Dielectric studies of ferroelectric NH₄HSO₄ nanoparticles embedded into porous matrices

ABSTRACT

Dielectric studies were carried out for the ammonium hydrogen sulphate, NH₄HSO₄, nanopartiles confined to three different mesoporous silica matrices: opal (photonic crystal), porous glass (mean pore size of 7 nm), and SBA-15 molecular sieves (pore size of 7.5 nm). Measurements were made within a temperature range 100 to 300 K which covers two structural phase transitions bounded the intermediate ferroelectric phase. The temperature of the upper second order phase transition was found not to shift compared to that in bulk. The lower phase transition shifted compared to bulk leading to the expansion of the ferroelectric phase. The transition temperature reduction, diffusion of transitions, and width of the thermal hysteresis differed for different nanocomposites and did not correlate to the pore size. The experimental data were treated within the framework of the models developed for isolated small ferroelectric particles and arrays of coupled particles. The rise of the space charge polarization effects was also observed.

KEYWORDS:

• Ammonium hydrogen sulphate, NH₄HSO₄
• nanoparticles
• nanoconfinement
• molecular sieves
• opal
• porous glass
• phase transitions
• permittivity

Funding

We acknowledge the financial support from Russian Foundation of Basic Researches, grant 13-07-12416.