The DTA signal was studied in comparison with X-ray phase analysis of potassium nitrate particles in carbon nanotubes. It is shown that, for potassium nitrate particles in nanotubes, the temperature range of the existence of the KNO3 ferroelectric phase expands up to 300 K and the ferroelectric and low-temperature paraelectric phases coexist.

The results of studies of the dielectric constant ε′ and the DTA signal of a new organic ferroelectric (R)-3-quinuclidinol (C 7 H 13 NO), embedded in porous glasses with an average pore size of 100 nm, are presented. The phase transition was found to shift to low temperatures by 3 K upon heating and 6 K upon cooling, in comparison with bulk (R)-3-quinuclidinol. A decrease in the phase transition temperature in composites with (R)-3-quinuclidinol nanoparticles is consistent with theoretical models of the influence of size effects on the structural phase transition.

The results of the study of phase transitions of KNO3 encapsulated in carbon nanotubes are presented. It is shown that the temperature range of existence of KNO3 particle ferroelectric phase in nanotubes narrows, similarly to that in ferroelectric semiconductors. The results obtained suggest that external screening by the conductive matrix acts similarly to spontaneous polarization screening in conducting ferroelectrics.

Ferroelectric nanocomposites have great potential applications and are in the focus of modern studies. Their polar properties are due to spontaneous polarization in nanoparticles confined to insulator matrices. The crucial problem is the persistence of ferroelectricity under nanoconfinement as the ferroelectric phase transition can shift because of size effects and other grounds. We report the 31P nuclear magnetic resonance studies of nanoparticles of well known ferroelectric potassium dihydrogen phosphate (KDP) embedded into silica opal matrices. Two NMR techniques, static and magic angle spinning (MAS), were applied to confined KDP particles with different levels of deuteration, 80% and > 95%. Measurements were carried out using a Bruker Avance400 pulse spectrometer. Our findings proved unambiguously the pronounced reduction of the ferroelectric transition temperatures in the deuterated KDP/opal nanocoposites compared to the bulk counterparts in striking contrast to previous results.

The results of studies of phase transitions of KNO3, embedded in carbon nanotubes, are presented. It is shown that for KNO3 particles in nanotubes, a narrowing of the tempera-ture range of the existence of the ferroelectric phase is observed, similarly to what hap-pens in ferroelectric semiconductors. The results obtained indicate that the external screening from the side of the conducting matrix acts similarly to the screening of spon-taneous polarization in conducting ferroelectrics.

The study aims at investigating dielectric properties and DTA signal of composite ceramics (BiFeO3)(1-) (x) /(BaTiO3) (x) (x = 0, 0.25, 0.50, 0.75) from 300 to 720 K. The obtained results indicated that the Neel temperature determined at the peaks of dielectric constant near the antiferromagnetic phase transition in (BiFeO3)(1-) (x) /(BaTiO3) shifted toward lower temperatures with increasing barium titanate content. This anomaly was also confirmed by the movement of DTA signal peaks.

Room-temperature changes in the structure of a new diisopropylammonium chloride (C 6 H 16 ClN, DIPAC) molecular ferroelectric have been investigated by high-resolution cross polarization/magic-angle spinning nuclear magnetic resonance (CP/MAS NMR) and X-ray diffraction (XRD) methods. The NMR measurements are carried out using 13 C nuclei. Depending on time and heat treatment, monoclinic ferroelectric or orthorhombic nonpolar phases (as well as their coexistence) are observed. It is shown that the polar DIPAC modification at room temperature is transformed in the course of time into the nonpolar orthorhombic structure.

The results of studying the linear and nonlinear dielectric properties of a new organic ferroelectric diisopropylammonium iodide (DIPAI), embedded in porous alumina films, in comparison with bulk DIPAI, are presented. It was found, for DIPAI in pores 300 and 60 nm in diameter the ferroelectric phase is formed in the heating and cooling modes in the temperature interval between two structural phase transitions above room temperature. No noticeable temperature hysteresis was observed for both phase transitions. It was shown that the boundaries of the intermediate polar phase for nanostructured DIPAI shift to low temperatures with decreasing pore size. For bulk DIPAI, two structural transitions were revealed during heating with the formation of an intermediate polar phase and only one transition during cooling, below which ferroelectricity occurred. The temperature of this transition was much lower than the corresponding temperature during heating. It is assumed that the observed differences in phase transitions for DIPAI in pores and bulk DIPAI are associated with acceleration of the phase transitions kinetics under conditions of nanoconfinement.

