Thickness effects on the sinterability, microstructure, and nanohardness of SiC‐based ceramics consolidated by spark plasma sintering

Abstract

This study aimed to investigate the effects of the original thickness on the densification, microstructure, and nanoindentation hardness of silicon carbide (SiC) ceramics prepared by the spark plasma sintering (SPS) process. The densification of SiC ceramics with different initial thicknesses ranging from 50 to 2000 µm was investigated in combination with varying SPS sintering temperature at 1700–1900°C. The results indicated that the densification of SiC sample with the initial thickness of 50 µm was complete after sintering at 1700°C. On the contrary, when the initial thickness exceeded 50 µm, it resulted in a porous microstructure. When the initial thickness varied from 50 to 100 µm, dense SiC monolithic could be obtained after sintering at 1800°C. All the samples were fully densified after sintering at 1900°C. The predominant factors for the thickness effect were mainly derived from the unique characteristics of SPS. The hardness of SiC ceramics was measured using nanoindentation, and it was found to have a strong correlation with the initial thickness, mainly attributed to the densification status. The dense SiC product demonstrated nanoindentation hardness with high values of ∼28.0 GPa.

Bismuth Ferrite-Based Lead-Free High-Entropy Piezoelectric Ceramics

“…S max and S p–p initially increase with x and then decrease sharply after reaching the maxima. The shape of S – E curve is found to change from the typical ferroelectric feature with a symmetric butterfly loop to a budding one, which is correlated to the deviation from the MPB structure to a relaxor ferroelectric at x = 0.45. , Notably, a maximum S max of 0.50% was recorded when x = 0.40 ceramics were subjected to an electric field of 100 kV/cm (Figure e). The maximum d 33 * ∼ 500 pm/V was recorded at the crossover point from ferroelectric behavior (0.25 ≤ x ≤ 0.40) to electrostriction ( x ≤ 0.4), as verified by the dielectric characterization, domain structure, P – E , and I – E loops, which is a similar trend observed in previous BF–BT-based and NBT-based lead-free systems. , This is one of the largest S max and d 33 * values recently recorded for BF-based ceramics, to the best of our knowledge, as shown in Table summary of the reported S max and d 33 * = S max / E max values for BF-based ceramics.…”

“…The shape of S−E curve is found to change from the typical ferroelectric feature with a symmetric butterfly loop to a budding one, which is correlated to the deviation from the MPB structure to a relaxor ferroelectric at x = 0.45. 12,58 Notably, a maximum S max of 0.50% was recorded when x = 0.40 ceramics were subjected to an electric field of 100 kV/cm (Figure 8e). The maximum d 33 * ∼ 500 pm/V was recorded at the crossover point from ferroelectric behavior (0.25 ≤ x ≤ 0.40) to electrostriction (x ≤ 0.4), as verified by the dielectric characterization, domain structure, P−E, and I−E loops, which is a similar trend observed in previous BF−BT-based and NBT-based lead-free systems.…”

“…Particularly, the increase of Δ S config has significantly enhanced the total resistivity from 3.6 kΩ·cm ( x = 0.15) to 300 kΩ·cm ( x = 0.40) that is almost a 100-fold. The activation energy ( E a ) was obtained by fitting the conductivity at each temperature using Arrhenius law (Figure b): , σ = σ 0 exp true( E normala k normalB T true) σ = l RS where σ 0 is a pre-exponential factor, T is the measured temperature, k B is Boltzmann’s constant, σ is the electrical conductivity, l is the thickness of the ceramic, S is the cross-sectional area of the ceramic, and R is the extrapolated intercept of the real-part impedance ( Z ″). With Δ S config increasing, E a increases from 0.61 eV to a maximum value of 1.12 eV (Figure c), which is close to half the optical band gap, suggesting that the electronic conduction for the BF– x BSCBNT ceramics is close to the intrinsic (band gap) mechanism and beneficial for high insulation.…”

“…Piezoelectric materials play a crucial role as core components in high-precision actuators, sensors, and transducers. − Currently, lead-based materials, like lead zirconate titanate (PZT), are widely used in commercial applications due to their exceptional piezoelectric properties. − However, lead-based materials contain more than 60% of highly toxic lead, which poses a significant environmental and health hazard. − Therefore, the exploration of new lead-free piezoelectric materials is of the utmost importance. Among the various lead-free material systems, BiFeO 3 (BF)-based lead-free ceramics are promising alternatives of lead-based materials because of their high Curie temperature ( T c ) and ferroelectric properties. − BF can be solidly dissolved with BaTiO 3 (BT), SrTiO 3 (ST), and other compounds with ABO 3 structure to form a morphotropic phase boundary (MPB), which is a well-known strategy to achieve high ferroelectric and piezoelectric properties. − The coexistence of multiple phases at the MPB reduces the energy barrier for polarization switch processes, enhances domain mobility, and leads to improved piezoelectric properties. ,− Notably, previous studies have demonstrated promising results for BF-based materials. For instance, Lee et al obtained piezoelectric coefficient ( d 33 = 402 pC/N) and T c = 454 °C in the MPB range by quenching 3 mol % Ga-doped BF–0.33BT ceramics, while Habib et al achieved d 33 = 436 pC/N and piezoelectric strain coefficient ( d 33 * = 550 pm/V) through Sm-doped BF–0.33BT quenching and a novel AC cyclic polarization method.…”

Excellent Energy Storage Performance Achieved in Sr(Sc0.5Nb0.5)O3-Doped Bi0.5Na0.5TiO3-Based Lead-Free Relaxor Ferroelectric Ceramics

“…Improving E b is also a crucial factor in optimizing the ESP of BNT-based ceramics. The E b of ceramic materials can be optimized by adjusting grain size, thickness, and dense property, as it is primarily related to their highly insulating grain boundaries. ,, Currently, enhancing E b can be achieved through grain refinement, , introducing high band gap ( E g ) compositions, , and optimizing thickness processes. , For example, Wang et al introduced BiScO 3 into BNST, which significantly diminished the grain size from 2.81 to 0.71 μm and boosted the E b from 185 to 480 kV·cm –1 . Lin et al introduced NaTaO 3 ( E g ∼ 4.1 eV) into the binary matrix BNT-BAT, which significantly reduced the grain size while increasing the E g , resulting in an improvement in E b from 240 to 420 kV·cm –1 .…”