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Langatate (La3Ta0.5Ga5.5O14, LTG) has been widely used in piezoelectric sensors in high temperature applications because of its structural and piezoelectric reliability at high temperature. However, in the low oxygen partial pressure and elevated temperature ranging from 300 to 700 °C, an increase of electrical conductivity originated from intrinsic oxygen vacancies have been observed in a previous experimental result. In this study, to elucidate the oxygen vacancies effects on LTG, formation energy of each electronic state of oxygen vacancies ( V O , V O and V O × ) at non-equivalent Wyckoff positions (2d and 6g) and their electronic structures were calculated by combining GW quasi-particle scheme and conventional density functional theory (DFT). The formation energy of VO(6g) was lower than the formation energy of VO(2d) in each electronic state. Thus, relatively stable oxygen vacancies at 6g sites (VO(6g)) can be major oxygen vacancies in LTG system. Also, calculated band gaps of LTG with thermodynamically stable defects such as V O ( 6 g ) or V O ( 6 g ) × were higher than band gaps of LTG with V O ( 2 d ) or V O ( 2 d ) × at Γ-point. By the band interpolation based on Boltzmann transport theory, calculated electrical conductivities per unit relaxation time (σ/τ) of the LTG with V O ( 2 d ) and V O ( 6 g ) were similar at the same electron energy, however, σ/τ of the LTG with V O ( 2 d ) × was higher than that of the LTG with V O ( 6 g ) × .

Single Crystalline Langatate (La3Ta0.5Ga5.5O14, LTG) Has Been Widely Used in Piezoelectric Sensors for High Temperature Applications because of its Structural Stability at High Temperature. however, in the Recent Experiment, an Increase of Electrical Conductivity Has Been Also Observed at the Intermediate Temperature Region Ranges from 300 to 700°C. Also, in Theoretical Calculations, Penta-Valent Ta Vacancy Can Be Easily Generated and Influence Resistivity Degradation of the Crystal. In this Study, to Elucidate the Ta Vacancy Effects on Electrical Conductivity of LTG and Recently Proposed Ba-Based P321 Crystal such as BTGS and BTAS, Electrical Conductivity of those Materials Were Calculated and Compared by Utilizing Boltzmann Transport Theory. The Calculated GW Band Gaps of Perfect BTGS and BTAS (5.94 Ev and 6.69 Ev, Respectivily) Were much Larger than that of LTG (5.36 Ev). Also, at Intermediate Temperature (1000K), the Calculated Electrical Conductivity of LTG with V'''''Ta (in Kröger-Vink Notation [13]) Was around Twelve Times Higher than the Conductivity of BTGS and BTAS with Ta Vacancy.

Single crystalline langatate (La 3 Ta 0.5 Ga 5.5 O 14 , LTG) has been widely used in piezoelectric sensors for high temperature applications because of its structural stability at high temperature. Ionic conduction originated from oxygen vacancy diffusion has been reserved at high temperature regime (over 700 °C). Similarly, an increase of electrical conductivity has been also observed at the intermediate temperature region ranges from 300 to 700 °C. Thus, it can be presumed that spontaneously generated point defects influence resistivity degradation of the crystal. In this study, to elucidate the oxygen vacancy effects on electronic structures and transport properties of LTG, formation energy curves of three different states of oxygen vacancy (V •• O , V • O and V × O ) and their electronic structures and transport properties, such as carrier concentration and electrical conductivity were calculated by utilizing first principles calculations. The calculated band gaps by the GW method were 5.36 eV, 4.34 eV and 4.66 eV for defect-free LTG, LTG with V •• O and V × O , respectively. Also, the GW result showed higher transition level of oxygen vacancy compared with the transition level calculated from the conventional DFT method. Although, in a previous experimental result, Ga loss was observed in Langasite (LGS) crystal, however, the formation energy of V O was much lower than the formation energy of V Ga in LTG. At 900 K, the calculated electrical conductivity of LTG with two stable oxygen vacancy (V •• O and V × O ) were ten times higher than the conductivity of defect-free LTG around the Fermi levels. Therefore, at intermediate temperature, oxygen vacancy generation can cause an increase of electrical conductivity.

Performance characteristics of micro, single-chamber, intermediate temperature solid oxide fuel cell (IT–SOFC) has been successfully evaluated by computational simulation based on macro modelling. The system has composite electrodes that are alternately placed on the ceria-based electrolyte. The polarization curve is obtained through the series of computational processes for structural parameters such as distance between the anode and the cathode and the thickness of the electrolyte. Also, the effect of the inflow direction of fuel–air mixture on the performance of the fuel cell is quantitatively investigated.

A new layered chalcogenide semiconductor, Bi2MnTe4, was discovered. It was prepared by melting and annealing methods and its crystal structure was determined by powder X-ray diffraction and Rietveld refinement. It showed p-type conducting behavior at room temperature and it was quite consistent with our density functional theory calculations. Furthermore, based on the metastability of Bi2MnTe4, a nanostructuring strategy was attempted to fabricate nanostructured bulk composites. Nanostructured Bi2Te3/MnTe2 composite was successfully achieved in this work, and its thermoelectric properties were discussed.

We present the impact of Al-doped ZnO (AZO) layer of polycrystalline silicon (poly-Si) thin films grown at different annealing temperatures using aluminum-induced crystallization (AIC). In situ observation revealed that the increase of crystallized fraction was fast in poly-Si films grown with AZO layer compared to those without AZO. It is explained that the roughness of interface between Si and Al by introducing AZO layer was increased, which contributes to enhancement of diffused Si concentration into Al layer. Those results were also quantitatively demonstrated by calculating of Si concentration diffused into the Al layer. Therefore, we exhibit that controlling interface roughness is shown to be important to determine the growth rate of poly-Si thin films.

Performance characteristics of micro scale single-chamber intermediate temperature SOFC (IT-SOFC) has been successfully evaluated by computational modeling. The micro scale SOFC system with composite electrodes and ceria based electrolyte was employed for modeling. The polarization curve was obtained through a series of computational process for structural parameters such as distance between anode and cathode and thickness of electrolyte. Also the effect of the inflow direction of fuel-air mixture on the performance of the fuel cell was quantitatively investigated.