Low-firing Li<Subscript>2</Subscript>ZnTi<Subscript>3</Subscript>O<Subscript>8</Subscript> microwave dielectric ceramics with BaCu(B<Subscript>2</Subscript>O<Subscript>5</Subscript>) additive

Phase purity, microstructure, sinterability and microwave dielectric properties of BaCu(B₂O₅)-added Li₂ZnTi₃O₈ ceramics and their cofireability with Ag electrode were investigated. A small amount of BaCu (B₂O₅) can effectively reduce the sintering temperature from 1075°C to 925°C, and it does not induce much degradation of the microwave dielectric properties. Microwave dielectric properties of ε _r = 23·1, Q × f = 22,732 GHz and τ _f = − 17·6 ppm/°C were obtained for Li₂ZnTi₃O₈ ceramic with 1·5 wt% BaCu(B₂O₅) sintered at 925°C for 4 h. The Li₂ZnTi₃O₈ +BCB ceramics can be compatible with Ag electrode, which makes it a promising microwave dielectric material for low-temperature co-fired ceramic technology application.     

Dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> prepared by sol–gel self combustion technique

The preparation of Calcium copper titanate (CCTO) nanopowder was carried out by a sol–gel self combustion method. The X-ray diffraction analysis indicated that the samples calcined at 800 °C were fully crystallized in the CCTO phase. The results of atomic force microscope showed the particles size of CCTO was in the range of 60–80 nm. The absorption bands corresponding to vibrations of Cu–O, Ti–O–Ti and νCa–O were observed at 512, 450 and 562 cm⁻¹ using FTIR. The samples sintered at 950 °C showed the densities as high as 97% of theoretical density. The grain sizes of sintered pellets were determined by HRSEM. The dielectric properties of prepared samples were studied by LCR meter.     

Microwave dielectric properties and its compatibility with silver electrode of LiNb<Subscript>0.6</Subscript>Ti<Subscript>0.5</Subscript>O<Subscript>3</Subscript> with B<Subscript>2</Subscript>O<Subscript>3</Subscript> and CuO additions

The influences of B₂O₃ and CuO (BCu, B₂O₃: CuO = 1:1) additions on the sintering behavior and microwave dielectric properties of LiNb_0.6Ti_0.5O₃ (LNT) ceramics were investigated. LNT ceramics were prepared with conventional solid-state method and sintered at temperatures about 1,100 °C. The sintering temperature of LNT ceramics with BCu addition could be effectively reduced to 900 °C due to the liquid phase effects resulting from the additives. The addition of BCu does not induce much degradation in the microwave dielectric properties. Typically, the excellent microwave dielectric properties of ε_r = 66, Q × f = 6,210 GHz, and τ _f  = 25 ppm/^oC were obtained for the 2 wt% BCu-doped sample sintered at 900 °C. Chemical compatibility of silver electrodes and low-fired samples has also been investigated.     

Low-temperature sintering and microwave dielectric properties of MgTiO<Subscript>3</Subscript> ceramics

The effects of CuO–Bi₂O₃–V₂O₅ additions on the sintering temperature and the microwave dielectric properties of MgTiO₃ ceramics were investigated systematically. The CuO–Bi₂O₃–V₂O₅ (CuBiV) addition significantly lowered the densification temperature of MgTiO₃ ceramics from 1400 °C to about 900 °C, which is due to the formation of the liquid-phase of BiVO₄ and Cu₃(VO₄)₂ during sintering. The saturated dielectric constant (ε_r) increased, the maximum quality factor (Qf) values decreased and the temperature coefficient of resonant frequency (τ_f) shifted to a negative value with the increasing CuBiV content, which is mainly attributed to the increase of the second phase BiVO₄. MgTiO₃ ceramics with 6 wt.% CuBiV addition sintered at 900 °C for 2 h have the excellent microwave dielectric properties: ε _r= 18.1, Qf = 20300 GHz and τ_f = −57 ppm/ °C.     

