We report in-situ measurements of impedance spectroscopy during flash experiments with single crystals of cubic-yttria stabilized zirconia, conducted in ambient air at 300 °C to 700 °C under a direct ...current electric field. Platinum electrodes transition from blocking to non-blocking behavior before the onset of flash, indicating a transition to partial electronic conductivity during the incubation period. Even though the conductivity continued to increase with temperature the electron transport remained at a plateau of approximately 0.25. This result has ramifications not only in the fundamental understanding but also in technological significance of the flash phenomenon.
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We report on the discharge of the capacitance formed at the electrodes in flash experiments with yttria stabilized zirconia. The experiments were carried out by disconnecting the current, and, ...instead, short circuiting the electrodes through a resistor. The time dependent voltage across the resistor was measured; the ratio yielded the discharge current. The current decayed exponentially with time, as expected in an RC circuit, which allowed the measurement of the capacitance. Experiments were carried out in two ways. In one case the specimens were flashed within a glove box filled with Ar (< 1 ppm O2): these yielded electronic conductors. In the other case the specimens were flashed in ambient air: while electronically conducting in‐flash these specimens recover their prior insulating behavior as soon as the current is turned off. The stored charge was two orders of magnitude greater in the Ar experiments. Rather unexpectedly, the sign of the voltage expressed at the electrodes was opposite in experiments carried out in air and in Ar. The capacitance measured in the discharge experiments is attributed to the formation of space charge adjacent to the electrodes. In the case of Ar experiments, the capacitance is very large, approaching 1 F; in this case the space charge is expected to be constituted from ions. In the air experiments the specimen becomes insulating, trapping the electrons as a space charge. Hall effect measurements of the carrier density and X‐ray photoelectron spectroscopy characterization of electronically conducting single crystal specimen of cubic zirconia are reported.
It is known that once flash has been triggered with furnace heating, specimens can be held in the state of constant flash, or Stage III, outside the furnace at ambient temperature. The flash is ...maintained by the current flowing through the specimen. We show that this in‐flash state is further preserved when the specimen is immersed into liquid nitrogen. Furthermore, we show that the nature of the material existing in Stage III can be quenched by turning off the power to the specimen while it is still in immersion. Normally, during furnace cool, the specimens revert to their original state when the flash is turned off. However, yttria‐stabilized zirconia retrieved from in‐flash immersion‐and‐quench is discovered to be electronically conductive at room temperature, at approximately 11 S/m. The conductivity declines somewhat when the specimen is heated slightly above room temperature, suggesting metal‐like behavior. These in‐flash immersed specimens, with their Stage III structure frozen in place, will enable ex‐situ characterization of changes in the crystallographic, chemical, defect and electronic structure induced by flash activation.
A single‐crystal specimen of rutile (titania) was flashed repetitively, while increasing the electric field after each cycle. As expected, the flash onset temperature continued to drop modestly at ...higher fields. However, when the field was increased from 400 to 450 V cm–1, the flashed onset fell dramatically down to room temperature. We have investigated the electrical and optical properties of this room temperature flashed specimen (called SZ). The specimen was electronically conducting. Optical absorption spectroscopy revealed a narrow band of new energy levels that were generated just below the conduction band. The gap between the conduction band and this flash‐induced energy level agreed with the peak in the electroluminescence spectrum. Optical second harmonic generation (SHG) is reported. The flash‐on condition significantly lowered the SHG, which rebounded when the flash was turned off. This result suggests that the structure becomes more centrosymmetric in the state of flash, which may represent a disordered state of defects. The possibility of studying flash behavior at room temperature, without a furnace (as in SZ type specimens), opens a considerable simplification for in‐situ characterization of flash behavior. For example, a possible relationship between memristor physics and the flash phenomenon can be studied.
This is the second report on the retention of electronic conductivity in yttria‐stabilized zirconia at room temperature after cooling down from the state of flash . In the first report, the specimens ...(which were flashed in air) were quenched by in‐flash immersion into liquid nitrogen. Now we show that if the specimens are flashed in Ar in a glove box (O2 < 1 ppm), then they remain electronic conductors under nominal cooling. Indeed, the conductivity of the Ar‐flashed specimens is higher than the conductivity of LN2‐quenched samples. In both instances, their conductivity increases with flash current. In contrast, specimens flashed in air, and then air‐cooled, become insulating akin to their original condition. We propose a possible pathway for such a reaction. In addition, we report measurements of the interface resistance at the anode and the cathode by the four‐point technique. In air, the resistance at anode is higher than at the cathode, and the sum of the interface resistances is about one half of the total end‐to‐end resistance.
