• 한국세라믹학회지
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• 제21권3호
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• pp.239-244
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• 1984

The effect of tetragonal $ZrO_2$ phase on the mechanical behavior in 7 mole% calcia partially stabilized zirconia has been studied. The $ZrO_2$ powder containg 7 mole% CaO prepared by Hot Petroleum Drying Method calcined at 80$0^{\circ}C$ for 1 hour was nearly 100% tetragonal but as the calcining temperature increased certain amount of monoclinic phase appeared. The sintered specimen at 1$700^{\circ}C$ for 5 hours was aged at 130$0^{\circ}C$ for 0, 24, 48, 72 hours. X-ray diffraction data showed that in the aged specimen monoclinic tetragonal and cubic phase coexisted. The Kc value of aged specimen for 48 hr was about 4.5MN/m3/2 much greater than unaged sample. But aged for 72 hr the KiC value was decreased. The increasing of toughness in PSZ is based on the Stress-Induced Phase Transformation that is metastable tetra-gonal $ZrO_2$ changes t stable monoclinic phase within the stress field of crack and the mechanical fracture energy absorption is occured But in this case due to certain amount of tetragonal phase transformed to monoclinic phase during cooling the microcrack effect by transformation also considered. Trerefore both Stress-Induced Phase Transformation and inclusion induced microcracking effect contrbute to the increase of fracture toughness of 7 mole% CaO-$ZrO_2$ containing monoclinic and tetragnola phase simulataneously.

• 한국재료학회지
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• 제9권8호
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• pp.854-857
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• 1999

Fe-Se-Te계(FeSe(sub)1-xTe(sub)x, x=0.2, 0.5, 0.8)의 특성을 X-선 회절법 및 Mossbauer 분광법에 의해 조사하였다. 결정구조는 세 시료 모두 주된 tetragonal PbO 구조와 hexagonal NiAs 구조가 일부 혼합된 형태를 보였으며 x=0.5의 경우 tetragonal 구조의 격자상수 값은 a=3.795$\AA$, c=5.896$\AA$ 이며 c/a=1.55로 나타났다. 다양한 온도변화에 의해 측정된 Mossbauer 스펙트럼은 전체 시료 모두 초미세 자기구조를 갖지 않는 강한 이중선(doublet)이 관측되었다. 조성 및 온도변화에 대해 뚜렷한 선형(line shape)의 변화는 관측되지 않았으나 결합상태에 약간의 변화를 보였다. 이성질체 이동(isomer shift)값과 사중극자 분열(quadrupole splitting)값 및 온도의존성을 분석한 결과 Fe는 low spin이 +2가 상태로 존재하며 강한 공유 결합상태임을 알 수 있었다. x=0.8의 경우 이성질체 이동값의 온도변화는 제2차 도플러 효과(second order Doppler effect)의 영향인 것으로 나타났다.

• 한국진공학회지
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• 제2권2호
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• pp.220-226
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• 1993

Bridgman 방법으로 성장된 $TlGa_xIn_{1-x}Se_2$ 단결정의 격자상수와 energy gap의 성분의존성을 조사하였다. $TlGa_xIn_{1-x}Se_2$ solid solution의 불연속 특성이 tetragonal과 monoclinic 구조를 가진 0.25$0.0{\leq}X{\leq}0.25$)로부터 monoclinic 구조($0.65{\leq}X{\leq}1.0$)로 변하는 구조적 상전이가 이 성분영역에서 관측되었다. $TlGaSe_2$ 단결정의 energy gap과 유전상수의 온도의존성으로부터 각각 1차 및 2차 상전이에 상당하는 107 K와 120 K에서 변칙특성을 발견하였다.

• 한국결정성장학회지
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• 제25권4호
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• pp.160-165
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• 2015

Lead-free piezoelectric materials have been actively studied to substitute for conventional PZT based solid solution, $Pb(Zr_xTi_{1-x}O_3)$, which occurs unavoidable PbO during the sintering process. Among them, Bismuth Sodium Titanate, $Na_{0.5}Bi_{0.5}TiO_3$ (abbreviated as NBT) based solid solution is attracted for the one of excellent candidates which shows the strong ferroelectricity, Curie temperature (Tc), remnant polarization (Pr) and coercive field (Ec). Especially, the solid solution of rhombohedral phase NBT with tetragonal perovskite phase has a rhombohedral - tetragonal morphotropic phase boundary. Modified NBT with tetragonal perovskite at the region of MPB can be applied for high frequency ultrasonic application because of not only its low permittivity, high electrocoupling factor and high mechanical strength, but also effective piezoelectric activity by poling. In this study, solid state ceramic processing of NBT and modified NBT, $(Na_{0.5}Bi_{0.5})_{0.93}Ba_{0.7}TiO_3$ (abbreviated as NBT-7BT), at the region of MPB using 7 % $BaTiO_3$ as a tetragonal perovskite was introduced and the structure between NBT and NBT-7BT were analyzed using rietveld refinement. Also, the ferroelectric and piezoelectric properties of NBT-7BT such as permittivity, piezoelectric constant, polarization hysteresis and strain hysteresis loop were compared with those of pure NBT.

