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We investigated the influence of oxygen vacancies (varying) on the structure and properties (dielectric and magnetic) of Co (fixed) and Mn (varied) co-doped ZnO nanoparticles (NPs) fabricated using the chemical precipitation technique. The oxygen vacancies in the lattice increased with an increase in dopants (Co, Mn) concentration. Annealing of the doped nanoparticles decreased their dielectric properties due to reduced grain boundaries caused by enhanced grain growth. Replacement of Zn ions with dopants in the lattice enhanced the samples' electrical conductivities due to the reduction in grain boundaries and increase of charge carriers. The co-doped nanoparticles annealed at 600 °C exhibited some hysteresis loop changes and became ferromagnetic (FM). The magnetization increased with an increase in dopants content in the ZnO matrix, while coercivity decreased. This shows that the properties of the doped samples are strongly related to the number of oxygen vacancies. These results demonstrated that the enhanced dielectric and magnetization responses of Co (fixed) and Mn (varied) co-doped ZnO nanoparticles are strongly correlated with the oxygen vacancies. The enhancement in optical, dielectric, and magnetic properties make transition metals (TM)-doped ZnO nanoparticles suitable for spintronics, and optoelectronic-based applications.

Samples having the composition BaFe12−2xCoxSmxO19 (x = 0.0, 0.2, 0.4, 0.6) are prepared by a WOWS (without water and surfactants) sol–gel technique, and the structural, morphological, and AC and DC electrical and magnetic properties of the samples are investigated. The phase formation of M-type hexaferrite is studied by using indexed x-ray diffraction patterns. Scanning electron microscopy images show that the particle size of the synthesized nanopowder varies from 295 nm to 440 nm. The dielectric constant (e′) exhibits a decreasing trend while the dielectric loss (tan δ) increases with increased doping. DC electrical resistivity (ρDC) is investigated in a temperature range of 373–673 K and indicates an increasing trend with doping. The magnetic hysteresis loops reveal an increase in saturation magnetization (Ms) and remanence (Mr), and a decrease in coercivity (Hc), with the increase in doping content.

Oxide-based films and nanostructures have emerged as important materials for a wide range of applications such as photovoltaics, optoelectronics, gas sensing and electronics. To develop an appropriate understanding of the properties of these oxides, it is necessary to address the material preparation methods and defect probing issues. This work reports on the synthesis processes of TiO 2 based transparent conductive films, their stoichiometry control and defect identifying, in relation with their electrical and optical properties. Un-doped and TiO 2 :Nb films were deposited by RF co-sputtering from TiO 2 and Nb 2 O 5 targets in Ar plasma. The chemical species present in the plasmas used in deposition process were investigated by optical emission spectroscopy, which was later on correlated with the defects structure of the films. Analysis by X-ray photoelectron spectroscopy shed more light on the nature of the vacancies and on the effect of the latter on the optical and electrical properties of the films. In terms of results, we measured electrical resistivity in the range 10 − 2 –10 − 3 Ω cm for the intrinsically and extrinsically doped films (films doped with oxygen vacancies and Nb + 5 respectively) while the lowest resistivity was obtained for intrinsically-extrinsically co-doped TiO 2 films (7.4 × 10 − 4 Ω cm). The films transparency was also actively determined by the defects in the lattice and highly transparent films (65–85% in the visible range) were obtained by controlling the density of defects. The approach adopted in this work for the generation of oxygen vacancies could be useful for other oxide-based films, where the oxygen vacancies-dependent properties are crucial, for room temperature ferromagnetism and photocatalytic applications.

The authors report a comparative study of the electrical and optical properties of Nb:TiO2 thin films (TNO) in relation with their chemical properties. Two types of niobium containing targets, Nb metal and Nb2O5 oxide were employed simultaneously with ceramic TiO2 target for the films growth, in Ar and Ar-O2 discharge. Niobium is found to incorporate easily and substitutionally into titanium lattice site when deposited from oxide targets in oxygen-deficient discharge (Ar plasma). Consequently, the TNO film exhibits lowest resistivity of 1.4×10−3 Ω cm with optical transparency of more than 80% in the visible region. On the contrary, doping was not effective in case the TNO films were grown from Nb metal and TiO2 targets in Ar and Ar-O2 plasma, probably due to the growth of niobium sub-oxide phases and lack of oxygen vacancies. The possible reasons of diverse electrical properties are discussed and are link with the growth conditions. Our result indicates that highly conductive and transparent doped-TiO2 film can be obtained by choosing appropriate target material and sputtering gas. The obtained results can significantly contribute to the development of transparent electrodes by RF sputtering, a suitable technique for coating on large area substrates.

The effects of frequency on the alternating-current (AC) conductivity of polycrystalline La0.65Ca0.35MnO3 compounds prepared by solid-state reaction with various heat treatments have been studied. The AC conductivity and magnetoresistance (MR) are affected by the heat treatment temperature. The MR is enhanced at and below the transition temperature (TC). The AC transport behavior of this system shows pronounced negative MR even at small applied magnetic fields for temperatures well below TC. It is observed that such effects originate from spin-dependent scattering at grain boundaries as a consequence of spin disorder at the interfaces of the boundaries and spin scattering within the grains. The real part of the AC conductivity σ′ exhibits a pronounced frequency dependence, measured in the frequency range f < 100 kHz. The minimum occurs at a frequency that is temperature dependent. The MR below TC and the frequency dependence of the AC electrical conductivity σ′(f) are interpreted as being consequences of cluster and grain boundary effects.