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Strontium silicates doped with an alkali metal are extensively investigated after their high conductivity reported in the moderate range of temperature (773 K < T < 1073 K). This work aims to study the structural, microstructural, morphological, thermal, and electrical investigation of Sr3-3xNa3xSi3-3yGe3yO9-δ (0 < x < 0.20, y = 0.1; SNSG) system. A solid-state reaction method was adopted for synthesis of the compositions. Composition's phase formation was examined using X-rays Rietveld refinement techniques. X-Ray Diffraction (XRD) patterns were mapped by the monoclinic symmetry having space-group C12/c1. Moreover, along with monoclinic phase a few minor peaks of Sr2SiO4 were also detected along with prominent peaks of parent SrSiO3. To comprehend the surface morphology of the compositions, scanning electron microscopy has been employed. Studies using Fourier transform infrared spectroscopy and Raman spectroscopy have been carried out to investigate the characteristic bands and vibrations modes of the system. Characteristic valence states of constituent elements and stability of the sintered samples in air were confirmed by the X-ray Photoelectron Spectroscopy (XPS) analysis. The electrical behavior of this system was studied by electrochemical impedance spectroscopy (EIS) techniques. Electrical conductivity of the platinum-coated sintered pellet samples was also calculated to check its feasibility as a cost-effective electrolyte for intermediate temperature range. It has also been observed that in Na-doped compositions, a few amorphous phases of Sodium silicate (Na2Si2O5) formed as impurity that may contribute to the total conductivity. [ABSTRACT FROM AUTHOR]

The signature of oxide ion conductivity was perceived in acceptor‐doped (alkaline‐earth metals) Y3GaO6. An acceptor doping of 2%Ca in Y3GaO6 (i.e., Y2.94Ca0.06GaO6) has been found to exhibit a remarkable conductivity. The present work examines the conductivity behavior of 2% Ca‐doped tri‐yttrium gallate (Y2.94Ca0.06GaO6) and also the effect of Mg‐substitution on the phase formation and electrical conductivity of Y2.94Ca0.06GaO6 for its possible application as a solid electrolyte. Polycrystalline dense ceramic samples of Y2.94Ca0.06Ga1−xMgxO6−δ (with x =.00–.04) were fabricated using the conventional solid‐state reaction route. The X‐ray diffraction patterns were recorded to confirm the phase formation. The solid solubility limit of Mg2+ at Ga3+ site was found for x <.03. All the samples were observed to exhibit orthorhombic structure with Cmc21 symmetry (ICSD no.: 155086). Scanning electron microscopy (SEM) morphology reveals dense polygonal grains with vibrant grain boundaries. A significant increase in the conductivity is observed by substituting 1 mol% of Mg2+ at the Ga3+ site of Y2.94Ca0.06Ga1−xMgxO6−δ. However, a further addition of higher dopant concentration of Mg2+ leads to a decline in the electrical conductivity. A relationship between the dopant concentration, phase formation, and structural characterizations has been established to analyze the conductivity behavior. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sr 1-x K x SiO 3-δ (0.00 ≤ x ≤ 0.30) were synthesized by SSR method and crystallizes in the monoclinic space group C12/c1. • BET study shows the high surface area for the composition Sr 0.70 K 0.30 SiO 3-δ. • FE-SEM suggest the presence of K 2 Si 2 O 5 glassy phase along the grain boundaries. • Sr 0.70 K 0.30 SiO 3-δ exhibits dc conductivity of ∼0.38 × 10−2 S cm−1 at 600 °C. • Sr 0.70 K 0.30 SiO 3-δ system can used as ionic conductor in electrochemical devices. Excellent ionic conductivity of alkali metal doped strontium meta silicate solid electrolytes has widely made consideration to their usage in electrochemical devices e.g. solid oxide fuel cells (SOFCs). The present study aimed to explore the conductivity enhancement in the potassium (K) doped monomeric SrSiO 3 solid electrolyte with its structural changes by variation of dopant concentration. A series of different K-doped monomeric system SrSiO 3 (i.e. Sr 1-x K x SiO 3) were synthesized with varying K concentration (in %) as x = 0, 10, 15, 20, 25, 30. The structural, optical and transport properties were investigated via XRD, BET, SEM, FTIR, Raman and Impedance spectroscopy techniques. The investigations confirm the co-existence of crystalline phase along with amorphous phases and strengthened by visualizing SEM micrographs which was further correlated with the Raman and FTIR results. The thermal stability measurement of the prepared samples conducted through TGA analysis led to the inference that introduction of K in this system results in generation of K-rich glassy phases. The above deduction was strengthened by impedance measurements showing highest conductivity of 0.38 × 10−3 S-cm−1, at 873 K in air for Sr 0.7 K 0.3 SiO 3 , among all synthesized samples. Furthermore, un-doped strontium silicate showed presence of more than one phase apart from monoclinic phase and behave as nonconducting phase material in the deliberated temperature range (473 K – 973 K). Changes in crystallinity or the formation of secondary phases can impact transport dynamics through altered grain boundaries, defect concentrations, and diffusion pathways. [ABSTRACT FROM AUTHOR]

