• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.783-792
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• 1995

Sol-Gel derived ferroelectric PZT thin films were fabricated on ITO/Glass and Si/SiO2 substrates. In order to investigate the effect of catalysts on the densification and crystallization of PZT thin films, a nitric acid or ammonium hydroxide was added to the PZT stock solution at the state of partial hydrolysis reaction. The measured pH for a stable PZT sol was 5.2~9.3. In case of an acid-catalyzed PZT sol, a highly condensed particulate PZT sol was formed by accelerating the hydrolysis reaction. But weakly branched polymeric PZT sol was formed with a base-catalyzed condition. The difference in densification behavior was not found in the pH range of added catalyst, but the refractive index of PZT thin film was increased rapidly as the annealing temperature increased. The PZT thin film annealed at 54$0^{\circ}C$ for 10 min was fully densified and its refractive index was above 2.4. When the annealing temperature increased, the transition from the pyrochlore phase to perovskite appeared at 54$0^{\circ}C$. The base-catalyzed PZT thin film suppressed to form the pyrochlore phase and proceeded effectively to convert the perovskite phase. This was due to the formation of polymeric molecular structure by controlling the hydrolysis and condensation reaction through the additiion of the ammonium hydroxide.

• Journal of Magnetics
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• v.19 no.3
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• pp.227-231
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• 2014

We fabricated textured polycrystalline $CoFe_2O_4$ thin films on $Pt(111)/TiO_2/SiO_2/Si$ substrate through a sol-gel method. We varied the thickness of the films, by using precursor solutions with different concentrations of 0.1, 0.2, and 0.3 M, and by depositing 5, 8, or 10 layers on the substrate by spin-coating. X-ray diffraction spectra indicated that when the precursor concentration of the solution was higher than 0.1 M, the spin-coated films were preferentially oriented in the <111> direction. Inspection of the surface morphology by scanning electron microscopy revealed that $CoFe_2O_4$ thin films prepared with 0.2 M solution and 5-time spin-coatings had smoother surface, as compared to the other conditions. Each coating had an average thickness of about 50 nm. The magnetic properties measured by vibrating sample magnetometer showed magnetic anisotropy, as evidenced from the difference in the in-plane and out-of-plane hysteresis loops, which we attributed to the textured orientation of the $CoFe_2O_4$ thin films.

• Korean Journal of Materials Research
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• v.28 no.7
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• pp.371-375
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• 2018

The manganese-, nickel-, and aluminum-doped cobalt ferrite powders, $Mn_{0.2}Co_{0.8}Fe_2O_4$, $Ni_{0.2}Co_{0.8}Fe_2O_4$, and $Al_{0.2}CoFe_{1.8}O_4$, are fabricated by the sol-gel method, and the crystallographic and magnetic properties of the powders are studied in comparison with those of $CoFe_2O_4$. All the ferrite powders are nano-sized and have a single spinel structure with the lattice constant increasing in $Mn_{0.2}Co_{0.8}Fe_2O_4$ but decreasing in $Ni_{0.2}Co_{0.8}Fe_2O_4$ and $Al_{0.2}CoFe_{1.8}O_4$. All the $M{\ddot{o}}ssbauer$ spectra are fitted as a superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the $Fe^{3+}$ ions. The values of the magnetic hyperfine fields of $Ni_{0.2}Co_{0.8}Fe_2O_4$ are somewhat increased in the A and B sites, while those of $Mn_{0.2}Co_{0.8}Fe_2O_4$ and $Al_{0.2}CoFe_{1.8}O_4$ are decreased. The variation of $M{\ddot{o}}ssbauer$ parameters is explained using the cation distribution equation, superexchange interaction and particle size. The hysteresis curves of the ferrite powders reveal a typical soft ferrite pattern. The variation in the values of saturation magnetization and coercivity are explained in terms of the site distributions, particle sizes and the spin magnetic moments of the doped ions.

• Transactions on Electrical and Electronic Materials
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• v.18 no.6
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• pp.364-369
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• 2017

Double molybdate $NaGd_{1-x}(MoO_4)_2:Ho^{3+}/Yb^{3+}$ phosphors with proper doping concentrations of $Ho^{3+}$ and $Yb^{3+}$ ($x=Ho^{3+}+Yb^{3+}$, $Ho^{3+}=0$ and 0.05, and $Yb^{3+}=0$, 0.35, 0.40, 0.45, and 0.50) were successfully synthesized using the microwave sol-gel method. Well-crystallized particles formed after heat-treatment at $800^{\circ}C$ for 16 h showed fine and homogeneous morphologies with particle sizes of $1{\sim}3{\mu}m$. The spectroscopic properties were examined using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the upconversion doped samples exhibited strong yellow emissions, from the combination of strong emission bands at 545 nm and 655 nm in the green and red spectral regions, respectively. The strong 545 nm emission band in the green region corresponded to the $^5S_2/^5F_4{\rightarrow}^5I_8$ transition in the $Ho^{3+}$ ions, while the strong 655 nm band in the red region appeared because of the $^5F_5{\rightarrow}^5I_8$ transition in the $Ho^{3+}$ ions. The pump power dependence and the Commission Internationale de L'Eclairage chromaticity of the upconversion emission intensity were evaluated in detail.

