Thickness Dependence Of Polarization Research Articles

The Investigation for Thickness-Dependent Electrical Performance on BaTiO3/BiFeO3 Bilayer Ferromagnetic Capacitors

Bilayer barium titanate (BaTiO3, BTO)/bismuth ferrite (BiFeO3, BFO) capacitive devices were fabricated and systematically analyzed from the aspects of thin-film material crystallography and electrical characterization. The tetragonal phase (T) of BTO with the reducing thickness (150 nm) was demonstrated through carefully adjusting the conditions of sputtering process and post-thermal treatments. The thickness dependence of polarization, energy density, permittivity, and leakage current was investigated in the BTO/BFO bilayer system. It showed that 150-nm BFO film is an optimal thickness, which led to the substantial increase in energy density up to 920 mJ/cm3 with the charge/discharge efficiency of 79.7% at 10 V. The permittivity of 150-nm BFO bilayer device was found to be 258, which is much higher than the single -layer BFO and other BTO/BFO devices with different BFO thicknesses. Leakage current could be reduced by three orders with the increasing thickness of BFO layer from 30 to 225 nm. In addition, the leakage current of BTO/BFO bilayer capacitors was 102 times lower than BFO single layer with the same total thickness. The result showed that the leakage current of BFO material could be significantly reduced in the bilayer system. The performance of BTO/BFO bilayer capacitors indicates that it is a promising technique for the implementation of nanoscale, lead-free, and nonelectrochemical thin-film energy storage-related applications.

Thickness dependence of polarization in ferroelectric perovskite thin films

The dependence of the polarization of ferroelectric perovskite thin films on the film thickness is explicitly calculated by using a generalized Landau–Ginzburg–Devonshire thermodynamic theory. Both residual stress and stress relaxation in the films have a significant effect on the thickness-dependent polarization. Our calculations demonstrate that the coexistence or competition between the surface effect and the constraint effect results in significant size effects at a finite nanoscale. This is especially so for the compressively strained perovskite films, in which there are two characteristic thicknesses, i.e. hc (a few nanometres), below which the ferroelectricity disappears, and hm (∼10hc), where the polarization exhibits a maximum. The theoretical results describe the available experimental data quite well.

Thickness dependence of polarization and response characteristics in thin FLC films

The effects of cell thickness on the pretransitional behaviour of ferroelectric liquid crystals are studied experimentally and theoretically for thin cells. The temperature and field dependences of the tilt angle, polarization, polarization to tilt angle ratio, dielectric permeability and relaxation frequency are considered in detail in the framework of a simple model for the surface tension. Apparent values of the phenomenological coefficients in the free energy expansion and some bulk and surface material parameters are estimated.