Suppression of Acoustic Resonances in BST-Based Bulk-Ceramic Varactors by Addition of Magnesium Borate

This work presents a method for reducing acoustic resonances in ferroelectric barium strontium titanate (BST)-based bulk ceramic varactors, which are capable of operation in high-power matching circuits. Two versions of parallel-plate varactors are manufactured here: one with pure BST and one with 10 vol-% magnesium borate, Mg3B2O6 (MBO). Each varactor includes a 0.85-mm-thick ferroelectric layer. Acoustic resonances that are present in the pure BST varactor are strongly suppressed in the BST-MBO varactor and, hence, the Q-factor is increased over a wide frequency range by the addition of small amounts of a low-dielectric-constant (LDK) MBO. Although the tunability is reduced due to the presence of non-tunable MBO, the increased Q-factor extends the varactor’s availability for low-loss and high-power applications.

Synthesis and characterisation of HIP Ca0.80Ce0.20ZrTi1.60Cr0.40O7 zirconolite and observations of the ceramic–canister interface

A sample of zirconolite with nominal composition Ca0.80Ce0.20ZrTi1.60Cr0.40O7 was processed via Hot Isostatic Pressing (HIP), with a dwell temperature and pressure of 1320 °C/100 MPa maintained for 4 h. The produced wasteform was characterised by powder XRD, SEM–EDS, Ce L3 and Cr K-edge XANES. A significant portion of the Ce inventory did not fully partition within the zirconolite phase, instead remaining as CeO2 within the microstructure. Inspection of the stainless steel–ceramic interface detailed the presence of an interaction region dominated by a Cr-rich oxide layer. No significant Cr or Fe migration was observed, although a greater concentration of perovskite was observed at the periphery, relative to the bulk ceramic matrix. The X-ray absorption features of Cr remained analogous with Cr3+ accommodation within TiO6 octahedra in the zirconolite matrix. The absorption edge of Ce was comprised of contributions from zirconolite-2M and unincorporated CeO2, with an average oxidation state of Ce3.9+. As zirconolite-2M accounted for > 92 wt% of the overall phase assemblage, it is clear that the dominant oxidation state of Ce in this phase was Ce4+. Graphic abstract

An alternating multilayer architecture boosts ultrahigh energy density and high discharge efficiency in polymer composites

Poly(vinylidene fluoride) (PVDF)-based polymers with excellent flexibility and high breakdown strengths are desirable compared to the traditional bulk ceramic in dielectric material applications.

Significantly enhanced room temperature electrocaloric response with superior thermal stability in sodium niobate-based bulk ceramics

This work simultaneously achieved a large temperature change (ΔT, ∼0.70 K) at room temperature and ultra-stable ΔT(±1.4% variation between 300 K with 380 K) in 0.78NaNbO3–0.22BaTiO3bulk ceramic.

Ultrahigh room temperature electrocaloric response in lead-free bulk ceramicsviatape casting

An ultrahigh room temperature adiabatic temperature change (∼1.6 K) was realized in a BaTiO3-based bulk ceramic prepared by the tape casting technique, which makes a giant step-forward for electrocaloric refrigeration.

Piezoelectricity in the {AxA`(1-x)}BO3 and A{BxB`(1-x)}O3 Ceramic Alloys

ABO3 perovskite ceramics due to their chemical nature and size difference of the cations A (where A is a divalent metal) and B (where B is a tetravalent metal) have non-centro-symmetric polymorphs and display significant piezoelectric properties. One path to improve piezoelectric properties is through alloying these materials. In order to assess the feasibility of this, we have investigated the structure, elastic and piezoelectric properties of prototypical cubic and tetragonal phases of ABO3 bulk ceramic oxides and their alloys: {AxA`(1-x)}BO3 and A{BxB`(1-x)}O3 by density functional theory based first-principle calculations. Using 2x2x2 super cells as models in our calculations, we have covered the full alloying range by varying concentration, x, in steps of 12.5%. We have created models using Ba, Sr, Pb, for A and A`, and Ti, Zr for B and B` both in cubic and tetragonal super cells. Here, we will report the structural and piezoelectric properties of tetragonal phases of ABO3 bulk ceramic oxides and their alloys.

Towards Two-Dimensional Oxides for Optoelectronic Applications

ABSTRACTPreliminary thin films of barium zirconate-titanate (BZT) are grown by pulsed laser deposition from bulk ceramic targets on magnesium oxide (001) substrates. Growth conditions are optimized for film crystallinity and thick (100 nm) films are deposited. These films are seen to be growing with a cube-on-cube epitaxial relation. The lattice constant of the alloy follows Vegard’s law as expected but shows a reasonable amount of non-linearity in the relation between band gap and composition.