Properties of porous glasses with embedded ferroelectric materials

Abstract

Methods of introducing two ferroelectric materials, viz. NaNO 2 and (CH 3 NH 3 ) 5 Bi 2 Cl 11 (PMACB), into porous glass matrices and the results of dielectric, pyroelectric, thermal expansion and SEM investigations are presented. The best filling degree was achieved for NaNO 2 introduced from the melt, whereas a significantly worse filling effect was achieved for a water solution as the introducing agent. A splitting was observed in the temperature dependence of dielectric permittivity related to the incommensurate phase of NaNO 2 embedded in porous glass from a water solution, whereas no incommensurate phase was observed in the case of glass filled with NaNO 2 from the melt. The confined materials turned out to possess ferroelectric properties and exhibited phase transitions. The negative size effect was observed for porous glasses filled with NaNO 2 and PMACB. The above conclusions are based on the anomaly of dielectric, pyroelectric and dilatometric properties observed in the phase transition regions.

Adsorption Isotherm of CO on Pt(111) Electrodes

“…According to phenomenological and microscopic models, one should expect a negative shift of the ferroelectric phase transition temperature with decreasing particle sizes. Negative size effects were observed in previous studies of NaNO 2 nanoparticles confined within photonic crystals and porous glasses (see 5–8, 10 and references therein). Phase transition temperatures in sodium nitrite embedded into molecular sieves 10–12 were also lower or very close to that in bulk.…”

Calorimetric investigations of NaNO3 and NaNO2 embedded into porous glasses

“…They also noticed that the modulated phase vanished. In a previous work [7] we found that the modulated phase existed in NaNO 2 embedded into porous glasses with a mean pore diameter of 320 nm. NaNO 3 crystals at room temperature belong to the trigonal system with symmetry R3c À D 6 3d ; Z ¼ 2.…”

Phase transitions and macroscopic properties of NaNO3 embedded into porous glasses

“…-The suppression of the incommensurate phase transition (PT) at decreasing of particle sizes (for large pores) [3] and the crossover of the ferroelectric PT from the first-order PT to the second-order one as a function of pore diameter [4,5] for small particles. -The formation of specific volume "pre-melted state" above T c accompanied by increasing of unit cell volume, RMS ion displacements, sodium ions mobility and conductivity [6][7][8].…”