Woo Sup Kim

Microwave Dielectric Properties and Far Infrared Reflectivity Spectra of the (Zr0.8Sn0.2)TiO4 Ceramics with Additives

Microwave dielectric properties and far infrared reflectivity spectra were investigated in the (Zr0.8Sn0.2)TiO4 ceramics with 1 mol% Sb2O5, Sb2O3 and Nd2O3, respectively. Dielectric constant was not significantly changed, while the unloaded Q value was affected with additives. The unloaded Q of the pure (Zr0.8Sn0.2)TiO4 specimens was higher than that of the specimens with Sb2O3 and/or Nd2O3, but lower than that of the specimens with Sb2O5. The high unloaded Q value of 6600 at 7 GHz was obtained for the specimens with 1 mol% Sb2O5 due to elimination of oxygen vacancies. The effects of additives on the intrinsic microwave losses of the specimens were investigated by the infrared reflectivity spectra from 50 to 4000 cm-1, which were evaluated using the Kramers-Kronig analysis and classical oscillator model. The relative tendency of microwave dielectric properties calculated from the reflectivity data was in good agreement with the results by the Hakki and Colemans method.

Dielectric properties of Ca1-xSm2x/3TiO3-Li1/2Ln1/2TiO3 ceramics

The physical and microwave dielectric properties of Ca 1-x Sm 2x/3 TiO 3 -Li 1/2 Ln 1/2 TiO 3 (Ln=Sm, Nd) have been investigated as a function of the degree of Sm substitution (x = 0.0-1.0). As the calcium vacancy concentration increased with increasing Sm substitution, high Q.f values were obtained due to the formation of a superlattice. The Q.f values of the specimens with Nd increased throughout the entire composition range, due to the formation of complete solid solutions, while those of the specimens with Sm increased up to the solid solution limit x = 0.6, and then decreased due to the formation of a secondary phase Sm 2 Ti 2 O 7 . Dielectric constant (K) and temperature coefficient of resonant frequency (TCF) decreased linearly with increasing Sm substitution. In the (1-y)Ca 2/5 Sm 2/5 TiO 3 -yLi 1/2 Sm 1/2 TiO 3 system, the microwave dielectric properties could be controlled by the variation of y. Typical values of K = 95.5, Q.f = 7200 and TCF = Oppm/°C were obtained for 0.67Ca 2/5 Sm 2/5 TiO 3 -0.33Li 1/2 Sm 1/2 TiO 3 .

Microwave Dielectric Characteristics of the Ca2/5Sm2/5TiO3-Li1/2Nd1/2TiO3 Ceramics

Microwave dielectric properties of the (1-x)Ca2/5Sm2/5TiO3-xLi1/2Nd1/2TiO3 ceramics were investigated in the range of 0.2 ≤x ≤0.8. The unloaded Q values and the temperature coefficients of the resonant frequency (TCF) of the specimens decreased with increasing Li1/2Nd1/2TiO3. Nearly zero TCF value composition with high dielectric constant was obtained at x=0.3. Dielectric constant increased with an increase of Li1/2Nd1/2TiO3, and showed a maximum value around x=0.6, and then decreased with further addition of Li1/2Nd1/2TiO3. The change in the dielectric constant of the specimens with the addition of Li1/2Nd1/2TiO3 could be explained by the intrinsic factor such as lattice anharmonicity, which was obtained from the far infrared reflectivity spectra in the range of 50 to 4000 cm-1.

Far-infrared reflectivity spectra of CaTiO3–Li1/2Sm1/2TiO3 microwave dielectrics

Abstract Microwave dielectric properties and far-infrared reflectivity spectra of the (1 − y)CaTiO 3 –yLi 1/2 Sm 1/2 TiO 3 ceramics were investigated in the range of 0.0 ≤ y ≤ 1.0. The dielectric constant, unloaded Q value, and temperature coefficients of the resonant frequency (TCF) of the specimens decreased with increasing Li 1/2 Sm 1/2 TiO 3 . At y = 0.7, a nearly zero TCF value was obtained, with a high dielectric constant (K = 114) and an unloaded Q (Q·f = 3700). Based on analysis of the far-infrared reflectivity spectra from the 50 to 4000 cm −1 range, which were evaluated using Kramers–Kronig analysis and the classical oscillator model, the change in the Q·f value and dielectric constant of the specimens could be explained by intrinsic factors such as ionic polarization and dielectric loss (tan δ j ). The relative tendency of calculated dielectric constant and Q·f values agreed well with that of the measured values.

