High temperature and high electric field applications in tantalum and niobium capacitors are limited by the mechanism of ion migration and field crystallization in a tantalum or niobium pentoxide insulating layer. The study of leakage current (DCL) variation in time as a result of increasing temperature and electric field might provide information about the physical mechanism of degradation. The experiments were performed on tantalum and niobium oxide capacitors at temperatures of about 125°C and applied voltages ranging up to rated voltages of 35 V and 16 V for tantalum and niobium oxide capacitors, respectively. Homogeneous distribution of oxygen vacancies acting as positive ions within the pentoxide layer was assumed before the experiments. DCL vs. time characteristics at a fixed temperature have several phases. At the beginning of ageing the DCL increases exponentially with time. In this period ions in the insulating layer are being moved in the electric field by drift only. Due to that the concentration of ions near the cathode increases producing a positively charged region near the cathode. The electric field near the cathode increases and the potential barrier between the cathode and insulating layer decreases which results in increasing DCL. However, redistribution of positive ions in the insulator layer leads to creation of a ion concentration gradient which results in a gradual increase of the ion diffusion current in the direction opposite to the ion drift current component. The equilibrium between the two for a given temperature and electric field results in saturation of the leakage current value. DCL vs. time characteristics are described by the exponential stretched law. We found that during the initial part of ageing an exponent n = 1 applies. That corresponds to the ion drift motion only. After long-time application of the electric field at a high temperature the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5. Here, the equilibrium between the ion drift and diffusion is achieved. The process of leakage current degradation is therefore partially reversible. When the external electric field is lowered, or the samples are shortened, the leakage current for a given voltage decreases with time and the DCL vs. time characteristics are described by the exponential stretched law with an exponent n = 0.5, thus the ion redistribution by diffusion becomes dominant.

Textile industry emits daily huge amounts of sewage rich in non-biodegradable organic compounds, especially in textile dyes. Such contaminants are highly soluble in water, which makes their removal difficult. Other studies suggest their carcinogenicity, toxicity and mutagenicity. A promising chemical treatment of textile wastewater is the photodegradation of dye molecules in the process of photocatalysis in the presence of a photocatalyst. One-dimensional nanostructures exhibit a high surface-to-volume ratio and a quantum confinement effect, making them ideal candidates for nanophotocatalyst material. Nb2O5 is, among other metal oxides with a wide band gap, gaining popularity in optical applications, and electrospun niobium oxide nanostructures, despite their ease and low cost, can increase the chemical removal of textile dyes from wastewater. Facile synthesis of electrospun one-dimensional niobium oxide nanofibers is presented. The nanophotocatalysts morphology, structure, chemical bonds and optical properties were examined. Based on photodegradation of aqueous solutions (ph=6) of methylene blue and rhodamine B, the photocatalytic activity was established. The photocatalytic efficiency after 180 minutes of ultraviolet irradiation in the presence of Nb2O5 nanofibers was as follows: 84.9% and 31.8% for methylene blue and rhodamine B decolorization, respectively.