• 한국전기전자재료학회논문지
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• 제18권9호
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• pp.821-826
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• 2005

In this paper, in order to develop lead-free piezoelectric ceramics, $(Li_{0.04}Na_{0.44}K_{0.52)(Nb_{0.86}Ta_{0.10}Sb_{0.04})O_3$ ceramics were fabricated with the variation of calcination temperature and sintering temperature. The ceramics couldn't be sintered at temperature less than $1110^{\circ}C$ and showed the highest density at calcination temperature of $800^{\circ}C$. Crystal structure of the ceramics showed pseudo-tetragonal phase. At the calcination temperature of $800^{\circ}C$ and sintering temperature of $1110^{\circ}C$, the optimal values of $density=4.64g/cm^3,\;kp=0.45,\;{\varepsilon}r=1336,\;d_{33}=254pC/N\;and\;Tc=335^{\circ}C$ were obtained.

• 한국세라믹학회지
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• 제41권2호
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• pp.111-117
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• 2004

고순도 3Y-TZP에 알루미나를 0.3∼l.2wt%까지 첨가하여 attrition milling을 하고 slip-casting하여 시료를 제조하였다. 1390∼151$0^{\circ}C$까지 열처리하여 소결체의 소결특성을 기제적 물성과 미세구조 분석을 통하여 확인하였다. XRD를 이용하여 monoclinic-ZrO$_2$의 생성량을 정량적으로 확인하였으며, 147$0^{\circ}C$ 이장에서 열처리한 시료의 경우 m-ZrO$_2$의 생성으로 밀도의 저하를 보였으며, 비정상 입자성장을 유발하여 경도가 저하되었다. 알루미나의 첨가량이 0.9wt% 미만, 열처리 온도143$0^{\circ}C$에서 microhardness가 1360Hv 이상의 소결체를 제조할 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.589-589
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• 2012

Indium sulfide thin films have been grown onto glass substrates using radio frequency magnetron sputtering at room temperature. The as-deposited film were annealed in nitrogen atmosphere at different temperatures of 100, 200, 300, 400 and $500^{\circ}C$ with an 1 h annealing time. The effect of annealing temperature on composition, structure, morphology and optical properties of the as-grown In2S3 films has been studied. The XRD results indicate that the as-deposited films are composed by a mixture of both cubic ${\alpha}$ and ${\beta}$ crystalline phases, with some fraction of tetragonal phase. The thermal annealing on the films produces the conversion of the cubic crystalline phases to the tetragonal ${\beta}$ one and a crystalline reorientation of the latter phase. The surface morphological analysis reveals that the films grown at $300^{\circ}C$ have an average grain size of ~ 58 nm. These films show a S/In ratio of 0.99. The optical band gap is found to be direct and the films grown at $300^{\circ}C$ shows a higher optical transmittance of 80% and an energy band gap of 2.52 eV.

• 한국전기전자재료학회논문지
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• 제19권8호
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• pp.707-711
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• 2006

ZnO was doped up to 0.3 wt% for improving the electrical properties of lead-free $[Li_{0.04}(Na_{0.44}Ko_{0.52})-(Nb_{0.86}\;Ta_{0.10}\;Sb_{0.04})]O_3$ piezoelectric ceramics. The ceramics were fabricated with the conventional sintering processes. Crystal structure of the samples was tetragonal phase regardless of ZnO amount. However, the piezoelectric properties were varied with the ZnO amount. The electro-mechanical coupling factor $(k_p)$ was with the ZnO amount up to 0.2 wt% but decreased with the further addition. the maximum value of $k_p$ was 0.475. Density, piezoelectric charge constant and relative dielectric constant was also showed maximum value at 0.2 wt%. The maximum values are $4.75g/cm^3$, 275 pC/N, 1403, respectively. In contrast, the mechanical quality factor $(Q_m)$ was not varied with increasing the ZnO addition up to 0.2 wt% but rapidly increased at 0.3 wt%.

