Synthesis and characterization of borosilicate glass/β-spodumene/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites with low CTE value for LTCC applications

Glass?+?ceramic composites based on low-softening-point borosilicate (BS) glass, β-spodumene and Al₂O₃ were produced in this work. The influence of ceramic filler composition on the microstructure, sintering quality, mechanical properties, thermal properties and dielectric properties of composites were studied. XRD and DSC indicated that both kinds of ceramic filler as well as the BS glass maintained their characteristics after sintering. The addition of β-spodumene would decrease the coefficient of thermal expansion (CTE) value of composites to match with silicon well. The better wetting behavior between β-spodumene and BS glass would lead to better sintering quality, microstructure and dielectric properties for composites containing more β-spodumene. With appropriate Al₂O₃ content, the flexural strength of composites could be enhanced. Composite with 45 wt% BS glass, 30 wt% β-spodumene and 25 wt% Al₂O₃ sintered at 875 °C showed good properties which meet the requirements of low temperature co-fired ceramic applications: dense microstructure with high relative density of 96.27%, proper CTE value of 3.57 ppm/°C, high flexural strength of 156 MPa, low dielectric constant of 6.20 and low dielectric loss of 1.9?×?10^?3.     

Estimation of apparent fracture toughness of ceramic laminates

The paper presented deals with the fracture behaviour of ceramic laminates. The residual stresses in individual layers of Al₂O₃/5vol.%t-ZrO₂ (ATZ) and Al₂O₃/30vol.%m-ZrO₂ (AMZ) are determined. Assumptions concerning linear elastic fracture mechanics and small scale yielding are considered. In this frame the procedure based on a generalization of Sih’s strain energy density factor to the case of a crack touching the interfaces between two dissimilar materials is used for determination of effective values of the stress intensity factor on material interfaces. An important increase of fracture toughness at the AMZ/ATZ interface was predicted in comparison to the fracture toughness of individual material components. Predicted values were compared with data available in the literature and mutual good agreement was found. The procedure suggested can be used for estimation of resistance to crack propagation through multilayered structures and its design. The procedure can contribute to enhancing the reliability and safety of structural ceramics or, more generally, of layered composites with strong interfaces.     

Effects of Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> addition on the microstructure,electrical, and mechanical properties of PZT/ZnO nanowhisker piezoelectric composites

Nb₂O₅-modified PZT/ZnO nanowhisker (denoted as PZT/ZnO_w–Nb₂O₅) piezoelectric composites were prepared by a solid state sintering technique. Effects of Nb₂O₅ addition on the microstructure, electrical, and mechanical properties of the PZT/ZnO_w composites were investigated. With increasing Nb₂O₅ content, the grain size of the composites was reduced and the fracture mode changed from intergranular to intragranular gradually. Compared with the PZT/ZnO_w composites, the dielectric, piezoelectric, and ferroelectric properties of the PZT/ZnO_w–Nb₂O₅ composites were improved significantly, while mechanical properties were enhanced slightly. The optimum electrical and mechanical properties were achieved for the PZT/ZnO_w composites modified with 0.75 wt% Nb₂O₅ sintered at 1150 °C, with dielectric permittivity ε_r, piezoelectric coefficient d ₃₃, planar electromechanical coupling k _p, remnant polarization P _r, fracture toughness K _IC, and flexural strength σ_f being on the order of 4930, 600 pC/N, 0.63, 29.2 μC/cm², 1.56 MPa m^1/2 and 130 MPa, respectively. The Nb₂O₅-modified PZT/ZnO_w piezoelectric composites, with comparable electrical properties and improved mechanical properties than those of commercial PZT-5H ceramics, are promising candidates for further applications.     

Control of properties of PZT ceramics during liquid-phase sintering

A PZT ceramic modified by 0.4Pb-(1–x)(B₂O₃)–x(GeO₂) glass, and glass-ceramics modified by V₂O₅, have been obtained. The influence of the chemical composition of the glasses on the mechanical strength and dielectric parameters of these ceramics is investigated. The mechanical and electrical parameters of PZT ceramics are considerably improved by small additions of glass ( 1 mass %) of suitable composition. During heat treatment, the mobility of the domain walls may be changed as a result of the interaction of smelt glass with the surface layer of the crystallites (resulting from a change of V _Pb ^t" vacancy concentration in grains and decreased mechanical tension on the grain boundaries). By introducing the glass, we can decrease the porosity of the ceramics and thus decrease the attenuation of surface acoustic waves in piezoelectric filters. The origin of the liquid phase during sintering of the PZT glass-ceramics prevents PbO evaporation. This determines the preservation of the solution's stoichiometry. The glass addition leads to a decrease in the sintering temperature of PZT, which simplifies the technological process. The glass ceramics are obtained by common ceramic technology which is used for commercial piezoceramic production. The main technological problem is choosing the chemical composition and concentration of the glass and thermal process parameters.     

