Keiji Shiga

Complex impedance and ionic conduction of single-crystalline BaTiO3

ABSTRACT Dielectric properties of single-crystalline BaTiO3 in the direction to <001> were investigated by impedance spectroscopy. The complex plane plots showed high- and low-frequency semicircles and an inclined spike at 548–648 K. The spectroscopic plots of M″ comprised a single relaxation peak at 102–104 Hz, whereas those of Z″ exhibited a peak at high frequencies (102–104 Hz), a low-frequency peak, and dispersion. The high-frequency relaxation was attributed to the ferroelectric bulk. The low-frequency peak and dispersion were associated with the charge transfer and the Warburg impedance, respectively. The low-frequency impedance response implied the ionic conduction of BaTiO3.

Dielectric Properties and Optical Absorption of Single-Crystalline BaTi2O5 Synthesized Using High-Purity BaCO3 as Source Material

Highly pure transparent single-crystalline BaTi2O5, 6 mm in diameter and 15 mm in length, was prepared by a floating zone (FZ) method using high purity BaCO3 as a source material. The as-prepared crystal was partially dark blue and became transparent by annealing at 773 K in air. The maximum value of permittivity (εmax) was 36000 at the frequency of 100 kHz and the Curie temperature (TC) was 757 K.

In-situ observation of instability of a crystal–melt interface during the directional growth of pure antimony

The instability of a crystal–melt interface during the directional growth of pure antimony was studied using an in-situ observation technique. The morphology of the crystal–melt interface was planar at a low growth velocity, while the interface transitioned to wavy and then zig-zag faceted at 60 μm s−1. Calculating the thermal field at the crystal–melt interface using a diffusion equation showed that the temperature gradient in the melt becomes negative when the moving velocity of the interface is higher than 52 μm s−1. These results demonstrate that perturbations introduced into the planar interface are amplified by a negative temperature gradient and these amplified perturbations result in zig-zag facets.The instability of a crystal–melt interface during the directional growth of pure antimony was studied using an in-situ observation technique. The morphology of the crystal–melt interface was planar at a low growth velocity, while the interface transitioned to wavy and then zig-zag faceted at 60 μm s−1. Calculating the thermal field at the crystal–melt interface using a diffusion equation showed that the temperature gradient in the melt becomes negative when the moving velocity of the interface is higher than 52 μm s−1. These results demonstrate that perturbations introduced into the planar interface are amplified by a negative temperature gradient and these amplified perturbations result in zig-zag facets.

Formation of radioactive fullerenes by using nuclear recoil

The formation of As and Se atom-incorporated fullerenes has been investigated by using radionuclides produced by nuclear reactions. From the trace of radioactivities of 72As, and 75Se after High Pressure Liquid Chromatography (HPLC), it was found that the formation of endohedral fullerenes or heterofullerenes is possible by a recoil process following the nuclear reactions. To confirm the produced materials, ab initio molecular-dynamics simulations based on an all-electron mixed-basis approach were carried out.

Formation of new materials in fullerenes by using nuclear recoil

The formation of Sb or Te atom-incorporated fullerenes has been investigated by using radionuclides produced by nuclear reactions. From the trace of radioactivities of 120Sb(122Sb) or 121Te after High Pressure Liquid Chromatography (HPLC), it was found that the formation of endohedral fullerenes or heterofullerenes in atoms of Sb or Te is possible by a recoil process following the nuclear reactions. To confirm the produced materials, ab initio molecular-dynamics simulations based on an all-electron mixed-basis approach was carried out. We present possibility of the formation of endohedral fullerenes or substitutional heterofullerenes incorporated with Sb or Te atoms.The formation of Sb or Te atom-incorporated fullerenes has been investigated by using radionuclides produced by nuclear reactions. From the trace of radioactivities of 120Sb(122Sb) or 121Te after High Pressure Liquid Chromatography (HPLC), it was found that the formation of endohedral fullerenes or heterofullerenes in atoms of Sb or Te is possible by a recoil process following the nuclear reactions. To confirm the produced materials, ab initio molecular-dynamics simulations based on an all-electron mixed-basis approach was carried out. We present possibility of the formation of endohedral fullerenes or substitutional heterofullerenes incorporated with Sb or Te atoms.