Grain boundaries are known to block ionic conduction across grain boundaries in oxide ion conductors due to adjacent space charge layers. Since the positively charged grain boundary core is intensified with a high local concentration of defects such as oxygen vacancies, uniform distribution of a dopant may mitigate the formation of space charge layers and enhance the ionic conductivity. To investigate the dopant segregation effect on the space charge layer and ionic conductivity, we provided thermal energy to nanocrystalline gadolinia-doped ceria (GDC) thin film by post-annealing at different temperatures of 700 • C, 900 • C, and 1100 • C. STEM-EELS analysis demonstrates strong dopant segregation and a higher Ce 3+ content near the grain boundary than in the bulk after post-annealing. The concurrent segregation of dopants and Ce 3+ ions implies that once thermal treatment is applied to nanocrystalline GDC thin films, complete space charge layers are formed while the non-thermally treated GDC film with a uniform distribution of dopants has less of a space charge effect and exhibits superior ionic conductivity.Nanocrystalline materials have attracted a great deal of attention for applications in various energy conversion and storage systems including rechargeable lithium ion batteries, oxygen/ozone gas sensors, oxygen storage systems, and solid oxide fuel cells (SOFCs). 1-5 Compared to macro-or micro-scale materials, nanocrystalline materials possess extraordinary electrical or electrochemical properties (i.e., ionic conduction or surface exchange reactions). One major cause of the unusual properties is related to the fine grain size (<100 nm), which corresponds to an extremely high grain boundary density. For instance, nanocrystalline calcium oxide-stabilized zirconia (0.14 um grain size) showed a 15 times higher specific grain boundary conductivity than microcrystalline materials (>4 um grain size). 6 In terms of the surface kinetics, a nanocrystalline interlayer (∼65 nm grain size) applied to the interface between the cathode and electrolyte of a SOFC exhibited a 5-6 times lower electrode interface resistance than a microcrystalline interlayer (∼6 um grain size). 7 Therefore, understanding the grain boundary properties is important to appropriately utilize nanocrystalline materials for energy conversion devices due to their exceptional features compared to bulk materials.Recently, oxide ion conductors (e.g., gadolinia-, samaria-, or yttriadoped ceria (GDC, SDC, or YDC)) usually with a polycrystalline structure, have been widely studied as electrolyte materials for lowtemperature SOFCs (LT-SOFCs) since they exhibit higher ionic conductivity and surface exchange rate than the most commonly used electrolyte, yttria-stabilized zirconia (YSZ), especially in the low operating temperature regime (<500 • C). 7-9 In terms of the ionic conductivity, polycrystalline acceptor-doped ceria has shown grain boundary blocking of ionic conduction originating from the space charge effect. 10-14 A high local concentration of oxygen...

In this study, scandia-stabilized zirconia (ScSZ) electrolyte thin-film layers were deposited via chemical solution deposition (CSD). We selected 10ScSZ (10% Sc 2 O 3 , 90% ZrO 2 molar ratio) as the target material, and the precursor solution was prepared by precise calculations. The 10ScSZ solution was deposited on Al 2 O 3 substrate using a spin-coating method. Then, the substrate was sintered using two methods: flash light irradiation and thermal. The characteristics of the thin films were compared, including ionic conductivity, surface morphology, and chemical composition. Pulsed light sintering was applied in the sintering step under a variety of energy density conditions from 80 to 130 J/cm 2 , irradiation on/off times of 10 ms and 10 ms/500 ms, number of pulses, and bottom heat from 300 to 600 • C. The ionic conductivity of the ScSZ electrolyte layers fabricated by thermal or flash light irradiation methods was tested and compared. The results show that the ScSZ electrolyte layer sintered by flash light irradiation within a few seconds of process time had similar ionic conductivity to the electrolyte layer that was thermal sintered for about 10 h including cooling process.Coatings 2020, 10, 9 2 of 13 at low temperature. However, cerium oxide-based electrolytes have chemical instability due to a reduction of cerium ions from Ce 4+ to Ce 3+ when the electrochemical reaction occurs on the anode side in a high-temperature reduction environment. This reduction of cerium causes electronic conduction and results in loss of open-circuit voltage (OCV) of the SOFCs when it is used as an electrolyte by itself. In addition, it causes lattice expansion of the cerium oxide electrolyte on the fuel side, which leads to mechanical instability of the SOFC components [4,5]. To resolve these instability issues from ceria-based thin electrolyte layers and the relatively low ionic conductivity of YSZ, scandia-stabilized zirconia (ScSZ) was introduced. ScSZ is a zirconia-based oxide ion-conducting electrolyte material in which the dopant of YSZ is replaced with scandium, which is from the same family in the periodic table. The ionic radii of Zr 4+ is 0.84 Å, whereas the dopant ions are 0.87 Å for Sc 3+ and 0.94 Å for Y 3+ . Sc 3+ has an ionic radii similar to that of Zr 4+ , which reduces the steric-blocking effect during oxygen ion transport. Therefore, ScSZ has higher ionic conductivity than YSZ due to the ionic radii difference between the host (Zr 4+ ) and dopant ions (Y 3+ , Sc 3+ ). In addition, zirconia-based materials have superior chemical stability compared to ceria-based materials [6][7][8][9].Many deposition methods have been used to fabricate thin-film electrolyte layers for SOFCs, with an aim to minimize ionic transport resistance from the solid electrolyte. The methods can be generally categorized into two groups: vacuum processes and non-vacuum processes. The vacuum process deposition methods, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), allow for precise control of film microstruc...

This paper presents a new method for estimating muscle fatigue level based on surface electromyography (EMG) of femoral and gastrocnemius muscles during repetitive motions with various load. The relationship between fatigue level and EMG signals was examined through repetitive movements of the femoral and gastrocnemius muscles with the use of leg extension and squat machines. The fatigue level was based on the maximum voluntary contraction (MVC) levels with various loads. The integrated EMG (IEMG) value and the mean frequency value for each load cycle were obtained through the surface EMG signal. This work presents a global EMG index map by using the new analytical technique based on the relationship between the average IEMG and mean power frequency (MPF) values. The proposed method enables simultaneous estimation of muscle fatigue level and force using real-time EMG signals from the femoral and gastrocnemius muscles.

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