We have examined the co-doping effects of 1/2mol% NiO and 1/4mol% Cr2O3 (Ni:Cr=1:1) on the reaction,microstructure, and electrical properties, such as the bulk defects and the grain boundary properties, of ZnO-Bi2O3-Sb2O3 (ZBS;Sb/Bi=0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Ni,Cr-doped ZBS, ZBS(NiCr) varistors werecontrolled using the Sb/Bi ratio. Pyrochlore (Zn2Bi3Sb3O14), α-spinel (Zn7Sb2O12), and δ-Bi2O3 were detected for all ofcompositions. For the sample with Sb/Bi=1.0, the Pyrochlore was decomposed and promoted densification at lowertemperature by Ni rather than by Cr. A homogeneous microstructure was obtained for all of the samples affected by α-spinel.The varistor characteristics were not dramatically improved (non-linear coefficient, α=5~24), and seemed to formZni..(0.17eV) and Vo.(0.33eV) as dominant defects. From impedance and modulus spectroscopy, the grain boundaries werefound to have been divided into two types, i.e., one is tentatively assigned to ZnO/Bi2O3 (Ni,Cr)/ZnO (0.98eV) and the otheris assigned to a ZnO/ZnO (~1.5eV) homojunction.

Nickel oxide was doped with a wide range of concentrations (mol%) of Aluminum (Al) by solvothermal synthesis;single-phased nano powder of nickel oxide was generated after calcination at 900oC. When the concentration of Al dopant wasincreased, the reduced intensity was confirmed through XRD analysis. Lattice parameters of the synthesized NiO powder weredecreased after treatment of the dopant; parameters were increased when the concentration of Al was over the doping limit(5mol% Al). The binding energy of Ni2+ was chemically shifted to Ni3+ by doping Al3+ ion, as confirmed by the XPS analysis.The tilted structure of the synthesized NiO with 5mol% Al dopant and the polycrystalline structure of the Ni0.75Al0.25O wereobserved by HR-TEM analysis. The electrical conductivity of the newly synthesized NiO was highly improved by Al dopingin the conductivity test. The electrical conductivity values of the commercial NiO and the synthesized NiO with 5mol% Aldopant (Ni0.95Al0.05O) were 1,400s/cm and 2,230s/cm at 750oC, respectively. However, the electrical conductivity of thesynthesized NiO with 10mol% Al dopant (Ni0.9Al0.1O) decreased due to the scattering of free-electrons caused by the largenumber of impurity atoms; the electrical conductivity of Ni0.9Al0.1O was 545s/cm at 750oC.

Joining of NiO-YSZ to 316 stainless steel was carried out with B-Ni2 brazing alloy (3 wt% Fe, 4.5 wt% Si, 3.2 wt% B, 7 wt% Cr, Ni-balance, m.p. 971-) to seal the NiO-YSZ anode/316 stainless steel interconnect structure in a SOFC. In the present research, interfacial (chemical) reactions during brazing at the NiO-YSZ/316 stainless steel interconnect were enhanced by the two processing methods, a) addition of an electroless nickel plate to NiO-YSZ as a coating or b) deposition of titanium layer onto NiO-YSZ by magnetron plasma sputtering method, with process variables and procedures optimized during the pre-processing. Brazing was performed in a cold-wall vacuum furnace at . Post-brazing interfacial morphologies between NiO-YSZ and 316 stainless steel were examined by SEM and EDS methods. The results indicate that B-Ni2 brazing filler alloy was fused fully during brazing and continuous interfacial layer formation depended on the method of pre-coating NiO-YSZ. The inter-diffusion of elements was promoted by titanium-deposition: the diffusion reaction thickness of the interfacial area was reduced to less than 5 compared to 100 for electroless nickel-deposited NiO-YSZ cermet.

Thermoelectric power, dc conductivity, and the dielectric relaxation properties of La2NiO4.03 are reported in the temperature range of 77 K - 300 K and in a frequency range of 20 Hz - 1 MHz. Thermoelectric power was positive below 300K. The measured thermoelectric power of La2NiO4.03 decreased linearly with temperature. The dc conductivity showed a temperature variation consistent with the variable range hopping mechanism at low temperatures and the adiabatic polaron hopping mechanism at high temperatures. The low temperature dc conductivity mechanism in La2NiO4.03 was analyzed using Mott's approach. The temperature dependence of thermoelectric power and dc conductivity suggests that the charge carriers responsible for conduction are strongly localized. The relaxation mechanism has been discussed in the frame of the electric modulus and loss spectra. The scaling behavior of the modulus and loss tangent suggests that the relaxation describes the same mechanism at various temperatures. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with activation energy of ~ 0.106eV. At low temperature, variable range hopping and large dielectric relaxation behavior for La2NiO4.03 are consistent with the polaronic nature of the charge carriers.

WO3에 NiO를 첨가하여 제조한 후막형 시편의 미세구조와 전기적 성질에 대해 연구하였다. NiO 첨가에 따른 WO3의 결정립 성장이 억제되었고, 입도 분포도 균일하였으나 첨가량에 따른 결정립 크기 변화정도는 작았다. 산소 분압 감소로 WO3의 전도성은 증가하였고, NiO 첨가에 의해 고용한계 이하에서는 전도성이 증가하였고, 이상에서는 전도성이 감소하였다. 온도 증가에 따라 외인성 (extrinsic) 구간에서는 전도성 변화가 적었고, 고온의 진성 (intrinsic) 구간에서는 전도도가 급격히 증가하였으며, 이들의 중간 온도에서는 산소흡착에 따라 전도도가 감소하였다.

본 연구에서는 hexagonal-ferrite에서 NiO, CuO의 몰비와 B-Bi-Zn 첨가제에 따른 미세구조, 밀도 흡수율, 수축율, 주파수에 따른 투자율 등의 특성을 관찰하여 수 GHz대역의 고주파 침 인덕터용 재료로서의 가능성을 확인하고자 하였다. 투자율의 측정은 impedance analyzer 와 network analyzer를 이용하여 100kHz∼3GHz 대역까지 실시하였다. 특성의변화를 살펴본 결과 사용된 B-Bi-Zn 유리분말은 전극돠의 동시소결이 가능하게 보였으며, 복수투자율의 결과에 의하며, 1.8GHz까지는 그 값이 변화를 보이지 않고 일정하였고, 복소투자율의 허수값이 최고값에서 나타나는 공진주파수는 2 GHz 부근에서 관찰되었다.