Conductivity properties such as the impedance contributions of grain, grain boundary, and electrode–material interface of brownmillerite-type Ca₂Fe₂O₅ are studied using alternate current (AC) impedance at different temperatures over a wide range of frequencies. The compound was synthesized at 1000 °C by a solid-state reaction. Powder X-ray diffraction confirmed the pure and single-phase formation. The correlation of the electrical properties with the microstructure of the compound was studied by an AC impedance spectroscopic technique at different temperatures (25–300 °C), which demonstrated the contribution of both the grain (bulk) and grain boundary to the impedance. The frequency-dependent electrical conductivity was used to study the conductivity mechanism. The electric impedance and the frequency at different temperatures supported the suggested conduction mechanism.

Development in high-rate electrode materials capable of storing vast amounts of charge in a short duration to decrease charging time and increase power in lithium-ion batteries is an important challenge to address. Here, we introduce a synthesis strategy with a series of composition-controlled NMC cathodes, including LiNi_0.2Mn_0.6Co_0.2O₂(NMC262), LiNi_0.3Mn_0.5Co_0.2O₂(NMC352), and LiNi_0.4Mn_0.4Co_0.2O₂(NMC442). A very high-rate performance was achieved for Mn-rich LiNi_0.2Mn_0.6Co_0.2O₂ (NMC262). It has a very high initial discharge capacity of 285 mAh g⁻¹ when charged to 4.7 V at a current of 20 mA g⁻¹ and retains the capacity of 201 mAh g⁻¹ after 100 cycles. It also exhibits an excellent rate capability of 138, and 114 mAh g⁻¹ even at rates of 10 and 15 C (1 C = 240 mA g⁻¹). The high discharge capacities and excellent rate capabilities of Mn-rich LiNi_0.2Mn_0.6Co_0.2O₂ cathodes could be ascribed to their structural stability, controlled particle size, high surface area, and suppressed phase transformation from layered to spinel phases, due to low cation mixing and the higher oxidation state of manganese. The cathodic and anodic diffusion coefficient of the NMC262 electrode was determined to be around 4.76 × 10⁻¹⁰ cm² s⁻¹ and 2.1 × 10⁻¹⁰ cm² s⁻¹, respectively.

Materials with low thermal conductivity are essential to providing thermal insulation to many technological systems, such as electronics, thermoelectrics and aerospace devices. Here, we report ultra-low thermal conductivity of two oxide materials. Sr₂FeCoO_6−δ has a perovskite-type structure with oxygen vacancies. It shows a thermal conductivity of 0.5 W m⁻¹ K⁻¹, which is lower than those reported for perovskite oxides. The incorporation of calcium to form Ca₂FeCoO_6−δ, leads to a structural change and the formation of different coordination geometries around the transition metals. This structural transformation results in a remarkable enhancement of the thermal insulation properties, showing the ultra-low thermal conductivity of 0.05 W m⁻¹ K⁻¹, which is one of the lowest values found among solid materials to date. A comparison to previously reported perovskite oxides, which show significantly inferior thermal insulation compared to our materials, points to the effect of oxygen-vacancies and their ordering on thermal conductivity.

Ternary glassy electrolytes containing K₂S as a glass modifier and P₂S₅ as a network former are synthesized by introducing a new type of complex and asymmetric salt, potassium triflate (KOTf), to obtain unprecedented K⁺ ion conductivity at ambient temperature. The glasses are synthesized using a conventional quenching technique at a low temperature. In general, alkali ionic glassy electrolytes of ternary systems, specifically for Li⁺ and Na⁺ ion conductivity, have been studied with the addition of halide salts or oxysalts such as M₂SO₄, M₂SiO₄, M₃PO₄ (M = Li or Na), etc. We introduce a distinct and complex salt, potassium triflate (KOTf) with asymmetric anion, to the conventional glass modifier and former to synthesize K⁺-ion-conducting glassy electrolytes. Two series of glassy electrolytes with a ternary system of (0.9–x)K₂S-xP₂S₅-0.1KOTf (x = 0.15, 0.30, 0.45, 0.60, and 0.75) and z(K₂S-2P₂S₅)-yKOTf (y = 0.05, 0.10, 0.15, 0.20, and 0.25) on a straight line of z(K₂S-2P₂S₅) are studied for their K⁺ ionic conductivities by using electrochemical impedance spectroscopy (EIS). The composition 0.3K₂S-0.6P₂S₅-0.1KOTf is found to have the highest conductivity among the studied glassy electrolytes at ambient temperature with the value of 1.06 × 10⁻⁷ S cm⁻¹, which is the highest of all pure K⁺-ion-conducting glasses reported to date. Since the glass transition temperatures of the glasses are near 100 °C, as demonstrated by DSC, temperature-dependent conductivities are studied within the range of 25 to 100 °C to determine the activation energies. A Raman spectroscopic study shows the variation in the structural units ${PS}_4^{3-}{, P_2\mathrm{S}}_7^{4-}, {\mathrm{a}\mathrm{n}\mathrm{d} P_2\mathrm{S}}_6^{4-}$ of the network former for different glassy electrolytes. It seems that there is a role of ${P_2\mathrm{S}}_7^{4-}{ \mathrm{a}\mathrm{n}\mathrm{d} P_2\mathrm{S}}_6^{4-}$ in K⁺-ion conductivity in the glassy electrolytes because the spectroscopic results are compatible with the composition-dependent, room-temperature conductivity trend.

The perovskite oxides CaMnO_3-δ, Ca_0.5Sr_0.5MnO_3-δ, and SrMnO_3-δ were synthesized in air using a solid-state method, and their structural, electrical, and electrocatalytic properties were studied in relation to their oxygen evolution reaction (OER) performance. Iodometric titration showed δ values of 0.05, 0.05, and 0.0, respectively, indicating that Mn is predominantly in the 4+ oxidation state across all materials, consistent with prior reports. Detailed characterization was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), iodometric titration, and variable-temperature conductivity measurements. Four-point probe DC measurements revealed that CaMnO_3-δ (δ = 0.05) has a semiconductive behavior over a temperature range from 25 °C to 300 °C, with its highest conductivity attributed to polaron activity. Cyclic voltammetry (CV) in 0.1 M KOH was employed to assess OER catalytic performance, which correlated with room-temperature conductivity. CaMnO_3-δ exhibited superior catalytic activity, followed by Ca_0.5Sr_0.5MnO_3-δ and SrMnO_3-δ, demonstrating that increased conductivity enhances OER performance. The conductivity trend, CaMnO_3-δ > Ca_0.5Sr_0.5MnO_3-δ > SrMnO_3-δ, aligns with OER activity, underscoring a direct link between electronic transport properties and catalytic efficiency within this series.