BaTi4O9 Ceramics Research Articles

Sintering Characteristics and Microwave Dielectric Properties of BaTi4O9 Ceramics with CuO–TiO2 Addition

Sintering characteristics, phase evolutions, microstructures, and microwave dielectric properties have been investigated for BaTi4O9 ceramics prepared by traditional low temperature sintering using CuO–TiO2 (CT) additions as aids. The sintering temperature of BaTi4O9 ceramics was found to evidently reduce from 1350 °C to about 1100 °C with a very small amount of 0.5 wt% CT addition. When the CT addition increased to beyond 0.5 wt%, however, it was not expected to further lower the sintering temperature. Meantime, the secondary phases of Ba4Ti13O30, BaTiO3, and TiO2 were observed in these BaTi4O9-based ceramics when the CT content was beyond 2 wt%. With the introduction of the CT addition, the permittivity (ε) had little enhancement, and the temperature coefficient of the resonant frequency (τf) was improved to near zero. The BaTi4O9 ceramics with 0.5 wt% CT additions, sintered at 1100 °C, exhibited excellent microwave dielectric properties, such as ε = 36.9, Q × f = 23100 GHz, and τf = 2.5 ppm/°C. In addition, the densification mechanism and variations of the microwave dielectric properties have also been discussed with the crystal phase and microstructure’s evolution.

BaTi4O9 mesocrystal: Topochemical synthesis, fabrication of ceramics, and relaxor ferroelectric behavior

A two-step topochemical process was developed for the BaTi4O9 platelike mesocrystal synthesis from a layered titanate H1.07Ti1.73O4x.H2O (HTO) single crystal by combining hydrothermal and solid-state reactions for the first time. The formation mechanism and nanostructure of the BaTi4O9 mesocrystal are investigated by XRD, TEM, SAED, and FE-SEM. The formation reactions from the HTO to the BaTiO3/HTO nanocomposite and the BaTiO3/HTO nanocomposite to the BaTi4O9 mesocrystal are topotactic structural transformation reactions. The BaTi4O9 phase with high purity and crystallinity can be obtained by using this two-step topochemical process. Furthermore, the obtained BaTi4O9 platelike mesocrystal is successfully applied to the fabrication of BaTi4O9 ceramics. A dielectric study is carried out and the results reveal that the generated BaTi4O9 ceramics exhibit a relaxor ferroelectric behavior with a curie zone around 700 °C, and larger dielectric constant and higher temperature stability of the dielectric constant than those fabricated by conventional solid-state reaction method.

The influence of BBZ glass on phase evolution, sintering behavior and dielectric properties of BaTi4O9 ceramics

A low temperature co-fired ceramic (LTCC) material has been fabricated by mixing BaTi4O9 ceramic powder with a BaO–B2O3–ZnO (BBZ) glass and sintering the mixture at 925 °C/2 h. The influence of the BBZ glass on sintering behavior, phase evolution, microstructure and microwave dielectric properties of the BaTi4O9-based LTCC material has been investigated. The results show that the BBZ glass can significantly lower the sintering temperature of the BaTi4O9 ceramics from 1350 °C to below 950 °C. The XRD patterns exhibit that remarkable chemical reactions happen between BaTi4O9 and the BBZ glass during sintering, forming two new phases BaTi(BO3)2 and Ba4Ti13O30 in the material. As BBZ glass is increased from 5 to 30 wt%, BaTi(BO3)2 phase gradually dominates the material and BaTi4O9 decreases and almost disappears at the end. At the same time, the dielectric constant decreases from 33 to 25, the temperature coefficient of resonant frequency decreases from +25.44 to −3.19 ppm/°C, and the quality factor firstly increases and then decreases with the peak value of 29500 GHz. The changes of the dielectric properties with the BBZ glass content are correlated with the phase evolution of the material during sintering. Typically, the BaTi4O9-based ceramics with 25 wt% BBZ glass sintered at 925 °C for 2 h displays excellent comprehensive properties with a maximum density of 4.33 g/cm3, the dielectric constant of 27.08, quality factor of 29,500 GHz and temperature coefficient of resonant frequency of +3.5 ppm/°C. In addition, the good chemical compatibility of this material with Ag electrode makes it a potential candidate for LTCC technology.

