• Progress in Superconductivity
• /
• 제13권3호
• /
• pp.163-168
• /
• 2012

The effects of Ta substitution on the superconducting and magnetic properties of the $(Ru_{1-x}Ta_x)Sr_2(Gd_{1.4}Ce_{0.6})Cu_2O_z(0{\leq}x{\leq}0.5)$ system have been investigated. The X-ray diffraction measurements indicate that the Ta ion replaces Ru sites up to x = 0.4. It is found that the Ta substitution for Ru significantly reduces the weak-ferromagnetic component of the field-cooled magnetic susceptibility without an appreciable change of room temperature thermopower at lower Ta doping level below x = 0.2. The resistive transition temperature tends to decrease monotonically from 27 K for the x = 0 sample to 16 K (9 K) for the x = 0.4 (x = 0.5) sample. These results suggest that superconductivity of the $(Ru_{1-x}Ta_x)Sr_2(Gd_{1.4}Ce_{0.6})Cu_2O_z$ compound is not significantly affected by the magnetic state of the Ru sublattice. The experimental results are discussed in connection with previous reports on the effects of Nb substitution.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1996년도 하계학술대회 논문집 C
• /
• pp.1621-1623
• /
• 1996

The dielectric and polarizable properties of 0.85Pb$Mg_{1/3}Nb_{2/3}$)$O_3$-$0.125PbTiO_3$-$0.25BaTiO_3$ Ceramics have been investigated as a addition of the amount of $La_{2}O_{3}$($0{\leq}x{\geq}0.05$). The Temperature-dependant electrostictive characteristics of 0.85PMN-0.125PT-0.25BT relaxor ferroelectic system were improved by enhencing the extent of the diffuse phase transition(DPT). This was achieved using PMN-PT-BTceramics by the partial substitution of La at the Pb site. The curie temperature and the maximum dielectic permittivity decreased by substituting $La_{2}O_{3}$ and the electic field-related hysteresis phenomena decreased with increasing $La_{2}O_{3}$ substitution amount. It is showed decreasing in induced strain for electric field with increasing $La_{2}O_{3}$ substitution.

• 한국전기전자재료학회논문지
• /
• 제24권8호
• /
• pp.627-631
• /
• 2011

[ $[Li_{0.04}(Na_{0.54}K_{0.46})_{0.96}](Nb_{1-0.04-X}TaxSb_{0.04})O_3$ ]lead-free piezoelectric ceramics have been prepared by normal sintering at $1,100^{\circ}C$ for 5 h. X-ray diffraction analysis indicated that specimens demonstrate orthorhombic symmetry when $Ta\leq5$ mol%. While transforming into tetragonal symmetry when $x\geq20$ mol%. These suggest that the orthorhombic and tetragonal phases co-exist in the ceramics with 5 mol% $cm^3$. As the result of SEM images, the grain growth was decreased with the increase of Ta substitution. The ceramics become 'softening', leading to improvements in $k_p$, $\varepsilon_r$ and $d_{33}$, but a decrease in $Q_m$. Excellent properties of $k_p$= 0.46, $d_{33}$= 293 pC/N, ${\varepsilon}_r$= 1,583 and Tc= $340^{\circ}C$ were obtained when Ta= 15 mol%.

• 한국전기전자재료학회논문지
• /
• 제26권3호
• /
• pp.204-208
• /
• 2013

In this study, $KNbO_3$-substituted (Li,Na,K)(Nb,Sb,Ta)$O_3$ ceramics were investigated to develop Pb-free composition ceramics for multilayer actuator and energy harvester applications. The X-ray diffraction analysis indicated that all samples were pure perovskite phase and no secondary phase was found. A tetragonality as a function of $KNbO_3$ substitution showed the maximum value at 1.5 mol% $KNbO_3$ and then decreased. The SEM image analysis showed the maximum grain size of $3.14{\mu}m$ at 1.5mol% $KNbO_3$. In the composition ceramics with 1.5 mol% $KNbO_3$ sintered at $1,100^{\circ}C$, excellent properties of density= 4.75 $g/cm^3$, electromechanical coupling factor ($k_p$)= 0.50 and piezoelectric constant($d_{33}$)= 290 pC/N were obtained, respectively, suitable for piezoelectric actuator and energy harvester applications.

• 한국재료학회지
• /
• 제29권3호
• /
• pp.150-154
• /
• 2019

This study investigates the effect of MnO2 and CuO as acceptor additives on the microstructure and piezoelectric properties of $0.96(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}Nb_{0.93}Sb_{0.07}O_3-0.04BaZrO_3$, which has a rhombohedral-tetragonal phase boundary composition. $MnO_2$ and CuO-added $0.96(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}Nb_{0.93}Sb_{0.07}O_3-0.04BaZrO_3$ ceramics sintered at a relatively low temperature of $1020^{\circ}C$ show a pure perovskite phase with no secondary phase. As the addition of $MnO_2$ and CuO increases, the sintered density and grain size of the resulting ceramics increases. Due to the difference in the amount of oxygen vacancies produced by B-site substitution, Cu ion doping is more effective for uniform grain growth than Mn ion doping. The formation of oxygen vacancies due to B-site substitution of Cu or Mn ions results in a hardening effect via ferroelectric domain pinning, leading to a reduction in the piezoelectric charge coefficient and improvement of the mechanical quality factor. For the same amount of additive, the addition of CuO is more advantageous for obtaining a high mechanical quality factor than the addition of $MnO_2$.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2006년도 추계학술대회 논문집 Vol.19
• /
• pp.208-209
• /
• 2006

