thermal analysis also confirmed that the synthesized precipitates show typical structure of LMHs. The chemical formulae, $Ca_{2.04}Al_1(OH)_6(NO_3){\cdot}5.25H_2O$ and $Ca_{2.01}Fe_1(OH)_6(NO_3){\cdot}4.75H_2O$ were determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Particle morphology and thermal behavior for the synthesized LMHs were examined by field emission scanning electron microscopy and thermogravimetricdifferential scanning calorimetry.

• 한국결정성장학회지
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• 제25권3호
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• pp.121-126
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• 2015

A novel $Ce^{3+}$ doped $Lu_3MgAl_3SiO_{12}$ phosphor ($Lu_{2.94}Ce_{0.06}MgAl_3SiO_{12}$) was successfully synthesized by a conventional solid-state reaction at $1450^{\circ}C$ for 5 h. The crystal structure of the synthesized phosphor powder was characterized by X-ray diffraction and Rietveld refinement. The prepared phosphor powder showed a broad peak at 550 nm, and the temperature dependence on photoluminescence properties of the prepared $Lu_{2.94}Ce_{0.06}MgAl_3SiO_{12}$ phosphor was investigated from 300 to 525 K. The activation energy for thermal quenching was determined by Arrhenius fitting. The experimental results clearly indicate that prepared $Lu_{2.94}Ce_{0.06}MgAl_3SiO_{12}$ phosphor has great potential for a down-conversion yellow phosphor in white light-emitting diodes.

• 한국세라믹학회지
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• 제47권2호
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• pp.163-168
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• 2010

Effects of compositions on the microwave dielectric properties of the MgO-$TiO_2$ system were investigated as a function of the molar ratio of MgO to $TiO_2$ ($0.9{\leq}MgO/TiO_2\;(x){\leq}1.2$). With the compositional changes, secondary phases of $MgTi_2O_5$ and $Mg_2TiO_4$ were also detected along with $MgTiO_3$. Microwave dielectric properties of the specimens were dependent on the types of phases developed in the sintered specimens. A single phase of $MgTiO_3$ showed a dielectric constant (K) of 18.2, a quality factor (Qf) of 198,000 GHz, and a temperature coefficient of resonant frequency (TCF) of $-51\;ppm/^{\circ}C$. However, the dielectric properties of the specimens with a secondary phase of $MgTi_2O_5$ (K=19.9, Qf=48,000 GHz) and/or $Mg_2TiO_4$ (K=15.6, Qf=56,000 GHz) were worsened. Dependence of the microwave dielectric properties on the secondary phase of the MgO-$TiO_2$ system was also discussed in terms of dielectric mixing rules.

• Journal of Magnetics
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• 제14권4호
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• pp.161-164
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• 2009

Iron-doped $Sn_{1-x}Fe_xO_2$ (x = 0.0, 0.05, 0.1, 0.2, 0.33) thin films on Si(100) substrates and powders were prepared by a chemical solution process. The x-ray diffraction (XRD) patterns of the $Sn_{1-x}Fe_xO_2$ thin films and powders showed a polycrystalline rutile tetragonal structure. Thermo gravimetric (TG) - differential thermal analysis (DTA) showed the final weight loss above $430{^{\circ}C}$ for all powder samples. According to XRD Rietveld refinement of the powders, the lattice parameters and unit cell volume decreased with increasing Fe content. The magnetic properties were characterized using a vibrating sample magnetometer (VSM) and M$\ddot{o}$ssbauer spectroscopy. The thin film samples with x = 0.1 and 0.2 showed paramagnetic properties but thin films with x = 0.33 exhibited ferromagnetic properties at room temperature. Mossbauer studies revealed the $Fe^{3+}$ valence state in the samples. The ferromagnetism in the samples can be interpreted in terms of the direct ferromagnetic coupling of ferric ions via an electron trapped in a bridging oxygen deficiency, which can be explained using the F-center exchange model.