Ba0.6Sr0.4TiO3 Ceramics Research Articles

Exploring the low temperature fabrication and properties of barium strontium titanate tunable dielectric ceramics

Ba1−xSrxTiO3 compounds are widely recognized as leading dielectric materials for tunable electronic applications. To expand their applicability and enable integration with polymers and metals, there is a need for low-temperature processing. Here we show that Cold Sintering Process (CSP) enables the fabrication of Ba0.6Sr0.4TiO3 (BST) tunable dielectric ceramics, using Ba(OH)2·8 H2O as a flux, at a temperature as low as 350 ºC. A dielectric permittivity with a low magnitude of ∼ 340 at 10 kHz, an electric-field tunability of 11%, and a thermal stability of ±7.1% over the temperature range of −90 ºC to 85 ºC are obtained for CSP BST that thus outperforms conventionally sintered BST ceramics. Significant decrease in the sintering temperature and enhanced dielectric performance respond to the current sustainability concerns related to energy efficiency and tunable device requirements.

Effect of sintering temperature on microstructure, crystal structure and dielectric performance of Ba0.67Sr0.33TiO3 ceramics prepared by a novel direct coagulation casting via high valence counter ions (DCC-HVCI) method

Perovskite Ba0.67Sr0.33TiO3 (BST) ceramics with improved dielectric performance were fabricated by a novel direct coagulation casting via high valence counter ions (DCC-HVCI) method using 0.5 mol% MgO as the coagulation agent. The influence of sintering temperature on micromorphology, crystal structure, and dielectric performance of BST ceramic components was systematically evaluated. The densification rate of BST samples could reach the maximum at a heating temperature around 1305 °C and end up approximately at 1380 °C. As increasing the sintering temperature from 1400 to 1550 °C, the relative density of BST ceramics decreases from 98.82 ± 0.16% to 96.72 ± 0.06%, and the mean grain size drops gradually from 9.96 to 4.68 μm. The increased sintering temperature promotes the lattice expansion due to Ti4+ replacement at B site by Mg2+, as well as the generation of oxygen vacancies. In addition, as increasing sintering temperature, the dielectric permittivity (εr) of BST ceramic components decreases first and then slightly increases, while the dielectric loss (tanδ) of ceramics shows the opposite trend. The results indicate that the initial tanδ increase is mainly attributed to the lattice expansion of BST ceramics, and the subsequent loss reduction results from the easily localized conduction electrons on Mg2+ sites reducing the carrier concentration. The samples sintered at 1550 °C show the lowest dielectric loss (tanδ≈0.013), which is significantly reduced by an order of magnitude compared with that of dry-pressed samples (tanδ≈0.262).

Influence of solid loading on densification behavior, micromorphology and dielectric properties of Ba0.67Sr0.33TiO3 ceramics fabricated by a novel DCC-HVCI method

Ba0.67Sr0.33TiO3 (BST) ceramics with highly improved dielectric performance were fabricated by a novel direct coagulation casting via high valence counter ions (DCC-HVCI) method. The influence of solid loading on densification behavior, micromorphology, and dielectric performance of the samples was investigated. With the increase of solid loading from 40 to 50 vol%, the maximum densification rate of BST ceramics increased from 0.090 to 0.122 s−1, and the densification temperature decreased from 1424 to 1343 °C, which indicated that high solid loading could promote the densification behavior of samples during sintering. BST ceramics fabricated by the DCC-HVCI method showed uniform grain size and microstructure, which was beneficial for the dielectric properties of BST ceramics. Samples obtained from 45 vol% suspensions possessed the lowest dielectric permittivity (εr ≈ 2801), and the dielectric loss (tanδ≈0.0262) was about 1/10 of that of dry-pressed samples (tanδ≈0.301), which could be attributed to the composition homogenization.

Polar nano-clusters in nominally paraelectric ceramics demonstrating high microwave tunability for wireless communication

Dielectric materials, with high tunability at microwave frequencies, are key components in the design of microwave communication systems. Dense Ba0.6Sr0.4TiO3 (BST) ceramics, with different grain sizes, were prepared in order to optimise the dielectric tunability via polar nano cluster effects. Dielectric permittivity and loss measurements were performed at both high and low frequencies and were supported by results from X-ray powder diffraction, scanning and transmission electron microscopies, Raman spectroscopy and piezoresponse force microscopy. The concentration of polar nano clusters, whose sizes are found to be in the range 20–50 nm, and the dielectric tunability increase with increasing grain size. A novel method for measurement of the microwave tunability in bulk dielectrics is presented. The highest tunability of 32 % is achieved in ceramics with an average grain size of 10 μm. The tunability of BST ceramics with applied DC field is demonstrated in a prototype small resonant antenna.

