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Temperature-dependent d.c. electric conductivity of some recently synthesized organic compounds, 4,7-phenanthroline derivatives is studied. Thin-film samples (d=0.34-0.63 m) spin-coated from dimethylformamide solutions onto glass substrates have been used. Organic films with reproducible electron transport properties can be obtained if, after deposition, they are submitted to a heat treatment within temperature range of 298523K. Examined organic compounds in thin films are polycrystalline and display typical n-type semiconductor behavior. The activation energy of d. c. electric conduction ranges between 0.09 and 0.46 eV and is influenced by nature of substituents, degree of conjugation systems and packing capacity of compounds. In the higher temperature range (T>433 K), the electron transport in examined compounds can be interpreted in terms of the band gap representation model, while in the lower temperature range, the Mott's variable-range hopping conduction model was found to be appropriate. Some of the investigated compounds hold promise for thermistor applications.

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Double perovskite metal oxides with formula A 2 DyBiO 6 (A ¼ Mg, Ca, Sr, Ba) were synthesised by a sol-gel autocombustion method, using citric acid as the combustion agent. The effects of A-site cation on the structure, morphology, and dielectric properties were examined. The synthesis was monitored using Fourier transform infrared spectroscopy (FTIR) to indicate the absence of organic phase. X-ray diffraction (XRD) analysis showed that the compounds have three different perovskite structures. Structural characterisation of the samples was evaluated using XRD patterns. Scanning electron microscopy showed that all samples are formed by agglomerated particles. Dielectric properties were evaluated using dielectric permittivity and dielectric losses. Cole-Cole plots show a single semicircle for all materials, indicating that the double perovskites obtained are composed of well conducting grain boundaries and poorly conducting grains.

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