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Lead-free piezoelectric ceramics are expected to be used for artificial bone scaffolds since they can generate electrical signals and promote recovery, but it is still difficult to fabricate piezoelectric scaffolds with complex structures. In this work, digital light processing (DLP) technology was used to fabricate potassium sodium niobate (K 0.48 Na 0.52 NbO 3 , KNN) bone scaffolds with gyroid triply periodic minimal surface. Suspension was first optimized to ensure both high solid loading (42 vol%) and high cure depth (>50 μm). KNN porous scaffolds (porosity: 60%) and other samples for tests were printed successfully. Then, influences of sintering temperature on microstructure, relative density and mechanical properties were discussed. Results showed that when sintered at 1090 °C, printed KNN ceramics had the highest relative density (90.11%) and lowest open porosity (5.75%), and exhibited the most satisfying mechanical properties (compressive strength: 33.85 MPa, elastic modulus: 1.87 GPa, flexural strength: 35.40 MPa, hardness: 2.39 GPa), which can meet the requirements of cancellous bone. Finally, the electric properties of samples at room temperature were verified. With d 33 being 113.67 ± 2.49 pC/N and P r being 19.94 μC/cm2, printed KNN ceramics showed comparable piezoelectric and ferroelectric performances with traditionally dry-pressed samples. These results indicated that DLP technology is competitive in preparing KNN piezoelectric bone scaffolds for implantation. [ABSTRACT FROM AUTHOR]

The effects of hot-pressing sintering on the phase composition, microstructure, thermal and electrical properties of AlN ceramics with CeO 2 –CeF 3 additives were studied. During hot-pressing sintering, high pressure reduced the grain boundary phase CeAlO 3 and decreased the concentration of oxygen in AlN ceramics. The hot-pressing sintered AlN samples had a much higher thermal conductivity of 191.9 W/m·K than pressureless sintered ones because of the great reduction of grain boundary phases and oxygen impurities in AlN ceramic. As the carbon content in hot-pressing sintered sample was very high, carbon contamination led to the decrease in electrical resistivity and changes in polarization mechanisms for AlN ceramics. The relaxation peak in the dielectric temperature spectrum with an activation energy of 0.64 eV for hot-pressing sintered samples was caused by electrons from free carbon at low temperature. Overall, hot-pressing sintering can effectively increase the thermal conductivity and change the electrical properties of AlN ceramics. [ABSTRACT FROM AUTHOR]

The effect of oxidation in air on the phase composition, microstructure, flexural strength and thermal property of AlN ceramics was investigated. Oxidation was found to produce a continuous oxide layer on the surface of AlN samples. The flexural strength and thermal conductivity of AlN ceramics significantly improved after oxidation at 1000 °C and 1100 °C. Residual stress in the AlN ceramic matrix was enhanced by oxidation. The enhanced residual compressive stresses inhibited crack propagation and reduced interfacial thermal resistance, thereby improving the flexural strength and thermal conductivity of AlN ceramics. Electrochemical impedance spectroscopy was further used to analyze the defects in AlN ceramics. The increase in fitting grain resistance revealed a decrease in aluminum vacancy concentration in oxidized AlN sample, which resulted in high thermal conductivity. Therefore, oxidation at a certain temperature is pretty effective to obtain excellent performance for AlN ceramics. [ABSTRACT FROM AUTHOR]