Structural and dielectric properties of B2O3/Li2O-added Ba0.6Sr0.4TiO3 multilayer ceramics for tunable devices

B2O3 and Li2O (B/L)-added Ba0.6Sr0.4TiO3 (BST) ceramics sintered at 940 °C exhibited a dense microstructure with large grains. The amount of B/L additive was 4.5 wt% with a B/L ratio of 1.5:1. The B/L-related liquid phase assisted the densification of the BST ceramics. This BST ceramic displayed a large dielectric constant (εr) of 2834 with a low dielectric loss (tan δ) of 0.21% at 1.0 MHz. It also displayed a large tunability (28.2% at 10 kV/cm) and a high figure of merit (FOM) of 134. BST thick-films were synthesized using the tape casting method. The thick-film densified at 940 °C exhibited a large tunability of 18.7% at 10.0 kV/cm and an FOM of 208; these are higher than the values reported in the literature. Multilayer ceramics (MLCs) consisting of five layers of 40-μm-thick BST thick-films and Ag electrodes were also fabricated at 940 °C. No diffusion occurred between the Ag electrode and BST thick-film. A large tunability of 67.6% at 52 kV/cm with a high FOM of 294 was obtained from this MLC. This verified that the B/L-added BST ceramic is effective for application in tunable multilayer devices.

Highly enhanced dielectric loss of MgO-doped Ba0.67Sr0.33TiO3 ceramics prepared by a non-contamination DCC-HVCI method

MgO-doped Ba0.67Sr0.33TiO3 (BST) ceramics with uniform microstructure and enhanced dielectric loss were prepared by direct coagulation casting via high valence counter ions (DCC-HVCI) method. MgO was utilized as acceptor dopant as well as coagulating agent to release Mg2+ solidifying ceramic suspensions. Effect of sintering temperature and MgO doping content on microstructure and dielectric properties of BST ceramics was investigated. It was found that the loss tangent value (tan δ) decreased remarkably from 0.025 to 0.004 with increasing MgO concentration from 0.5 to 1.5 mol%. The 1.5 mol% MgO-doped BST ceramics processed high density of 99.5% and tan δ of 0.004 which is improved by 150% compared with that of dry-pressed samples. This improvement can be attributed to the ubiquitous distribution of MgO in BST ceramic matrix leading to the enhanced inhibitive effect. This paper provides a novel facial route to prepare high-performance functional ceramics with high reliability and low cost.

Porous (Ba,Sr)TiO3 ceramics for tailoring dielectric and tunability properties: Modelling and experiment

3D Finite Element Method simulations were employed in order to describe tunability properties in anisotropic porous paraelectric structures. The simulations predicted that properties of a ceramic can be tailored by using various levels of porosity. Porous Ba0.6Sr0.4TiO3 (BST) ceramics have been studied in order to investigate the influence of porosity on their functional properties. The BST ceramics with various porosity levels have been obtained by solid-state reaction. Lamellar graphite in different concentration of 10, 20 and 35 vol.%was added as sacrificial pore forming agent. The structural, microstructural, dielectric and tunability properties were investigated. By comparison with dense BST ceramic, porous samples present a fracture mode transformation from intragranular to an intergranular fracture and a decrease of grain size. Lower dielectric constants, low dielectric losses, but higher values of tunability than in the dense material were obtained in the porous BST structures as a result of local field inhomogeneity generated by the presence of air pores-ceramic interfaces.

Enhanced electrocaloric effect in Mn + Y co-doped BST ceramics near room temperature

Electrocaloric effect (ECE) of Ba0.67Sr0.33TiO3 (BST) and Mn+Y co-doped BST (BSTMY) ceramics prepared using citrate-nitrate combustion derived powders was investigated. The densification and dielectric strength can be improved by Mn+Y co-doping and citrate-nitrate combustion processes. The maximum electrocaloric temperature change (ΔT) in BSTMY is much larger than that in BST. Large ΔT of 2.63K and electrocaloric strength of 0.0239KcmkV−1 are obtained in BSTMY ceramic at room temperature.