• 한국세라믹학회지
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• 제21권2호
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• pp.149-155
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• 1984

The effect of $ZrO_2$ dispersed phase on the mechanical properties in $Al_2O_3$-$ZrO_2$system has been studied. There are both metastable tetragonal phase and stable monoclinic phase of $ZrO_2$particles diespersed in Al2O3 matrix at room temperature. Metastable tetragonal $ZrO_2$ changes to the stable monoclinic structure within the stress field of the crack. And microcracks are formed by the expansion of $ZrO_2$during the tetragonal-monoclinic transformation on cooling. Therefore stress-induced phase transformation and inclusion-induced microcracking contribute to the mec-hanical properties of $Al_2O_3$-$ZrO_2$system. Sintered composites containing 10m/o $ZrO_2$ yield KiC values of 6.5MN/$m^{3/2}$ much greater than that of pure $Al_2O_3$ This increase results from microcrack extension and stress-induced phase transformation absor-bing energy by crack propagation. Flexural strength of composites is decreased considerably in comparison with pure $Al_2O_3$ This decrease results from microcrack as a crack former and higher porosity than pure $Al_2O_3$.

• 한국잠사곤충학회지
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• 제17권2호
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• pp.101-118
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• 1975

가잠에 있어서 세포질 다각체 바이러스의 병원성 및 이형 바이러스 접종에 의한 유발 간섭현상을 구명하기 위하여 현장여품종인 잠103$\times$잠104의 원종과 교잡종에 있어서 육각형 및 사각형 세포질다각체 바이러스의 병원성 이형 세포질다각체 바이러스 접종에 의한 잠재성 바이러스의 활성화 및 활성화된 세포질다각체 바이러스와 접종한 세포질다각체 바이러스 사이의 간섭현상을 조사한 결과는 다음과 같다. 1. 세포질다각체 바이러스의 병원성 1) 가잠의 원종 (잠103, 잠104) 및 교잡종(잠103$\times$잠104)에 있어서 육각형 세포질다각체 바이러스의 병원성은 상호간에 고도의 유의성이 있어 교잡종이 가장 낮은 발병률을 보였고 일본종이 중간을 나타냈으며 중국종이 가장 높은 발병률을 보였다. 사각형 세포질다각체 바이러스에서도 유의성을 나타내어 있었으나 교잡종과 일본종이 같은 수준이고, 일본종과 중국종이 같은 수준이었으며, 교잡종과 중국종 사이에는 유의성이 있었다. 2) 접종령기에 따르는 병원성은 육각형 및 사각형 세포질다각체 바이러스가 다같이 고도의 유의성이 있었으며 2령기잠의 접종이 4령기잠이 접종보다 발병률이 높았다. 3) 접종된 병원체의 농도에 있어서 육각형 및 사각형 세포질다각체 바이러스의 병원성은 다같이 고도의 유의성이 있었으며, 농도가 높을수록 병원성이 높았다. 2. 이형 바이러스 접종에 의한 유발 및 간섭현상 1) 원종 및 교잡종에 있어서는 교잡종보다 원종에서 유발률이 높았으며 원종에서는 일본종보다 중국종에서 유발률이 높았다. 2) 접종 령기에 있어서는 2령기잠 접종이 4령기잠 접종보다 유발률이 높았다. 3) 사각형 세포질다각체 바이러스의 경구접종에 의한 육각형 세포질다각체 바이러스이 활성화 정도는 저농도에서 높았으며 고농도에서는 매우 낮았다. 4)육각형 세포질다각체 바이러스의 경구접종에 의한 사각형 세포질다각체 바이러스의 활성화 정도는 저농도에서는 매우 낮았으며 고농도에서는 전혀 나타나지 않았다. 5) 혼합감염은 2령기잠의 접종이 4령기잠의 접종보다 높았으며 4.2$\times$$10^{6}$/ml 농도에서 가장 높았다. 6)2령기잠에 사각형 세포질다각체 바이러스를 접종할 경우 저농도에서는 활성화한 육각형 세포질다각체 바이러스가 접종한 사각형 세포질다각체 바이러스가 활성화한 육각형 세포질다각체 바이러스를 간섭하는 것으로 생각된다. 또한 4.2$\times$$10^{6}$/ml 농도를 중심으로 개체 안에서의 육각형과 사각형 세포질다각체 바이러스 사이의 간섭현상이 평형상태를 이루는 것으로 생각된다.

