Yoshifumi Torimoto

Electric Field Emission of High Density O − Ions from 12CaO ⋅ 7Al2 O 3 Engineered to Incorporate Oxygen Radicals

We succeeded in extracting intense O - ion beam by applying dc voltage to a microporous crystal 12CaO.7Al 2 O 3 (C12A7) engineered to incorporate extremely large amounts of O - (1.3 X 10 2 0 cm - 3 ) and O 2 - (2.7 X 10 2 0 cm - 3 ) in crystallographic cages. The O - ion beam is monochromatic and the current density (∼2 μA/cm 2 ) is higher by three orders of magnitude than the maximum value recorded for yttrium-stabilized ZrO 2 (YSZ). A surface metal electrode, essential for the YSZ to dissociate a drifted O 2 - in the bulk into an O - and an electron on the surface, is not needed for the C12A7. The presence of extremely large concentrations of O - and O - 2 ions and fast oxygen-ion-conductive nature of C12A7 allow extraction of O - ions directly from the surface.

Emission of O- Radical Anions from a Solid Electrolyte Surface into the Gas Phase

We have observed the emission of O- radical anions from a solid electrolyte surface. A simple experimental apparatus was designed to incorporate a gap between a YSZ (yttria stabilized zirconia) anode and a stainless steel space electrode. By applying a DC voltage of 100 V across the gap, O- radical anions and electrons were produced which could be detected using a quadrupole mass spectrometer. Recently, Greber et al.. reported the observation of O- radical anion emission from a cesium-coated surface when the surface was exposed to thermal oxygen molecules. However, this method cannot maintain O- emission without adsorbed oxygen molecules. In the present work, the possibility of obtaining continuous emission of O- from a YSZ surface was examined.

Reproducibility of O- Negative Ion Emission from C12A7 Crystal Surface

Reproducibility, stability and oxygen-pressure dependence of O- negative ion emission from a synthesized crystal 12CaO7Al2O3 (C12A7) surface have been investigated. We found the continuous O- implantation into the C12A7 crystal can be simply realized by supplying electron and oxygen on the Au-deposited C12A7 surface via electrocatalytic reactions. The O- emission from the consumed C12A7 surface was recovered after the implantation operation (O2: 0.13 Pa; 770°C) for 30 minutes. In contrast, the implantation influence on electron emission is negligible. The O- emission intensity is nearly constant in the O2 pressure lower than 1×10-3 Pa. The O- implantation mechanism will be addressed.

Features and mechanism of atomic oxygen radical anion emission from yttria-stabilized zirconia electrolyte

Abstract Anion and electron emissions from Y 2 O 3 -stabilized ZrO 2 (YSZ) electrolyte were investigated by time of flight (TOF) spectroscopy. The atomic oxygen radical anion (O − ) is the only anion species emitted from the YSZ surface. The emission branch ratio between O – and electrons is close to one. The Arrehenius plots for both O – and electron emission, derived from the temperature dependences, exhibit double linear behavior. The apparent activation energies in the low-temperature region ( 620 °C). It was also found that the extraction field can enhance the O – emission. The maximum emission current density for O – is 3.5 nA/cm 2 in our investigated range. The observed O – and electron emissions are attributed to the dissociation of the intermediate anions, O 2– , present on the YSZ anode surface. The rate-determining step for the O – emission is believed to be the desorption process in the low-temperature region, and the electron desorption or the electrochemical reaction in the high-temperature region.

Desorption of the C2- anion from the Au-C-deposited Y2O3-Stabilized ZrO2 surface

Carbon dimer anions (C2-) and atomic oxygen radical anions (O-) desorbed from an Au−C-deposited Y2O3-stabilized ZrO2 (YSZ) surface have been observed. Both the emitted anions and electrons were found to be strongly dependent on the surface temperature and applied extraction field. The Arrhenius plots for the anions and electrons exhibit double-linear behavior, resulting in lower apparent activation energies in the high-temperature region (>913 K). It was found that the apparent activation energies can be reduced by the extraction field. Measurements of the absolute emission current density show similar temperature and field features as derived by TOF (time-of-flight) spectroscopic investigations. The observed anions of O- are attributed to the detachment of the transient anions of O2-(s) (i.e., O2-(s) → O-(s) + e-(s)), which migrate from the YSZ bulk onto the emission surface. The C2-(s) anions are attributed to the surface anion-exchange reactions between O-(s) and surface carbon atoms. An emission mecha...