Effects of LiF addition on the sintering behavior and microwave dielectric properties of Li<Subscript>2</Subscript>Mg<Subscript>3</Subscript>SnO<Subscript>6</Subscript> ceramics

Li₂Mg₃SnO₆ (abbreviation for LMS) ceramics doped with 1–4 wt% lithium fluoride (LiF) were prepared by the conventional solid-state reaction method. The effects of LiF addition on the phase compositions, sintering behaviors and microwave dielectric properties of LMS ceramics were investigated. A small amount of LiF addition could effectively decrease the sintering temperatures due to the liquid phase in the sintering process and induced no apparent degradation of the microwave dielectric properties. The optimized quality factor values for each composition firstly increased and then decreased with the increase of the LiF content. Whereas, the optimized dielectric permittivity increased with increasing of the LiF content. Distinguished microwave dielectric properties with a dielectric constant (ε _r) of 11.13, a quality factor (Q·f) of 104,750 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?10.83 ppm/°C were obtained for LMS ceramics sintered at 950?°C doped with 3 wt% LiF, which showed that the materials were suitable for the low temperature co-fired ceramics applications (LTCC).     

Microwave dielectric properties of Ba<Subscript>5</Subscript>Nb<Subscript>4</Subscript>O<Subscript>15</Subscript> ceramic by molten salt method

Ba₅Nb₄O₁₅ powders were synthesized by molten-salt method in NaCl–KCl flux at a low temperature of 650–900 °C for 2 h, which is lower than that of the conventional solid-state reaction. This simple process involved mixing of the raw materials and salts in a certain proportion. Subsequent calcination of the mixtures led to Ba₅Nb₄O₁₅ powders at 650–900 °C. XRD and SEM techniques were used to characterize the phase and morphology of the fabricated Ba₅Nb₄O₁₅ powders, respectively. After sintering at 1,300 °C for 2 h, the densified Ba₅Nb₄O₁₅ ceramics with good microwave dielectric properties of ε_r = 39.2, Q × f approximated as 27,200 GHz and τ _f  = 72 ppm/°C have been obtained.     

Chemical solution deposition of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin film

CaCu₃Ti₄O₁₂ (CCTO) thin film was successfully deposited on boron doped silica substrate by chemical solution deposition and rapid thermal processing. The phase and microstructure of the deposited films were studied as a function of sintering temperature, employing X-ray diffractometry and scanning electron microscopy. Dielectric properties of the films were measured at room temperature using impedance spectroscopy. Polycrystalline pure phase CCTO thin films with (220) preferential orientation was obtained at a sintering temperature of 750°C. There was a bimodal size distribution of grains. The dielectric constant and loss factor at 1 kHz obtained for a film sintered at 750°C was k ∼ 2000 and tan δ ∼ 0.05.     

Dielectric properties of B<Subscript>2</Subscript>O<Subscript>3</Subscript> doped Sm(Co<Subscript>1/2</Subscript>Ti<Subscript>1/2</Subscript>)O<Subscript>3</Subscript> ceramics at microwave frequency

The microwave dielectric properties and the microstructures of Sm(Co_1/2Ti_1/2)O₃ ceramics with B₂O₃ additions (0.25 and 0.5 wt%) prepared by conventional solid-state route have been investigated. The prepared Sm(Co_1/2Ti_1/2)O₃ exhibited a mixture of Co and Ti showing 1:1 order in the B-site. Doping with B₂O₃ (up to 0.5 wt%) can effectively promote the densification of Sm(Co_1/2Ti_1/2)O₃ ceramics with low sintering temperature. It is found that Sm(Co_1/2Ti_1/2)O₃ ceramics can be sintered at 1,260 °C due to the grain boundary phase effect of B₂O₃ addition. At 1,290 °C, Sm(Co_1/2Ti_1/2)O₃ ceramics with 0.5 wt% B₂O₃ addition possess a dielectric constant (ε _r) of 27.7, a Q × f value of 33,600 (at 9 GHz) and a temperature coefficient of resonant frequency (τ_f) of −11.4 ppm/ °C. The B₂O₃-doped Sm(Co_1/2Ti_1/2)O₃ ceramics can find applications in microwave devices requiring low sintering temperature.     

Influence of CuO and B<Subscript>2</Subscript>O<Subscript>3</Subscript> on sintering and dielectric properties of tungsten bronze type microwave ceramics: a case study in Ba<Subscript>4</Subscript>Nd<Subscript>9.3</Subscript>Ti<Subscript>18</Subscript>O<Subscript>54</Subscript>

The effect of CuO and B₂O₃ co-doping on the sintering behavior, microstructure and microwave dielectric properties of tungsten bronze type Ba₄Nd_9.3Ti₁₈O₅₄ (BNT) ceramics has been investigated by means of a traditional solid-state mixed oxide route. On the one hand, it was indicated that the mixture of CuO and B₂O₃ is an effective sintering aid for BNT matrix compositions owing to the existence of a low-temperature eutectic reaction. On the other hand, it was found that the addition of CuO and B₂O₃ has an obvious effect on microwave dielectric properties of BNT ceramics, depending on the amount of sintering aids, the sample density and microstructure. The liquid phases from sintering aids can promote densification, but simultaneously induce grain growth which tends to decrease the sintering driving force. BNT ceramics doped with 3 wt% CuO–B₂O₃ mixture can be well sintered at 950°C for 4 h and still exhibit relatively good microwave dielectric properties.     