Low dielectric loss and enhanced tunable properties of donor–acceptor co-doped Ba0.67Sr0.33TiO3 ceramics

Ba0.67Sr0.33TiO3 (BST) ceramics with 0.7 mol% Mn and y mol% Y (y = 0.6, 1.2, 1.8, 2.4) additions were fabricated via citrate–nitrate combustion derived powders, and the microstructure, dielectric properties and tunable properties of BST ceramics were investigated. The doping behavior of Y changes from acceptor doping to donor doping with increasing the content of Y, and the dielectric constant and loss tend to decrease with increasing doped concentration. The ceramic sample with 1.8 mol% Y exhibits the optimal properties with dielectric constant of 5520, dielectric loss of 0.003 and tunability of 43 % at 10 kHz and 20 oC, respectively. Both the low dielectric loss and enhanced tunable properties of the BST ceramic are useful for tunable applications.

Dielectric properties of La/Zr codoped Ba0.67Sr0.33TiO3 ceramics prepared from citrate–nitrate combustion derived powders

La/Zr codoped Ba0.67Sr0.33TiO3 (BST) ceramics were fabricated via citrate–nitrate combustion derived powders, and the microstructure and dielectric properties of BST ceramics were investigated. All ceramic samples show a pure perovskite structure. The dielectric constant and loss decrease with increasing Zr content. The additions effectively suppress the grain growth of BST ceramics. It is found that the temperature-permittivity characteristics for codoped BST ceramics could be controlled using various doping content.

Nanocrystalline Barium Strontium Titanate Ceramics Synthesized via the “Organosol” Route and Spark Plasma Sintering

Dense nanocrystalline barium strontium titanate Ba0.6Sr0.4TiO3 (BST) ceramics with an average grain size around 40 nm and very small dispersion were obtained by spark plasma sintering at 950°C and 1050°C starting from nonagglomerated nanopowders (~20 nm). The powders were synthesized by a modified “Organosol” process. X‐ray diffraction (XRD) and dielectric measurements in the temperature range 173–313 K were used to investigate the evolution of crystal structure and the ferroelectric to paraelectric phase transformation behavior for the sintered BST ceramics with different grain sizes. The Curie temperature TC decreases, whereas the phase transition becomes diffuse for the particle size decreasing from about 190 to 40 nm with matching XRD and permittivity data. Even the ceramics with an average grain size as small as 40 nm show the transition into the ferroelectric state. The dielectric permittivity ε shows relatively good thermal stability over a wide temperature range. The dielectric losses are smaller than 2%–4% in the frequency range of 100 Hz–1 MHz and temperature interval 160–320 K. A decrease in the dielectric permittivity in nanocrystalline ceramics was observed compared to submicrometer‐sized ceramics.

Structural, mechanical and dielectric properties of Ba0.6Sr0.4TiO3—The benefits of a colloidal processing approach

This paper reports on the benefits gathered from a proper colloidal dispersion/deagglomeration of a Ba0.6Sr0.4TiO3 (BST) powder in water followed by spraying the aqueous suspension against liquid nitrogen to obtain homogeneous granules. The density of green compacts derived from the freeze granulated (FG) powder was compared with that of compacts prepared from the same starting BST powder but non-granulated (NG). The sintering ability of the greens and the density, mechanical and functional properties of the obtained ceramics sintered at various temperatures properties were shown to be strongly enhanced by the freeze granulation step. Freeze granulation enabled decreasing the optimal sintering temperature for 50°C, and enhanced all the relevant measured properties, which showed a good correlation with sintered density. Maximum values of dielectric constant (εrmax=5087) and dielectric loss (tanδ=0.009) were measured at the phase transition temperature (Tc=−3°C) and at a constant frequency of 10kHz for the FG BST ceramics sintered at 1250°C, which also showed a flatter temperature-dependent dielectric profile.

Microstructure and dielectric properties of BST ceramics derived from high-energy ball-milling

Abstract Ba0.6Sr0.4TiO3 (BST) ceramics were prepared via a High-energy ball-milling (HEBM) method. Its sintering temperature and grain size were effectively reduced. Better temperature stability and decreased dielectric constant were obtained due to the refined grains, but the tunability was not deteriorated heavily. In addition, the dielectric loss of the HEBM samples kept at the same level with the traditional coarse-grained ceramics, lower than the nano-grained specimens prepared by chemical routes. The formation of BaWO4 phase had no “bad” effects on the dielectric performance of BST, indicating that HEBM was an effective way in preparing temperature-stable BST ceramics at a lower sintering temperature for tunable applications.