Control of coring effect in BaTi4O9 microwave dielectric ceramics by doping with Mn4+

In the present work, we have attempted to reduce the effect of coring effect in the titanate ceramic system BaTi4O9 (BT4) by doping it with Mn4+. The microwave dielectric BaTi4O9 ceramics doped with 0, 0.5 and 1.0mol% Mn4+ were synthesized by conventional ceramic processing route. The XRD studies confirmed a single phase crystalline structure for all the ceramic samples studied. The SEM micrographs of the ceramics reveal a microstructural change leading towards a more uniform grain size distribution as the Mn4+ content increases to 1.0mol%. In the low frequency region (100Hz to 1MHz), the temperature stability of dielectric properties exhibits a marked improvement with the increasing amount of Mn4+ in the ceramic system. In the microwave frequency region (9.3GHz), Q-factor increases from 11,625GHz to 46,500GHz for BaTi4O9 ceramic doped with 1.0mol% Mn4+. The present paper reveals that the commonly observed degradation of dielectric properties due to coring effect in the BaTi4O9 ceramic system can be controlled by doping it with an appropriate quantity of Mn4+.

Phase evolution and electrical properties of copper-electroded BaTi4O9 materials with BaO–ZnO–B2O3–SiO2 glass system in reducing atmosphere

BaTi4O9 (BT4) microwave dielectric ceramics using a copper electrode and containing 10wt% BaO–ZnO–B2O3–SiO2 (BZBS) glass frit were sintered under reducing atmosphere at 950°C and were investigated on the phase evolutions, microstructures and dielectric properties of BT4 with various BaO/SiO2 and ZnO/SiO2 ratios of BZBS glasses. Experimental results show that the BaO/SiO2 ratio contributes to wettability of glass with BaTi4O9 ceramics, and ZnO/SiO2 ratio determines the densification of BaTi4O9 ceramics. The different Ba–Ti–O and Ba–Cu–O phases with various Ba/Ti and Ba/Cu ratios can be attributed to the contents of BaO in glass. Ba4Ti13O30 and Ba2Cu3O5+X may form when BaO contents are too high, and inducing copper diffusion due to the reactions of BaO and Cu, accompanying with degrading of the dielectric characteristics. If the ZnO contents of BZBS glasses were raised, a little bit of ZnSiO3 and Ba2Cu3O5+X phases appear without Cu diffusion due to non-reaction of ZnO and CuO. The high ZnO/SiO2 ratio of glass reveals the lower softening point, indicating that the high ZnO glass could enhance the density and therefore increase the dielectric constant and quality factor.

Sintering Behavior and Microwave Dielectric Properties of BaTi<sub>4</sub>O<sub>9</sub> Ceramics Prepared from Different Size Powders by Sol-Gel Method

The BaTi4O9 submicron powders were synthesized by a sol-gel method, and the sintering behavior and microwave dielectric properties of BaTi4O9 ceramics prepared from powders with different particle sizes were also investigated. The particle size of powders calcined at 700 °C, 800 °C, 900 °C and 1000 °C were 8-10 nm, 70-90 nm, 100-120 nm and 140-170 nm, respectively. The 70-170 nm powders benefited the sintering process and microwave dielectric properties, whereas nanoparticles with the size of 8-10 nm damaged the sintering behavior due to the more amorphous phases and lower green density introduced by the large surface area. Sintered at 1175 °C, the BaTi4O9 ceramic prepared from 100-120 nm size nanoparticles had compact structure and exhibited good microwave dielectric properties of εr = 36.91 and Q×f = 29,833 GHz.

Microstructure and Microwave Dielectric Properties of BaTi<sub>4</sub>O<sub>9</sub> Ceramics Derived from a Sol-Gel Precursor

In the present work, the microstructure and microwave dielectric properties of BaTi4O9 ceramics derived from a sol-gel precursor were presented. Density measuring results demonstrated that the largest densities of ceramic sample about 96.7% could be reached by virtue of a cool iso-static press and a sintering process at at 1300 °C for 6 hours. The dielectric constant (εr), quality factor (Q×f) and the temperature coefficients (τf) of the BaTi4O9 ceramic samples were 36.65, 28000 GHz, +20.2 ppm/°C, respectively. XRD, SEM and XPS were used to characterize the microstructure of the ceramics samples. Substantial Ti3+ was proposed to be the cause of dielectric loss.