Influence of different dopant sites by lanthanum on the dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

The effects of La³⁺ doped in calcium copper titanate (CCTO) at Ca²⁺ site and Cu²⁺ site were examined. The doped compositions, La_0.1Ca_0.85Cu₃Ti₄O₁₂ (LCCTO) ceramics and CaLa_0.1Cu_2.85Ti₄O₁₂ (CLCTO) ceramics were prepared by the solid-state method. The microstructure, dielectric properties, complex impedance and nonlinear I–V characteristics were studied. And it was found that La³⁺ doped at Ca²⁺ site achieved lower sintering temperatures than that doped at Cu²⁺ site in CCTO ceramics. The dielectric loss (tan δ) of LCCTO ceramics was about 0.05 at 40 kHz when the sample was sintered at 1080 °C. Dielectric constant (ε′) of LCCTO ceramics was about 3.2 × 10⁴ when the sample was sintered at 1100 °C, which was larger than CLCTO ceramics examined under the same process condition with sintering temperatures vary. The impedance analysis revealed that LCCTO ceramics had an influence of resistance of grain boundaries, which was stronger than that of CLCTO ceramics. Meanwhile, both LCCTO ceramics and CLCTO ceramics had a nonlinear-Ohmic property.     

Formation behavior of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> from CaTiO<Subscript>3</Subscript>, CuO and TiO<Subscript>2</Subscript>

The formation behavior of CaCu₃Ti₄O₁₂ (CCTO) had been investigated via solid state reaction from CaTiO₃, CuO and TiO₂ powders. In the temperature range from 750 to 1,200 °C, the reaction sequence was traced by XRD, and the microstructure evolution of calcined powders was also investigated by SEM. CCTO began to form owing to the reaction between CaTiO₃, CuO and TiO₂ at around 850 °C, and became the major phase at 1,000 °C. Finally, the single phase CCTO was obtained at 1,150 °C. However, CCTO was decomposed at CaTiO₃, CuO and TiO₂ when the temperature increased to 1,200 °C. In addition, no other intermediate phases occurred in the synthesized process. The formation behaviors indicated that CaTiO₃ prevented the formation and growth of CCTO.     

Effect of lithium magnesium zinc borosilicate glass addition on densification temperature and dielectric properties of Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript> ceramics

Mg₂SiO₄ (Forsterite) ceramics were synthesized by solid state route. The effect of lithium magnesium zinc borosilicate (LMZBS) glass addition on the densification temperature and microwave dielectric properties of forsterite ceramics was investigated. The crystal structure and microstructure of ceramic–glass composites were studied by X-ray diffraction and scanning electron microscopic techniques. The dielectric properties of the sintered samples were measured in the microwave frequency range by the resonance method. Addition of 0.5 wt% LMZBS glass improved densification with ε _r = 7.3 and Qxf = 121,200 GHz. Addition of 15 wt% LMZBS glass lowered the sintering temperature to about 950 °C with ε _r = 6.75 and Qxf = 30,600 GHz. The reactivity of 15 wt% LMZBS glass added forsterite with silver was also studied. The result shows that forsterite doped with suitable amount of LMZBS glass is a possible material for LTCC and microwave substrate applications.     

Low-temperature synthesis of Sr<Subscript>0.3</Subscript>Ba<Subscript>0.7</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> ultrafine powder and its characteristics

Ultrafine strontium barium niobate (Sr_0.3Ba_0.7Nb₂O₆, SBN30) powders were prepared by urea method starting from a precursor solution constituting of Sr (NO₃)₂, Ba (NO₃)₂, NbF₅, urea and polyvinyl alcohol (PVA) as surfactant. Their structural behavior and morphology were examined by means of X-ray diffractometry (XRD) and Scanning electron microscopy (SEM). The results showed that the SBN30 powders crystallized to a pure tetragonal phase at annealing temperatures as low as 750 °C. The average particle size of SBN powders subjected to 750 °C was of the order of 150–300 nm. With increasing calcination temperature,however, the average particle size of the calcined powders increased. The SBN30 ceramic prepared from urea method can be sintered at temperature as low as 1,225 °C. The transition temperature from the ferroelectric phase to the paraelectric phase and the relative dielectric permittivity of the SBN30 powder were less than the corresponding values of the bulk ceramic. The permittivity and loss tangent (tan δ) at room temperature (1 kHz) was found to be 930 and below 0.025.     

