Atsushi Aruga

Structure and Photoacoustic Spectra of Ag-doped Cu2SiS3 particles

Ag-doped Cu2SiS3 particles were prepared by the reaction of elements at 800 °C for 7 days. Their crystal structure were determined from single crystal X-ray diffraction data. The solid solution limit of Ag atom into Cu atom in Cu2SiS3 was estimated to be 2.0 mol % from the change of unit cell volumes. Crystal structure of 2 mol % Ag-doped Cu2SiS3 was isostructure with monoclinic Cu2SiS3, superstructure of 3 times of sphalerite type. Optical absorption of above particles, whose Ag contents were from 0.0 to 3.0 mol % against to Cu, was measured by a microphone photoacoustic spectroscopy. Midpoint of main transition on Cu2SiS3 particles was 499 nm (2.48 eV) and an absorption in the IR region was from 710 to 730 cm-1 corresponding to the activation energy of Cu atom bonded by S atoms. The effect of Ag addition was almost nothing up to the limit of solid solution of 2 mol % Ag, but excess Ag addition caused to a slight shift to a wide gap. So it might be consider to a photoelectric or photocatalytic application by use of sunlight.

Direct Measurement of Optical Absorption for Si?Ge?Au Amorphous Thin Films by Using Photoacoustic Spectroscopy

We have already reported the extremely high thermoelectric properties of Si–Ge–Au amorphous thin films. The thermoelectric properties of such films change slowly during annealing cycles. In this paper, we describe the absorption spectra of the films by using photoacoustic spectroscopy (PAS) to clarify the change mechanism of these thermoelectric properties. Si–Ge–Au amorphous thin films were prepared by the alternate deposition of a non doped Si layer and a heavily Au doped Ge layer. The peak positions of the absorption spectra shift in a complex way with annealing, where the thermoelectric properties change. In these annealing cycles, we assume three stages to explain the mechanism of the change in the thermoelectric properties: the collapse of the superlattice, compositional diffusion and the termination of recrystallization at 673 K. We conclude that the change in the thermoelectric properties is explained by these three stages.

Effect of shock compression on optical and structural properties of Eu2O3 and Y2O3:Eu3+ powders

Shock-recovery experiments on Eu2O3 and Y2O3:Eu3+ powders using a metal plate projectile accelerated by a single-stage powder-propellant gun were performed to investigate phase stability and response at high pressures and temperatures. The recovered samples were characterized using powder X-ray diffraction analysis and photoluminescence spectroscopy. The onset of the structural phase transition from the cubic (C-type) to monoclinic (B-type) phase was observed for both Eu2O3 and Y2O3:Eu3+ powders at shock pressures of 8 and 13 GPa, respectively. For Eu2O3, the amount of B-type phase increases with increasing shock pressure up to 23 GPa, whereas for Y2O3:Eu3+, a maximum was reached at 25 GPa followed by a decrease with increasing shock pressure; only the C-type phase was detected in the sample shocked at 51 GPa. The change in the amount of B-type phase indicates stability for the monoclinic phase against shock-induced heat and mechanical deformation. The large range in shock pressure for which the C-type an...

Photoluminescence studies of shock-recovered Y2O3:Eu3+

A series of shock-recovery experiments on Y2O3:Eu3+ powder were conducted involving the impact of a flyer plate accelerated by a single-stage powder-propellant gun. The recovered samples were characterized by X-ray diffraction (XRD) analysis and photoluminescence (PL) spectroscopy. The XRD and PL results of samples shocked at pressures of 13 GPa indicated that a phase transition from a cubic phase to a monoclinic phase occurred. The recovered samples shocked at 21 and 25 GPa consisted of Y2O3:Eu3+ with the cubic phase and the monoclinic phase. These results indicated that the shock-induced phase transition was the partial completion of the phase transition.