Fabrication and influence of sintering temperature on material properties of Mn/Y codoped Ba0.67Sr0.33TiO3 ceramics via using citrate–nitrate combustion derived powder

Mn/Y codoped Ba0.67Sr0.33TiO3 (BST) ceramics were fabricated via using citrate–nitrate combustion derived powder, and the effect of sintering temperature on microstructure and electrical properties of BST ceramics were mainly investigated. Agglomerated BST powder, with nano-size particles, was obtained at 700°C. Sintering temperature has a strong influence on the microstructure and electrical properties of BST ceramics. The density, dielectric and ferroelectric properties are improved by optimizing sintering temperature. The relative density of the BST ceramics sintered at an optimum sintering temperature (1260°C) reaches 97.9% of the theoretical value. The measured values of remanent polarization (2Pr) and coercive field (2Ec) of the BST ceramics are 16.33μC/cm2 and 3.548kV/cm, respectively. The dielectric loss of the BST ceramics is 0.003 in the para-electric state. Therefore, nanocrystalline powder, sintering with optimum temperature and Mn/Y codoping help improve the electrical properties of BST ceramics.

Preparation and Dielectric Properties of Dy-B-Si-O Glass-Doped Ba<sub>0.6</sub>Sr<sub>0.4</sub>TiO<sub>3</sub> Ceramics

Dy-B-Si-O glass-doped Ba0.6Sr0.4TiO3 (BST) ceramics based on sol-gel-derived powders were prepared. Effects of B2O3-SiO2 in Dy-B-Si-O glass on phase structure, microstructures and dielectric properties of the BST ceramics were investigated. The results showed that the main crystal phase of BST ceramics with appropriate B2O3-SiO2 in Dy-B-Si-O glass had a perovskite type structure. Grain size decreased and density increased compared with pure BST ceramics. However, the secondary phase Ba2TiSi2O8 was detected when the percentage of B2O3-SiO2 in Dy-B-Si-O glass additive was over 7 mol%, and increased with the increasing of B2O3-SiO2. With the increasing of B2O3-SiO2, the dielectric constant increased firstly and then decreased, the dielectric loss decreased firstly and then increased, the Curie temperature moved to lower temperature firstly and then to higher temperature.

Microstructure and electrical properties of Mn/Y codoped Ba0.67Sr0.33TiO3 ceramics

Pure and Mn/Y codoped Ba0.67Sr0.33TiO3 (BST) ceramics were fabricated via the citrate–nitrate combustion technique, and the microstructure and electrical properties of BST ceramics were mainly investigated. The Mn/Y codoping concentration has a strong influence on the microstructure and electrical properties of BST ceramics. All BST ceramics possess a pure polycrystalline structure. The density, dielectric loss, leakage current, and ferroelectric properties are improved by codoping 0.5mol% Mn and 1.0mol% Y to BST. The relative density of 0.5mol% Mn/1.0mol% Y-codoped BST (BST0510) ceramics reaches 97.5% of the theoretical value. BST0510 ceramics have the lowest dielectric loss (tanδ<0.0073 at 1kHz) among all BST ceramics. BST0510 ceramics also demonstrate a low leakage current density (1.23×10−7A/cm2) at an applied field of 10kV/cm, and excellent ferroelectric properties with a remanent polarization of 2Pr=15.327μC/cm2 and a coercive field of 2Ec=3.456kV/cm. Therefore, the Mn and Y with optimum content help improve the electrical properties of BST materials.

The Influence of Doped MgF&lt;sub&gt;2&lt;/sub&gt; on the Dielectric Properties of Barium Strontium Titanate Ceramics

Barium-strontium titanate Ba1-xSrxTiO3[0≤x≤1] has been investigated for tunable microwave application due to their high permittivity, low losses and high tunability. The influence of MgF2additives on the dielectric performance of Ba0.6Sr0.4TiO3(BSTO) were investigated in this paper. MgF2doped BSTO ceramics were prepared using the conventional mixed oxide techniques. The phase structure, microstructure and dielectric properties of MgF2doped BSTO ceramics were studied. The XRD patterns showed that all the samples exhibit a perovskite phase. A secondary phase of MgO was observed with excessive MgF2additives. The grain size of MgF2doped BSTO ceramics was slightly increased with the increasing of MgF2additives, while the distributed porosity was concentrated to get larger. The relative permittivity, dielectric loss and tunability were decreased accordingly. The relative permittivity was reduced from 3717 (pure Ba0.6Sr0.4TiO3) to 680 (6 wt % MgF2doped BSTO), while the tunability changed from 51.7 % to 6.5 %. The dielectric losses were decreased from 0.004 to less than 0.001. The Curie temperature of MgF2doped BSTO was first decreased with the additives of MgF2(x&lt;2 wt %) then remain the same with the rise of MgF2(2≤x≤6) content.

