An enhanced polaron conductivity in LiFePO4 by decreasing the crystallite size as evidenced due to the reduction of hopping length of electrons and enhanced polaron concentrations.

We have studied alkaline-earth-metal-doped Y 3 GaO 6 as a new family of oxide-ion conductor. Solid solutions of Y 3 GaO 6 and 2% −Ca 2+ -, −Sr 2+ -, and −Ba 2+ -doped Y 3 GaO 6 , i.e., Y (3−0.06) M 0.06 GaO 6−δ (M = Ca 2+ , Sr 2+ , and Ba 2+ ), were prepared via a conventional solid-state reaction route. X-ray Rietveld refined diffractograms of all the compositions showed the formation of an orthorhombic structure having the Cmc2 1 space group. Scanning electron microscopy (SEM) images revealed that the substitution of alkaline-earth metal ions promotes grain growth. Aliovalent doping of Ca 2+ , Sr 2+ , and Ba 2+ enhanced the conductivity by increasing the oxygen vacancy concentration. However, among all of the studied dopants, 2% Ca 2+ -doped Y 3 GaO 6 was found to be more effective in increasing the ionic conductivity as ionic radii mismatch is minimum for Y 3+ /Ca 2+ . The total conductivity of 2% Ca-doped Y 3 GaO 6 composition calculated using the complex impedance plot was found to be ∼0.14 × 10 −3 S cm −1 at 700 °C, which is comparable to many other reported solid electrolytes at the same temperature, making it a potential candidate for future electrolyte material for solid oxide fuel cells (SOFCs). Total electrical conductivity measurement as a function of oxygen partial pressure suggests dominating oxide-ion conduction in a wide range of oxygen partial pressure (ca. 10 −20 −10 −4 atm). The oxygen-ion transport is attributed to the presence of oxygen vacancies that arise from doping and conducting oxide-ion layers of one, two-, or three-dimensional channels within the crystal structure. The oxide-ion migration pathways were analyzed by the bond valence site energy (BVSE)-based approach. Photoluminescence analysis, dilatometry, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy studies were also performed to verify the experimental findings.

No abstract

Vacancies are ubiquitous in nature, usually playing an important role in determining how a material behaves, both physically and chemically. As a consequence, researchers have introduced oxygen, sulphur and other...

No abstract

Perovskite anodes, nowadays, are used in any solid oxide fuel cell (SOFC) instead of conventional nickel/yttria-stabilized zirconia (Ni/YSZ) anodes due to their better redox and electrochemical stability. A few compositions of samarium-substituted strontium titanate perovskite, Sm x Sr 1−x TiO 3−δ (x = 0.00, 0.05, 0.10, 0.15, and 0.20), were synthesized via the citrate-nitrate auto-combustion route. The XRD patterns of these compositions confirm that the solid solubility limit of Sm in SrTiO 3 is x < 0.15. The X-ray Rietveld refinement for all samples indicated the perovskite cubic structure with a Pm3m space group at room temperature. The EDX mapping of the field emission scanning electron microscope (FESEM) micrographs of all compositions depicted a lower oxygen content in the specimens respect to the nominal value. This lower oxygen content in the samples were also confirmed via XPS study. The grain sizes of Sm x Sr 1−x TiO 3 samples were found to increase up to x = 0.10 and it decreases for the composition with x > 0.10. The AC conductivity spectra were fitted by Jonscher's power law in the temperature range of 500-700 • C and scaled with the help of the Ghosh and Summerfield scaling model taking ν H and σ dc T as the scaling parameters. The scaling behaviour of the samples showed that the conduction mechanism depends on temperature at higher frequencies. Further, a study of the conduction mechanism unveiled that small polaron hopping occurred with the formation of electrons. The electrical conductivity, in the H 2 atmosphere, of the Sm 0.10 Sr 0.90 TiO 3 sample was found to be 2.7 × 10 −1 S·cm −1 at 650 • C, which is the highest among the other compositions. Hence, the composition Sm 0.10 Sr 0.90 TiO 3 can be considered as a promising material for the application as the anode in SOFCs.Energies 2019, 12, 4042 2 of 16 SOEC technology [1][2][3][4][5][6][7][8]. SOFCs are more efficient in comparison to a conventional power plant and lower temperature polymer-based fuel cells [9,10]. Electrolyte and electrodes are the essential component of a solid oxide fuel cell. Even if anionic, protonic [11,12] and dual-membrane cells [13] are reported, the first are the most studied in the literature. The state of the art material for the electrolyte is fluorite-structured yttria-stabilized zirconia (YSZ) because of its wide range of stability in oxidizing and reducing media [14], although doped ceria [15] and perovskite Sr-and Mg-incorporated lanthanum gallate (LSGM) are considered as alternatives for intermediate operative temperatures. Lanthanum strontium manganite (LSM)-YSZ composite and Sr-and Fe-doped lanthanum cobaltite (LSCF) are extensively used for cathodes, while Ni-based cermets are conventionally used as anode materials for SOFCs [16,17], although this Ni-based cermet anode material should demonstrate volume instability upon redox cycling and low-tolerance to carbon deposition when exposed to hydrogen [18]. Therefore, nickel-free, alternate-structured anode materials are essential to overcome these issues. Recen...

No abstract

No abstract