Binder derived semi-conductive graphite/alumina composites via novel one-step pulsed electric current sintering

Semi-conductive graphite/Al₂O₃ ceramic composites were successfully fabricated via a novel and facile approach by pulsed electric current sintering of binder embedded Al₂O₃ powders, which were prepared by a simple ball-milling assisted mixing of Al₂O₃ powder with polyvinyl alcohol solution. By altering the sintering conditions with respects to temperature and pressure controlling and concentration of binder, relative density, and microstructure of fabricated graphite/Al₂O₃ ceramic composites, and the electrical properties were schematically investigated in this study. The fabricated graphite/Al₂O₃ ceramic composites exhibit superior semi-conductive properties. Moreover, the carrier type in fabricated semi-conductive graphite/Al₂O₃ composites was successfully modified by adding polycarboxylic acid as a dispersant in binder embedded Al₂O₃ powders. The contents in this work present a new strategy for the design and development of functional ceramic composites.     

High-strength zirconium diboride-based ceramic composites consolidated by low-temperature hot pressing

Abstract

Two compositions of ZrB₂-based ceramic composites containing Si₃N₄, Al₂O₃ and Y₂O₃ have been hot-pressed at different temperatures between 1673 and 1773 K for 60 min in vacuum. The densification behavior of the composites was examined during the sintering process. The microstructures of the composites were characterized by scanning electron microscopy, and the crystalline phases were identified by x-ray diffraction. The effects of Al₂O₃ and Y₂O₃ additives on the densification behavior and flexural strength were assessed. A relative density of ～95% was obtained after sintering at 1723 K or higher temperatures. The microstructures of the composites consisted of (Zr,Y)B₂, α-Si₃N₄ and Y₃(Al,Si)₅O₁₂ phases. The room-temperature flexural strength increased with the amount of additives and approached 1 GPa.     

Influence of Al2O3/SiO2 ratio on the microstructure and properties of low temperature co-fired CaO–Al2O3–SiO2 based ceramics

In this work, in order to obtain the materials for low temperature co-fired ceramics applications, CaO–Al₂O₃–SiO₂ (CAS) based ceramics were synthesized at a low sintering temperature of 900 °C. The influences of Al₂O₃/SiO₂ ratio on the microstructure, mechanical, electrical and thermal properties were studied. According to the X-ray diffractomer and scanning electron microscopy results, the addition of the Al₂O₃ is advantageous for the formation of the desired materials. Anorthite(CaAl₂Si₂O₈) is the major crystal phase of the ceramics, and the SiO₂ phase is identified as the secondary crystal phase. No new crystal phase appears in the ceramics with the increasing Al₂O₃ content. More or less Al₂O₃ addition would all worsen the sintering, mechanical and dielectric properties of CAS based ceramics. The ceramic specimen (Al₂O₃/SiO₂ = 20/18.5) sintered at 900 °C shows good properties: high bending strength = 145 MPa, low dielectric constant = 5.8, low dielectric loss = 1.3 × 10^?3 and low coefficient of thermal expansion value = 5.3 × 10^?6 K^?1. The results indicate that the prepared CAS based ceramic is one of the candidates for low temperature co-fired ceramic applications.     

Sintering, densification and crystallization of Ca–Al–B–Si–O glass/Al2O3 composites for LTCC application

Ca–Al–B–Si–O glass/Al₂O₃ composites were prepared based on the borosilicate glass powders (D₅₀ = 2.84) and Al₂O₃ ceramic powders (D₅₀ = 3.26), and the sintering, densification, crystallization of samples were investigated. The shrinkage of sample starts to have a sharp increase at 600 °C. The shrinkage of sample starts to have a further rapid increase after the glass softening temperature of about 713 °C. Glass/Al₂O₃ composites can be sintered at 875 °C/15 min and exhibit better properties of a relative density of 98.4 %, a λ value of 2.89 W/mK, a ε _r value of 7.82 and a tan δ value of 5.3 × 10^?4. The interface between glass and Al₂O₃ grains and the interface between anorthite and glass phase depicts a good compatibility according to transmission electron microcopy test. It is the low sintering temperature, high density and good compatibility with Ag electrodes that, guarantee borosilicate glass/Al₂O₃ composites suitable for low temperature co-fired ceramic materials.     