For polymer matrix microwave composites, the agglomeration of ceramic particles at a high filling ratio will cause the microwave dielectric properties, mechanical properties and thermal conductivity of the materials to deteriorate sharply. This paper examines the reinforcement effect of LCP A950 fibers on PTFE and ZnNb 2 O 6 /PTFE composites to prevent this phenomenon. SEM, DMA, and other analysis methods showed that the incorporation of a small amount of LCP can promote the crystallization of PTFE and the mechanical strength of composites. When the volume fraction of the ZnNb 2 O 6 /PTFE/LCP three-phase is 50/45/5, the composites have a medium dielectric constant (ε r = 6.46), extremely low loss (t a n δ = 7.54 × 10−4) and a near-zero temperature coefficient of the dielectric constant (τ ε = +2.25 ppm/°C). Under the same conditions, the linear expansion coefficient of the material is 45.4 ppm/°C, which is 30.5% lower than that before doping with LCP, and the flexural strength is 37.8 MPa, which is an increase of 17% com、pared to the previous value. The LCP-reinforced composites have excellent overall properties, but when the LCP content is too high, its reinforcement effect on the composites is gradually weakened. [ABSTRACT FROM AUTHOR]

A novel and simple gelling system based on a water-soluble copolymer of isobutylene and maleic anhydride (commercial name, Isobam) was adopted to manufacture various ceramics via spontaneous gelation. The gelation mechanism of AlN slurry was investigated using infrared spectroscopy. Results show that Isobam was hydrolyzed to produce the –COOH group, and the hydrogen bonding was formed between the –COOH and –CONH 2 groups of Isobam during spontaneous gelation. Meanwhile, the gelling process of the Isobam system could be accelerated via enhancing hydrogen bonding through APS addition. With 1 wt% addition of APS, the gelation time reduced to 23 h, the viscosity of 50 vol% AlN slurry decreased to 0.21 Pa·s, and the flexural strength of green body improved by 48%. Therefore, the presence of hydrogen bonding in the Isobam gelation mechanism was confirmed, and it could be enhanced by introducing APS to accelerate gelation. [ABSTRACT FROM AUTHOR]

This study systematically investigated the structural, dielectric, and ferroelectric properties of BaAl(2−2x)(Mg0.5Ti0.5)2xO4 ceramics in the 0 ≤ x ≤ 0.04 range. Single‐phase solid solutions in the P63 space group with hexagonal crystal symmetry were confirmed in the composition range of 0 ≤ x ≤ 0.03. The bond lengths of Al1/(Mg,Ti)–O, Al2/(Mg,Ti)–O, and Al3/(Mg,Ti)–O increased with the increase in x, as confirmed through the Rietveld refinement and evolutions of corresponding modes in Raman spectra. The temperature stability of dielectric properties improved at a composition around x = 0.03, and the dielectric constant εr ascended with the increase in x. Ultrabroad temperature stability (−100°C to 700°C) was obtained, and an optimal combination (εr = 18.5, tan δ < 10−3, −22 ppm/°C ≤ TCC ≤ +20 ppm/°C, resistivity ~4.5 × 1014 Ω·cm) was achieved for the x = 0.03 ceramic sintered at 1260°C in air for 6 hours. The increase in stability was ascribed to the variations in axial bonds, and lattice distortions were determined through high‐resolution transmission electron microscopy. The x = 0.03 ceramic could be a promising candidate for C0G or NP0 multilayer ceramic capacitors because of its low loss, high reliability, superior insulating properties and comparatively low‐cost raw materials. [ABSTRACT FROM AUTHOR]

Low‐permittivity ZnAl2‐x(Zn0.5Ti0.5)xO4 ceramics were synthesized via conventional solid‐state reaction method. A pure ZnAl2O4 solid‐state solution with an Fd‐3m space group was achieved at x ≤ 0.1. Results showed that partial substitution of [Zn0.5Ti0.5]3+ for Al3+ effectively lowered the sintering temperature of the ZnAl2O4 ceramics and remarkably increased the quality factor (Q × f) values. Optimum microwave dielectric properties (εr = 9.1, Q × f = 115,800 GHz and τf = −78 ppm/°C) were obtained in the sample with x = 0.1 sintered at 1400°C in oxygen atmosphere for 10 h. The temperature used for the sample was approximately 250°C lower than the sintering temperature of conventional ZnAl2O4 ceramics. [ABSTRACT FROM AUTHOR]

