The spontaneous oxidation of a magnetite surface and shape design are major aspects of synthesizing various nanostructures with unique magnetic and electrical properties, catalytic activity, and biocompatibility. In this article, the roles of different organic modifiers on the shape and formation of an oxidized layer composed of maghemite were discussed and described in the context of magnetic and electrical properties. It was confirmed that Fe₃O₄ nanoparticles synthesized in the presence of triphenylphosphine could be characterized by cuboidal shape, a relatively low average particle size (9.6 ± 2.0 nm), and high saturation magnetization equal to 55.2 emu/g. Furthermore, it has been confirmed that low-frequency conductivity and dielectric properties are related to surface disordering and oxidation. The electric energy storage possibility increased for nanoparticles with a disordered and oxidized surface, whereas the dielectric losses in these particles were strongly related to their size. The cuboidal magnetite nanoparticles synthesized in the presence of triphenylphosphine had an ultrahigh electrical conductivity (1.02 × 10⁻⁴ S/cm at 10 Hz) in comparison to the spherical ones. At higher temperatures, the maghemite content altered the behavior of electrons. The electrical conductivity can be described by correlated barrier hopping or overlapping large polaron tunneling. Interestingly, the activation energies of electrons transport by the surface were similar for all the analyzed nanoparticles in low- and high-temperature ranges.

Wastes accumulated at Piekary Śląskie, Poland, are the result of 150 years of continuous working of the Orzeł Biały smelting plant. Slags are composed of: oxides (spinel, hematite, zincite); silicates and aluminosilicates (olivine, monticellite–kirschteinite, titanite, merwinite, pyroxene, melilite, feldspars: plagioclases and plumbean K-feldspar, nepheline, kalsilite, leucite); sulfides (pyrrhotite, rudashevskyite, galena), metallic phases (pure iron and iron–arsenic mixture) and secondary phases (gypsum, rapidcreekite, apatite). Interstices between the crystalline phases are filled by glass, concentrating toxic and potentially harmful elements, e.g. up to 53.22 wt.% PbO. The sequence of crystallization of primary phases depended on the local variability of oxygen fugacity and degree of calcination, while the texture type resulted from the cooling time and partial pressure of volatiles. Suggested crystallization temperatures are in the range of 1200–1500°C. Bulk chemical analyses show that the slags are composed mainly of SiO₂, Al₂O₃,Fe₂O₃, MgO and CaO. Among the potentially harmful elements, Zn is the most common, reaching up to 5.93 wt.%, Pb is present in concentrations up to 3.9 wt.% and As in weathered samples exceeds 1 wt.%. Leaching tests of these elements confirms As mobility as Zn and Pb are preferably leached from fresh slags, while As is present in greater amounts in leachate from weathered slag samples. The documented amounts of As, Zn, Pb and their mobility in slags produce an environmental risk, as this material is currently used widely for commercial purposes.

Fe-doped Bi₁₂MnO₂₀–BiMn₂O₅ ceramics was sintered at 1130 K for 6 h in ambient air. Two centro-symmetric phases formed thermodynamically stable self-composite material that was deduced from X-ray pattern analysis. The lattice parameters were a = 10.147(8) Å—for the cubic I23 Bi₁₂MnO₂₀ phase; and a = 7.545(4) Å, b = 8.538(1) Å, c = 5.758(3) Å—for the orthorhombic Pbam BiMn₂O₅ phase. The ⁵⁷Fe Mössbauer spectrum, recorded at room temperature, has shown pure electronic quadrupolar split. The major doublets reflected the occurrence of Fe³⁺ ions distributed in two sites, i.e., octahedral Fe⁴⁺O₆ and square pyramidal Fe³⁺O₅, with preferential occupation of the pyramidal sites, that was consistent with the Pbam phase symmetry. The third doublet resulted from the presence of iron Fe³⁺ in tetrahedral Fe³⁺O₄ coordination and corresponded to a small admixture of the I23 phase. The DC resistivity ρ_DC(T) dependence on temperature has shown thermally activated features, and the value of E_a,DC varied in the range of 0.22–0.37 eV. The electric impedance was measured in the f = 20 Hz–1 MHz and 100–690 K range. Two electrical relaxations were determined using the electric modulus formalism M″(T). Low-temperature relaxation has shown the temperature-dependent activation energy E_A,1 = 0.14–0.20 eV and characteristic time values of τ₀₁ = 10⁻¹⁰–10⁻¹² s in 100–200 K range. It was attributed to the charge transfer between Mn⁴⁺/Mn³⁺ sites. The other relaxation occurred in the 170–220 K range, and it exhibited the following values: τ₀₂ = 10⁻¹¹ s, and E_A,2 = 0.27 eV. A disorder-related VRH polaron model was proposed for ρ_DC(T) and for electric relaxation processes.