Effects of Gd doping on the sintering and microwave dielectric properties of BiNbO<Subscript>4</Subscript> ceramics

Gd³⁺ was chosen as a substitute for Bi³⁺ in BiNbO₄ ceramics, and the substitution effects on the sintering performance and microwave dielectric properties were studied in this paper. The high temperature triclinic phase was observed only in the Bi_0.98Gd_0.02NbO₄ ceramics when sintered at 920 °C. Both bulk densities and dielectric constant (ε_r) increased with the sintering temperature, while decreased with the Gd content. The quality factor (Q) exhibited a correlation to the Gd content and the microstructures of Bi_1−x Gd _x NbO₄ ceramics. At the sintering temperature of 900 °C, Bi_0.992Gd_0.008NbO₄ ceramics exhibited microwave dielectric properties of ε_r ∼ 43.87, Q × f ∼ 16,852 GHz (at 4.3 GHz), and its temperature coefficient of resonant frequency (τ_f) was found to be near-to-zero.     

Synthesis and microstructure of SrTiO<Subscript>3</Subscript> and BaTiO<Subscript>3</Subscript> ceramics by a reaction-sintering process

Strontium titanate and barium titanate ceramics prepared by a reaction-sintering process were investigated. The mixture of raw materials of stoichiometric SrTiO₃ and BaTiO₃ was pressed and sintered into ceramics without any calcination stage involved. A density 4.99 g/cm³ (97.5% of the theoretic value) was found in SrTiO₃ after 6 h sintering at 1,370 °C. Grains less than 1.5 μm were formed at 1,300–1,330 °C and became 2.2–3.3 μm at 1,350–1,370 °C SrTiO₃. A density 5.89 g/cm³ (97.9% of the theoretic value) was found in BaTiO₃ after 6 h sintering at 1,400 °C. Merged grains were observed in BaTiO₃ and were less than 10 μm after sintered at 1,400 °C.     

Effect of replacement of MgO by CaO on sintering,crystallization and properties of MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system glass-ceramics

The effects of replacement of MgO by CaO on the sintering and crystallization behavior of MgO–Al₂O₃–SiO₂ system glass-ceramics were investigated. The results show that with increasing CaO content, the glass transition temperature firstly increased and then decreased, the melting temperature was lowered and the crystallization temperature of the glass-ceramics shifted clearly towards higher temperatures. With the replacement of MgO by less than 3 wt.% CaO, the predominant crystalline phase in the glass-ceramics fired at 900 °C was found to be α-cordierite and the secondary crystalline phase to be μ-cordierite. When the replacement was increased to 10 wt.%, the predominant crystalline phase was found to be anorthite and the secondary phase to be α-cordierite. Both thermal expansion coefficient (TCE) and dielectric constant of samples increases with the replacement of MgO by CaO. The dielectric loss of sample with 5 wt.% CaO fired at 900 °C has the lowest value of 0.08%. Only the sample containing 5 wt.% and10 wt.% CaO (abbreviated as sample C5 and C10) can be fully sintered before 900 °C. Therefore, a dense and low dielectric loss glass-ceramic with predominant crystal phase of α-cordierite and some amount of anorthite was achieved by using fine glass powders (D₅₀ = 3 μm) fired at 875–900 °C. The as-sintered density approaches 98% theoretical density. The flexural strength of sample C5 firstly increases and then decreases with sintering temperature, which closely corresponds to its relative density. The TCE of sample C5 increases with increasing temperature. The dielectric property of sample C5 sintered at different temperatures depends on not only its relative density but also its crystalline phases. The dense and crystallized glass-ceramic C5 exhibits a low sintering temperature (≤900 °C), a fairly low dielectric constant (5.2–5.3), a low dielectric loss (≤10⁻³) at 1 MHz, a low TCE (4.0–4.25 × 10⁻⁶ K⁻¹), very close to that of Si (∼3.5 × 10⁻⁶ K⁻¹), and a higher flexural strength (≥134 MPa), suggesting that it would be a promising material in the electronic packaging field.     

