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The current study investigated the dielectric and electrical properties of BaAl (2−2 x) (Zn 0.5 Ti 0.5) 2 x O 4 ceramics, with x = 0, 0.4%, 0.8%, 1.2% and 1.6%, via impedance spectroscopy. The co-doping of Zn and Ti improved the temperature stability over −100 °C–700 °C of ε r and lowered tan δ due to the electron-pinned defect-dipoles. Effects of oxygen partial pressure on the electrical, dielectric and ferroelectric properties of x = 1.6% ceramic were studied as well. The bulk conductivity of the N 2 –H 2 -sintered and O 2 -sintered samples was attributed to the e ' and h • , respectively. [ABSTRACT FROM AUTHOR]

The structure and dielectric properties of BaAl (2−2 x) (Zn 0.5 Ti 0.5) 2 x O 4 ceramics were investigated. Single-phase solid solutions in space group P6 3 (No. 173) were confirmed when 0% ≤ x ≤ 1.6%. [Zn 0.5 /Ti 0.5 ]3+ averagely occupied four symmetrically inequivalent Al sites, and Al1/(Zn,Ti)–O, Al2/(Zn,Ti)–O and Al3/(Zn,Ti)–O bond lengths increased with increased x. Two dielectric anomalous peaks existed, the first peak referred to second-order ferroelectric transition. Stability was significantly improved by moving the first dielectric abnormal peak from 123 °C to −22 °C due to the lower atomic shift amplitude Δz of B cations along the polar axis. The co-doping of Zn2+ and Ti4+ played a decisive role in realizing an ultrabroad temperature range (−100 °C–700 °C) of stability (−27 ppm/°C ≤ TCC ≤ +10 ppm/°C), which met the conditions of C0G or NP0 multilayer ceramic capacitors (±30 ppm/°C). Superior insulating properties were performed by high resistivity of > 1014 Ω cm. [ABSTRACT FROM AUTHOR]

Thephase transition, sinterability, and microwave dielectric properties of Zn(Mn 1- x Al x ) 2 O 4 (0.2≤ x ≤0.9)solid solutions synthesized through a solid-state reaction were investigated. The densification temperature of the solid solutions decreased to 1250 °C, which is much lower than that of the end members. All compositions showed a single phase with a tetragonal structure at x≤0.6and a cubic structure at 0.7≤ x≤ 0.9. As the x value increased, the εr value decreased gradually along with an inflection point of a sharp drop at x=0.7. The Q×f value significantly increased initially and reached the maximum value of 14460 GHz at x=0.8;it decreased thereafter. Meanwhile, the τf value was near the typical value of about ‒60 ppm/°C to ‒80 ppm/°C. TiO 2 and ZnO–B 2 O 3 (ZB) glass co-doping can effectively adjust the τf value of Zn(Mn 0.2 Al 0.8 ) 2 O 4 composition, with the highest Q×f value near zero, and can reduce its sintering temperature to 950 °C.The (1- y )Zn(Mn 0.2 Al 0.8 ) 2 O 4 - y TiO 2 (y=0.26)ceramics with 5 wt%ZB glass exhibited microwave dielectric properties (εr=12.71,Q×f=8126 GHz, and τf=1.02 ppm/°C) appropriate for application in low-temperature co-fired ceramics (LTCC). [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]

The effect of yttrium fluoride (YF 3) on the densification behavior, microstructure, phase composition and thermal conductivity of aluminium nitride (AlN) ceramics with yttrium oxide (Y 2 O 3) and YF 3 additives were studied. Since YF 3 provided liquid phases and promoted densification at a lower temperature, the sintering temperature required to reach the full density of AlN samples decreased with the increase in YF 3 content. Appropriate addition of YF 3 could improve the thermal conductivity of AlN ceramics, but the values of thermal conductivity decreased as YF 3 increased further. It is attributed to the ability of YF 3 to react with oxygen impurity was worse than that of Y 2 O 3. Moreover, the reducing atmosphere significantly affected the phase composition, and the oxygen content in grain boundary phases decreased at 1750 °C and 1800 °C. Therefore, the proper proportion of Y 2 O 3 –YF 3 additives could simultaneously improve densification and the thermal conductivity of AlN samples at a low sintering temperature. [ABSTRACT FROM AUTHOR]

