At the IV III phase transition the third

At the IV→III phase transition, the third harmonic coefficient γ3ω for nanostructured (as well as for bulk) potassium iodate (Fig. 3b) takes the minimal value, increasing by about four times with further heating. Thus, the temperature studies of the capacitance and the third harmonic coefficient have revealed that the increase in the temperature of the transition from phase III to phase IV is approximately 20K for KIO3 in NCC pores, compared with bulk KIO3. The phase transition from phase III to phase II for the composite with potassium iodate is also observed as two diffuse peaks on the С(Т) curve: the first one at about 346 ± 1K (corresponding to bulk KIO3), and the second at 370 ± 1K (corresponding to nanostructured KIO3, see inset in Fig. 3a). The harmonic coefficient γ3ω has no anomalies at these temperatures, which is associated with small variations in the composite capacitance around the temperatures of 346 and 370K. Thus, based on the obtained С(Т) dependence, we can conclude that the temperature of the transition from phase III to phase II increases by about 24K for nanostructured KIO3 compared with bulk potassium iodate. The increase in the temperatures of the structural phase transitions IV→III and III→II for KIO3 in restricted geometry is not consistent with the predictions of the theoretical models of size effects in ferroelectrics based on the Landau myc pathway or the Ising model [18]. These models predict the ferroelectric transition to shift deeper into the ferroelectric phase, i.e., towards lower temperatures. A decrease in the phase transition temperature was found earlier for sodium nitrite in the pores of the MCM-41 and SBA-15 molecular sieves and opals, as well as for Rochelle salt in the pores of molecular sieves (see [1,19] and references therein). On the other hand, the region in which the ferroelectric phase existed was found to broaden for the same ferroelectrics in porous aluminum oxide [20,21]. The increase in the phase transition temperature was associated with the interaction between the ferroelectric particles in the pores and the matrix walls, or with pore geometry (see Ref. [21] and references therein), as well as with the dipole-dipole interaction between the individual ferroelectric particles in the composite [22]. Thus, the increase in the transition temperature in the NCC–KIO3-based composite can be explained by the dipole-dipole interaction of particles with the walls of the NCC matrix pores. This interaction leads to the stabilization of the polarized state in KIO3 nanoparticles. The presence of primary hydroxyl (OH) groups on the walls of NCC nanochannels supports this explanation. An increase in temperature by 9K was previously observed for the triglycine sulfate/NCC nanocomposites [6,7].
Conclusion In this study we have obtained and described the nanocomposites based on potassium iodate and nanocrystalline cellulose. We have discovered a significant increase in the temperature of the phase transitions between the ferroelectric phases of nanostructured potassium iodate embedded in the NCC pores. The temperatures of the phase transitions from phase IV to phase III and from phase III to phase II increase by about 20 and 24K, respectively. The significant increase in the phase transition temperature for potassium iodate is not consistent with the theoretical models describing the size effect on the ferroelectric phase transition in isolated small particles. The observed effect is attributed to the interaction of particles with the walls of the NCC matrix channels, which leads to the stabilization of the polarized state in KIO3 nanoparticles.
Introduction The materials modified by manganese dioxide (MnО2) are currently widely used in various areas [1–6], including the purification of waters and various technological solutions [1, 2, 6, 7–14]. In this regard, creating MnО2-modified materials based on clinoptilolite (CL), a natural zeolite, is a promising direction [15–18], since periosteum allows to obtain new materials with sufficiently high performance characteristics (sorption capacity, catalytic activity, chemical resistance and mechanical strength).