Solid electrolytes are the principal component of solid oxide fuel cells (SOFCs) and play a vital role in controlling the conduction mechanism. We have prepared multiple compositions of Sr3 − 3xK3xSi3O9 (0.0 ≤ x ≤ 0.2) via solid-state reaction route for the possible application as solid electrolyte for SOFCs. We have studied the phase formation and phase evolution via XRD, Raman and FTIR; morphological transformation via SEM and EDX and the ion-conducting behaviour of the system via conductivity measurements with varying the potassium concentration. Band gap of the investigated compositions was determined via the Tauc plot of UV-Vis measurement. A correlation between the dopant concentration, phase formation and conductivity has been established to explain the conductivity behaviour. The results indicate that high K concentration is helpful in achieving the required transport behaviour as required for IT-SOFC electrolytes. [ABSTRACT FROM AUTHOR]

The different alkali metal substitution strategies of the strontium meta -silicate based ion conductors have been enormously cross-examined to synthesize cost-effective novel electrolyte for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs). In the present investigation, crystal structure, phase formation, microstructure, total conductivity and stability of the Potassium and Germanium incorporated Sr 3 Si 3 O 9 based system, Sr 3-3x K 3x Si 3-3y Ge 3y O 9-δ (0 ≤ x ≤ 0.20, y = 0.1), is examined for their application as solid electrolyte for electrochemical devices such as ITSOFCs. These samples have been made via solid state reaction route. X-ray Rietveld refinement method was used for the structural investigation. Raman and FT-IR spectroscopy were performed to examine the phase formation and absorption of light by the bonds of vibrating molecules to provide molecular characteristics and vibrational modes of the molecules. The X-ray Photoelectron Spectroscopy study was used to validate the characteristic valence states of the constituting elements. Thermo-gravimetric analysis was performed to inspect the thermal stability and weight changes in the compounds during heating process. In the SEM and EDS mapping, an amorphous phase of K 2 Si 2 O 5 can be visualized which seems to segregate along grain boundaries and this amorphous complexion augmented with K+ dopant concentration. AC Electrical impedance spectroscopy studies suggest that the ionic conduction in Sr 3-3x K 3x Si 3-3y Ge 3y O 9-δ could be from the oxide ions along with mobility of K+ ions of the glassy phase. In this study, we also tried to get the optimal doping condition with compositions to minimize numerous concern of the system. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • First-time substitution of trivalent Ru3+ cation into the Zr4+ site to enhance the ionic conductivity. • The Ru-doped electrolyte showed high ionic conductivity of 2.1 x 10-3 Ω-1cm−1. • The electrolyte demonstrated plating/stripping at 0.5 mA-cm−2 for 100 h. • Cell with Ru-doped electrolyte exhibited initial capacity of 87 mAh-g−1 at 0.3C. • All-solid-state cell demonstrated stable cycling with an 87% capacity after 100 cycles. Recently remarkably high ionic conductivities (up to 5.5 x 10-3 Ω-1cm−1) at 25 °C have been achieved in sodium superionic conducting (NASICON) solid-state electrolytes via aliovalent cation doping. Doping in NASICON leverages the synergic effects of bottleneck opening (lattice expansion) and correlated migration (higher carrier concentration). However, there is no report published that isolates the effect of correlated migration induced by heterovalent doping without the influence of structural/bottleneck changes. Therefore, here we report for the first time the substitution of trivalent Ru3+ cation into the Zr4+ site to enhance the ionic conductivity of the NASICON electrolyte. Even though Ru3+ has a smaller ionic radius than Zr4+ and leads to bottleneck shrinkage, high ionic conductivity is achieved on doping Ru as compared to undoped NZSP. Using first-principles calculations, we show that even though the bottleneck for Na+ migration shrinks, the diffusion barriers are nearly the same owing to the weaker Na-framework interaction. The doped electrolyte showed an ionic conductivity of 2.1 x 10-3 Ω-1cm−1, an ionic transference number of ∼ 98.9 %, and exhibited stable sodium plating/stripping at 0.5 mA-cm−2 for 100 h with an overpotential of 20 mV owing to the fused microstructure. The assembled all-solid-state battery with Ru-doped electrolyte exhibited an outstanding initial capacity of 87 mAh-g−1 at 0.3C as compared to 70 mAh-g−1 with undoped electrolyte. Compared to the pristine sample, which had capacity retention of 60 % after 100 cycles, the cell containing Ru-doped electrolyte demonstrated stable cycling with an 87 % capacity retention without external pressure. [ABSTRACT FROM AUTHOR]