In this paper, the failure mechanism of PTC heater were examined closely by failure analysis and based on it, accelerated life test were conducted. Finally, life distribution and acceleration model were established. The failure mechanism of PTC heater such as crack, increase of resistance due to heating were identified. Two acceleration factors such as temperature, humidity were chosen with two levels each and accelerated life test were done. Life distribution were identified as Weibull distribution with shape parameter 5.4 and Temperature-Humidity model was fitted as an acceleration model.

Nano-size BaTiO3 powder was synthesized by relatively simple hydrothermal reaction method. Finely dispersed Ti hydroxide precursor was first precipitated using Ti(SO4)2 and NaOH solution by applying ultrasonic power and washed thoroughly to remove SO4 2- and Na+ ion. Then hydrothermal reaction was done at 160℃ for 6 hrs using solution prepared by washed Ti hydroxide precursor slurry and Ba(OH)2ㆍ8H2O with Ti:Ba mole ratio of 1:1. 200 ~ 500 nm size and uniform size distributed BaTiO3 powder was synthesized by relatively low temperature and simple process.

BaTiO3 nano powder can be synthesized by hydrate salt method at 120℃ in air. Decreasing the thickness of thick film, the nano dielectric particle is needed in electronic ceramics. However, the synthesis of BaTiO3 nano particle at low temperature in air and their mechanism were not reported enough. And ultrasonic treatment can be tried because of low temperature process in air. Therefore, in this study, the BaTiO3 nano powder was synthesised with the synthesis time and ultrasonic treatment at120oC in air. In the synthesis process, the effects of process were evaluated. From the experimental observation, the synthesis mechanism was proposed. The homogeneous BaTiO3 particle was synthesized by KOH salt solution at 120℃ for 1hour. It was conformed that the ultrasonic treatment effected on theincrease of synthesis rate. After cutting the salt powder using FIB, BaTiO3 nano particles observed homogeneously in the cross-section of the salt particle.

Bi0.5+x(Na0.78K0.22)0.5-3xTiO3 ceramics with an excess Bi3+ and a deficiency of Na+ and K+ were synthesized by a conventional solid state reaction method. The structure and morphology ofBi0.5+x(Na0.78K0.22)0.5-3xTiO3 ceramics were characterized by X-ray diffraction and field emission scanning electron microscopy. The electric polarization and mechanical strain induced by external electric field, and the temperature dependence of dielectric constant were investigated. These results demonstrated that anergodic relax or phase can be induced by controls of the mole ratio of Bi3+, Na+ and K+. A phase boundary between non-ergodic and ergodic relaxor phases can be observed at ambient temperature. Theergodic relaxor phase can be transferred to the ferroelectric phase by application of the electric field. The stability of the induced ferroelectric phases strongly depends on the mole ratio of Bi3+, Na+ and K+. The maximum strain of 0.31% was observed in Bi0.51(Na0.78K0.22)0.47TiO3 ceramics sintered at 1,150℃ for 2 h.

The 0.99Bi0.5(Na0.78K0.22)0.5TiO3?0.01LaAlO3, 0.01LaMnO3 or 0.01LaFeO3 (0.99BNKT?0.01LA,0.01LM or 0.01LF) ceramics were prepared by a conventional mixed mothod. The structure andmorphology of the lead free ceramics were characterized by XRD (X-ray diffraction) and FE-SEM (fieldemission scanning electron microscopy). XRD results indicated that the BNKT ceramics modified by LA,LM or LF induced a transition from a ferroelectric tetragonal to a non-polar pseudo-cubic phase, leadingto decrease in the remnant polarization (Pr) and coercive field (Ec) in the P-E hysterisis loops. Theeffects of the BNKT ceramics modified by La-based ABO3 pervskite structure on the electric-fieldinduced strain were investigated, and the largest normalized unipolar strain (Smax/Emax) was found inBNKT-0.01LF ceramic.

Oxides possess several interesting properties, such as ferroelectricity, magnetism, superconductivity, and multiferroic behavior, which can effectively be used oxide electronics based on epitaxially grown heterostructures. The microscopic properties of oxide interfaces may have a strong impact on the electrical transport properties of these heterostructures. It was recently demonstrated that high electrical conductivity and mobility can be achieved in the system of an ultrathin LaAlO3 film deposited on a TiO2-terminated SrTiO3 substrate, which was a remarkable result because the conducting layer was at the interface between two insulators. In this study, we observe that the current-voltage characteristics exhibit LaAlO3 thickness dependence of electrical conductivity in TiO2-terminated SrTiO3. We find that the LaAlO3 layers with a thickness of up 3 unit cells, result in highly insulating interfaces, whereas those with thickness of 4 unit cells and above result in conducting interfaces.

0.935BaTiO3-0.065(Bi0.5Na0.5)TiO3+xmol%MnO2 (BBNTM-x) ceramics with 0≤x≤0.05 were fabricated with muffled sintering by a modified synthesis process. Their microstructure and enhanced positive temperature coefficient of resistivity (PTCR) characteristics were systematically investigated in order to obtain lead-free high TC PTCR thermistors. All specimens showed a perovskite structure with a tetragonal symmetry and no secondary phase was observed. Grain growth was achieved when the doped MnO2 was increased above 0.02 mol%. This is due to the effect of positive Mn ion doping as an acceptor compensating a Ba vacancy occurred by the higher donor dopant concentration of Bi3+ ion. Especially, enhanced PTCR characteristics of the extremely low ρRT of 99 Ω·㎝, PTCR jump of 5.1×10(3), α of 15.5%/℃ and high TC of 167℃ were achieved for the BBNTM-0.04 ceramics.

(1-x)BaTiO3-x(Bi0.5Na0.5)TiO3 (0.01≤x≤0.10) ceramics were fabricated with muffled sintering by a modified synthesis process. Their positive temperature coefficient of resistivity (PTCR) characteristics were investigated systematically. All specimen showed a perovskite structure with a tetragonal symmetry. Both the lattice parameter of a and c axes were slightly decreased with increasing (Bi0.5Na0.5)TiO3 (BNT) content. Grain growth was achieved when the incorporated BNT was increased to 6 mol% and the inhibition of grain growth is considered to be due to the appearance of Ba vacancy (V"(Ba)) in the (1-x)BaTiO3-x(Bi0.5Na0.5)TiO3 (0.08≤x). With 4 mol% BNT addition, room temperature resistivity decreased to 48 Ω·㎝ and a resistivity jump (ρmax/ρmin) was as high as 1.1×10(4), respectively. Curie temperature was also increased to 171˚C with increasing BNT content.