Tailoring microwave dielectric properties of BaTi<sub>4</sub>O<sub>9</sub> ceramics by addition of Sm<sub>2</sub>O<sub>3</sub>

BaTi4O9 ceramics with Sm2O3 addition were prepared in a form of xSm2O3+BaTi4O9 (x = 1, 3, 5, 7 mol %) and the microstructures and microwave dielectric properties of the ceramic samples were characterized. SEM shows when x greater than 3 mol %, BaSm2Ti4O12 crystallized in a fiber shape along the crystalline boundary. With the increase of Sm2O3 addition, the dielectric constant increases from 36.65 to 39.8, while the quality factor decreases from 28000 to 19000, τf from +20.2 to +10.1 ppm/°C. Results of curve fitting of FIRS show extrinsic dielectric loss could account for the increase of dielectric loss, which should be attributed to the substantial increase of Ti3+ and Ti2+.

Low-fire Processing of Microwave BaTi4O9 Dielectric with BaO–Li2O–B2O3–SiO2–ZnO Glass

The effects of BaO–Li2O–B2O3–SiO2–ZnO (BLBSZ) glass addition on the densification and dielectric properties of BaTi4O9 (BT4) have been investigated. The microwave BT4 ceramics with 5–10 vol % BLBSZ glass can be densified at 900–925 °C, which is 400 °C lower than that required for pure BT4. The resulting microwave BT4+BLBSZ ceramics have a dielectric constant of 33–34, and the product (Q·fr) of the quality factor (Q) and resonant frequency ( fr) of 14,000–20,000 GHz at 6.6 GHz.

Preparation and Structure of Ba<sub>2</sub>Ti<sub>9</sub>O<sub>20</sub> and BaTi<sub>4</sub>O<sub>9</sub> Ceramics Derived from Sol-Gel Powders

Ba2Ti9O20 (B2T9) and BaTi4O9 (BT4) ceramics have been fabricated using sol-gel technique. The sol-gel derived powder was produced from barium acetate and butyl titanate using acetic acid as solvent. The as-prepared powders were then calcined at different temperatures ranging from 600° to 1200°C. After that, the powder was pressed into pellets and further sintered at different temperatures ranging from 1250°C to 1380°C. XRD characterization and Raman spectroscopy showed that after calcining the sol-gel powder at 900°C for 2 h and sintering the pressed pellets at 1330°C for 4 h, triclinic B2T9 and orthorhombic BT4 ceramics could be obtained. The dielectric constant and Q-value are 35 and 1910 at 6.1 GHz.

Effect of B2O3 and CuO on the sintering temperature and microwave dielectric properties of the BaTi4O9 ceramics

The effect of B2O3 and CuO on the sintering temperature and microwave dielectric properties of BaTi4O9 ceramics was investigated. The BaTi4O9 ceramics were able to be sintered at 975∘C when B2O3 was added. This decrease in the sintering temperature of the BaTi4O9 ceramics upon the addition of B2O3 is attributed to the formation of BaB2O4 second phase whose melting temperature is around 900∘C. The B2O3 added BaTi4O9 ceramics alone were not sintered below 975∘C, but were sintered at 875∘C when CuO was added. The formation of BaCu(B2O5) second phase could be responsible for the decrease in the sintering temperature of the CuO and B2O3 added BaTi4O9 ceramics. The BaTi4O9 ceramics containing 2.0 mol% B2O3 and 5.0 mol% CuO sintered at 900∘C for 2 h have good microwave dielectric properties of er = 36.3, Q× f = 30,500 GHz and τf = 28.1 ppm/∘C