Enhanced piezoelectric and mechanical properties of ZnO whiskers and Sb2O3 co-modified lead zirconate titanate composites

ZnO whiskers and Sb₂O₃ co-modified lead zirconate titanate (denoted as PZT/ZnO_w/Sb₂O₃) piezoelectric composites were fabricated using a solid state sintering technique. The characteristic diffraction peaks of the PZT perovskite and ZnO phases were identified from all the composites, suggesting the retention of these individual phases. The grain size of PZT was found to be reduced with Sb₂O₃ addition. A high relative density of 96.5%-99.1% was achieved in PZT co-doped with ZnO_w and Sb₂O₃. Both the piezoelectric and mechanical properties of the PZT/ZnO_w/Sb₂O₃ composites showed significant improvement over the monolithic PZT. The intrinsic effects of ZnO_w and Sb₂O₃ on the electrical and mechanical properties of the PZT/ZnO_w/Sb₂O₃ composites were discussed.     

Effect of sintering parameters on the microstructure and properties of strontium modified PZT ceramics prepared using spray-dried powders

PZT powders of the composition Pb_0.94Sr_0.06 (Zr_0.53Ti_0.47)O₃, prepared by spray drying and calcining techniques, were processed to sintered ceramics by conventional cold pressing and sintering at various temperatures and periods between 1000 to 1250°C for 0.5 to 12h. Sintered ceramics were evaluated for their microstructure and electromechanical properties. Highly dense ceramics having bulk density of the order of 97% of the theoretical value could be obtained after sintering at a considerably lower temperature of 1000°C in comparison to the 1300°C generally required for powders prepared by conventional ceramic processing. However, the increase in sintering temperature of reactive spray-dried powders causes the entrapment of closed pores as a result of exaggerated grain growth and subsequent pore coarsening thereby leading to a decrease in the bulk density of the ceramics. It has been observed that minor variations in the sintering parameters influence the porosity, grain size and electromechanical properties. Values of the dielectric constant, piezoelectric strain coefficient and electromechanic coupling factor increase with the increase in grain size and decrease with the increase in porosity of the sintered ceramic whereas the dielectric dissipation factor decreases with the increase in sintering temperature.     

New lithium bismuth phosphate ceramic: crystal structure,microstructure, microwave dielectric properties and co-firing compatibility with aluminum electrode

A new type of lithium bismuth phosphate 3Li₂O–Bi₂O₃–6P₂O₅ (3L1B6P) microwave dielectric ceramics were prepared via a conventional solid-state route. Crystal structure, microstructure, microwave dielectric properties and aluminum electrode co-firing compatibility of the 3L1B6P ceramics were investigated. The 3L1B6P ceramics mainly consists of a new phase similar to the NdLiP₄O₁₂ with monoclinic structure [C2/C(15)]. The 3L1B6P ceramics are composed of BiLiP₄O₁₂ grains of?~?10 μm in length and?~?2 μm in width and BiPO₄ grains of?~?1 μm in size. The 3L1B6P ceramic sintered at 625 °C shrinkage and the corresponding microwave dielectric properties are dielectric constant ε_r?=?6.8, Q?×?f?=?16,900 GHz and negative temperature coefficient of resonant frequency TCF?=???71 ppm/°C. More importantly, the 3L1B6P ceramic with ultra-low sintering temperature (625 °C) can be co-fired with aluminum electrode, which illustrates it can be applied for the ultra-low temperature co-fired ceramic (ULTCC) application.

     

High-strength zirconium diboride-based ceramic composites consolidated by low-temperature hot pressing

Two compositions of ZrB₂-based ceramic composites containing Si₃N₄, Al₂O₃ and Y₂O₃ have been hot-pressed at different temperatures between 1673 and 1773 K for 60 min in vacuum. The densification behavior of the composites was examined during the sintering process. The microstructures of the composites were characterized by scanning electron microscopy, and the crystalline phases were identified by x-ray diffraction. The effects of Al₂O₃ and Y₂O₃ additives on the densification behavior and flexural strength were assessed. A relative density of ∼95% was obtained after sintering at 1723 K or higher temperatures. The microstructures of the composites consisted of (Zr,Y)B₂, α-Si₃N₄ and Y₃(Al,Si)₅O₁₂ phases. The room-temperature flexural strength increased with the amount of additives and approached 1 GPa.     