We present direct evidence, for the first time, for the flash‐induced generation of crystal defects in single‐crystal cubic zirconia. The defects are characterized by multiple techniques. The ...crystals were flashed and then cooled down to ambient temperature in Ar atmosphere to preserve the electronic conductivity from the steady state of flash. Transmission electron microscopy revealed colonies of defects. The crystal structure, the non‐stoichiometry, and the electronic structure of oxygen ions within these colonies were characterized. They consist of oxygen‐depleted compositions. Selected area electron diffraction revealed the structure of these zirconia suboxides to be epitaxially coherent with the parent cubic structure but with a smaller lattice parameter. Electron energy loss spectroscopy spectra showed the peak near 25 mV to shift toward metallic zirconium. The electronic conductivity of the flashed cubic zirconia is attributed to this suboxide phase. The phase also gave rise to new peaks in Raman spectroscopy. A surprising finding was the presence of a distinct, ∼30 nm thick layer of the suboxide on the surface of the crystal. The surface layer showed a high degree of oxygen deficiency. It was also epitaxial, but with an even smaller lattice parameter than the defect colonies underneath the surface. Mechanical polishing of the crystal to remove this surface layer gave a broad view of the interconnected network of defects across the entire specimen; the length scale of this network was about 0.2 mm. Recent work, where an overlay of a magnetic field caused the flash to migrate from a flashing surface into a free‐standing workpiece, suggests the presence of evanescent plasma, which may have a connection to this surface layer.
In order to achieve a high energy density, Ni-rich polycrystalline materials have been explored as cathode materials for application in ASSLB applying sulfide solid electrolyte. However, the ...interaction between the electrode and the solid electrolyte comes with severe problems, such as a poor solid electrolyte interface and interfacial stress fracturing during the charge-discharge process. To alleviate the side reaction and the interfacial resistance, a coating layer between the cathode and sulfide electrolyte has since been proposed and developed. However, the inner surface of the primary particles in the polycrystalline can also be a form of coating layer, which does not meet the solid electrolyte and it is hence an inefficient coating mechanism for an ASSLB where the cathode/electrolyte interface occurs purely at the cathode outer surface. Here, we report a new coating strategy for Ni-rich polycrystalline cathode materials using a sol-gel process that focusses on improving the cathode/electrolyte interface of ASSLB. Commercial polycrystalline LiNi
0.8
Co
0.1
Mn
0.1
O
2
was coated with 1 wt% lithium and cobalt acetate precursor with different coating coverage being achieved via control of the stirring speed (200 and 600 rpm). The coating materials, which uniformly coated on the inner and outer surfaces of the polycrystalline (I-NCM), showed effectively improved electrochemical performance with the structural stability in LIB, where the liquid electrolyte has contact with inner surface of polycrystalline materials. However, the cathode material, which was mainly coated on the outer surface of polycrystalline materials (O-NCM), exhibited improved performance in the ASSLB, which only has contact with the electrolyte at the surface of the active material polycrystalline. The physical properties of the coated cathode material were analyzed using SEM and XRD, and the electrochemical performance was investigated through initial charge/discharge capacity and cycle stability in both LIB and ASSLB simultaneously. This concept of intentionally surface coating the polycrystalline material can be applied as a new coating strategy to realize improvements in both electrochemical properties and electrode structural stability of ASSLB.
The amorphous In─Ga─Zn─O (a‐IGZO) thin film transistors (TFTs) have attracted attention as a cell transistor for the next generation DRAM architecture because of its low leakage current, high ...mobility, and the back‐end‐of‐line (BEOL) compatibility that enables monolithic 3D (M3D) integration. IGZO‐based electronic devices used in harsh environments such as radiation exposure can be vulnerable, resulting in functional failure. Here, the behavior of subgap density‐of‐states (DOS) over full subgap range according to the impactful gamma‐ray irradiation in a‐IGZO TFTs is investigated by employing DC current–voltage (I−V) data with multiple‐wavelength light sources. To understand the origins of the radiation effect, IGZO films have been also analyzed by x‐ray photoelectron spectroscopy (XPS). Considering in‐depth electrical and chemical analysis, the unexpected increase of subthreshold leakage current caused by total ionizing dose (TID) is strongly correlated with newly discovered deep‐donor states (gDDγ(E)$g_{DD}^\gamma ( E )$) at the specific energy level. In particular, oxygen vacancies caused by the gamma‐ray irradiation give rise to undesirable electrical characteristics such as hysteresis effect and negative shift of threshold voltage (VT). Furthermore, the TCAD simulation results based on DOS model parameters are found to exhibit good agreement with experimental data and plausible explanation including (gDDγ(E)$g_{DD}^\gamma ( E )$).
IGZO oxide semiconductors promising as next‐generation 2T0C DRAM architectures increase oxygen vacancy when gamma‐ray are irradiated, resulting in increased instability of IGZO films. The full range DOS of IGZO TFTs changed from gamma‐rays is investigated by the proposed observation method based on the multi‐wavelength light source, which is verified by TCAD simulation.
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