Electronic structures, mechanical and thermodynamic properties of cubic alkaline-earth hexaborides from first principles calculations

Alumina, thanks to its superior thermal and dielectric properties, has been the leading substrate over several decades, for power and microelectronics circuits. However, alumina lacks thermal stability since its temperature coefficient of resonant frequency (τf) is far from zero (−60 ppmK−1). The present paper explores the potentiality of a ceramic composite 0.83ZnAl2O4-0.17TiO2 (in moles, abbreviated as ZAT) substrates for electronic applications over other commercially-used alumina-based substrates and synthesized using a non-aqueous tape casting method. The present substrate has τf of + 3.9 ppmK−1 and is a valuable addition to the group of thermo-stable substrates. The ZAT substrate shows a high thermal conductivity of 31.3 Wm−1K−1 (thermal conductivity of alumina is about 24.5 Wm−1K−1), along with promising mechanical, electrical and microwave dielectric properties comparable to that of alumina-based commercial substrates. Furthermore, the newly-developed substrate material shows exceptionally good thermal stability of dielectric constant, which cannot be met with any of the alumina-based HTCC substrates.

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Can zinc aluminate-titania composite be an alternative for alumina as microelectronic substrate?

Cubic-shaped ultrafine alkaline-earth hexaborides (MB6, M = Ca, Ba, Sr) have been synthesized via a solid-state reaction of MO with NaBH4 at 1150 °C. Phase composition, grain morphology, microstructure, magnetic and optical absorption properties were investigated using XRD, FESEM, HRTEM, a SQUID magnetometer and optical measurements. Results show that all of the synthesized hexaborides are composed of a CsCl-type single phase and the average grain sizes of nanocrystalline CaB6, SrB6 and BaB6 are 150 nm, 20 nm and 30 nm at a reaction temperature of 1150 °C. The magnetic measurement results show that all of the synthesized samples show a weak ferromagnetic behavior at room temperature. This is the first time that we have found ferromagnetic properties in nanocrystalline alkaline-earth hexaborides. Moreover, the HRTEM results strongly supported that the magnetic moment of the alkaline-earth hexaborides originated from the intrinsic defects of the nanocrystals. The optical absorption results show strong light absorption in the visible light region and transparency for near infrared rays for nanocrystalline alkaline-earth hexaborides. This interesting optical property should have important effects for extending optical applications, such as in near infrared filtering or detectors.

Synthesis, and magnetic and optical properties of nanocrystalline alkaline-earth hexaborides

Ceramic matrix composites reinforced with carbon nanotubes are becoming increasingly popular in industry due to their astonishing mechanical properties and taking into account the fact that advanced production technologies make carbon nanotubes increasingly affordable In the present paper, the most convenient contemporary methods used for the compaction of molding masses composed of either technical ceramics or ceramic matrix composites reinforced with carbon nanotubes are surveyed This stage that precedes debinding and sintering plays the key role in getting pore-free equal-density ceramics at the scale of mass production The methods include: compaction in sealed and collector molds, cold isostatic and quasi-isostatic compaction; dynamic compaction methods, such as magnetic pulse, vibration, and ultrasonic compaction; extrusion, stamping, and injection; casting from aqueous and non-aqueous slips; tape and gel casting Capabilities of mold-free approaches to produce precisely shaped ceramic bodies are also critically analyzed, including green ceramic machining and additive manufacturing technologies

Methods Used for the Compaction and Molding of Ceramic Matrix Composites Reinforced with Carbon Nanotubes

Adhesion strength and thermal shock properties of nanostructured 5La3TiYSZ, 8LaYSZ and 8CeYSZ coatings prepared by atmospheric plasma spraying

Boron carbide green sheet processed by environmental friendly non-aqueous tape casting

Impact of microscopic bonding on the thermal stability and mechanical property of CaB6: A first-principles investigation

The homogeneous B 4 C ceramics are successfully prepared through tape casting, laminating and hot pressing. The obtained B 4 C slurry exhibited a shear thinning behavior. After tape casting, both sides of the green sheets were smooth and homogeneous. After lamination and decomposition treatment developed in argon, hot press sintering of laminated boron carbide was proceed at 2000 °C. The results indicate that the strength and fracture toughness of B 4 C specimens are 585 MPa and 4.9 MPa m 1/2 , respectively. The primary fracture mode is an intergranular type. The reasons for the improvement in mechanical properties should lie in the tape casting processing technique and the presence of carbonaceous residues in specimen.

Preparation of homogeneous B4C ceramics with high toughness by tape casting

Method for synthesizing boron carbide in low-temperature

Carbon nano-tube modified molybdenum disilicide based material and preparation method thereof

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