Takashi Teranishi

Polarization behavior in diffuse phase transition of BaxSr1−xTiO3 ceramics

Ultrawide band dielectric spectroscopy analysis of barium strontium titanate [BaxSr1−xTiO3 (BST)] ceramics at different temperatures disclosed a contribution of the dipole and the ionic polarizations to their diffuse phase transition (DPT). In the BST ceramics, thermal behavior of the ionic polarization governs the DPT. The dielectric maximum temperature (Tm) is in agreement with the maximum temperature of the permittivity determined by the ionic polarization. The maximum of the permittivity determined by the ionic polarization at the Tm is caused from the decrement of the vibration frequency of the soft mode. The dipole polarization gives small contribution to the DPT. The gradual increase in the permittivity determined by the dipole polarization with decreasing temperature could be explained by the increase in the size of the polar nanoregions.

Ultrawideband dielectric spectroscopy of BaZrxTi1−xO3 ceramics and its microscopic mechanism of polarization

Ultrawideband dielectric spectroscopy analysis of barium zirconate titanate (BaZrxTi1−xO3, BZT) ceramics at different temperatures disclosed the contribution of both the dipole and the ionic polarizations to permittivity at around dielectric maximum temperature (Tm). In BaZr0.25Ti0.75O3 ceramics, the permittivity around Tm is dominated by the temperature dependence of the permittivity determined by the dipole polarization (edipole). In relaxor ferroelectrics, the diffuse dielectric response around Tm could be derived from the temperature dependence of edipole. The variation of edipole with temperature could be also explained by the growth process of polar nanoregions (PNRs) and the damping process of the thermal fluctuation of dipoles in PNRs.

Size Effect and Domain-Wall Contribution of Barium Titanate Ceramics

Barium titanate (BaTiO3) ceramics with various grain sizes from 0.7 to 13 μm were prepared by a conventional sintering method and a two-step sintering method. The permittivity of the BaTiO3 ceramics with an average grain size of 1.1 μm exhibited a maximum around 8,000. By ultrawide range dielectric spectroscopy, the domain-wall contribution to the permittivity was investigated. For the BaTiO3 ceramics with grain sizes over 1 μm, the dipole and ionic polarizabilities were enhanced by the high domain density. In contrast, for the BaTiO3 ceramics with grain sizes below 1 μm, these polarizabilities were weakened.

Wide Band Dielectric Spectroscopy at Ferroelectric Phase Transition of BaTiO3 Ceramics

Ultrawide band dielectric spectra from kHz to THz were measured to investigate quantitatively the contributions of ionic and dipole polarizations to the ferroelectric phase transition in BaTiO3 (BT) ceramics. Permittivity derived from ionic polarization (eionic) exhibited its maximum at the Curie temperature (Tc), attributing to the softening of the soft phonon mode. Permittivity derived from dipole polarization (edipole) was nearly constant below the Tc, while edipole remained above the Tc and edipole increased on cooling, exhibiting its maximum near the Tc. The behavior in edipole above the Tc could be interpreted as precursor phenomenon of ferroelectric phase transition and the edipole above the Tc was due to the local tetragonal type distortion in paraelectric phase.

Measurement of Micro-Wave Dielectric Properties of SrTiO3 Substrate Thin Plates Using Planar Electrodes

