Kanokwan Kanchiang

Crystal-structure dependent domain-switching behavior in BaTiO3 ceramic

Crystal-structure dependent dynamic scaling behavior was investigated for BaTiO3 ceramic. The scaling relation of the form 〈 〉∝ Af E mn 0 , (where 〈〉 A is the area under the hysteresis loop, while f and E0 represent the frequency and amplitude of the applied electric field signal) was used to determine the values of parameters m and n at various temperatures in the range of �90 °C to 170 °C. The variations in the values of parameters m and n with temperature are explained in terms of the effect of the crystallographic nature of BaTiO3. The values of parameters m and n obtained for the paraelectric regime suggest that the hysteresis in the P–E (polarization–electric field) loops is related to the dielectric loss rather than any domain-related phenomenon.

Monte Carlo Investigation of Mixed Normal and Relaxor Ferroelectrics

In this work, Monte Carlo simulation was used to model the ferroelectric behavior of mixed normal and relaxor ferroelectrics using the single polarization-flip algorithm. The purpose is to investigate the dependence of ferroelectric properties on the field frequency, the temperature and the normal ferroelectric concentration in the relaxor ferroelectrics. Results obtained from both static and dynamic simulation stress the significant effect of the larger ferroelectric interaction caused by the normal ferroelectric contents. For instance, with increasing normal ferroelectric concentrations, the transition between zero and nonzero polarization phases shifts to a higher temperature due to stronger ferroelectric interaction. In addition, the stronger ferroelectric interaction also causes less polarization switching, where the hysteresis gets larger in size at low frequencies, but smaller at high frequencies. This strong ferroelectric interaction also shifts the frequency at maximum phase-lag between polarization and field signal to a lower frequency. These results are in good agreement with experiments, where applicable.

Phase formation behavior of perovskite ferroelectric lead zirconate titanate - lead zinc niobate powders by X-ray absorption spectroscopy

ABSTRACT Lead zirconate titanate - lead zinc niobate (PZT-PZN) powders were prepared by a modified mixed-oxide synthetic route via a combination of Zn2Nb34O87 precursor and vibro-milling techniques. The effects of calcination temperature and chemical composition on phase formation were investigated by x-ray absorption spectroscopy. The Zn K-edge x-ray absorption near edge structure (XANES) was simulated with PZT-PZN in pyrochlore phase and perovskite phase. The comparison between simulated and measured XANES shows the increasing perovskite phase formation of PZT-PZN with increasing calcination temperature and the optimization of calcination temperature lead to 100% yield of PZT-PZN in perovskite phase. In addition, the Zn K-edge x-ray absorption near edge structure (XANES) was simulated with various compositions of PZT in PZT-PZN. The comparison between simulated and measured XANES shows the increasing perovskite phase formation of PZT-PZN with increasing composition of PZT. The results show the optimization of calcination conditions lead to formation of PZT-PZN in perovskite phase.

Probing local structure of pyrochlore lead zinc niobate with synchrotron x-ray absorption spectroscopy technique

Local structure of lead zinc niobate (PZN) ceramic, synthesized via B-site oxide precursor route in atmospheric pressure, was investigated using synchrotron x-ray absorption spectroscopy (XAS) technique. The x-ray absorption near-edge structure (XANES) simulation was first carried out. The XANES simulation results indicate that the PZN ceramic is in pyrochlore phase having Zn2+ substituted on Nb5+ site. Afterwards, the extended x-ray absorption fine structure (EXAFS) analysis was performed to extract the bond length information between Zn2+ and its neighboring atoms. From the EXAFS fitting, the bond length between Zn2+ and Pb2+ in the pyrochlore phase was found to be longer than the previously reported bond length in the perovskite phase. Further, with the radial distribution information of Zn2+s neighboring atoms, the formation energies along the precursor-to-pyrochlore and precursor-to-perovskite reaction paths were calculated using the density functional theory (DFT). The calculated results show that ...

Monte Carlo Simulations of Relaxor Ferroelectric Dielectric Permittivity in Films Structure

In this study, the Monte Carlo simulation was used to investigate relaxor films using the spin-glass Hamiltonian with the surface effect. The single polarization flip algorithm was used to update the local polarizations where the relaxation time was measured to calculate the dielectric permittivity and loss as varying temperature, field frequency and films thickness. From the results, in the vicinity of the electrodes on the topmost and bottommost layers, the relaxor films exhibit thickness-dependent dielectric properties in qualitatively good agreement with experiments. The maximum dielectric permittivity enhances in the films with increasing the films thickness as expected. The relations of how maximum dielectric permittivity and its corresponding temperatures vary with thickness are also explained.