Effect of BaO/WO3 on the Microwave Loss Quality of Ba(Mg1/3Ta2/3)O3

Effects of BaO/WO3 ratio on the loss quality of complex perovskite Ba(Mg1/3Ta2/3)O3 were investigated as a function of the amount of (1-y)BaO-yWO3 (y=0.56, 0.8) from 0.3 wt.% to 7.0 wt.% at 10 GHz. The specimens with 1.5 wt.% of y=0.56 and/or with 1.0 wt.% of y=0.8 showed a maximum value of loss quality, respectively, and then decreased with an increase of additive content. The increase of loss quality with (1-y)BaO-yWO3, is resulted that the W6+ ions substitution of Ta5+ ions is enhanced the B-site ordering of Ba(Mg1/3Ta2/3)O3. The dielectric constant and temperature coefficient of resonant frequency (TCF) were decreased slightly with additives, which are due to the increase of BaWO4 phase as a secondary phase. The effects of additives on the intrinsic microwave losses of the specimens were investigated by the infrared reflectivity spectra from 50 to 4000 cm-1.

Effect of excess TiO2 on the microwave dielectric properties of the Ca2/5Sm2/5TiO3-Li1/2Ln1/2 TiO3 (Ln=Sm, Nd) ceramics

Abstract Dielectric properties of the Ca2/5Sm2/5TiO3-Li1/2Ln1/2TiO3 (Ln=Sm, Nd) ceramics have been investigated as a function of excess TiO2 at microwave frequencies. The variation of the dielectric constant and the temperature coefficient of the resonant frequencies (TCF) of the specimens with an increase of the amount of TiO2 could be explained by the volume mixing rule. The Q·f values of the specimens were decreased with an increase of the amount of TiO2. Typically, k of 92.5, Q·f of 4900 and TCF of +9 ppm/°C were obtained in the Ca2/5Sm2/5TiO3-Li1/2Sm1/2TiO3-0.8TiO2 specimen and k of 107, Q·f of 3300 and TCF of 0.0ppm/° C were also obtained in the Ca2/5Sm2/5TiO3-Li1/2Nd1/2TiO3-0.6TiO2 specimen

Piezoelectric properties of (Pb, Ca) (Ti, Co, W)O3/epoxy composites

Abstract Interconnected porous (Pb0.76Ca0.24)(Ti0.96(Co0.5W0.5)0.04)O3 (CPT) ceramic/epoxy composites have been prepared by Burn Out Plastic Spheres(BURPS) method and vacuum impregnation of epoxy. The piezoelectric properties of CPT/epoxy composites have been investigated as a function of initial pore size and CPT volume fraction. The piezoelectric coefficient(d33), dielectric constant, piezoelectric voltage coefficient(g33), electromechanical coupling factor(Kt) and thickness frequency coefficient(Nt) increase with CPT volume fraction than initial pore size.

Effects of BaWO4 and MnWO4 on the microwave dielectric properties of (Zr0.8 Sn0.2)TiO4 ceramics

Abstract The effects of BaWO4 and MnWO4 on the microwave dielectric properties for (Zr0.8Sn0.2)TiO4 ceramics have been investigated as a function of additives concentrations (0–5 mol%). As the amount of BaWO4 and MnWO4 increase up to 1 mol%, the unloaded Q increases due to reduction of the oxygen vacancy concentration. Further addition of BaWO4 or MnWO4 causes the unloaded Q to decrease due to the presence of secondary phases, either BaWO4 itself or a needle shaped undetermined MnWO4 phase. The temperature coefficient of resonant frequency can be controlled by the volume mixing rule for (Zr0.8Sn0.2)TiO4 and secondary phases.