• Bulletin of the Korean Chemical Society
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• 제13권6호
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• pp.605-612
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• 1992

Chromium oxide/zirconia catalysts were prepared by dry impregnation of powdered $Zr(OH)_4$ with ($NH_4$)$_2$CrO$_4$aqueous solution. The characterization of prepared catalysts was performed using FTIR, XPS, XRD and DTA methods, and by the measurement of surface area. The addition of chromium oxide to zirconia shifted the transitions of $ZrO_2$ from amorphous to tetragonal phase and from tetragonal to monoclinic phase to higher temperature due to the strong interaction between chromium oxide and zirconia, and the specific surface area of catalysts increased in proportion to the chromium oxide content. Since the $ZrO_2$ stabilizes supported chromium oxide, chromium oxide was well dispersed on the surface of zirconia, and ${\alpha}$-$Cr_2O_3$ was observed only at the calcination temperature above 1173 K. Upon the addition of only small amount of chromium oxide (1 wt% Cr) to $ZrO_2$, both the acidity and acid strength of catalyst increased remarkably, showing the presence of two kinds of acid sites on the surface of $CrO_x$/$ZrO_4$-Bronsted and Lewis.

• Journal of Magnetics
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• 제1권2호
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• pp.82-85
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• 1996

Magnetic properties and microstructures of melt spun misch metal-ferroboron alloys were investigated. The major phase is the tetragonal (rare earth)$_2Fe_{14}B$ phase. Magnetic properties showed coercivity of 5.6 kOe, remanence of 7.85 kG, and so energy product 8.9 MGOe. Microsturctures in optimum properties showed that matrix was composed of Ce-rich phase while second phase La-rich-oxygen phase with less amount of Fe element than matrix, and triple junction with La-rich phase contrary to matrix.

• Advances in materials Research
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• 제9권4호
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• pp.323-335
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• 2020

This article reviews findings and progresses in the past decade on manganese-aluminium (MnAl) based magnets as the interest has been revived to fulfill their potential as commercial magnets. The challenges in developments of these rare-earth-free magnets are to acquire a high remanence and coercivity from the ferromagnetic τ-phase in MnAl alloys. To this end, the phase transformation to this τ-MnAl with L10 body centered tetragonal structure has been promoted by a variety of methods and a few percents of carbon (C) is often added to prevent the phase decomposition. Magnetization and coercivity are not only influenced by the phase composition but also the microstructure. The fabrication processes and factors affecting the phase and microstructure are therefore covered. Finally, the productions of bulk MnAl magnets are addressed.

• 한국세라믹학회지
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• 제22권1호
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• pp.40-46
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• 1985

The effect of calcining temperature ranged from $700^{\circ}C$ to 110$0^{\circ}C$ on sintering characteristics of morphotropic $Pb(Zr_{0.53}Ti_{0.47})O_3 doped with $Nb_2O_5$ has been investigated. The ratio of sintered grain size to calcined grain size decreased as the calcining temperature increased. The hardness as well as the sintered density of the samples reached a maximum at about 90$0^{\circ}C$. The X-ray diffraction pattern of the sintered sample showed both tetragonal and rhombohedral phases. The tetragonal phases intensity increased with the calcining temperature going through a maximum at about 90$0^{\circ}C$ while the rhombohedral phase intensity remained uneffected. The both intensity were about the same at 90$0^{\circ}C$ The dielectric constant of the sintered samples reached a maximum um while the dielectric dissipation factor showed a minimum at the calcining temperature of about 100$0^{\circ}C$.

• 한국세라믹학회지
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• 제25권4호
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• pp.321-328
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• 1988

The sintering phenomena, electrical resistivity, dielectric and piezoelectric properties of lead titanate ceramics modified by the partial substitution of La for Pb and Mn for Ti, (Pb1-1.5xLax)(Ti1-yMny)O3 ceramics, have been investigated. In (Pb1-1.5xLax)(Ti1-yMny)O3 system, with increasing lanthanum content, the realtive bulk density increased, but the Curie point and tetragonality (c/a) decreased. The tetragonal-to-cubic phase transition boundary existed in the range of 0.20

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1991년도 추계학술대회 논문집
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• pp.20-23
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• 1991

In this study, 0.05Pb(Mn$\_$1/3/Nb$\_$2/3/)O$_3$+ 0.95Pb(Zr/Ti)O$_3$+x[wt%]Cr$_2$O$_3$piezoelectric ceramics were fabricated by Hot-press method, and its structural, dielectrical, piezoelectrical properties, temperature stability and aging characteristics were investigated. Among the MPB and tetragonal compositions, the specimens with 0.2, 0.3 and 0.4 [wt%] Cr$_2$O$_3$ additive amount had the poisson ratio more than 1/3. At tetragonal phase, the aging was small, and the temperature stability was improved by Cr addition. The specimen most suitable to the HF device substrate was the one with the composition of 47/53 (Zr/Ti) an 0.4 [wt%] Cr$_2$O$_3$addition.