Microstructure and Dielectric Properties of Ba&lt;sub&gt;0.6&lt;/sub&gt;Sr&lt;sub&gt;0.4&lt;/sub&gt;TiO&lt;sub&gt;3&lt;/sub&gt; Ceramics Co-Doped Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-MgO

The Ba0.6Sr0.4TiO3 (BSTO) ceramics were prepared by a traditional electrical ceramic method. Effects of co-doping low dielectric constant oxides Al2O3and MgO on microstructure and dielectric properties of Ba0.6Sr0.4TiO3ceramics were investigated. The results show that BSTO/MgO/Al2O3(BMA) ceramics can be sintered at 1300°C. The main crystal phases are cubic perovskite structure Ba0.6Sr0.4TiO3and face-centered-cubic spinel structure MgAl2O4. Al3+is easier to enter Ba0.6Sr0.4TiO3lattice in the replacement of Ti4+than Mg2+. When Al2O3content exceeds 20wt%, Al2O3would react with BaAl2O4to generate a new phase of BaAl12O19. Proper amount of Al2O3-MgO can reduce the dielectric constant of BSTO ceramics and result in the higher tunability. There is obvious frequency dispersion characteristic in BMA ceramics and the curie temperature of ceramics decreases with the increase of Al2O3. The BMA ceramics with 20 wt% Al2O3exhibit good dielectric properties, with εrof 1314, tanδ of 0.003 at 10 kHz, and the dielectric constant tunability of 35.2% under a dc electric field of 1.0 kV/mm, which are useful for potential tunable device applications.

Influence of 4ZnO–B2O3 Addition on Dielectric Properties and Microstructures of Barium Strontium Titanate

This study investigates the effect of 4ZnO–B2O3 on the sintering behavior, dielectric properties, and microstructures of Ba0.6Sr0.4TiO3 (BST) ceramics. These ceramics were sintered in air at temperatures ranging from 900°C to 1080°C. BST ceramics with 4ZnO–B2O3 addition can be sintered to a theoretical density higher than 95% at 1050°C. A secondary phase (Ba2ZnTi5O13) is produced in the BST ceramics during 4ZnO–B2O3 addition. Compositional analysis using TEM‐EDX of the BST ceramics with 3 wt% 4ZnO–B2O3 revealed that the Zn ion is generally located at the triple points. This result indicates that BaO, TiO2, and ZnO form a liquid phase that acts as a secondary phase at the lower sintering temperatures. The amount of secondary phase was observed to increase as the amount of 4ZnO–B2O3 additives increased. In addition, the original Ba0.6Sr0.4TiO3 phase was shifted to the Ba0.5Sr0.5TiO3 phase by the addition of 3 wt% 4ZnO–B2O3 at 1050°C. The Ba0.6Sr0.4TiO3 ceramic with 2 wt% 4ZnO–B2O3 sintered at 1050°C in air for 2 h exhibited dielectric properties of ɛr=1883 and dissipation loss=0.36%. Moreover, BST with 1 wt% 4ZnO–B2O3 addition sintered at 1080°C exhibits dielectric properties of ɛr=2330, dissipation loss=0.29%, and bulk density &gt;95% of theoretical density.

Dielectric Properties of Low-Temperature Sintered Ba&lt;sub&gt;0.6&lt;/sub&gt;Sr&lt;sub&gt;0.4&lt;/sub&gt;TiO&lt;sub&gt;3&lt;/sub&gt; Ceramics by Addition of Bi&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-CuO Mixed Oxides

The effect of 9Bi2O3-CuO mixed oxides as sintering agent on sintering behaviors and dielectric properties of Ba0.6Sr0.4TiO3 (BST) ceramics were investigated. It was found that 9Bi2O3-CuO mixed oxides lowered the sintering temperature about 300°C and that highly denser BST ceramic pellets were obtained by sintering at 975oC with addition of 5.0-10.0wt% mixed oxides. For BST ceramics with 5.0wt% CB content sintered at 975°C, had a moderate dielectric constant (ε=1315), low dielectric loss (0.0067) and high tunability (36%) at dc electric field of 20kV/cm and at room temperature and at 10kHz.