Linear and nonlinear dielectric properties of new organic ferroelectric diisopropylammonia iodide (DIPAI) introduced into porous aluminum oxide films have been studied in comparison with the properties of a bulk DIPAI. In DIPAI, in pores 300 and 60 nm in diameter, it has been found that the ferroelectric phase forms on heating and on cooling in the temperature range between two structural phase transitions above room temperature. No marked temperature hysteresis is observed for both the phase transitions. The boundaries of the intermediate polar phase in the nanostructured DIPAI is shown to shift to lower temperatures as the pore size decreases. For the bulk DIPAI, two structural transitions are observed on heating with the formation of an intermediate polar phase and only one transition below which the ferroelectricity forms is observed on cooling. This transition temperature is significantly lower than the corresponding temperature on heating. It is assumed that the observed differences of the phase transition in DIPAI in pores and in the bulk DIPAI are related to an acceleration of the kinetics of the phase transitions in the nanoconfinement conditions.

Changes in structure of a new molecular ferroelectric diisopropylammonium chloride (C6H16ClN, DIPAC) at room temperature were studied by high-resolution (CP-MAS) nuclear magnetic resonance (NMR) and X-ray analysis. NMR measurements were carried out for ^{13}С nuclei. Monoclinic ferroelectric and orthorhombic nonpolar phases as well as their coexistence were observed depending on time and thermal treatment. It was shown that the polar modification of DIPAC at room temperature transforms with time to the nonpolar orthorhombic structure. N. I. Uskova, E. V. Charnaya, L. Yu. Podorozhkin, S. V. Baryshnikov, I. V. Egorova, A. Yu. Milinskii

The diisopropylammonium chloride (C6H16ClN, DIPAC) and diisopropylammonium bromide (C6H16BrN, DIPAB) molecular crystals are recently discovered ferroelectrics with sufficiently high spontaneous polarization and Curie temperature. We performed first studies of these crystals by 13C NMR. CP MAS spectra were collected within large temperature ranges covering the Curie points. The reconstructive phase transition from the initial orthorhombic P212121 structure of DIPAB to the monoclinic ferroelectric P21 structure leads to an abrupt alteration in the 13C spectrum. The 13C spectra for DIPAC and DIPAB in the ferroelectric P21 phase are quite similar with four lines at lower frequencies, which correspond to the CH3 groups, and two lines with close chemical shifts, which correspond to two CH groups. The transition into the paraphase leads to gradual reduction of the interline distances in the low-frequency quadruplet and in the doublet. The step-like changes in the interline frequency shifts at this transition indicating its first order. The analysis of the spectrum evolution in the paraphase shows that only a CH group lays in the reflection plane above the P21  →  P21/m transition, while the second CH group only moves closer to the reflection plane upon further heating.

The properties of the molecular ferroelectric diisopropylammonium bromide (C6H16BrN, DIPAB) particles embedded into a nanoporous opal matrix were studied by high-resolution nuclear magnetic resonance (NMR) in the temperature range from 295 to 450 K. The 13C NMR spectra were obtained using CP-MAS technique. The results showed that structural changes in nanostructured DIPAB particles are more complex than it was previously expected. The NMR spectra of DIPAB embedded into the opal matrix revealed the coexistence of two different crystalline structures within a wide temperature range. The monoclinic ferroelectric and orthorhombic non-polar phases were seen in nanoconfined DIPAB at room temperature, meanwhile the orthorhombic phase only was found in the bulk DIPAB crystalline powder. The NMR spectra showed that the transition from the orthorhombic to the ferroelectric phase upon heating is reconstructive. The total nanocomposite transforms into the ferroelectric structure at a temperature much higher than that for the relevant transition in bulk. The size effect also leads to the increase of the temperature of the phase transition from the ferroelectric P21 phase to the P21/m paraphrase.

A powder sample of potassium dihydrophosphate KH 2 PO 4 has been studied by the 31 P NMR method in a wide temperature range covering the ferroelectric phase transition. Changes in the position and shape of the resonance line at the transition to the ferroelectric phase have been revealed. The parameters of the chemical shift tensor of 31 P (isotropic shift, anisotropy, and asymmetry) in the ferroelectric phase have been calculated from the experimental data. A sharp increase in the anisotropy of the tensor at the phase transition has been demonstrated. Dielectric measurements have also been carried out to verify the transition temperature.