Chien-Chih Huang

Effects of ZrO2 additions on the dielectric properties of CaCu3Ti4O12

The dielectric spectra of CaCu3Ti4O12 is characterized by a large permittivity (er>10000) with only a weak dependence on temperature over the temperature range 200–400 K. In this work, doping with 0.1–1.0 wt % ZrO2 has been shown to dramatically reduce the dielectric loss. At 0.5 wt % ZrO2,tanδ remains below 0.05 over the frequency range 50 Hz–30 kHz and is just 0.065 at 100 kHz. While there is some diminution of the permittivity (er≈5000 at 10 kHz) Zr-doped ceramics, exhibited very little bias dependence (ΔC∕C0<1.0% up to 40 V). In summary, results suggest that ZrO2 doping is an effective method for maintaining a high permittivity and low loss over a broad range in temperature, bias, and frequency.

Phase transitions and dielectric properties in Bi(Zn1/2Ti1/2)O3−BaTiO3 perovskite solid solutions

A group of (1¿x)Bi(Zn1/2Ti1/2)O3-¿ABO3 (ABO3=BaTiO3, NaNbO3, BiScO3 and Bi1/2K1/2TiO3) polycrystalline ceramics were prepared by solid-state processing techniques. Based on x-ray diffraction results, the presence of Bi(Zn1/2Ti1/2)O3 in the solid solution decreases the structure stability of perovskite phase. The dielectric characterization revealed that the trends of transition temperature Tm as a function of composition of Bi(Zn1/2Ti1/2)O3-ABO3 could be described into two groups. The first one is Tm decreased until second phase appeared and the second one is Tm decreased and then increased as Bi(Zn1/2Ti1/2)O3 content increased. In addition, with substitution of Li for Na of NaNbO3-Bi(Zn1/2Ti1/2)O3 the diffuseness of the transition peak decreased and transition temperature increased.

Phase transitions and ferroelectric properties in BiScO3-Bi(Zn1∕2Ti1∕2)O3-BaTiO3 solid solutions

Ceramics solid solutions within the ternary perovskite system Bi(Zn1∕2Ti1∕2)O3-BiScO3-BaTiO3 were synthesized via solid-state processing techniques. The crystal structure of sintered ceramics was analyzed by x-ray diffraction. A stable perovskite phase was obtained for all compositions with a BaTiO3 content greater than 50 mol %. Furthermore, a change in symmetry from pseudocubic to tetragonal was observed as the mole fraction of BaTiO3 increased. Dielectric measurements show a dielectric anomaly associated with a phase transformation over the temperature range of 30 °C–210 °C for all compositions. Examination of the polarization hysteresis behavior revealed weakly nonlinear hysteresis loops. With these data, ferroelectric phase diagrams were derived showing the transition between the pseudocubic relaxor behavior to the tetragonal normal ferroelectric behavior. This transition was also correlated with changes in the diffuseness parameter.

Structure and ferroelectric properties of Bi(Zn 1/2 Ti 1/2 )O 3 -(Bi 1/2 K 1/2 )TiO 3 perovskite solid solutions

Lead-free piezoelectric ceramics based on chiBi(Zn_1/2Ti_1/2)O₃-(1-chi)(Bi_1/2K_1/2)TiO₃ were obtained via solid state processing techniques. A single perovskite phase with tetragonal symmetry was obtained for Bi(Zn_1/2Ti_1/2)O₃ (BZT) substitutions up to 20 mol%. The maximum density was 97.1% at the composition of chi = 0.1. The dielectric measurement indicated that the transition temperature decreased linearly with increasing BZT content. The P-E loops revealed an increase in remanent polarization (P_r) with the addition of BZT. The maximum planar coupling coefficient, kappa_r, for the chi = 0.1 composition was 21.6 and the piezoelectric coefficient, d₃₃, for chi = 0, chi = 0.05, and chi = 0.1 was 108, 185, and 235 pm/V, respectively. Overall, the dielectric and piezoelectric properties showed significant improvement when BZT was added.

Structure and electrical properties of double perovskite Sr(Ni1/2Mo1/2)O3 ceramics

The double perovskite Sr(Ni1∕2Mo1∕2)O3 has been prepared with solid-state reaction and was characterized by x-ray diffraction technique. It has been indicated that the single phase is formed at 1300°C in air. The compound undergoes a phase transition at 280°C, where the structure of the ordered perovskite type changes from tetragonal (I4∕m) to cubic (Fm3¯m). Dielectric constant (er) and dielectric loss (tanδ) are observed at the transition point. The conductivity of the sample has been studied, and the slope of dc conductivity versus the inverse of temperature corresponds to an Arrhenius activation energy in the range of 0.34–0.46eV. This range of activation is nearly double ionized oxygen vacancies VO⋅⋅ in the resistivity transition of other perovskite oxides.