• 디지털산업정보학회논문지
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• 제12권3호
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• pp.25-31
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• 2016

Mechanical properties of Y2O3-containing tetragonal ZrO2 polycrystals(Y-TZP) were investigated. Several additives were used to modify the hardness and fracture toughness of Y-TZP. The effects of these individual additives were discussed and their interactions were also analysed. Each additive, such as CoO, Fe2O3, MnO2 was found to deteriorate the mechanical properties of Y-TZP when it was used singly. But the fracture toughness of Y-TZP was significantly improved when these additives and Al2O3 were added in combination at a certain ratio. The addition of CoO, Fe2O3 and MnO2 into Y-TZP resulted in the more complex behavior of fracture toughness and hardness. The specimen with 1.5 wt%-Fe2O3, 3.0 wt% -Al2O3 and 1.5 wt%-CoO showed the monoclinic to tetragonal phase ratio of 18% and the highest toughness of $10.8MPa{\cdot}m1/2$ with Vickers hardness of 1201 kgf/mm2. However, the toughness decreased as the ratio increased and macrocracks developed beyond the ratio of 25%. Sample No. 16 is improved high Physical and Mechanical Properties.

• 한국세라믹학회지
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• 제34권12호
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• pp.1254-1260
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• 1997

Influence of applied electric field on the low temperature degradation of 3 mol% YaO3 stabilized tetragonal zirconia polycrystals(3Y-TZP) was investigated using X-ray diffractometry of specimens aged under the dc field of 1.1 kV/mm in silicone oil both of 12$0^{\circ}C$-21$0^{\circ}C$. After the aging, the tetragonal to monoclinic phase transformation was observed only on the specimen surface of 3Y-TZP faced to the anode. This indicated that the surface was overcrowded with oxygen ions as a result of diffusion of oxygen vacancies toward the cathode-sided surface. To elucidate an influence of the applying time of the electric field on the extent of the degradation of 3Y-TZP in air, specimens were aged fore 0-2 hours under the electric field in the oil bath of 12$0^{\circ}C$ and then subsequently aged for 3h at 22$0^{\circ}C$ in air. The longer the specimens were aged under the field, the more extensive the transformation to the monoclinic phase was on the specimen surface faced to the cathode, probably originated from a high diffusion rate of oxygen ions due to a steep oxygen vacancy concentration gradient.

• 한국세라믹학회지
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• 제26권5호
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• pp.719-727
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• 1989

By using commercial zirconia powder CeO2-ZrO2 ceramics containing 8~16mol% CeO2 was made by heat treatment at 1350~155$0^{\circ}C$ for 1~10hr. The minimum amount of CeO2 for obtaining complete tetragonal phase was 12mol%, and in the tetragonal phase region fracture toughness of Ce-TZP was decreased with increasing CeO2 content and the maximum value was obtained when 12mol% CeO2 was added. The bending strength goes through maximum at 14mol% CeO2. Fracture mode of Ce-TZP transformed from intergranular to transgranular fracture with increasing CeO2 content, so the morphology of fracture surface of 16mol% Ce-TZP was wholly transgranular and this tendency was independent on grain size. The crystal structure of the 12mol% Ce-TZP was monoclinic with fringes along the grain boundaries which are lying in the particular plane from the TEM observation. The chemical composition of the sintered body was homogeneous as a whole and some amorphism or air pocket was observed at the triple junction.

• 한국세라믹학회지
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• 제31권2호
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• pp.155-160
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• 1994

PZT ceramics substituted by La3+ and Nd3+ were fabricated according to the formula: [Pb1-x(La or Nd)x][Zr0.58Ti0.42]1-x/4$\square$x/4O3(x=0.00, 0.02, 0.05, 0.08, 0.15, 0.20). The crystal structure and microstructure were investigated by XRD and SEM. It was observed that the phase transitions among rhombohedral, tetragonal, and cubic symmetry occured as the substitutional quantity increased. Dielectric constant, dissipation factor and piezoelectric coefficient (d33), of each sample were measured. The dielectric properties were changed as the substitutional quanity of rare earth ion increased. These changes could be explained by crystal structure and compositional fluctuaction. Its d33 was higher at tetragonal region near to phase boundry between rhombohedral and tetragonal, which was explained by reorientation of domain wall.