Dielectric Studies of Thiourea, SС(NH₂)₂, Embedded into Molecular Sieves

Abstract

Studies of temperature dependences of linear permittivity and third harmonic generation were carried out for ferroelectric thiourea, SС(NH 2 ) 2 , particles embedded into molecular sieves SBA-15 and МСМ-41 with pore sizes of 7.5 nm and 4.0 nm, respectively. Temperatures of the ferroelectric phase transition and transition from the incommensurate phase into paraphase were shown to be higher than in bulk thiourea. The shifts of the transitions increased with decreasing pore size. Both phase transitions were strongly diffused. The obtained data evidenced that the third harmonic generation can be used to find temperatures of the diffused ferroelectric transition.

Исследование фазовых переходов сегнетоэлектрика SС(NH-=SUB=-2-=/SUB=-)-=SUB=-2-=/SUB=- в нанопористых матрицах на основе Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-

“…Температура несоразмерного перехода T i увеличивается при умень-шении размера пор на 39 и 49 K соответственно. Подоб-ное увеличение температур T c и T i было обнаружено ранее для тиомочевины, внедренной в нанопористые силикатные материалы МСМ-41 и SBA-15 [21].…”

Polymorphism of Metallic Sodium under Nanoconfinement

“…A metastable polymorph of acetaminophen (paracetomol), a common drug, was shown to stabilize within nanopores . The ferroelectric phase transitions under nanoconfinement can shift and be suppressed for particular ferroelectrics (see refs and and references therein). These phenomena are of great potential importance as they can be used for fine-tuning the polymorphism of solid phases and producing advanced nanocomposites for applications in electronics, information techniques, medicine, and biology.…”