• Progress in Superconductivity
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• v.6 no.1
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• pp.37-40
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• 2004

We investigated the effects of impurity doping on the electrical transport and magnetic properties of TEX>$(Ru, Sn)(Sr, La)<_2$$EuCeCu_2$$O_{z}$ samples. We found that Sn substitution fur Ru causes a significant decrease of the volume fraction of ferromagnetic phase, as well as a decrease of the temperature where the ferromagnetic component is observed. La substitution for Sr leads to an increase of the magnetic ordering temperature with a moderate change of ferromagnetic component. The experimental results are discussed in conjunction with the structural data, transport properties and a possible change of oxygen content.

• Progress in Superconductivity and Cryogenics
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• v.17 no.4
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• pp.8-11
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• 2015

We studied on the visible emission of Cu-ion-doped perovskite hafnate $SrHfO_3$ (SHO:Cu) with the photo-excitation energy dependence. The polycrystalline SHO:Cu samples were newly synthesized in the solid state reaction method. From the X-ray diffraction measurement it was found that the crystalline structure of SHO:Cu is nearly identical to that of undoped $SrHfO_3$. Interestingly, the photoluminescence excitation (PLE) spectra change significantly with the emission energy, which is linked to the strong dependence of the visible emission on the photo-excitation energy. This unusual emission behavior is likely to be associated with the mixed valence states of the doped Cu ions, which were revealed by X-ray photoelectron spectroscopy. We compared our finding of tunable visible emission in the SHO:Cu compounds with the cases of similar materials, $SrTiO_3$ and $SrZrO_3$ with Cu-ion-doping.

• Korean Journal of Materials Research
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• v.13 no.12
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• pp.846-849
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• 2003

Doping effect of various ions in Bi-layered ferroelectric $SrBi_2$$Nb_2$$O_{9}$ (SBN) ceramics was studied. Undoped SBN ceramic and SBN ceramics doped with $Ba^{2＋}$, $Pb^{2＋}$,$ Ca^{2＋}$ , $Bi^{3＋}$ , $La^{3＋}$ , $Ti^{4＋}$ , $Mo^{6＋}$ , and $W^{6＋}$ ions were made by a solid state reaction. Dielectric constants were measured with temperature. Ferroelectric transition temperature decreased with $Pb^{2＋}$ , $Ba^{2＋}$ , $La^{3＋}$ doping, but the transition temperature increased with $Ca^{2＋}$ , $Bi^{3＋}$ , $Ti^{4＋}$, $Mo^{6＋}$ , or$ W^{6＋}$ ionic doping. These results show that the ion size plays an important role in the ferroelectricity of SBN ceramic.

• Korean Journal of Materials Research
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• v.14 no.8
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• pp.529-534
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• 2004

$Sr_{4}Al_{14}O_{25}$ was synthesized by solid state reaction with flux. $H_{3}BO_3$ was used to synthesize $SrO-Al_{2}O_{3}$ phosphor system as a flux. The effect of doping system such as Eu+Dy, Eu, and Ce on the luminescent properties of $Sr_{4}Al_{14}O_{25}$ was investigated. Both PL spectra of $Sr_{4}Al_{14}O_{25}$:Eu and $Sr_{4}Al_{14}O_{25}$:Eu+Dy excited at 390 nm showed greenish-blue emission at about 490 nm, while the emission wavelength was shifted to 400 nm by doping Ce. The reduction of $Eu^{3+}$ ions to $Eu^{2+}$ could be accomplished by the annealing process under $N_{2}^{+}$ vacuum atmosphere, and attributed to the emission at 490 nm. It is verified that $Sr_{4}Al_{14}O_{25}$:Eu phosphor is suitable for white LEDs became of a broad absorption band peaking at 390 nm.

• Progress in Superconductivity and Cryogenics
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• v.20 no.2
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• pp.24-28
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• 2018

To understand the effects of Cd substitution for Cu, $(Pb_{0.5}Cu_{0.5-x}Cd_x)Sr_2(Ca_{0.7}Y_{0.3})Cu_2O_z$ (x = 0 ~ 0.5) compounds were synthesized and the structural and superconducting properties of the compounds were characterized. Resistivity data revealed that superconducting transition temperature rises initially up to x = 0.25 and then decreases as the Cd doping content increases. Room-temperature thermoelectric power decreases at first up to x = 0.25 and then increases with higher Cd doping content, indicating that the change in $T_c$ is mainly caused by the change in the hole concentration on the superconducting planes by the Cd doping. The non-monotonic dependence of the lattice parameters and the transition temperature with Cd doping content is discussed in connection with the possible formation of $Pb^{+2}$ ions and the removal of excess oxygen caused by Cd substitution in the charge reservoir layer. A correlation between transition temperature and c/a lattice parameter ratio was observed for the $(Pb_{0.5}Cu_{0.5-x}Cd_x)Sr_2(Ca_{0.7}Y_{0.3})Cu_2O_z$ system.

