• 한국세라믹학회지
• /
• 제27권3호
• /
• pp.361-368
• /
• 1990

The properties of the powder of ZrO2＋3m/o Y2O3 system prepared by co-precipitation method at the pH values of 7, 9, 10 and 11 were investigated. ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent. Zirconium hydroxide near by Zr(OH)4 structure showed more excellent crystallinity and lower formation temperature of tetragonal ZrO2. In the range of this study, cubic ZrO2 was not formed and stability of tetragonal ZrO2 prepared in the conditiion of pH 7 was most excellent. Average particle sizes and specific surface areas of tetragonal ZrO2 powders, prepared as calcining amorphous zirconium hydroxides at $600^{\circ}C$ for 1h, were 0.6-0.8${\mu}{\textrm}{m}$ and 45-70$m^2$/g, respectively.

• 한국자기학회지
• /
• 제27권4호
• /
• pp.129-134
• /
• 2017

합금 제조에 흔히 이용되는 기존의 용해, 응고, 열처리 등의 가공 공정으로 덩치 형태의 체심정방정 구조의 Fe-Co계 합금상을 합성하고, 그 결정학적, 자기적 특성을 조사하였다. $(Fe_{100-x}Co_x)_{1-y}C_y$ 합금에서 체심정방정 구조의 단일상(martensite)이 얻어지는 Co 및 C의 함량은 크게 제한되어, Co의 함량 x = 2.5, C의 함량 y = 0.062로 제한된 조성에서 체심정방정 구조의 단일상 합금이 얻어졌다. 합성된 조성 $(Fe_{97.5}Co_{2.5})_{0.938}C_{0.062}$인 체심정방정 구조의 단일상 합금의 정방성(tetragonality, c/a)은 1.05였으며, 이 합금의 결정자기 이방성 상수, $K_1$ 값은 순수 철(${\alpha}-Fe$)의 $K_1$ 값에 비하면 3.1배 정도 높은 $1.5{\times}10^5J/m^3$였다.

• 한국결정성장학회:학술대회논문집
• /
• 한국결정성장학회 2000년도 Proceedings of 2000 International Nano Crystals/Ceramics Forum and International Symposium on Intermaterials
• /
• pp.243-248
• /
• 2000

Effect of NiO addition on microstructure, stability of tetragonal phase and mechanical properties was investigated. (Y, Ni)-TZP solid solution was obtained by pressureless sintering. The fracture toughness was increased by solid solution of NiO. Neither reaction phase nor glassy phase was observed at the grain boundaries. From these results, it was determined that solid solution of NiO was destabilized tetragonal phase of Y-TZP. Y-TZP/Ni nanocomposite that contained nano-sized Ni particles was also fabricated by internal reduction method. Some evaluations and discussions were carried out for both (Y, Ni)-TZP solid solution and Y-TZP/Ni nanocomposite.

• 대한치과의사협회지
• /
• 제49권5호
• /
• pp.260-264
• /
• 2011

Zirconia ($ZrO_2$) is a crystalline dioxide of zirconium. Dental zirconia blocks for CAD/CAM are usually fabricated with powders of tetragonal zirconia polycrystals (TZP) stabilized with 3mol% yttria. Because of its mechanical properties similar to those of metals and color similar to tooth, it is evaluated to attain the two purposes at a time, strength and aesthetic in prosthetic dentistry. The ability of transformation of Y-TZP from tetragonal to monoclinic helps to prevent crack propagation and contributes the increase of strength and fracture toughness. Two different types of blocks, soft and hard, are used to prepare the zirconia frameworks. The fuzzy-sintered block is difficult in machining, so pre-sintered soft 3Y-TZP block is usually used to mill by computer aided machining.

• 한국세라믹학회지
• /
• 제25권5호
• /
• pp.488-494
• /
• 1988

Effects of MnO2 addition on themicrostructure, dielectric and piezoelectric properties of Rhombohedral, Tetragonal and Morphotropic phase boundary(MPB) in Pb(Ni1/3Nb2/3)O3-PbTiO3-PbZrO3 system were investigated and respectively the amount of MnO2 addition was 0, 0.2, 0.5, 1.0, 3.0wt%. In the tetragonal region, compared with the Rhombohedral and Morpotropic phase boundary, Mechanical quality factor(Qm), Curie temperature(Tc) and Dissipation factor were promoted by addition of MnO2. According to the results of the microstructure, dielectric and piezoelectric properties, the solid solution range of MnO2 addition in this system was 0.2-0.5wt%.

• 한국세라믹학회지
• /
• 제29권10호
• /
• pp.806-814
• /
• 1992

The aim of this study was to investigate the change in compressive strength, freacture behavior and degradation of piezoelectric properties with compressive cyclic loading in Pb(Zr, Ti)O3 of tetragonal, morphotropic phase boundary and rhombohedral composition. The highest compressive strength was found in rhombohedral composition. After poling treatment the strength increased by 8.4% and 6.5% in tetragonal and morphotropic phase boundary compositions respectively while changed little in rhombohedral. The increase of compressive strength after poling treatment is believed to be due to the internal stress around grain boundary by domain alginment toward electric field direction in the microstructures having tetragonality and the occurrence of domain switching to the direction perpendicular to electrical field during fracture. Fracture mode relatively change from transgranular to intergranular was observed in the large grain sized tetragonal and morphotropic phase boundary compositions before and after poling but the transgranular fracture mode always remained in the rhombohedral composition. From the X-ray diffractometer analysis the domains parallel to the electric field direction is known to undergo rearrangement during the cyclic loading into random direction that is responsible for the degradation of piezoelectric property.

• 한국세라믹학회지
• /
• 제31권8호
• /
• pp.829-834
• /
• 1994

The aim of this study is to investigate the changes in dielectric properties, Young's modulus and remnant compressive strength with compressive cyclic loading in PZT of tetragonal, MPB and rhombohedral composition. Higher relative dielectric constants appeared in the poled condition than the unpoled condition for all the compositions. After poling treatment remarkably higher relative dielectric constants were observed particularly in MPB, tetragonal compositions. Until five percent of the expected fatigue life was exhausted, the dielectric constant increased with compressive cyclic stress in MPB and rhombohedral while it remained nearly constant in tetragonal. During the subsequent compressive cyclic stress, dielectric constant decreased in all the three compositions. As the compressive cyclic stress is applied the change of Young's modulus was coincided with the change of remnant compressive strength.

• 디지털산업정보학회논문지
• /
• 제12권3호
• /
• pp.25-31
• /
• 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
• /
• 제45권3호
• /
• pp.139-141
• /
• 2008

The piezoelectric properties of tetragonal 0.88Pb$(Zn_{1/3}Nb_{2/3)O_3-0.12PbTiO_3$ single crystals are characterized along the <111> direction, which composed the engineering domain configuration in the tetragonal phase. The <111>-oriented crystal possessed smaller $d_{33}$ values compared to the crystal along the <001> spontaneous polarization direction. Based on phenomenological theory, it is shown that the engineering domain configuration does not enhance the piezoelectric constant in tetragonal 0.88Pb$(Zn_{1/3}Nb_{2/3)O_3-0.12PbTiO_3$ single crystals. In addition, the electrostrictive coefficients of $Q_{12}=-0.03706m^4/C^2,\;Q_{11}=0.10765m^4/C^2,\;and\;Q_{44}=0.02020m^4/C^2$ of tetragonal 0.88PZN-0.12PT single crystals were calculated.

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