Effect of Mg loading on the high-frequency tunability of Ba_0.8Sr_0.2TiO₃ceramics

Abstract

The effect of Mg loading on the high-frequency tunable properties and dielectric loss of Ba 0.8 Sr 0.2 Ti 1%x Mg x O 3 (BSTM) ceramics was investigated. Variation in the lattice parameters and the 90°domain configuration with Mg loading indicated a decrease in the tetragonal distortion. Additionally, the 90°domain size decreased slightly with a low Mg loading, up to 0.1 mol %, resulting in a higher domain-wall density compared with the nondoped specimen. The 0.075 mol % Mg-loaded BSTM ceramic exhibited the highest tunability; this was attributed to the domain-size effect. The loss tangent (tan δ) roughly decreased with Mg loading, due to loaded oxygen vacancies. The maximum figure of merit value (FOM = tunability/tan δ) at 10 MHz was achieved for the 0.075 mol % Mg specimen, twice that of the non-doped specimen, due to an increase in the tunability and a decrease in the loss tangent with Mg loading.

Effect of the (Ba + Sr)/Ti ratio on the microwave‐tunable properties of Ba0.6Sr0.4TiO3 ceramics

“…Barium strontium titanate (Ba 1− x Sr x TiO 3 ; BST) is a well‐known tunable ferroelectric that has a large nonlinear dielectric response under an electric dc field. We have reported the polarization contribution to the overall tunability of the normal ferroelectric Ba 0.8 Sr 0.2 TiO 3 (0.8‐BST) that has ferroelectric domains at room temperature . The dipole polarization in normal ferroelectrics is derived from the dipole fluctuation in the 90° domain walls; the dipole polarization significantly contributes to the permittivity in normal ferroelectrics.…”

“…We have reported the polarization contribution to the overall tunability of the normal ferroelectric Ba 0.8 Sr 0.2 TiO 3 (0.8-BST) that has ferroelectric domains at room temperature. 11,12 The dipole polarization in normal ferroelectrics is derived from the dipole fluctuation in the 90°domain walls; the dipole polarization significantly contributes to the permittivity in normal ferroelectrics. The 90°domain size strongly affects the tunability and the dielectric constant; smaller domains improve tunability because of the larger density of the domain wall vibration.…”

Domain engineering enhanced microwave tunability in nonstoichiometric Ba0.8Sr0.2TiO3

“…The introduced were each compensated for by the formation of two (i.e., 2 mol% of oxygen vacancies for A/B = 1.01 BST to compensate the 1 mol% of Ti deficiencies). By comparison, samples loaded with 0.5 mol% of Mg (with each Mg being compensated for by one , leading to ~0.5 mol% of oxygen vacancies) showed that most of the ferroelectric domains vanished, accompanied by a marked reduction in the T m from 70°C to ˜ 40°C for the Mg‐BST system . However, this was not observed for the Ti‐deficient systems.…”

“…BSTs with x = 0.8‐1.0 possess 90° domains due to the nature of the present dipole polarization, i.e., flat temperature dependence of permittivity near room temperature due to the higher T m (70°C‐130°C) . We have previously reported this domain configuration effect on the resulting microwave tunability properties for polycrystalline Ba 0.8 Sr 0.2 TiO 3 (0.8 BST) . The microwave tunability of 0.8 BST ceramics was significantly enhanced by decreasing the 90° domain width.…”

“…In fact, the replacement of Ti 4+ by Mg 2+ generates a [ defect association, which behaves as a domain‐pinning agent, reducing the domain size ( d.s .). That is, tunability was increased due to the decrease in d.s ., while tan δ was effectively reduced by acceptor loading, giving rise to a greater FOM . This decrease in tan δ was ascribed to the decrease in the amplitude of individual domain wall vibrations from defect associations.…”