Effect of nano-sized TiO<Subscript>2</Subscript> powder addition on characteristics of silver–palladium electrodes

This study presents the sintering behavior of silver/palladium electrode powders to which have been added TiO₂ nanoparticles, and the effect this additive has on the ability of the electrode to match the characteristics of piezoelectric ceramics, Pb(Zr, Ti)O₃. The densification (shrinkage) of the electrodes was investigated as a function of sintering temperature, and the reaction between the ceramic matrix and the electrodes was studied. The densification of the TiO₂-enhanced electrode paste during the sintering process was explained with reference to a solid-state diffusion mechanism which integrated the TiO₂ into the ceramic. Reactions occurred between the ceramic and electrode layers, resulting in reduced internal stress and enhanced mechanical adhesion. Based on these results, it is clear that high adhesive strength and good electrical conductivity of more than 10⁴/Ω cm can be obtained in multilayer ferroelectric devices composed of stacks of ceramic and electrode layers provided the contain these nanoparticles. In the sintering process, interfacial diffusion of TiO₂ occurred and, as a consequence, coarse grains of PZT were formed at the interface.     

Fabrication of carbon nanofiber(CNF)-dispersed Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites by pulsed electric-current pressure sintering and their mechanical and electrical properties

Dense Al₂O₃-based composites (≥99.0% of theoretical) dispersed with carbon nanofibers (CNFs) were fabricated using the pulsed electric-current pressure sintering (PECPS) for 5 min at 1300°C and 30 MPa in a vacuum. The dispersion of CNFs into the matrix depended much on the particle size of the starting Al₂O₃ powders. Mechanical properties of the composites were evaluated in relation with their microstructures; high values of three-point bending strength σ_b (∼800 MPa) and fracture toughness K _IC (∼5 MPa·m^1/2) were attained at the composition of CNF/Al₂O₃ = 5:95 vol%, which σ_b and K _IC values were ∼25% and ∼5%, respectively, higher than those of monolithic Al₂O₃. This might be due to the small Al₂O₃ grains (1.6 μm) of dense sintered compacts compared with that (4.4 μm) for the pure Al₂O₃ ceramics, resulting from the suppression of grain growth during sintering induced by uniformly dispersed CNFs in the matrix. Electrical resistivity of CNF/Al₂O₃ composites decreased rapidly from >10¹⁵ to ∼2.1 × 10⁻² Ωm (5vol%CNF addition), suggesting the machinability of Al₂O₃-based composites by electrical discharge machining.

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Enhanced magnetoelectric coupling in Pb(Zr0.52Ti0.48)O3 film-on-CoFe2O4 bulk ceramic composite with LaNiO3 bottom electrode

By chemically depositing a conductive LaNiO₃ (LNO) electrode layer onto dense CoFe₂O₄ (CFO) ceramics, the magnetoelectric (ME) response in Pb(Zr_0.52Ti_0.48)O₃ (PZT)/CFO film-on-substrate system was significantly enhanced. Structural, morphological, ferroelectric, and piezoelectric analysis was performed for the present PZT/LNO/CFO film-electrode-substrate composites, whereby improved electric-related output was demonstrated. It was further shown that the maximum ME coefficient α _E31 could reach up to 155 mV/cm Oe, which was about 2.6 times higher than that in PZT film-on-CFO ceramics without bottom electrode layer. Further enhancement of ME response could be expected by preparing high-quality electrode layer with optimal thickness and improved fabrication processing for such film-electrode-substrate composites.     

Mechanical properties of hot-pressed SiC particulate-reinforced Al2O3 matrix

The effect of SiC particulate dispersoids on the fracture toughness and strength of hot-pressed Al₂O₃-based composites was evaluated. Addition of 20 vol % SiC particulates was found to increase both the fracture toughness and strength of Al₂O₃. The relationships between mechanical properties and SiC additions are discussed.     