Far-Infrared Study of BaTi4O9 Microwave Dielectric Ceramics

In this work, lattice vibrations in BaTi4O9 ceramic were investigated using far-infrared spectra (FIRS), which were transformed by Kramers–Kronig relations into the real and imaginary parts of permittivity spectra. Curve fitting of reflectance spectra shows that 32 vibration modes were observed, among which transverse vibrations at lower frequencies (stretching and bending vibration modes involving A-site cations and TiO6 octahedra) account for most dielectric loss. An evaluation of dielectric constants and quality factors using an extrapolation method was accomplished. The calculated dielectric constants agree well with the measured ones, while the calculated dielectric losses are about half the measured ones, indicating that noneigen elements such as defects and pores exist and play an important role in BaTi4O9 ceramics. A multimode behavior of vibration modes involving Ba-sites was proposed as the origin of dielectric loss.

Ba $\mathsf{_{0.1}}$Sr $\mathsf{_{0.9}}$TiO$\mathsf{_{3}}$-BaTi$\mathsf{_{4}}$O$\mathsf{_{9}}$ composite thin films with improved microwave dielectric properties

Ba0.1Sr0.9TiO3-BaTi4O9 composite thin films with different BaTi4O9 concentrations were deposited on (100) LaAlO3 (LAO) single crystal substrates via a pulsed laser deposition (PLD) using a combined target configuration of Ba0.1Sr0.9TiO3 and BaTi4O9 ceramics. The Ba0.1Sr0.9TiO3-BaTi4O9 thin films showed good crystal growth with c-orientation on (100) LAO substrates, which were characterized by X-ray diffraction (XRD). From scanning electron microscopy (SEM) measurements, we could see that the crystal grains of the Ba0.1Sr0.9TiO3-BaTi4O9 thin films changed from small ordered clusters to big triangle clusters with the increase of BaTi4O9 concentration. The microwave dielectric properties of the Ba0.1Sr0.9TiO3-BaTi4O9 thin films under low temperature range from 65 to 120 K were measured at 7.7 Ghz and the results showed that all the thin films were in the paraelectric state. The dielectric constant and loss tangent of the Ba0.1Sr0.9TiO3-BaTi4O9 thin films were modified by the addition of BaTi4O9. Specifically, the loss tangent of the composite thin films was greatly decreased from 0.025 for pure Ba0.1Sr0.9TiO3 to 0.020 for the 4.7% BaTi4O9 doped Ba0.1Sr0.9TiO3, and finally to 0.010 for the 15.9% BaTi4O9 doped Ba0.1Sr0.9TiO3 sample.

Lowering of sintering temperature and microwave dielectric properties of BaTi4O9 ceramics prepared by the polymeric precursor method

Abstract Low temperature sintering and microwave dielectric properties of barium polytitanate (BaO–4TiO 2 ) ceramics prepared by means of polymeric precursor route based on the Pechini process were investigated. Pure and fine BaTi 4 O 9 powders with particle sizes of 100–200 nm were derived by thermal decomposition of amorphous gel precursor (above 750 °C). They formed single orthorhombic BaTi 4 O 9 phase and showed fine and well-dispersed by XRD and SEM observation. The high sintering ability of the prepared powders enabled the fabrication of dielectric ceramics at low sintering temperatures (1200–1300 °C). The well-sintered BaTi 4 O 9 ceramics with high relative densities (95%) were found to show excellent microwave dielectric properties compared to those prepared by conventional method at the same sintering temperature.

The Microwave Characteristics of Glass-BaTi4O9 Ceramics

Microwave characteristics of BaTi4O9 ceramics combined with different amounts of MgO–CaO–SiO2–Al2O3 (MCAS) glass and sintered at different temperatures were examined. The temperature needed to densify the BaTi4O9 dielectric is lowered with an increase of the content of MCAS glass. The densities and the dielectric constants of densified MCAS-BaTi4O9 ceramics decrease with the an increasing amount of MCAS glass. The results of X-ray diffraction (XRD) patterns indicate that BaTi4O9 and MCAS glass (cordierite phase) exist as two different phases. For BaTi4O9 with 3 wt% addition of MCAS, the sintering temperature is lowered to 1200°C, and the ceramics have the optimum dielectric properties: Q=5720 (Q×f=42050), εr values=34.6, and τf=14.2.