Abstract Low-permittivity LiAl 1- x (Zn 0.5 Si 0.5) x O 2 microwave dielectric ceramics were prepared by the solid-state reaction method. Single-phase LiAlO 2 solid solutions with a tetragonal structure were achieved at x ≤ 0.12. Partial substitution of [Zn 0.5 Si 0.5 ]3+ for Al3+ could improve the microstructure and prevent from absorbing moisture of pure LiAlO 2 ceramics, which slightly increases their relative permittivity (ε r). The quality factor (Q × f) and temperature coefficient of resonant frequency (τ f) were closely related to the crystallinity and cation disorder of the B-site characterized by the full width at half-maximum of B 1 (1) –mode assigned to Li–O–Al stretching. The optimum microwave dielectric properties (ε r = 6.12, Q × f = 56986 GHz and τ f = -122 ppm/°C) were obtained in the sample with x = 0.02 sintered at 1300 °C. [ABSTRACT FROM AUTHOR]

Abstract The effects of two-step sintering on the microstructure, mechanical and thermal properties of aluminum nitride ceramics with Yb 2 O 3 and YbF 3 additives were investigated. AlN samples prepared using different sintering methods achieved almost full density with the addition of Yb 2 O 3 –YbF 3. Compared with the one-step sintering, the grain sizes of AlN ceramics prepared by the two-step sintering were limited, and the higher flexural strength and the larger thermal conductivity were obtained. Moreover, the electrochemical impedance spectroscopy of AlN ceramic was associated with thermal conductivity by analyzing the defects and impurities in AlN ceramics. The fitting grain resistance and the activation energy for the grain revealed the lower concentrations of aluminum vacancy in the two-step sintered AlN ceramics, which resulted in the higher thermal conductivity. Thus, mechanical and thermal properties for AlN ceramics were improved with Yb 2 O 3 and YbF 3 additives sintered using two-step regimes. [ABSTRACT FROM AUTHOR]

BaAl 2−2 x (ZnSi) x Si 2 O 8 ( x = 0.2–1.0) ceramics were prepared using the conventional solid-state reaction method. The sintering behaviour, phase composition and microwave dielectric properties of the prepared compositions were then investigated. All compositions showed a single phase except for x = 0.8. By substituting (Zn 0.5 Si 0.5 ) 3+ for Al 3+ ions, the optimal sintering temperatures of the compositions decreased from 1475 °C ( x = 0) to 1000 °C ( x = 0.8), which then slightly increased to 1100 °C ( x = 1.0). Moreover, the phase stability of BaAl 2 Si 2 O 8 was improved. A novel BaZnSi 3 O 8 microwave dielectric ceramic was obtained at the sintering temperature of 1100 °C. This ceramic possesses good microwave dielectric properties with ε r = 6.60, Q × f = 52401 GHz (at 15.4 GHz) and τ f = −24.5 ppm/°C. [ABSTRACT FROM AUTHOR]

Ba1+1/ M[Si2O5+1/ M] low-permittivity microwave dielectric ceramics are prepared using the conventional solid-state method. Pure phases are obtained in barium silicates with M = 1, 3, 4, 5, and ∞, except for M = 7, in which two phases, Ba5Si8O21 and BaSi2O5, are observed. As the complexity of the crystal structure described by the Shannon information per reduced unit cell increases, the τf value tends to change from a negative to a positive value, except for M = 5, which has the highest complexity. A single Ba5Si8O21 phase with εr anomaly peak at −180°C exhibits a rare positive τf value (+25 ppm/°C), which is a novel temperature compensator. [ABSTRACT FROM AUTHOR]