Effects of ZnO nanoneedles addition on the mechanical and piezoelectric properties of hard PZT-based composites

Hard PZT (PZT4)-based composites embedded by ZnO nanoneedles (denoted as PZT/ZnO_n) were fabricated by a solid state sintering technique. The characteristic diffraction peaks of the perovskite PZT and ZnO phases were identified from the studied composites, indicating the retention of ZnO_n. With increasing ZnO_n content, the grain size of the composites was reduced gradually. In contrast with the pure PZT, the PZT/ZnO_n composites possessed more excellent mechanical properties, while the piezoelectric properties were reduced by a certain extent. The best mechanical properties of PZT/ZnO_n composites were obtained by sintering at 1,150 °C with 1.5 wt% ZnO nanoneedles addition: fracture toughness K _IC ~ 2.04 MPa m^1/2, flexural strength σ _f ~ 105.44 MPa, compressive strength σ _c ~ 543.89 MPa. The piezoelectric properties of the PZT/ZnO_n composites were found to be lower than that of the pure PZT with dielectric permittivity ε _r of 768–893, piezoelectric coefficient d ₃₃ of 240–260pC/N, mechanical quality factor Q _m of 340–650 and planar electromechanical coupling k _p of 0.5–0.55.     

Influence of the connectivity pattern,the nature of the piezoelectric material,and rod thickness on the properties of 50 vol % PZT/50 vol % NiCo0.02Cu0.02Mn0.1Fe1.8O4 − δ magnetoelectric composites

We have studied the influence of the connectivity pattern, the nature of the piezoelectric material, and rod thickness on the properties of magnetoelectric composites with the composition 50 vol % PZT/50 vol % NiCo_0.02Cu_0.02Mn_0.1Fe_1.8O_{4 ? δ} (where PZT stands for various commercially available lead zirconate titanate based piezoelectric materials). The results indicate that the magnetoelectric conversion efficiency of the rod composites with any connectivity pattern (1-1, 1-3, or 3-1) is 10–20% higher than that of laminate composites. The largest magnetoelectric conversion coefficient ΔE/ΔH is offered by the 1-1 connectivity composites. The ΔE/ΔH of the composites correlates with both their piezoelectric sensitivity g ₃₃ and the piezoelectric sensitivity of the corresponding piezoelectric materials. ΔE/ΔH is shown to be inversely proportional to the thickness of the piezoelectric and ferrite rods. The highest ΔE/ΔH at a frequency of 1 kHz, 450 mV/(cm Oe), has been reached in the PZT-36 based composites with 1-1 connectivity and 0.3-mm-thick rods.     

Thermal and dielectric properties of the LTCC composites based on the eutectic system BaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The low-temperature co-fired ceramic (LTCC) composites containing quartz based on the eutectic system BaO–Al₂O₃–SiO₂–B₂O₃ are fabricated at the sintering temperature below 980 °C. Preparation process and sintering mechanism were described and discussed, respectively. The results indicated that the addition of quartz to the eutectic system can availably improve dielectric properties of the LTCC composites. In addition, The LTCC composites with optimum compositions, which were obtained by the regulation of an Al₂O₃ content in the composite, can express excellent dielectric properties (permittivity: 5.94, 5.48; loss: 7 × 10⁻⁴, 5 × 10⁻⁴), considerable CTE values (11.7 ppm. °C⁻¹, 10.6 ppm. °C⁻¹) and good mechanical properties (128 MPa,133 MPa).     

Effect of substitution of titanium by magnesium and niobium on structure and piezoelectric properties in (Bi<Subscript>1/2</Subscript>Na<Subscript>1/2</Subscript>)TiO<Subscript>3</Subscript> ceramics

To develop new (Bi_1/2Na_1/2)TiO₃-based ceramics with excellent piezoelectric properties, the similarities and the differences between PZT and (Bi_1/2Na_1/2)TiO₃ ceramics were analysed. Based on the analysis, a new (Bi_1/2Na_1/2)TiO₃-based piezoelectric ceramic of B-site substitution of complex ions (Mg_1/3Nb_2/3)⁴⁺ for Ti⁴⁺ was prepared by a conventional ceramic technique, and effect of complex ions (Mg_1/3Nb_2/3)⁴⁺ addition on the microstructure, dielectric and piezoelectric properties was investigated. The results show that all compositions are mono-perovskite phase and the grain size increases with increasing content of (Mg_1/3Nb_2/3)⁴⁺. The piezoelectric constant, d ₃₃, first increases and then decreases, and electromechanical coupling factor, k _p, varies insignificantly with increasing content of (Mg_1/3Nb_2/3)⁴⁺.