Sinterability and microwave dielectric properties of the $Zr1-x(Zn_{1/3}Nb_{2/3})xTiO_4$(x=4, 6) system ceramics have been investigated as functions of zinc-borosilicate(ZBS) glass contents and amount of $Zn_{1/3}Nb_{2/3}O_2$ substitution with a view to applying the composition to LTCC technology. The addition of 25 wt% ZBS glass ensured successful sintering below $925^{\circ}C$. With increasing ZBS glass and $Zn_{1/3}Nb_{2/3}O_2$ contents increased dielectric constant and sinterability but addition ZBS glass decreased the quality factor significantly due to the formation of an excessive liquid and second phases. The sintered $Zr4(Zn_{1/3}Nb_{2/3})6TiO_4$ system ceramics at $925^{\circ}C$ with 25 wt% ZBS glass demonstrated 27.7 in dielectric constant (${\varepsilon}_r$), 3,850 m quality factor($Q{\times}f_0$), and +6 ppm/$^{\circ}C$ in temperature coefficient of resonant frequency($\tau_f$).

• 한국재료학회지
• /
• 제13권5호
• /
• pp.317-322
• /
• 2003

Bismuth layered structure ferroelectric thin films, $Bi_4$$Ti_3$$O_{12}$ / (BTO) and Nb-doped BTO (BTN) were prepared on the Pt(111)/Ti/$SiO_2$/Si(100) substrates by a sol-gel route. We investigated the Nb-doping effect on the grain orientation and ferroelectric properties. $Nb^{5＋}$ ion substitution for $Ti^{4＋}$ ion in perovskite layers of BTO decreased the degree of c-axis orientation and increased the remanent polarization (2Pr). The fatigue resistance of Nb-doped BTO thin film was shown to be superior to that of BTO, and the leakage current of Nb-doped BTO thin film was decreased about 1 order of magnitude compared with BTO. The improvement of ferroelectric properties with $Nb^{5＋}$ doping in BTO could be attributed to the changes in space charge densities and grain orientation in the thin film.

• 한국자기학회지
• /
• 제5권1호
• /
• pp.38-41
• /
• 1995

$\alpha$-Fe를 주상으로 하는 새로운 Nd-Fe-B계 합금을 개발하기 위하여 Nd 함유량을 4at.%로 고정시킨 Nd-Fe-B 초미세결정립합금의 제조 및 자기특성이 조사되었다. 급속응고법으로 제조된 $Nd_{4}Fe_{85.5}B_{10.5}$ 비정질합금은 결정화하여 $\alpha$-Fe 기지상에 $Nd_{2}Fe_{14}B$이 형성되나 자기특성${_{i}H_{c}=95.5kA/m(1.2kOe),\;Br=1.2T}$은 열화된다. Nb 및 Cu를 첨가한 $Nd_{4}Fe_{82}B_{10}Nb_{3}Cu_{1}$ 합금은 $\alpha$-Fe 결정립미세화(<30nm)로 보자력이 207kA/m(2.6 kOe)로 증가하나 잔류자화는 개선되지 않았다. 이 합금조성에 8at.% Co 첨가는 결정립을 더욱 미세화시키며 자기특성을 개선 시킨다. 최적열처리조건에서 $Nd_{4}Fe_{74}Co_{8}B_{10}Nb_{3}Cu_{1}$ 합금의 잔류자화, 보자력 및 최대에너지적이 각각 1.34 T, 219 kA/m (2.75kOe) 및 $95.5kJ/m^{3}$(12MGOe) 이다.

• 한국재료학회지
• /
• 제6권12호
• /
• pp.1155-1161
• /
• 1996

Pb(In1/2Nb1/2)O3 (PIN)세라믹스에서 Pb+2이온 대신에 Ca+2, Sr+2, Ba+2 이온을 부분적으로 치환하여 상합성 과정 및 유전특성을 조사하였다. 페로브스카이트 PIN을 얻기위한 최적조건을 도출하기위하여 하소, 치환 이온의 종류 및 그량, 소결민돌, 유전특성의 관점에서 관찰하였다. 페로브로스카이트 PIN상을 합성하기 위해서는 Ba+2이온의 치환이 가장 효과적이었다.

• Journal of Magnetics
• /
• 제4권1호
• /
• pp.10-12
• /
• 1999

We report the salient features of the magnetic properties of amorphous$ Fe_{84-x}Nb_7B_{8+x}Cu_1$ (x=0, 1, 4) alloys. The study of dc-magnetization properties and the ac-susceptibility was carried out. The temperature dependence of the magnetization follows the predictions of spin wave excitations with long wavelengths. Especially, the addition of boron modifies the magnetic properties: the spin wave stiffness increases from 56.8 to 65.7 meV$\AA$2 and Curie temperature increases from 298 K to 352 K. This result indicates a magnetic hardening of the exchange interaction by higher exchange energy. Thus, the substitution of iron by boron favours the increase of magnetic order in this system.