Piezoelectric ceramics of Pb 0.98 Sr 0.02 (Mn 1/3 Sb 2/3 ) 0.05 Zr 0.48 Ti 0.47 O 3 with 0.25 wt% CeO 2 , 0.50 wt% Yb 2 O 3 , and x wt% Fe 2 O 3 ( x = 0.02, 0.05, 0.1, 0.15, and 0.2) additives were synthesized using a conventional solid-state reaction. Their piezoelectric properties and, in particular their nonlinear dielectric behaviors were systematically investigated. Iron was mainly present in the form of Fe 3+ based on X-ray photoelectron spectroscopy; a small amount of the iron was reduced to Fe 2+ . Iron occupied the B-site of the perovskite structure, as shown in the refinement results. The samples displayed both “soft” and “hard” properties because Fe 3+ can be incorporated at the Mn 2+ , Zr 4+ , Ti 4+ , and Sb 5+ sites. The domain wall motion was found to be related not only to the type of deficiency but also to the grain size and grain boundary effects based on the nonlinear dielectric behaviors under alternating electric fields. The optimal overall properties of d 33 = 360 pC/N, tan δ = 0.295%, Q m = 1500, k p = 0.61, ε r = 1055, α ε = 4.574*10 −4 m/V, and tan δ = 2.76% (under 500 V/mm) were obtained for samples sintered at 1150 °C( x =0.15). [ABSTRACT FROM AUTHOR]

The phase formation, microstructure, chemical structure, and microwave (MW) dielectric properties of the composite ceramics (1- x )Mg (1.04–3/2 y ) Ce y TiO 3 - x CaTiO 3 (MCT-CT) have been investigated systematically. The CaTiO 3 and MgTiO 3 phases coexist well with the formation of secondary phase MgTi 2 O 5 based on X-ray diffraction. Chemical structure analysis reveals the existence of oxygen vacancies ( V O • • ) whose concentrations increase with x , which consequently induce microwave dielectric loss. It has demonstrated that the behaviors of Q×f are influenced strongly by the phase composition and vacancy defects. Although an increasing amount of CaTiO 3 can improve the dielectric constant (ε r ) of the sample slightly, it renders a decrease in the Q×f value instead. The τ f value is strongly correlated to the compositions and the existing phases that can be controlled. An excellent combination of the MW dielectric properties ε r ∼23, Q × f ∼70, 800 GHz, and τ f ∼0 ppm/°C was obtained at x =0.08, sintered at an optimal temperature of 1300 °C/3 h. [ABSTRACT FROM AUTHOR]

Ba 2 ZnSi 2 O 7 ceramics with a monoclinic structure ( C 2/c ) were prepared using the conventional solid-state method at 1200 °C for 3 h in air. The as-prepared ceramics show signs of weak ferroelectricity from the P - E loop and ferroelectric domains with 90° and 103° directions. Although an ε r anomaly appears at approximately 510 °C, the Curie temperature ( T c ) of the Ba 2 ZnSi 2 O 7 ceramics is 750 °C or higher. The ceramics also display low-permittivity microwave dielectric properties ( ε r =8.09, Q × f =26,634 GHz, and τ f =−51.46 ppm/°C). Therefore, the coexistence of high- T c ferroelectricity and good microwave dielectric properties is beneficial to develop Ba 2 ZnSi 2 O 7 ceramics into tunable-microwave and millimeter-wave devices such as capacitors, phase shifters, and oscillators. [ABSTRACT FROM AUTHOR]

This study investigated the phase compositions and reaction models of zinc manganese oxides with different Zn/Mn ratios. These oxides were synthesized through a conventional solid-state reaction, and the reaction between ZnO and MnO 2 generates a ZnMn 2 O 4 -based spinel-like phase. Furthermore, a reaction model with a MnO 2 core and a ZnMn 2 O 4 -based shell was proposed in this work. The ZnO particles on the surface hardly diffuses into the core because of the protection provided by the shell, thus, a ZnO second-phase was detected in ZM11 and ZM12 ceramics calcined at 1000 °C for 3 h and sintered at 1450 °C for 3 h. A single ZnMn 2 O 4 -based spinel-like phase was generated when Zn/Mn ratio was less than 1:2 or when the calcining time was prolonged to 30 h for ZM12 ceramics. [ABSTRACT FROM AUTHOR]