Chemical and Physical Properties of the BLT4 Ultra Capacitor—A Suitable Material for Ultracapacitors

Abstract

This paper describes the properties of a lead-free ceramic material based on barium titanate, designed for the construction of ultracapacitors and sensors used in mechatronic systems. The admixture of lanthanum (La3+) served as a modifier. The ceramic powders were obtained by the solid phase reaction method (conventional method—mixed oxides method—MOM). Technological conditions of the synthesis process were determined on the basis of thermal analysis. The obtained samples are characterized, at room temperature (Tr < TC), by a single-phase tetragonal structure and a P4mm space group. Properly developed large grains (d = 5 µm) contributed to the increase in electric permittivity, the maximum value of which is at the level of εm ≈ 112,000, as well as to a strong decrease in specific resistance in the ferroelectric phase, whereas above the Curie temperature, by creating a potential barrier at their boundaries, there was a a rapid increase in resistivity. The temperature coefficient of resistance of the obtained posistor is 10.53%/K. The electrical properties of the obtained ceramics were examined using impedance spectroscopy. In order to analyze the obtained results, a method of comparing the behavior of the real object and its replacement system in a specific frequency region was used, whereas the Kramer–-Kroning (K–K) test was used to determine the consistency of the measured data. The proper selection of the stoichiometry and synthesis conditions resulted in the creation of an appropriate concentration of donor levels and oxygen gaps, which in turn resulted in a significant increase in the value of electrical permittivity, with small values of the angle of dielectric loss tangent. This fact predisposes the discussed material for certain applications (in the construction of ultracapacitors, among others).

Impedance Spectroscopy of Fe and La-Doped BaTiO3 Ceramics

“…The surplus charge of La 3+ ions is compensated, among others, by creating barium vacancies [30]. This substitution method is confirmed by the increase in electrical permeability noted by both the authors of this paper [31] and other scientists [32,33]. Similarly, Fe 3+ (0.61 Å) does not enter the barium sites due to its radius but replaces the Ti 4+ ions (0.68 Å).…”

Dielectric and Electrical Properties of BLT Ceramics Modified by Fe Ions

“…The dielectric permittivity of BaTiO 3 ceramics at room temperature (ε r ) equals 1350 ( Figure 4 a). The addition of 0.4 mol.% of lanthanum caused an increase of dielectric permittivity at room temperature up to ~39,500 as well as the increase of maximum value at Curie temperature [ 13 ]. The iron modification caused deterioration of dielectric properties.…”

“…Our previous studies have been focused only on an undoped ceramic material, namely Ba 0.996 La 0.004 Ti 0.999 O 3 (BLT4) [ 13 ]. The proper selection of synthesis conditions resulted in the creation of an appropriate concentration of donor levels and oxygen gaps, which in turn led to a significant increase in electrical permittivity, with small values of the dielectric loss factor.…”

Fe-Doped Barium Lanthanum Titanate as a Competitor to Other Lead-Free Piezoelectric Ceramics

“…One of the reasons for such improvement in piezoelectric properties is connected with the decrease in grain size of admixture ceramics. The grain size of pure BLT4 ceramics is equal to about 5 μm [ 39 ], whereas in modified ceramics it is in the range from 0.5 μm to 2 μm. Grain size plays an essential role in the shaping of ferroelectric and piezoelectric properties [ 40 ].…”