Dielectric response of potassium nitrate in a restricted geometry

Koroleva, Ekaterina; Набережнов, А. А.; Rysiakiewicz-Pasek, E.; Vakhrushev, S. B.; Sysoeva, A. A.; Kumzerov, Yu. A.

doi:10.1016/j.compositesb.2016.03.046

Cited by 11 publications

(7 citation statements)

References 20 publications

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“…Naberezhnov et al 37 , 38 obtained the maximum melting temperature drop of 40 °C for KNO3-filled nanoporous glass with a 7 nm pore size measured by dielectric spectroscopy. In another study, 39 for porous glass with different pore diameters (320, 46, and 7 nm) filled with KNO 3 , it was observed that ferroelectric phase transition temperatures of the salt decreased with decreasing the glass pore diameters.…”

Section: Resultsmentioning

confidence: 94%

Melting Temperature Depression and Phase Transitions of Nitrate-Based Molten Salts in Nanoconfinement

et al. 2022

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Hybrids of nitrate-based molten salts (KNO 3 , NaNO 3 , and Solar Salt) and anodic aluminum oxide (AAO) with various pore sizes (between 25 and 380 nm) were designed for concentrated solar power (CSP) plants to achieve low melting point (<200 °C) and high thermal conductivity (>1 W m –1 K –1 ). AAO pore surfaces were passivated with octadecyl phosphonic acid (ODPA), and the results were compared with as-anodized AAO. The change in phase transition temperatures and melting temperatures of salts was investigated as a function of pore diameter. Melting temperatures decreased for all salts inside AAO with different pore sizes while the highest melting temperature decrease (Δ T = 173 ± 2 °C) was observed for KNO 3 filled in AAO with a pore diameter of 380 nm. Another nanoconfinement effect was observed in the crystal phases of the salts. The ferroelectric phase of KNO 3 (γ-phase) formed at room temperature for KNO 3 /AAO hybrids with pore size larger than 35 nm. Thermal conductivity values of molten salt (MS)/AAO hybrids were obtained by thermal property analysis (TPS) at room temperature and above melting temperatures of the salts. The highest increase in thermal conductivity was observed as 73% for KNO 3 /AAO-35 nm. For NaNO 3 /AAO-380 nm hybrids, the thermal conductivity coefficient was 1.224 ± 0.019 at room temperature. To determine the capacity and efficiency of MS/AAO hybrids during the heat transfer process, the energy storage density per unit volume (J m –3 ) was calculated. The highest energy storage capacity was calculated as 2390 MJ m –3 for KNO 3 /AAO with a pore diameter of 400 nm. This value is approximately five times higher than that of bulk salt.

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Section: Resultsmentioning

confidence: 94%

Melting Temperature Depression and Phase Transitions of Nitrate-Based Molten Salts in Nanoconfinement

et al. 2022

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“…Results of their experimental characterization indicate that the polarization state of ferroelectric nanoinclusion may differ from its bulk counterpart at the same temperature. This important feature is demonstrated by the observed perceptible shifts of the Curie temperature and pronounced broadening of the stability range of ferroelectric state in nanocomposites [10,12,[14][15][16]. Furthermore, di electric measurements show that FE-DE nanocomposites are distinguished by strong enhancement of permittivity at high temperatures [10,15].…”

Section: Introductionmentioning

confidence: 91%

“…This important feature is demonstrated by the observed perceptible shifts of the Curie temperature and pronounced broadening of the stability range of ferroelectric state in nanocomposites [10,12,[14][15][16]. Furthermore, di electric measurements show that FE-DE nanocomposites are distinguished by strong enhancement of permittivity at high temperatures [10,15].…”

Section: Introductionmentioning

confidence: 91%

“…The mechanical matrix effect, which involves the elastic three-dimensional (3D) clamping of ferroelectric inclusions and the generation of thermal stresses due to dissimilar thermal expansion of two contacting materials [5][6][7][8][9], should be especially important for ferroelectric nanocrystals surrounded by rigid dielectric matrices such as glasses. Such FE-DE nanocomposites have been fabricated in many laboratories by embedding ferroelectric substances into various porous dielectrics, including synthetic opals [10,11], silica glass [12,13], sodium borosilicate glass [14,15], and aluminum oxide [16]. Results of their experimental characterization indicate that the polarization state of ferroelectric nanoinclusion may differ from its bulk counterpart at the same temperature.…”

