Dielectric properties of the nanoporous MCM-41 matrix filled with the (NH4)2SO4 ferroelectric

Variations with temperature of the linear dielectric permittivity and amplitude of the third harmonic were studied for nanoporous MCM-41 matrices with 4.0-nm channel pores filled with the (NH₄)₂SO₄ ferroelectric, in comparison with bulk ammonium sulfate. The measurements were performed upon heating and cooling in the temperature range from 100 K to room temperature. A noticeable shift to low temperatures (by approximately 25 K) for the ferroelectric phase transition in the MCM-41/(NH₄)₂SO₄ nanocomposite as compared to bulk (NH₄)₂SO₄ was revealed. The temperature hysteresis observed at the phase transition in the nanocomposite was approximately 2 K which is close to that in bulk ammonium sulfate. The significant decrease of the transition temperature in nanostructured ammonium sulfate agrees with the theoretical predictions based on the Landau and Ising models of the size effect on the ferroelectric phase transition in isolated small particles.     

Size Effect in Nanocomposites Based on Molecular Ferroelectric Diisopropylammonium Bromide

Physics of the Solid State - We present the results of studies of the dielectric properties of nanocomposites based on Al2O3 oxide films with a pore size of 330 and 60 nm with particles of an...     

Phase Transitions of KIO3 Ferroelectrics in Al2O3-Based Nanoporous Matrices

Physics of the Solid State - Temperature dependences of the linear permittivity ε' and the third harmonic amplitude γ3ω of composites prepared by introducing ferroelectrics KIO3...     

Dielectric and Thermal Properties of KNO3 Encapsulated in Carbon Nanotubes

Physics of the Solid State - 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...     

Dielectric and calorimetric investigations of KNO3 in pores of nanoporous silica matrices MCM-41

The temperature dependences of the linear dielectric permittivity, the third harmonic amplitude, and the heat capacity of nanoporous silica matrices MCM-41 with cellular channels (3.7 and 2.6 nm in diameter) filled with KNO₃ have been investigated in comparison with those obtained for bulk potassium nitrate. Measurements have been performed during heating and cooling in the range from room temperature to 463 K. Anomalies corresponding to structural phase transitions have been observed. A significant broadening of the temperature region of the existence of the ferroelectric phase III of potassium nitrate upon cooling has been revealed. This broadening increases with a decrease in the size of pores. It has been shown that, in the nanocomposites with potassium nitrate, the ferroelectric phase can also be formed during heating. The efficiency of observation of the third harmonic generation for studying nanocomposites with the ferroelectric phase has been demonstrated.     

Effects of Interaction in Mixtures of Ferroelectric Powders C6H16NBr and PbTiO3

Physics of the Solid State - Phase transitions in the mixture of powders C6H16NBr (DIPAB) and PbTiO3 and composites x-bTiO3–(1 – x)C6H16NBr at x from 0.05 to 0.45 have been studied by...     

Dielectric Properties of Ferroelectric Nanocomposites Based on KD2PO4

Russian Physics Journal - The temperature dependences of the dielectric permittivity ε' and dielectric loss tangent tgδ have been studied for KD2PO4 embedded into the pores of the...     

Studies of TGS in nanoscale silicate matrices by nonlinear dielectric spectroscopy

The results of studying triglycine sulphate (TGS) imbedded into nanoscale silicate matrices (opal matrices and SBA-15) by methods of linear and nonlinear dielectric spectroscopy are presented. The ferro-electric phase transition becomes noticeably smeared out, as compared to that in a single crystal, and its temperature rises, both effects becoming more pronounced with the decrease in pore sizes.     

Phase transitions of SC(NH<Subscript>2</Subscript>)<Subscript>2</Subscript> ferroelectrics in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-based nanoporous matrices

Temperature dependences of the linear permittivity ε' and the third harmonic amplitude γ_3ω of composites prepared by introducing ferroelectrics SC(NH₂)₂ into matrices of porous aluminum oxide Al₂O₃ with pore sizes 60 and 100 nm are determined. It is found that temperature T _c of the ferroelectric phase transition and the temperature T _i of the phase transition from incommensurable phase to the paraphrase increase significantly. The transition shifts increase as pore diameters decrease.