• Journal of the Korean Electrochemical Society
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• v.3 no.1
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• pp.11-14
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• 2000

Transparent conducting ITO thin films have been studied and developed for the solar cell substrate or LCD substrate. ITO thin film has been mostly fabricated by high cost sputtering method. In this research, sol-gel method is applied to fabricate ITO thin film at lower cost. The research is focused on the establishment of process condition and development of precursor. Organic sol was made of indium tri-isopropoxide dissolved in ethylene glycol monoethyl ether. The hydrolysis was controled by addition of acetyl acetone. Tin(IV) chloride was added as dopant. Inorganic sol was made of indium acetate dissolve din normal propanol. Spin coating technique was applied to coat ITO on borosilicate glass. The resistivity of ITO thin film was approximately $0.01\Omega{\cdot}cm$ and the transmittance is higher than $90\%$ in a visible range.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.12
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• pp.821-825
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• 2015

Anti-reflective (AR) thin film was fabricated on a glass substrate by sol-gel method. The coating solution was synthesized with TEOS (tetraethlyorthosilicate) and poly ethylene glycol (PEG, 4.0 wt%). As the withdrawal speed of coating was changed from 0.1 mm/sec to 0.3 mm/sec, the thickness and refractive index of prepared thin films were changed. The reflectance and transmittance of coating glass fabricated by the withdrawal speed of 0.1 mm/sec were 0.62% and 95.0% in visible light range. The refractive index and thickness of single layer thin film were n= 1.29 and ca. 99.0 nm.

• Journal of the Korean Magnetics Society
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• v.13 no.4
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• pp.165-170
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• 2003

M-type hexagonal BaFe$\sub$12/O$\sub$19/ ferrite powder was prepared by sol-gel process. The M-type hexagonal structure with ${\alpha}$ = 5.882 and c = 23.215 ${\AA}$ and its Curie temperature T$\sub$C/ was determined 780${\pm}$3 K. The isomer shifts of ,4f$_2$, 2a. 4f$_1$, 12k, and 2b were indicated 0.26, 0.24, 0.15, 0.25, and 0.24 mm/s, therefore, the valence states of the Fe ions were ferric (Fe$\^$3+/). By the law of approach to saturation (LAS), the effective anisotropy field H$\sub$A/ and crystalline anisotropy constant K$_1$ were estimated. The value of K$_1$ and H$\sub$A/ were K$_1$ = 2.5${\times}$10$\^6/erg/cm^3$ and H$\sub$A/ = 14 kOe, respectively.

• Journal of Magnetics
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• v.8 no.4
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• pp.138-141
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• 2003

$Ni_{0.65}Zn_{0.35}Fe_2O_4$thin films were prepared by using a sol-gel method. Their crystallographic, dielectric and magnetic properties were investigated as a function of Cu contents by means of an X-ray diffractometer (XRD), X-ray reflectivity, LCZ meter (NF2232), a vibrating sample magnetometer (VSM), and an atomic force microscope (AFM). From typical C-V measurements for $Ni_{0.65}Zn_{0.35}Fe_2O_4$ thin films on p-type silicon substrate, the surface charge density was calculated as 1.4 ${\mu}$C/$m^2$. The dielectric constant evaluated from the capacitance at the accumulation state was 28. The high $H_{c}$ and low $M_{sat}$ at x=0.0 and 0.1 were due to the growth of the ${\alpha}$-$Fe_2O_3$ phase having antiferromagnetic properties. The rapidly decreased $H_{c}$ and increased $M_{sat}$ at x=0.2 and 0.3 can be explained that the ${\alpha}$-$Fe_2O_3$ phases have completely disappeared at x=0.3 and so, non-magnetic defects are minimized. The $M_{sat}$ was slightly decreased and the $H_{c}$ was increased above at x=0.3 because the increase of grain boundary due to smaller grain size acts as defects during magnetization process.

• Journal of Magnetics
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• v.18 no.3
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• pp.230-234
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• 2013

The $Ni_{0.5}Zn_{0.5}Fe_2O_4$ nanoparticles about 30 nm were prepared using sol-gel method with metal nitrates dissolved in 2-methoxyathanol. The concentrations of the metal nitrates are adjusted from 0.1 to 0.75 M in order to study the influence on the structural and magnetic properties. The structure and morphology characterization revealed that the crystallinity was improved and the nanoparticle size was increased with the nutrition solution concentrations up to 0.5 M. Degraded crystallinity together with decreased nanoparticle size were observed for concentration of 0.75 M. The saturation magnetization at room temperature reached maximum at 0.5 M, which can be explained by considering the crystallinity and size effect.

• Journal of the Korean Ceramic Society
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• v.33 no.11
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• pp.1195-1202
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• 1996

To prepare the dielectric thin films of (Pb1-xSrx)TiO3 (x=0.1, 0.2, 0.3, 0.35, 0.5) by the sol-gel process titanium (IV) isopropoxide (Ti[OCH(CH3)2]4) and Pb Sr, acetate were used therefore the thin films were fabricated by dip-coating method. Stability of the sol decreased with addition of Sr content thin films could be fabricated up to 35mol% Over this range precipitation of sol occured thin films couldn't be obtained. Transmittance of thin films at visible range decreased with the increase of heat-treatment temperature but exhibited transmit-tance above 60% in all case. Moreover transmittance of thin films at visible range slightly increased with of addition of Sr,. When thin film containing 30 mol% srontium was heated at 600℃ the best perovskite phase was obtained. The dielectric constant (ε) was 280 and dielectric loss factor (tan δ) was 0.021 and curie tempera-ture (Tc) decreased with the increase of addition of Sr.