The microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of 0.1mol%Na2Ti6O13doped 0.94BaTiO3-0.06(Bi0.5Na0.5)TiO3 (BBNT-NT001) ceramics sintered at various temperatures from 1200oC to 1350oC wereinvestigated in order to develop eco-friendly PTCR thermistors with a high Curie temperature (TC). Resulting thermistors showeda perovskite structure with a tetragonal symmetry. When sintered at 1200oC, the specimen had a uniform microstructure withsmall grains. However, abnormally grown grains started to appear at 1250oC and a homogeneous microstructure with large grainswas exhibited when the sintering temperature reached 1325oC. When the temperature exceeded 1325oC, the grain growth wasinhibited due to the numerous nucleation sites generated at the extremely high temperature. It is considered that Na2Ti6O13 isresponsible for the grain growth of the 0.94BaTiO3-0.06(Bi0.5Na0.5)TiO3 ceramics by forming a liquid phase during the sinteringat around 1300oC. The grain growth of the BBNT-NT001 ceramics was significantly correlated with a decrease of resistivity.All the specimens were observed to have PTCR characteristics except for the sample sintered at 1200oC. The BBNT-NT001ceramics had significantly decreased ñrt and increased resistivity jump with increasing sintering temperature at from 1200oC to1325oC. Especially, the BBNT-NT001 ceramics sintered at 1325oC exhibited superior PTCR characteristics of low resistivityat room temperature (122Ω·cm), high resistivity jump (1.28×104), high resistivity temperature factor (20.4%/oC), and a highTc of 157.9oC.

For use in ultrasonic actuators, we investigated the structural and piezoelectric properties of (1 - x)Pb(Zr0.515Ti0.485)O3 - xPb(Sb1/2Nb1/2)O3 + 0.5 wt% MnO2 [(1 - x)PZT - xPSN + MnO2] ceramics with a variation of x (x = 0.02, 0.04, 0.06, 0.08). All the ceramics, which were sintered at 1250˚C for 2 h, showed a typical perovskite structure, implying that they were well synthesized. A homogeneous micro structure was also developed for the specimens, and their average grain size was slightly decreased to 1.3μm by increasing x to 0.8. Moreover, a second phase with a pyrochlore structure appeared when x was above 0.06, which resulted in the deterioration of their piezoelectric properties. However, the 0.96PZT-0.04PSN+MnO2 ceramics, which corresponds with a morphotropic phase boundary (MPB) composition in the (1 - x)PZT - xPSN + MnO2 system, exhibited good piezoelectric properties: a piezoelectric constant (d33) of 325 pC/N, an electromechanical coupling factor (kp) of 70.8%, and a mechanical quality factor (Qm) of 1779. The specimens with a relatively high curie temperature (Tc) of 305˚C also showed a significantly high dielectric constant (εr) value of 1109. Therefore, the 0.96PZT - 0.04PSN + MnO2 ceramics are suitable for use in ultrasonic vibrators.

Positive temperature coefficient of resistivity (PTCR) characteristics of (1-x)BaTiO3-x(Bi0.5K0.5)TiO3ceramics doped with Nb2O5 were investigated in order to develop the Pb-free PTC thermistor available at hightemperatures of >120oC. The PTCR characteristics appearing in the (Bi0.5Ki0.5)TiO3 (<5mol%) incorporatedBaTiO3 ceramics, which might be mainly due to Bi+3 ions substituting for Ba+2 sites. The 0.99BaTiO3-0.01(Bi0.5K0.5)TiO3 ceramics showed good PTCR characteristics of a low resistivity at room temperature (ρr) of31 Ω·cm, a high ρmax/ρmin ratio of 5.38×103, and a high resistivity temperature factor (α) of 17.8%/oC. Theaddition of Nb2O5 to 0.99BaTiO3-0.01(Bi0.5K0.5)TiO3 ceramics further improved the PTCR characteristics.Especially, 0.025mol% Nb2O5 doped 0.99BaTiO3-0.01(Bi0.5K0.5)TiO3 ceramics exhibited a significantly increasedρmax/ρmin ratio of 8.7×103 and a high α of 18.6%/oC, along with a high Tc of 148oC despite a slightly increasedρr of 39 Ω·cm.

The effects of an addition of ZrO2 on the microstructure and electrical properties of MgO films as a protective layer for AC plasma display panels were investigated. MgO + a 200 ppm ZrO2 protective layer prepared by e-beam evaporation exhibited a secondary electron emission coefficient (γ) that was improved by 21% compared to that of a pure MgO protective layer. The relative density and Vickers hardness increased with a further addition of ZrO2. These results suggest that the discharge properties and optical properties of MgO protective layers are closely related to the relative density and Vickers hardness. The good optical and electrical properties of γ, at 0.080, a grain size of 19 μm and an optical transmittance of 91.93 % were obtained for the MgO + 200 ppm ZrO2 protective layer sintered at 1700˚C for 5 hrs.

The structural and electrical properties of amorphous BaSm2Ti4O12 (BSmT) films on a TiN/SiO2/Si substrate deposited using a RF magnetron sputtering method were investigated. The deposition of BSmT films was carried out at 300˚C in a mixed oxygen and argon (O2 : Ar = 1 : 4) atmosphere with a total pressure of 8.0 mTorr. In particular, a 45 nm-thick amorphous BSmT film exhibited a high capacitance density and low dissipation factor of 7.60 fF/μm2 and 1.3%, respectively, with a dielectric constant of 38 at 100 kHz. Its capacitance showed very little change, even in GHz ranges from 1.0 GHz to 6.0 GHz. The quality factor of the BSmT film was as high as 67 at 6 GHz. The leakage current density of the BSmT film was also very low, at approximately 5.11 nA/cm2 at 2 V; its conduction mechanism was explained by the the Poole-Frenkel emission. The quadratic voltage coefficient of capacitance of the BSmT film was approximately 698 ppm/V2, which is higher than the required value (<100 ppm/V2) for RF application. This could be reduced by improving the process condition. The temperature coefficient of capacitance of the film was low at nearly 296 ppm/˚C at 100 kHz. Therefore, amorphous BSmT grown on a TiN substrate is a viable candidate material for a metal-insulator-metal capacitor.