• Progress in Superconductivity and Cryogenics
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• v.16 no.2
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• pp.33-35
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• 2014

We report here results of a study of superconductivity in the ($Ta_{1-x} Sn_x)Sr_2EuCu_2O_z$ system. We observe resistive superconducting transitions for the samples with x = 0.15-0.3, and the highest superconducting transition has been achieved for the sample with x = 0.2 which reveals onset $T_c$ of 43 K and zero-resistivity of 25 K. Thermoelectric power measurements indicate that Sn doping introduces holes into the system and thereby superconductivity can be achieved in the ($Ta_{1-x} Sn_x)Sr_2EuCu_2O_z$ system.

• Proceedings of the Materials Research Society of Korea Conference
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• 1996.05a
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• pp.35-35
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• 1996

• Journal of Sensor Science and Technology
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• v.18 no.1
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• pp.48-53
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• 2009

$Eu^{2+}$-doped ${SrAl_2}{O_4}$ and $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors have been synthesized by conventional solid state method. Photocurrent properties of $Eu^{2+}$ doped ${SrAl_2}{O_4}$ and $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors, in order to elucidate $Dy^{3+}$ co-doping effect, during and after ceasing ultraviolet-ray (UV) irradiation have been investigated. The photocurrent of $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors during UV irradiation was 4-times lower than that of $Eu^{2+}$-doped ${SrAl_2}{O_4}$ during UV irradiation, and 7-times higher than that of $Eu^{2+}$-doped ${SrAl_2}{O_4}$ after ceasing UV irradiation. The photocurrent results indicated that holes of charge carriers captured in hole trapping center during the UV irradiation and liberated after-glow process, and made clear that $Dy^{3+}$ of co-dopant acted as a hole trap. The photocurrent of ${SrAl_2}{O_4}$ showed a good proportional relationship to UV intensity in the range of $1{\sim}5mW/cm^2$, and $Eu^{2+}$-doped ${SrAl_2}{O_4}$ was confirmed to be a possible UV sensor.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.11
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• pp.550-554
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• 2001

$(Ba_{0.6}Sr_{0.4}Ca_x)TiO_3 + yAl_2O_3$ wt% (x=0.10, 0.15, 0.20, y=0~3.0) ceramics were fabricated by the mixed-oxide method, and their structural and dielectric properties were investigated with variation of composition ratio and $Al_2O_3$ doping content. As results of the X-ray diffraction and microstructure analysis, all BSCT specimens showed dense and homogeneous structure without presence of the second phase. The sintered density was decreased with an increase of $Al_2O_3$ doping content. The Curie temperature and relative dielectric constant at room temperature were decreased with increasing $Al_2O_3$doping content. The dielectric loss is minimum at BSCT doped with 1.5wt% $Al_2O_3$content. The tunability was decreased with increasing an Ca content and the BSCT(50/40/10) specimen doped with 2.0wt% $Al_2O_3$content showed the maximum value of 4.2%.

• Progress in Superconductivity and Cryogenics
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• v.2 no.1
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• pp.1-6
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• 2000

The effects of partial substitution of fluorine on physical properties were studied in Ag-sheathes tapes of $Tl_{0.8}Pb_{0.2}Sr_{1.8}Ba_{0.2} Ca_{2.2}Cu_3O_yF_x (0{\leq}x{\leq}1)$ nominal compositions. The tapes were prepared using the powder-in-tube method incorporating an in-situ reaction method. $CuF_2$ was used as a source of F. It was found that F-doping in Tl-1223 system resulted in a decrease in formation temperatire of Tl-1223 phase. and thus significantly deteriorated their superconducting properties. Such disadvantages seem to originate by the fromation of non-beneficial phases such as SrF2 in the early stage of the powder preparation process.