Eiji Asari

Infrared and Raman spectra of solid solutions Ti1−xZrxO2 (x⩽0.1)

Abstract Infrared and Raman spectra of solid solutions Ti 1− x Zr x O 2 ( x ⩽0.1) have been measured as a function of the concentration x at room temperature. The E g mode at 448cm 1 for rutile (TiO 2 ) noticeably softened and broadened with increasing x , while the A l g mode at 613 cm 1 remained unchanged in frequency but broadened slightly. The disorder induced Raman band(broad) at 235 cm 1 showed a decrease in frequency with x . Moreover, the infrared-active E u , modes at 398 cm 1 and 516 cm 1 softened with x in the solid solutions. X-ray diffraction confirmed that the lattice parameters, a and c , almost linearly increase with x in Ti 1− x Zr x O 2 , altering the positional parameter of the oxygen anions in TiO 6 . It turned out that the concentration dependence of optical modes for Ti 1− x Zr x O 2 is associated with the force constant change of the six cation-anion bonds based on the octahedral distortions of TiO 6 , as Ti 4+ is replaced by Zr 4+ with a larger ion radius than Ti 4+ .

Observation of relaxation processes of disorder in ion-irradiated graphite using Raman spectroscopy

Abstract Real-time Raman measurement has been applied to monitor the thermal relaxation processes in graphite at 411–463 K under 5 keV deuterium ion irradiation. The observed time dependence of density of defects revealed that the thermal relaxation process consists of three distinct stages. Dominant processes have been discussed for each stage.

Real-time observation of thermal relaxation of initial damage in graphite under ion irradiation

Abstract Real-time Raman measurements are conducted for graphite during and after helium ion and deuterium ion irradiation at the sample temperatures from 393 to 473 K. A transient behavior is observed in the thermal relaxation of lattice disorder. Results indicate that two processes exist for the restoration of the phonon correlation length by thermal relaxation. The fast process is suggested to be a recombination of vacancies and interstitials, and the activation energies have similar values: 0.89 ± 0.10 eV for helium ion irradiation and 1.0 ± 0.10 eV for deuterium ion irradiation. The slow process suggests a chemical effect; the activation energy for deuterium ion irradiation (0.36 ± 0.25 eV) is smaller than that for helium ion irradiation (1.8 ± 0.30 eV).

Thermal relaxation of lattice disorder in graphite induced by He+ irradiation

Abstract The transient behavior of thermal relaxation of lattice disorder in graphite induced by low energy He + irradiation has been studied by time-resolved Raman measurements. Our initial results show that disorder induced by irradiation relaxes with a characteristic time constant of ∼ 450 s at temperature as low as 473 K.