Ba 2 ZnSi 2 O 7 ceramic was prepared by conventional solid-state method and sintering under four different atmospheres (air, O 2 , N 2 , and N 2 –1 vol% H 2). The Ba 2 ZnSi 2 O 7 ceramic exhibited a single phase under air, O 2 , and, N 2 , whereas two phases (including BaSiO 3 impurity) were observed under the N 2 –1 vol% H 2 atmosphere due to Zn2+ evaporation. Dielectric loss was proportional to oxygen partial pressure due to the conduction mechanism of dominant holes. The Ba 2 ZnSi 2 O 7 ceramic exhibited good microwave dielectric properties (ε r = 8.3, Q × f = 27200 GHz, τ f = −41.5 ppm/°C) under the N 2 –1 vol% H 2 atmosphere, making it a novel candidate with good anti-reductive characteristics for base metal electrode–multilayer ceramic capacitor applications. [ABSTRACT FROM AUTHOR]

Ceramic stereolithography Three-Dimensional (SL-3D) printing has a unique advantage in forming ceramic parts with complex shapes. However, because of the effects of the slicing layer thickness, laser spot diameter, and curing inhomogeneity, its manufacturing dimensional accuracy still lags far behind traditional processing methods. In this study, a manufacturing process based on additive and subtractive technologies was used to prepare ceramic groove parts. The manufacturing process of ceramic groove parts is composed of SL-3D printing, debinding, micro-milling, and sintering processes. In order to improve the dimensional accuracy of ceramic groove parts, a model based on shrinkage compensation and micro-milling was proposed. The dimensional change pattern in the curing phase was modelled and a shrinkage compensation method was established to control the dimensional accuracy of the finished parts. A method to characterize the micro-chipping on machined edges of the workpiece was investigated by applying a micro-milling cutter to process the 3D-printed part pre-sintered at 1150 °C. The effectiveness of the proposed dimensional accuracy control method was verified by the case study of a ZrO 2 ceramic part. [ABSTRACT FROM AUTHOR]

Al 2 O 3 -SiC w toughened ceramic tools play vital role in high-speed machining of nickel-based superalloys due to their superior mechanical properties. Herein, owing to synergistic toughening mechanism, α-Si 3 N 4 particles are employed as reinforcement phase into Al 2 O 3 -SiC w ceramic composite to optimize mechanical properties of Al 2 O 3 -SiC w ceramic tools. Moreover, the influence of Si 3 N 4 content and sintering parameters on microstructure and mechanical properties of Al 2 O 3 -20 vol%SiC w ceramic tool material is systematically investigated. Results reveal that appropriate amount of Si 3 N 4 particles is required to effectively increase the density of Al 2 O 3 -SiC w ceramic composites. The presence of Si 3 N 4 particles leads to formation of novel β-sialon phase during hot-press sintering, which effectively enhances fracture toughness and flexural strength of Al 2 O 3 -SiC w ceramic composites. It is observed that grain size of newly formed β-sialon phase is extremely sensitive to hot-pressing sintering conditions. The degree of chemical transformation of α-Si 3 N 4 into Si 6-z Al z O z N 8-z (β-sialon) and z -value of Si 6-z Al z O z N 8-z are significantly influenced by sintering temperature. Overall, Al 2 O 3 -20 vol%SiC w -15 vol%Si 3 N 4 ceramic tool material, with 1.5 vol%Y 2 O 3 -0.5 vol%La 2 O 3 -0.5 vol%CeO 2 (YLC) sintering additive, rendered optimal mechanical properties after sintering at 1600 °C under 32 MPa for 30 min. Improved mechanical performance can be ascribed to synergistic toughening and strengthening influence of whiskers and particles. [ABSTRACT FROM AUTHOR]

Abstract Low-fired fluoride microwave dielectric ceramics (LiF, CaF 2 , SrF 2 and BaF 2) were prepared through a simple one-step sintering process. Fluoride ceramics, especially LiF, which had the lowest sintering temperature of 800 °C, could be well sintered below 1050 °C. Rietveld refinement results showed that LiF, CaF 2 , SrF 2 and BaF 2 ceramics crystallized into a cubic structure with space group Fm -3 m. The relative permittivity (ε r), quality factor (Q × f) and temperature coefficient of the resonant frequency (τ f) of the fluoride ceramics were closely related to relative density, the ionic polarizability of the primitive unit cell, the packing fraction and the bond valence. In this series of low-permittivity fluoride ceramics, LiF, CaF 2 and BaF 2 could be co-fired with Ag powders, and LiF ceramic exhibited the highest Q × f value of 73880 GHz, which is comparable to those of traditional oxide microwave dielectric ceramics. [ABSTRACT FROM AUTHOR]