Phase Transitions and Dielectric Properties in Bi(Zn1/2Ti1/2)O3–(Na1-yLiy)NbO3 Perovskite Solid Solutions

Perovskite solid solutions based on the system Bi(Zn1/2Ti1/2)O3–NaNbO3 were obtained via solid-state processing techniques. The crystal structure and ferroelectric phase transitions were studied by means of X-ray diffraction and dielectric measurements. A stable perovskite phase was obtained for Bi(Zn1/2Ti1/2)O3 substitutions up to 10 mol %. The dielectric characterization revealed that as the Bi(Zn1/2Ti1/2)O3 content increased, the transition temperature decreased and the transition peak became very diffuse. The polarization hysteresis loop and strain measurements presented evidence of an induced ferroelectric phase with 1 mol % Bi(Zn1/2Ti1/2)O3 substitutions. The planar coupling factor (kp) for 0.01Bi(Zn1/2Ti1/2)O3–0.99NaNbO3 was measured to be 0.28. In addition, with the substitution of Li for Na in the Bi(Zn1/2Ti1/2)O3–(Na1-yLiy)NbO3 system, the diffuseness of the transition peak decreased and the transition temperature increased.

Electrical Conductivity and Dielectric and Ferroelectric Properties of Chromium Doped Lead Zirconate Titanate Ceramic

In this study, the influence of the addition of chromium (Cr 3+) of 0.1–3 mol% on electrical conductivity, dielectric and ferroelectric properties of the morphotropic lead zirconate titanate (Pb(Zr 0.52 Ti 0.48 )O 3 ) ceramics has been investigated. The dielectric constant tends to slightly increase with increasing chromium concentration from 0.1–0.6 mol% while dielectric loss tends to decrease, but the trend is reversed with 1–3 mol% chromium content. In addition, the Curie temperature (T C ) does not change significantly with chromium addition from 0.1–0.6 mol% but decreases significantly from 1–3 mol%. From the hysteresis loop measurement, at low concentration of Cr, the loops reveal the high value of polarization and low coercive field that refers to soft behavior while the contrary is revealed at higher Cr concentration with hard behavior. The electrical conductivity of the doped PZT ceramic measured at 50–200°C decreases with increasing chromium concentration from 0.1–0.6 mol% but increases with 1–3 mol% Cr.

Phase transitions and dielectric properties in Bi(Zn1/2Ti1/2)O3-ABO3 perovskite solid solutions

A group of (1?x)Bi(Zn1/2Ti1/2)O3-?ABO3 (ABO3=BaTiO3, NaNbO3, BiScO3 and Bi1/2K1/2TiO3) polycrystalline ceramics were prepared by solid-state processing techniques. Based on x-ray diffraction results, the presence of Bi(Zn1/2Ti1/2)O3 in the solid solution decreases the structure stability of perovskite phase. The dielectric characterization revealed that the trends of transition temperature Tm as a function of composition of Bi(Zn1/2Ti1/2)O3-ABO3 could be described into two groups. The first one is Tm decreased until second phase appeared and the second one is Tm decreased and then increased as Bi(Zn1/2Ti1/2)O3 content increased. In addition, with substitution of Li for Na of NaNbO3-Bi(Zn1/2Ti1/2)O3 the diffuseness of the transition peak decreased and transition temperature increased.

Conductivity Measurement of ZnO Nanowires Using the Powder-Solution-Composite Technique

The powder solution composite (PSC) method was used to obtain the conductivity of ZnO nanowires from impedance spectroscopy measurements of ZnO nanowires dispersed in solution. The PSC method was calibrated by comparing impedance spectroscopy measurements of ZnO powder dispersed in solution with four-point probe measurements on bulk ZnO ceramic pellets. Conductivity values for ZnO nanowires obtained using this novel approach were found to be comparable to reported values obtained using two-point and four-point probe measurements of single or multiple nanowire devices isolated on a substrate. It is shown that application of the PSC method to ZnO nanowire solutions avoids the difficult process of forming electrical contacts to nanowires and allows for the non-destructive in-situ measurement of the average electrical properties of a large quantity of nanowires.

Effects of Niobium Doping on Dielectric and Ferroelectric Properties of Chromium Modified Lead Zirconate Titanate Ceramics

Effects of niobium doping on dielectric and ferroelectric properties of unmodified lead zirconate titanate (PZT) and chromium modified lead zirconate titanate (Cr-modified PZT) have been investigated. The x-ray structural study shows the phase formed depending on the dopant concentrations with increasing the doping content tending to an increase in the rhombohedral phase in both of PZT and Cr-modified PZT ceramics. Furthermore, the Curie temperature (T c ) and dielectric constant are decreased with increasing Nb concentration and the dielectric loss of Cr-modified PZT ceramics is lower than that of the PZT ceramics. From the hysteresis loop measurements, by increasing Nb concentration, the unmodified PZT ceramics show increase in the coercive field, while the remnant polarization decreases slightly. However, coercive field decreases, and the remanent polarization tends to increase with increasing niobium concentration from 1-3 mol% in Cr-modified PZT ceramics. Further increase in niobium concentration results in a drop of the remanent polarization and the coercive field.