Observation of an anomalous correlation between permittivity and tunability of a doped (Ba,Sr)TiO3 ferroelectric ceramic developed for microwave applications

Abstract

Anomalous dependencies of the dynamic (pulse) and static tunability [k(U)=C(0)/C(U)] as a function of permittivity (ε) were observed in ferroelectric varactors based on doped paraelectric state (Ba,Sr)TiO3 ceramics. The reduction of the relatively high permittivity value from ε≅810 down to ε≅260 by introducing various proportions of a Mg2TiO4 additive resulted in a 20% increase in tunability. Furthermore, ceramics with this additive have demonstrated dynamic tunability noticeably higher than the static tunability, also unexpected for this type of material.

Anomalous Correlation between Dielectric Constant and Tunability in (Ba,Sr)TiO3–MgO–Mg2SiO4 Composite Ceramics

“…The seemingly contradictory results between Ref. and maybe results from different Mg 2 TiO 4 content range. To date, only Kozyrev et al .…”

“…In the Ba 0.5 Sr 0.5 TiO 3 –Mg 2 TiO 4 system, with the increase in Mg 2 TiO 4 content from 50 to 80 wt%, the dielectric constant at 10 kHz decreased from 335 to 35, and the tunability at 3 kV/mm decreased from 18.4% to 10.8% . More recently, Kozyrev et al . reported that increasing Mg 2 TiO 4 content from 8.3 to 44.4 wt% led to the decrease in dielectric constant of BST–Mg 2 TiO 4 from 810 to 260, but the tunability increased anomalously.…”

“…Various methods have been investigated to lower the dielectric constant and loss tangent of BST. It is reported that forming a ferroelectric–dielectric composite is an efficient method to reduce material dielectric constant, loss tangent, and maintain tunability at a sufficiently high level . Some linear dielectrics with low dielectric constant were added into BST and it is found that a BST–MgO composite shows better dielectric properties .…”

The Impact of Composite Effect on Dielectric Constant and Tunability in Ferroelectric–Dielectric System

“…Generally, this phenomenon is considered to be an anomaly, because the linear dielectric has no nonlinear property. However, in the studies of Kozyrev et al . and Nenasheva et al., with increasing Mg 2 TiO 4 content in BST‐Mg 2 TiO 4 composite ceramics from 8.3 to 44.4 wt%, the tunability increased.…”

Electronic Band Structures and Phase Transitions of Ferroelectric and Multiferroic Oxides

“…[1][2][3] Moreover, materials that have coupled electric, magnetic, and structural order parameters that result in simultaneous ferroelectricity, ferromagnetism, and ferroelasticity are known as multiferroics. [4][5][6] These multiferroics materials have attracted a lot of attention in recent years because they can potentially offer a whole range of new applications, including nonvolatile ferroelectric memories, novel multiple state memories, and devices based on magnetoeletric effects.…”