Mareo Ishigame

Optical Spectra of Y2O3 Single Crystals in VUV

Optical absorption in the tail region and reflectivity at room temperature in the VUV region up to 42 eV are measured on Y 2 O 3 single crystals. Various optical constants as functions of photon energy are derived therefrom by use of the Kramers-Kronig relation. The Urbach rule parameters are also determined experimentally for the tail. A tentative interpretation is given on the spectral structures found in the optical constants, referring to the energy levels of Y 2+ and Y 3+ free ions.

Protonic conduction in the single crystals of SrZrO3 and SrCeO3 doped with Y2O3

Abstract Single crystals of SrZrO 3 and SrCeO 3 doped with Y 2 O 3 were made by floating zone method and their electric conductivities were measured. The bulk protonic conduction is confirmed for both crystals. The activation energies are evaluated to be 0.45 and 0.56 eV for SrZr 0.95 Y 0.05 O 3−α and SrCe 0.95 Y 0.05 O 3−α , respectively. From the isotopic effect, it is found that t proton tunneling effect is negligible and the protonic migration is well explained by the thermal activation mechanism. Infrared absorption measurements show that the proton is bound in the interstitial sites by oxygen ions.

A Solar-Pumped cw 18 W Nd:YAG Laser

The development of a solar-pumped Nd:YAG laser is reported. A solar energy collector consisting of a paraboloidal mirror 10 m in aperture and 3.2 m in focal length is used to pump a water-cooled Nd:YAG laser rod 4 mm in diameter and 75 mm in length. The maximum output of the laser is 18 W in multi-mode, the highest output power reported so far in solar-pumped lasers. Further improvements designed to increase the power are also discussed.

Protonic conduction in the single crystals of Y-doped SrZrO3

Protonic conduction is found in the single crystal of Y-doped SrZrO3. The isotope effect on electrical conductivity proves that the electrical conductivity is referred to the hole conduction at the temperature above 700°C and to the protonic conduction below 500°C. The protonic conductivities of SrZr1−xYxO3−α increase rapidly with the concentration of Y3+ ions and become almost constant at x≧0.05.

Proton sites and defect-interactions in SrZrO3 single crystals studied by infrared absorption spectroscopy

Abstract Infrared (IR) absorption spectra of OH-stretching mode have been studied in single samples of the protonic conductor, SrZrO 3 :M 3+ ( M 3+ = Sc 3+ , Y 3+ , Yb 3+ , Er 3+ ). Four absorption bands, which correspond to four different sites of protons, are observed in IR spectra. Proton dynamics in these sites are studied by the annealing time dependence of IR spectra, which are quenched from high temperature. We have found that the relative population of protons among different sites changes as the proton concentration changes the crystal. This result indicates that the trapping energy for protons is different among these sites.

A conductivity and thermal gravimetric analysis of a Y-doped SrZrO3 single crystal

Abstract From impedance spectroscopy combined with thermal gravimetric analysis (TGA), the conductivity properties and the defect chemistry of a nominally 5 mol% Y-doped SrZrO 3 single crystal are derived. In the temperature range from 60 to 740°C, in which the charge carrier concentrations are frozen-in, proton, hole and oxygen vacancy conductivity with migration energies of 0.47 eV, 0.84 eV and 1.0 eV dominate in different atmospheres. The proton concentration is determined consistently from the water incorporation measured by TGA and conductivity data yielding a saturation concentration of 0.08 mol%.

Study of the defect-induced Raman spectra in cubic zirconia

Abstract Polarized Raman spectra of (1−x)ZrO 2 − x YO 1.5 ( x = 1.18), which is a superionic conductor, has been studied. The Raman spectra exhibit a distinct polarization effect and many structures. Phonon dispersion curves of cubic zirconia are calculated by using a rigid ion model, assuming that cubic zirconia is a fluorite type perfect crystal consisting of virtual ions. It is found that the polarization characteristics of observed Raman spectra can be well explained by the frequency distributions of defect-induced Raman active modes in the whole Brillouin zone, which are estimated from the imaginary part of the simple projections of the phonon displacement-displacement Greens functions onto a defect space consisting of a vacancy and surrounding 6 oxygen ions.

Proton diffusivity in SrZrO3: Sc3+ single crystals studied by infrared absorption spectroscopy

Abstract The diffusivity of protons in Sc 3+ doped-SrZrO 3 single crystals have been determined by the infrared absorption technique in the temperature range of 400–750 °C. The proton diffusion coefficient D has been evaluated by two different methods, i.e. (1) the sudden change of P H 2 O and (2) the exchange between H + and D + -vapor. It is found that the D value of proton obtained in SrZrO 3 single crystals is smaller than that obtained in ceramics, and the activation energy of D obtained by the method (1) is larger than that of ceramics. From these results, comes a suggestion that the defect concentration (or distribution) in the ceramics grains may be different from that in single crystals.

Measurement of oxygen permeability in CeO2 doped CSZ

The oxygen permeability in [(ZrO2)1 − x(CeO2)x]0.9(CaO)0.1 (x = 0.1−0.4) was measured at 1100–1800 K under the gradient of oxygen partial pressure created between air and inert gas. Tube shaped specimens were used with 13 and 9 mm outer and inner diameters respectively and lengths of 5 and 15 mm. One end of each specimen was fixed to an alumina tube and the other end to an alumina disk with Pt-O-rings at 1800 K, and were set in a SiC furnace. Air and helium were supplied to the outsides and insides of specimens respectively. The oxygen permeation rate was calculated from the increase in oxygen concentration and the flow rate of helium. The oxygen permeability was obtained from the oxygen permeations of two specimens different in length to eliminate the short-circuiting effect of Pt-O-rings. It was shown that the oxygen permeability was determined by the electronic conductivity of the solid solution, which was n-type, and increased as the Ce concentration and the temperature were increased.

Protonic Conduction in the Single Crystals of SrZr0.95M0.05O3 (M=Y,Sc,Yb,Er).

The protonic conductivities of SrZr0.95M0.05O3 doped with four acceptor ions (M3+=Y3+, Sc3+, Yb3+, Er3+) have been studied in the single crystal form. The protonic conductivity is found in four acceptor ions, indicating that protons migrate by hopping from site to site. The Yb-doped crystal has the lowest activation energy and the highest conductivity amongst the four acceptor ions. This is considered to be due to the difference in strength of the O–H bond with different acceptor doping.