In this study, the possibility of accurate estimation of dielectric properties of ceramic thin plates was investigated. Thin plates were prepared from a SrTiO3 single crystal, and micro-planar electrodes were formed on to the plates using electron beam lithography. Electromagnetic analysis software was used to design the electrode structure and evaluate the dielectric properties. Two electrode structures, LC resonance patterns and interdigital patterns, were employed for the measurements. The dielectric constants of the plates as determined with the two electrode structures were in good agreement with literature (εr = 310) [1]. INTRODUCTION The ferroelectric and dielectric materials with perovskite type structure, such as BaTiO3, BaxSr1-xTiO3 and SrTiO3 with high dielectric constants are used for decoupling or as tunable capacitors in high frequency circuits. These ceramics capacitors can be in various forms, such as bulk ceramics, single crystals, thin films and even as artificial superlattices [2,3]. The dielectric properties of these samples have been measured by forming plate type capacitors in low frequency region, below few hundreds MHz [4]. Also a resonance method and an open-end coaxial probe method have been used for high frequency measurements. However, these two methods are acceptable only for ceramic specimens with designed shape and size [5]. In this study, we will present two methods to measure dielectric properties of a wide variety of samples in high frequencies. Both methods are based on some new planar electrode designs like the ones already published [6,7,8]. The first method is an LC resonance method and the second method is an admittance measurement method. In order to design these new electrodes and to evaluate the dielectric constant of a sample from the obtained data, electromagnetic field analysis is used. The validity of both methods will be verified on structures patterned on SrTiO3 single crystals. EXPERIMENT A SrTiO3 (STO) (001) single crystal with thickness about 500 μm was used as a sample. The relative permittivity (εr) and the dielectric loss (tan δ) of the STO single crystal were 310 and 5x10 -4 at 10 GHz, respectively [1]. The STO thin plate was mechanically polished to the thickness of 60 μm. Planar electrodes were formed by electron beam lithography followed by lift-off method after Au-sputtering. The thickness of the Au-sputtered electrodes was 60 nm, and the resistivity (ρ) of interdigital electrodes was measured by dc four-probes method using a RESITEST8200 (Toyo Corp., Japan). Two electrode structures, LC resonance patterns and interdigital patterns, were formed. Figure 1 shows the measuring system developed in this study. The complex admittance Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vol. 269, pp 215-218 doi:10.4028/www.scientific.net/KEM.269.215

Analysis of polarization behavior in relaxation of BaTiO 3 -based ferroelectrics using wideband dielectric spectroscopy

Wideband dielectric spectra from the kilohertz to terahertz range are discussed for BaTiO₃-based ferroelectrics. Ceramics of BaTiO₃ (BT), Ba_0.6Sr_0.4TiO₃ (BST-0.6), and BaZr_0.25Ti_0.75O₃ (BZT-0.25) were selected as normal ferroelectrics, ferroelectrics with diffuse phase transition (DPT ferroelectrics), and relaxor ferroelectrics, respectively. The variation of ionic polarization in both BT and BST-0.6 ceramics with temperature could be explained by the softening of the soft phonon mode. In BZT-0.25, a permittivity anomaly at the dielectric maximum temperature (T_m) at low frequencies is not attributed to the softening of the soft phonon mode, but originates from the permittivity derived from the dipole polarization (ε_dipole). Relaxor behavior in BZT-0.25 is derived from the increase in the depression of ε_dipole on cooling across the T_m with increasing frequency. In dipole polarization, BT, BST- 0.6, and BZT-0.25 all exhibited a similar tendency of ε_dipole above the Curie temperature (T_c) and T_m. However, behavior of ε_dipole below the T_c can be explained by the ferroelectric domains in BT, whereas the variation of ε_dipole below the Tm could be explained by growth process of polar nanoregions (PNRs) in BST-0.6 and BZT-0.25. Regarding this, BT can be distinguished from BST-0.6 and BZT-0.25. Relaxation in BT could be interpreted as successive change in polarization mechanism from normal ferroelectrics to relaxor ferroelectrics via DPT ferroelectrics.

Dielectric Properties of Barium Titanate Ceramics with Nano-Sized Domain

Barium titanate (BaTiO3) ceramics with various grain sizes from 0.7 to 13 μm on average were prepared by a conventional sintering method, a two-step sintering method and a rate controlled two-step sintering method. The permittivity of the ceramics was increased with decreasing grain size to 1.1 μm on average. However, the permittivity of the ceramics was decreased when the grain size was below 1 μm. The field emission scanning electron microscope (FE-SEM) observations revealed that the 90º domain width decreased with decreasing the grain size. By ultrawide range dielectric spectra from kHz to THz range of the BaTiO3 ceramics, the domain contribution to the permittivity was investigated. For the BaTiO3 ceramics with grain sizes over 1 μm, the dipole polarizability and the ionic polarizability were enhanced by high domain-wall density. In contrast, for the BaTiO3 ceramics with grain sizes below 1 μm, these polarizabilities were weakened.

Wide Range Dielectric Spectroscopy of Barium Strontium Titanate Ceramics

Wide band dielectric spectroscopy was applied from kHz to THz region for the analysis of both the ionic and the dipole polarization in Ba0.6Sr0.4TiO3 ceramics. The dielectric permittivity above the dielectric maximum temperature (Tm) is mostly dominated by the ionic polarization, while that below Tm is governed by the dipole polarization. Dielectric permittivity given by the dipole polarization increased and the relaxation frequency decreased with decreasing temperature. These phenomena are related to a increase of the size of polar nanoregions (PNRs).