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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 study reports in-situ nanocrystallization of Pb stabilized t-ZrO2 in an amorphous Si(Pb,Zr)OC matrix (PZSiOC) derived from lead zirconate modified poly(hydridomethylsiloxane) with thermally tunable dielectric behavior. The stabilization of t-ZrO2 phase in the amorphous silicon oxycarbide (SiOC) matrix is ascribed to the critical crystallite size effect and incorporation of Pb ion into the t-ZrO2 lattice. The dielectric behavior as a function of temperature (−50 °C–300 °C) and frequency (100 Hz–10 MHz) is comprehensively investigated. It is observed that these ceramic nanocomposites exhibit high permittivity and low loss in contrast to SiOC at all measured temperatures and reached colossal values (e’> 104) above critical temperature with an S-shaped frequency dependent dielectric loss. Thermally activated interfacial-charge polarization process can be reasoned out for this interesting behavior. The study paves the way for the attainment of cost-effective, tailored as well as highly functional PZSiOC ceramic nanocomposites with colossal permittivity for a wide array of applications. The dielectric permittivity results exemplify the huge potential of PZSiOC ceramic nanocomposites in energy storage devices. Studies are in progress to assess the suitability of PZSiOC ceramic nanocomposites in supercapacitors.

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 dielectric properties of nanocomposite materials (NCM) on basis of porous glasses with KNO3 embedded into the pores have been studied in the temperature interval 293 K–570 K and in the frequency diapason 0.1–107 Hz. The three types of porous glasses with average pore diameter 320 (PG320), 46 (PG46) and 7 (PG7) nm have been used for production NCM from melted KNO3. It is shown that dielectric permittivity demonstrates the essential growth in the high-temperature phase for all types of NCM. The temperature of the ferroelectric phase transition decreases at a reduction of average pore diameters and the temperature interval of stability of ferroelectric phase essentially enlarges. In case of NCM on basis of PG7 there is no any anomalies corresponding to the phase transition in this NCM and on cooling up to room temperature ferroelectric phase remains stable. From analysis of dielectric response, the relaxation process responsible for the ferroelectric phase transition has been detected and the temperature dependencies of process parameters have been determined.

The dielectric behavior of spark plasma sintered SiC(O)/HfCxN1-x nanocomposites synthesized through polymer derived ceramic route was investigated in the frequency range of 1 kHz to 1 MHz at room temperature. The nanostructural features revealed HfCxN1-x nanocrystals encapsulated in a nanometric thin layer of carbon dispersed uniformly in a SiC(O) matrix with segregated free carbon. The nanocomposites exhibited colossal permittivity values in the order of 103 at 1 kHz which reduced to 646 at 1 MHz. The interfacial polarization mechanism existing between complex nanostructural interfaces and the percolation of HfCxN1-x nanocrystals are believed to be responsible for the high permittivity values observed in the measured frequency range. The AC conductivity exemplified a frequency independent behavior at lower frequencies while at higher frequencies, the conductivity exhibited frequency dependence, indicating the existence of hopping type mechanism.

Dielectric properties and temperature evolution of the crystal structure of nanocomposites on the basis of porous glasses and KNO3 embedded into the pores have been studied on heating and cooling. It is shown that the stability of the ferroelectric phase depends on nanoparticle sizes and temperature prehistory of sample preparation and measurement procedure. The temperature interval, where the ferroelectric phase exists, increases on decreasing of the nanoparticle size. In the composite of KNO3 and porous glasses with the average pore diameters of 7 nm, the ferroelectric phase becomes stable down to 100 K after the first heating–cooling circle.

Combined neutron diffraction, dielectric and conductivity measurements of NaNO2 embedded into porous glasses with average pore diameter 7 nm are performed in the ferroelectric and paraelectric phases. The temperature interval of existence of a volume premelted state in this confined material is determined. It is shown that the observed earlier giant growth of dielectric constant above TC can be attributed with an appearance of ionic conductivity due to jumping diffusion (or hopping) of constituent ions. These data are in a good agreement with experimental results of our earlier measurements of temperature evolution of structure of this nanocomposite material.

The results of the detailed study of the dielectric properties of single crystal Na 1/2 Bi 1/2 TiO 3 (NBT) in wide frequency (0.1 Hz–10 MHz) and temperature (300–1000 K) ranges are reported. Analyses of dispersion curves of the complex dielectric response within existing phenomenological models are done. Relaxation processes are identified and their dynamics are traced. Activation energies of Arrhenius’ relaxation processes are obtained by fitting. Besides we have found a relaxation process described by Vogel-Fulcher law, indicating that in the system occurs freezing at 370 K.

An investigation was carried out on both the linear and nonlinear parts of the complex dielectric susceptibility in the frequency and temperature ranges 10-3-103 Hz and 100-450 K, respectively. The analysis of the imaginary part of the dielectric susceptibility has revealed the existence of a broad spectrum of relaxation times in the above temperature range. The temperature dependence of the most probable frequency of the spectrum was obtained. For temperatures T

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.