Effects of sintering additives and sintering methods on the mechanical, antimicrobial and optical properties of Si3N4 bioceramics.

Si3N4 bioceramics were fabricated using GPS and SPS method with MgO-RE2O3 (RE = La, Nd, Gd, Ho and Lu) sintering additives. The effect of sintering methods and sintering additives on the grain growth, mechanical, antimicrobial properties and color of Si3N4 bioceramics were studied. Samples sintered with GPS are composed of ß-Si3N4 and samples sintered with SPS are composed of α-Si3N4 and ß-Si3N4. The growth of ß-Si3N4 grains in samples sintered with GPS are more adequate. Samples sintered with GPS exhibit a S. aureus inactivation rate up to 98% and a bright color appearance with a hardness of about 13 GPa and a fracture toughness up to 7.5 MPa m1/2, suitable for dental implants. And samples sintered with SPS exhibit a hardness of about 17 GPa and a fracture toughness about 6 MPa m1/2.

Mn4+-Activated Double-Perovskite-Type Sr2LuNbO6 Multifunctional Phosphor for Optical Probing and Lighting.

Multifunctional phosphors have significant application and scientific value and are becoming a research hotspot in the field of luminescent materials. Herein, we report Mn4+-activated double-perovskite-type Sr2LuNbO6 multifunctional phosphors with excellent comprehensive properties in the fields of optical temperature/pressure sensing and w-LED lighting. The crystalline structure, elemental composition, optimal doping concentration, crystal-field strength, and optical bandgap of the phosphors are investigated in detail, and the mechanisms of concentration and thermal quenching are discussed. From the optimal Sr2LuNb0.998O6:0.2%Mn4+ phosphor, a LED lamp for indoor warm-white lighting is successfully fabricated. Further, the thermometric properties of the phosphors are explored for applications as FIR- and lifetime-based thermometers, showing a maximum relative sensitivity of 1.55% K-1 at 519 K. Upon pressure loading, a significant red-shift of the peak centroid is observed, and the pressure sensitivity is determined to be 0.82 nm/GPa. These results suggest that the Mn4+-activated Sr2LuNbO6 multifunctional phosphors have great potential to be utilized in the fields of optical thermometry, manometry, and lighting.

Plastic deformation in silicon nitride ceramics via bond switching at coherent interfaces.

Covalently bonded ceramics exhibit preeminent properties-including hardness, strength, chemical inertness, and resistance against heat and corrosion-yet their wider application is challenging because of their room-temperature brittleness. In contrast to the atoms in metals that can slide along slip planes to accommodate strains, the atoms in covalently bonded ceramics require bond breaking because of the strong and directional characteristics of covalent bonds. This eventually leads to catastrophic failure on loading. We present an approach for designing deformable covalently bonded silicon nitride (Si3N4) ceramics that feature a dual-phase structure with coherent interfaces. Successive bond switching is realized at the coherent interfaces, which facilitates a stress-induced phase transformation and, eventually, generates plastic deformability.