Domain engineering enhanced microwave tunability in nonstoichiometric Ba_0.8Sr_0.2TiO₃

Abstract

Domain engineering via oxygen vacancy, VnormalO∙∙, loading achieved by A/B modification as well as quenching treatment, was utilized for Ba0.8Sr0.2TiO3 (0.8 BSTs) in an attempt to enhance the microwave tunable characteristics. For similar grain sizes, the domain sizes were notably reduced for all nonstoichiometric BSTs, indicating that the loaded VnormalO∙∙ (as a consequence of Ti defects, VTi″″) played a role in the nuclei for new domain walls. The tunability T at 100 MHz under a direct current field of 30 V/20 μm increased steadily as the domain size (d.s.) declined for all BSTs, regardless of the A/B ratio, due to the d.s. effect. The tunable characteristics in nonstoichiometric BSTs having a similar d.s. of ˜190 nm were then compared. The tunability and tan δ decreased for A/B = 1.002 (0.2 mol% Ti defects). The introduced VnormalO∙∙ formed pinning centers that restricted domain wall motion, leading directly to lower tunability and smaller dielectric loss. However, VnormalO∙∙‐overloaded samples (i.e., A/B ≥ 1.005) exhibited increased values for tan δ due to VnormalO∙∙ conduction in the domains. The quench treatment of 0.8 BST (with A/B = 1.002) samples resulted in a d.s. reduction from 191 to 170 nm. These quenched specimens showed greater tunability, Ttotal, originating from the strengthened dipole contribution, Tdipole, as a consequence of the d.s. effect. The tan δ of the quenched specimens was essentially unchanged, indicating a homogenous VnormalO∙∙ distribution via the quench, effectively reducing the mobile VnormalO∙∙ (which contributes to electrical conduction) in the domains. Consequently, the achieved figure of merit via domain engineering was 2.25 at 100 MHz for the quenched BST with A/B = 1.002, which was 1.54 times larger than that of unmodified BST.

Domain contribution to the aging characteristics in BaTiO3 ceramics

“…This finding confirms the contribution of the DS in the BTO's aging characteristics in addition to the tunability contribution, as we previously reported. 4,20,21) Here, the magnitude of the reduction in the permittivity is unambiguously determined from the DS in both tunability and aging effects, for specimens of identical composition. Acceptor cation loading and nonstoichiometric compositions significantly change the DC bias characteristics even if the specimens have a similar DS.…”

“…The tunability of ferroelectrics is attributed to permittivity depression due to hardening in domain wall vibrations and to freezing of optical phonon modes. 20,21) The relaxation time τ of a domain wall vibration is less than microseconds, i.e. of at least MHz or even higher frequency, while the τ of dipole fluctuation in PNRs of relaxor ferroelectrics is nanoseconds or shorter, corresponding to GHz or even higher frequency.…”

“…a long-time. [22][23][24][25] We previously quantified 20,21) the dipole contribution of the tunable characteristics using broadband dielectric spectroscopy at low to microwave frequencies. 10,19,[26][27][28] The polarization contributions to the tunability, i.e.…”

Polarization contributions to DC bias characteristics of nanograined BaTiO3-based ceramics

“…within 10 s of the electric field application, is mainly originated from the tunability response, due to hardening in DW vibrations. [10][11][12][13] It is also noted the ionic and electronic contributions, ε ionic+el. , did not notably decrease under the DC field.…”

“…[7][8][9] The DC bias characteristics of a ferroelectric are interpreted as the sum of the electric field responses of three main polarizations: dipole, ionic, and electronic. [10][11][12][13] In conventional ferroelectrics [e.g. BaTiO 3 (BT)], the ferroelectric domain configurations related to dipole polarization strongly influence the resulting DC bias characteristics.…”