Section: Introductionmentioning

confidence: 99%

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Dielectric properties of ferroelectric nanocomposites: effects of thermal stresses and filler shape anisotropy

Nikitchenko

Azovtsev

Pertsev

2018

J. Phys.: Condens. Matter

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Ferroelectric nanocomposites are intriguing nonhomogeneous materials, which may have unusual phase states and specific physical properties useful for practical applications. Here we theoretically describe dielectric properties of nanocomposites comprising single-domain ferroelectric nanocrystals embedded into a linear dielectric medium. First, small-signal intrinsic permittivities of spheroidal PbTiO and BaTiO crystallites surrounded by an isotropic matrix with linear elastic properties are calculated with the aid of a nonlinear thermodynamic theory. It is shown that thermal stresses caused by differences in thermal expansion between the inclusions and the matrix may strongly influence the intrinsic permittivities of ferroelectric nanocrystals. Second, macroscopic dielectric responses of ferroelectric-dielectric composites are evaluated in the Maxwell Garnett approximation. For effective permittivities of such composites, generalized relations are derived, which allow for both the shape and dielectric anisotropies of ferroelectric nanocrystals. Numerical calculations of the effective permittivities are performed for composites comprising PbTiO and BaTiO nanocrystals embedded into representative dielectric matrices generating tensile (silica glass) or compressive (potassium silicate glass) thermal stresses inside ferroelectric inclusions. For nanocomposites involving randomly oriented and similarly aligned spheroidal inclusions, temperature dependences of the effective permittivities are determined with the account of phase transitions occurring in strained ferroelectric nanocrystals and suppression of their dielectric responses due to the depolarizing-field effect created by low-permittivity matrix. Our theoretical calculations show that effective permittivities of composites comprising needle-like or disc-shaped ferroelectric inclusions could strongly exceed the permittivity of the matrix. Most importantly, we predict that BaTiO-KO-SiO composites with such inclusions should exhibit a broad dielectric peak around the room temperature, which is associated with shifted structural transitions in strained BaTiO nanocrystals. The presented theory provides guidelines for the development of ferroelectric nanocomposites with enhanced dielectric responses, which could be suitable for applications in supercapacitors and other advanced electronic devices.

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“…В НКМ на основе пористых сред, заполненных различными сегнетоэлектриками, были обнаружены гигантский рост диэлектрической проницаемости в параэлектрической фазе [7][8][9][10][11][12], изменение параметров фазового перехода и типа фазового перехода [13][14][15][16][17], стабилизация метастабильных фаз [18][19][20], существование критических размеров наночастиц [13,18].…”

Section: Introductionunclassified

Структурный переход и температурные зависимости коэффициентов теплового расширения NaNO-=SUB=-3-=/SUB=-, внедренного в нанопористое стекло

Набережнов¹,

Алексеева²,

Кудрявцева³

et al. 2022

Физика Твердого Тела

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The temperature evolution of the crystal structure of a nanocomposite material obtained by introducing sodium nitrate NaNO3 from a melt under pressure into a nanoporous alkali borosilicate glass with an average pore diameter of 7 nm has been studied by the method of diffraction of synchrotron radiation in a wide temperature range upon heating. Analysis of the experimental diffraction patterns revealed a significant decrease in the temperature of the structural (orientational) transition by more than 50 K (up to 496 K) compared to bulk sodium nitrate. From the temperature dependence of the intensity of the superstructure peak (113), the dependence of the critical exponent β (T) for this transition was obtained and a significant difference from the critical exponent for a bulk material was found in the temperature range from 455 K to the transition temperature. Analysis of the broadening of Bragg reflections made it possible to estimate the average size (~ 40 nm) of sodium nitrate nanoparticles into the pores. An increase in the linear coefficient of thermal expansion in the [001] direction was found in NaNO3 nanoparticles in comparison with bulk material at temperatures above 450 K.

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Dielectric response of potassium nitrate in a restricted geometry

Cited by 11 publications

References 20 publications

Melting Temperature Depression and Phase Transitions of Nitrate-Based Molten Salts in Nanoconfinement

Melting Temperature Depression and Phase Transitions of Nitrate-Based Molten Salts in Nanoconfinement

Dielectric properties of ferroelectric nanocomposites: effects of thermal stresses and filler shape anisotropy

Структурный переход и температурные зависимости коэффициентов теплового расширения NaNO-=SUB=-3-=/SUB=-, внедренного в нанопористое стекло

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