Finite Size Scaling of Hysteresis Behavior: Monte Carlo Simulation on DIFFOUR Model

In this work, Monte Carlo simulation was used to study the size dependence of the dynamic hysteresis properties of 2 dimensional ferroelectric system. The DIFFOUR model and Metropolis algorithm were used to investigate the size effect on hysteresis properties. From the simulation, it was found that the competition between the electric field parameters and the system size plays a crucial role on the phase-lag between the polarization and the electric field signals, which defines particular hysteresis properties. In describing the hysteresis behavior qualitatively, finite size scaling formalism, in a power law form, was used to predict relations among the field parameters, system size, and hysteresis. The purpose was to establish phenomenological knowledge of how dynamic perturbations affect the hysteresis in finite ferroelectric system. Comparison with related experiments was also discussed.

Harmonic Analysis of Dynamic Hysteresis Response of BaTiO3 Bulk Ceramics

In this work, the dynamic ferroelectric hysteresis properties in response to dynamic electric field of BaTiO3 bulk ceramics was investigated using the harmonic analysis approach. Fourier transformation was used to analyze the periodic polarization signal on frequency domain via each discrete harmonic. From the results, the hysteresis area is found to depend only on the first harmonic of the real part. On the other hand, the remnant polarization depends on all odd harmonics of the real part. Further, the coercive field can be found from the phase-lag between the inverse Fourier signals re-calculated from the first harmonic of the real part and that of the imaginary part. The hysteresis properties from the harmonic analysis match well with those of the original measurement. This suggests that the harmonic analysis is one of the powerful techniques which can be used to predict hysteresis behavior.

The Debye Dielectric Behavior of Mixed Normal and Relaxor-Ferroelectrics: Monte Carlo Investigation

In this work, Monte Carlo simulation was used to investigate the Debye dielectric behavior of mixed normal- and relaxor-ferroelectrics. The results show that, with increasing temperature, the dielectric permittivity of the mixed system sharply increases at low temperatures but slowly decays at high temperatures, while still presenting the dielectric peaks close to the relaxor- and normal-ferroelectrics transition temperatures. Further, it is found that the sharpness, the magnitude, and the frequency dispersion of the dielectric peaks can be finely tuned by adjusting relevant normal-ferroelectric parameters in the model. However, the modified Curie-Weiss law shows that its exponent γ is governed by the inverse-temperature dependence as the exponent is very close to 2 regardless of normal-ferroelectric content. The functionalities of the Debye-type dielectric permittivity are then discussed along with the comparison with experiments.

Probing local structure of ZnO-modified Pb(Mg1/3Nb2/3)0.9Ti0.1O3 ceramic with synchrotron X-ray absorption spectroscopy technique

ABSTRACT This work aims to study the effects of ZnO modifications on local structures of Pb(Mg1/3Nb2/3)0.9Ti0.1O3 (PMNT) ceramics. Different contents of ZnO (0, 0.4, 2.0, 4.0 and 11.0 mol%) were added into PMNT ceramics. The local structures of the samples were characterized by synchrotron X-ray absorption spectroscopy (XAS). X-ray absorption near-edge structure (XANES) spectra of both Zn and Ti K-edges were displayed. The Zn K-edge energy values of all samples were in the range of 9660–9666 eV. The Zn ions incorporated in all ceramics were in the form of Zn2+. The value of Ti K-edge energy, which was equal to 4979 eV, did not change with ZnO modifications. Comparing the experimental Zn K-edge XANES spectra to the spectra simulated via FTFF program confirmed the substitution of the Zn ions for B-site ions. The intensity and the area under curve of the pre-edge peak of Ti K-edge gradually increased with increasing ZnO content up to 4.0 mol%. This suggested a gradual change in the displacement out from octahedral centers of Ti ions. This could be an evidence of the enhancement in ferroelectric order of ZnO-modified PMNT ceramics.

Effect of gold nanoparticles on lead zinc niobate–barium titanate structure by X-ray absorption spectroscopy

ABSTRACT The 0.93PZN-0.07BT ceramics containing 0.5 wt% AuNPs sintering was carried out for 3 – 5 h at various temperatures ranging from 1100 to 1150°C. The effect of AuNPs on 0.93PZN-0.07BT local structure and dielectric properties were investigated. The Au K-edge XANES spectrum indicated that AuNPs are not substituted into 0.93PZN-0.07BT structure. The dielectric constants and dielectric loss of 0.93PZN-0.07BT ceramics containing 0.5 wt% AuNPs after sintering at 1050°C for 3–5 h are higher and lower than that of 0.93PZN-0.07BT ceramics without AuNPs after sintering at 1100°C for 3–5 h, respectively, which can be described by assuming the connectivity series between the ceramics and the metal phases. In addition, Curie temperature shifting of 0.93PZN-0.07BT ceramics containing 0.5 wt% AuNPs due to the higher degree of chemical heterogeneity caused by the AuNPs addition. Therefore, the including of AuNPs into 0.93PZN-0.07BT ceramics can be improving dielectric properties with lower temperature and shorter time in sintering process.