Browsing by Author "Singh, K"

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    Electrical properties of hollandite-type Ba1.33Ga2.67Ti5.33O16, K1.33Ga1.33Ti6.67O16, and K1.54Mg0.77Ti7.23O16
    (American Chemical Society, 2019-03-28) Cao, C; Singh, K; Kan, WH; Avdeev, M; Thangadurai, V
    Electrical conductivity and electrochemical catalytic activity for H2 oxidation of Ti-based hollandite-type Ba1.33Ga2.67Ti5.33O16 (BGT), K1.33Ga1.33Ti6.67O16 (KGT), and K1.54Mg0.77Ti7.23O16 (KMT) were investigated, along with the chemical stability of KMT under H2 at elevated temperature. BGT, KGT, and KMT crystallized in a tetragonal structure with the space-group I4/m. The electrical conductivity in H2 increases with increasing Ti content, and the highest total electrical conductivity of 2 S/cm at 800 °C in H2 was observed for KMT. KGT:Fe (1:1) + 20% LSGM + 30% porosity composite electrode showed the lowest area specific resistance of ca. 1.6 Ω cm2 at 800 °C for hydrogen oxidation reaction (HOR) under the open circuit condition. Moderate catalytic activity for HOR could be attributed to poor oxide ion conductivity and exclusion of potassium and hydrogen uptake in H2 at elevated temperature. Bond valence sum mismatch map calculation showed that the ionic transport happens along the 1D channel of c-axis in the hollandite oxides. © 2019 American Chemical Society
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    Evaluation of polymorphism and charge transport in a BaO–CaO–Ta2O5 perovskite phase diagram using TOF-neutron and synchrotron X-ray diffraction, the bond-valence method and impedance spectroscopy
    (Royal Society of Chemistry (RSC), 2022-10-26) Singh, K; Yang, H; Zhang, Z; Avdeev, M; Huq, Ashfia; Wu, DY; Lee, JJ; Kan, WH; Thangadurai, V
    Among the alkaline earth-based perovskite oxides, the Ba-based perovskites have superior chemical stability and tunable electrical/catalytic property via chemical substitution/doping. One of the best-known examples is Ba3Ca1.18Nb1.82O8.73 as a ceramic proton conductor for all-solid-state steam electrolysis and solid oxide fuel cells (SOFCs). Structural ordering variation is often driven by chemical composition, which directly correlates with their chemical/physical properties. In the present work, we develop a comprehensive functional perovskite-type phase diagram for the Ba–Ca–Ta–O quaternary system Ba3Ca1+xTa2−xO9−3x/2 (0 ≤ x ≤ 0.36) with a wide chemical composition between 1000 and 1550 °C, coupled with theoretical calculations to investigate the cation ordering in supercells. Furthermore, the impact of cation clustering on the diffusion pathways of O2− ions was evaluated as a case study. Experimentally, precise cation ordering and other structural features are quantitively determined by TOF-neutron and synchrotron X-ray diffraction analyses. This work provides a comprehensive evaluation of some potential applications of the Ba–Ca–Ta–O quaternary system. The electrochemical impedance data were also systematically studied by impedance spectroscopy genetic programming (ISGP). The electrical conductivity was found to increase from x = 0 to x = 0.27 and then decrease for the end member when x = 0.36 due to a decrease in mobile charge carrier concentration. Interestingly, in dry air, the electrical conductivity was found to increase from x = 0 to x = 0.36. However, only Ba3Ca1.18Ta1.82O8.73 (BCT18) and Ba3Ca1.27Ta1.73O8.595 (BCT27) were found to show an increasing trend in conductivity in humid atmospheres, and this indicates that the clustering effect was pO2 dependent. © Royal Society of Chemistry 2024