Microwave dielectric properties of Bi(Sc<Subscript>1/3</Subscript>Mo<Subscript>2/3</Subscript>)O<Subscript>4</Subscript> ceramics for LTCC applications

A novel microwave dielectric ceramics Bi(Sc_1/3Mo_2/3)O₄ with low firing temperature were prepared via the solid reaction method. The specimens have been characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and DC conductivity. The Bi(Sc_1/3Mo_2/3)O₄ ceramics showed B-site ordered Scheelite-type structure with space group C2/c. Raman analysis indicated that prominent bands were attributed to the normal modes of vibration of MoO₄ ^2? tetrahedra. The dielectric loss of Bi(Sc_1/3Mo_2/3)O₄ ceramics can be depended strongly the bulk conductivity by DC measurement. The superior microwave dielectric properties are achieved in the Bi(Sc_1/3Mo_2/3)O₄ ceramic sintered at 875 °C/4 h, with dielectric constant?~?25, Q?×?f ~?51,716 GHz at 6.4522 GHz and temperature coefficient of resonance frequency ~???70.4 ppm/°C. It is a promising microwave dielectric material for low-temperature co-fired ceramics technology.     

Synthesis of Ba<Subscript>3</Subscript>ZnNb<Subscript>2</Subscript>O<Subscript>9</Subscript>−Sr<Subscript>3</Subscript>ZnNb<Subscript>2</Subscript>O<Subscript>9</Subscript> solid solution and their dielectric properties

Oxides of the type, Ba_3-xSr_xZnNb₂O₉ (0 ≤x ≤3), were synthesized by the solid state route. Oxides calcined at 1000°C show single cubic phase for all the compositions. The cubic lattice parameter (a) decreases with increase in Sr concentration from 4.0938(2) forx = 0 to 4.0067(2) forx = 3. Scanning electron micrographs show maximum grain size for thex = 1 composition (∼ 2 μm) at 1200°C. Disks sintered at 1200°C show dielectric constant variation between 28 and 40 (at 500 kHz) for different values of x with the maximum dielectric constant atx = 1.     

The influence of the segregation of Cu-rich phase on the microstructural and impedance characteristics of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

The influence of sintering conditions on the microstructural features and impedance characteristics of the giant dielectric constant material CaCu₃Ti₄O₁₂ (CCTO) was investigated. The microstructure and impedance characteristics were found to be strongly dependent on the sintering conditions. Sintering of the CCTO ceramics at elevated temperatures (>1100 °C) for prolonged durations resulted in the segregation of Cu-rich phase, mostly confined to the surface, which was in concomitance with the appearance of the additional semicircle at the low frequency end in Impedance (Z*) plots. The absence of this additional semicircle in the Cu-deficient CCTO ceramics and the appearance of the same in Cu-rich CCTO ceramics that were deliberately fabricated corroborated the above observations. Also, La_2/3Cu₃Ti₄O₁₂ (LCTO), a low dielectric constant member of CCTO family, which consisted of small grains without the segregation of Cu-rich phase at the grain boundary, did not reveal the presence of additional semicircle in the Z*plots.     

Low temperature sintering and microwave dielectric properties of Li<Subscript>6</Subscript>Mg<Subscript>7</Subscript>Ti<Subscript>3</Subscript>O<Subscript>16</Subscript> ceramics with LiF additive for LTCC applications

Li₆Mg₇Ti₃O₁₆ ceramics were prepared by the conventional solid-state method with 1–5 wt% LiF as the sintering aid. Effects of LiF additions on the phase compositions, sintering characteristics, micro-structures and microwave dielectric properties of Li₆Mg₇Ti₃O₁₆ ceramics were investigated. The LiF addition could effectively lower the sintering temperature of Li₆Mg₇Ti₃O₁₆ ceramics from 1550 to 900 °C. For different LiF-doped compositions, the optimum dielectric permittivity (ε _r ) and quality factor (Q·f) values first increased and then decreased with the increase of LiF contents, whereas the temperature coefficient of resonant frequency (τ _f ) fluctuated between ??14.39 and ??8.21 ppm/°C. Typically, Li₆Mg₇Ti₃O₁₆ ceramics with 4 wt% LiF sintered at 900 °C exhibited excellent microwave dielectric properties of ε _r ?=?16.17, Q·f?=?80,921 GHz and τ _f ?=???8.21 ppm/°C, which are promising materials for the low temperature co-fired ceramics applications.