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Different polymorphs of niobium pentoxide (Nb2O5) were synthesized using niobium ethoxide as a precursor by varying the pyrolyzing temperature. The room temperature X-ray diffractograms revealed the irreversible phase evolution from amorphous to pseudohexagonal (823 K) to orthorhombic (1023 K) and to monoclinic crystal structure (1223 K). While phase evolution was also confirmed by thermogravimetry and dilatometry, Raman spectroscopy clearly suggested complete elimination of free carbon in the pyrolysed ceramics. The sintering conditions were optimized to produce a highly dense (>95%) thermodynamically stable monoclinic Nb2O5. The electrical properties of stable monoclinic Nb2O5 sample were thoroughly studied. The monoclinic Nb2O5 was found to have a dielectric constant of around 28 with a dielectric loss of 0.008 at room temperature and at 100 kHz. At low measurement frequencies, an anomalous increase in the effective dielectric permittivity with increasing temperature was observed. Large values of the e’ are associated with polarization due to the accumulation of free electrons at the grain boundaries. An analysis of the dispersion curves of Nb2O5 revealed that two relaxation processes are responsible for the observed anomalies, and the temperature dependencies of their parameters (dielectric strength, relaxation time and spectrum broadening parameter) were determined. The low-frequency process (relaxation time τ0 ~ 0.45 s), which makes the largest contribution to the dielectric constant, was apparently due to the inhomogeneous conductivity of ceramics. It was revealed that the DC conductivity of ceramics has thermoactivation character with activation energy of about 660 meV and was determined by the oxygen vacancies.

The dielectric response and the effect of heat treatment on the properties of a potassium-sodium-niobium-silicate glass with a high content of niobium are studied in wide temperature and frequency ranges. Heat treatment of the glass results in the formation of sodium niobate nanocrystals that leads to a significant decrease in the dielectric losses and an increase in the dielectric constant and the activation energy of the DC conductivity of the medium. It is shown that the crystallization process takes place in two stages – the first is the liquid-liquid glass separation (segregation), and the second is the crystals growth. Based on the classical Johnson-Mehl-Avrami-Kolmogorov theory, it is confirmed that the nanocrystals are anisotropic and that no new nuclei arise during the crystallization. The main contribution to the dielectric response of the initial and heat-treated glasses is made by the low-frequency relaxation process associated with the conductivity (charge polarization).

The crystal structure and dielectric response of nanocomposite materials on base of porous glasses with average pore diameters of 320, 46 and 7 nm with embedding sodium nitrate have been studied by neutron diffraction and dielectric spectroscopy in low and high temperature phases up to melting. In porous glasses with 46 and 7 nm pores NaNO 3 forms dendrite nanoclusters with "diffraction" sizes of 50(2.5) and 20(2) nm. Decreasing of particle sizes results in decreasing of T c (temperature of order–disorder orientational transition) and T melt and in smearing of structure phase transition. The values of critical exponent β for orientational transition are estimated from temperature dependences of intensities of superstructure elastic peaks for these three types of nanocomposite materials.

Photo-induced current through nanocomposite heterojunction structures consisting of a TiO2 coating activated with embedded gold nanoparticles on top of Si, SiO2, and columnar structured SiO2 is studied. The highest photo-activity in the visible part of the spectrum is found in the composite containing pillar-like silicon dioxide nanostructures. Experimental results were qualitatively explained on the basis of Franz-Keldysh effect taking into account the effects of electrical inhomogeneities appearing at charged nanoparticles. It is established that processes at the interface between silicon and noble metal nanoparticles play an important role in charge carrier photo-generation which opens a new opportunity to tune the photo-response of a nanocomposite via changing heterostructure topology.

The structure and dielectric properties of sodium nitrite and its solid solutions confined in porous glasses have been studied. The temperature dependences of the order parameter and the unit cell volume for NaNO2 embedded into porous glasses with different pore sizes were studied by neutron diffraction in the ferro- and paraelectric phases. The characteristic sizes of nanoparticles are determined. It is shown that at a size of nanoparticles smaller than ~50 nm a crossover of the phase transition from first order to second order is observed. The effect of doping of sodium nitrite with potassium nitrite on the dielectric properties of the nanocomposite materials was studied and a strong lowering of the dielectric losses was observed.