High-temperature giant piezoresistivity of microstructured SiOC-based strain gauges

The foundation of this work is laid out based on the efficiency of silicon oxycarbide (SiOC) as a functional material for piezoresistive device applications. The realization of a cost-efficient strain gauge which can operate at elevated temperature serves as the foremost objective of this work. This goal is fathomed based on prevailing knowledge regarding the high piezoresistivity of SiOC at the range of 10 - 102 coupled with commendable properties such as electrical conductivity, good thermal resistance, and an excellent coating material for hostile environment. An optimized process of spin coating is used to deposit ~500 nm SiOC film onto the 100-mm diameter silicon substrate with a silica layer of 500 nm. The deposition process is screened with a Taguchi design of experiment resulting into a replicable and controlled process with a crack-free and homogenous coating. An in-house piezoresistivity test setup was fabricated with considerations of minimizing the electrical contact resistances, capability to perform mechanical cyclic loads, and the ability to operate at elevated temperature until 700 °C. After the annealing process, the SiOC film manifested round-shaped segregations which were identified as carbon-rich and oxygen-depleted, evenly dispersed in an oxygen-rich matrix. Deeper investigation of the segregated area revealed 2-level hierarchical microstructure of sp2-hybridized carbon, Si3N4 and SiC. On the other hand, Raman analysis confirmed presence of sp2-hybridized carbon not just on the segregated area but also on the matrix distinctive by the difference of crystal sizes. Larger domains of carbon including tortuosity (Leq) are present on the segregation than on the matrix of the film. Kinetics study showed that the segregations area results of free carbon diffusion through the silica layer with an activation energy equal to 3.05 eV. Platinum electrodes are printed on the surface of the SiOC film via photolithography for the PZR tests. The fabricated strain gauge prototypes have high sensitivity with gauge factors (GF) in the range of 2000 – 5000 tested at 25 – 400 °C. At 500 – 700 °C, the behavior of the material shifted from semiconducting to conducting decreasing its resistance to 11 Ω, and GF of 200. This GF is still comparably larger than commercial metal- and silicon-based strain gauges. The difference of mechanical cyclic loads applied on the prototypes influenced the degree of response’ hysteresis and the linearity of the strain range. In both cases, tests under compressive load showed superiority over tensile tests. Through these results, this study provides a working strain gauge prototype based on SiOC thin film with high sensitivity, reproducibility, and robustness. The giant piezoresistivity of the fabricated strain gauge at an elevated temperature, until 700 °C, surpasses the known application of the current commercial strain gauges. Furthermore, the perceived shift on electrical behavior of the material at 460 °C broadens its applications to current-limiting devices and temperature sensors

SiCO Ceramics as Storage Materials for Alkali Metals/Ions: Insights on Structure Moieties from Solid‐State NMR and DFT Calculations

Polymer‐derived silicon oxycarbide ceramics (SiCO) have been considered as potential anode materials for lithium‐ and sodium‐ion batteries. To understand their electrochemical storage behavior, detailed insights into structural sites present in SiCO are required. In this work, the study of local structures in SiCO ceramics containing different amounts of carbon is presented. ¹³C and ²⁹Si solid‐state MAS NMR spectroscopy combined with DFT calculations, atomistic modeling, and EPR investigations, suggest significant changes in the local structures of SiCO ceramics even by small changes in the material composition. The provided findings on SiCO structures will contribute to the research field of polymer‐derived ceramics, especially to understand electrochemical storage processes of alkali metal/ions such as Na/Na⁺ inside such networks in the future

Temperature‐dependent mechanical and oxidation behavior of in situ formed ZrN/ZrO₂‐containing Si₃N₄‐based composite

In this work, Si₃N₄ and Zr(NO₃)₄ were used as raw materials to prepare ZrN/ZrO₂‐containing Si₃N₄‐based ceramic composite. The processing, phase composition, and microstructure of the composite were investigated. Hardness and fracture toughness of the ceramics were evaluated via Vickers indentation in Ar at 25°C, 300°C, 600°C, and 900°C. During spark plasma sintering, Zr(NO₃)₄ was transformed into tetragonal ZrO₂, which further reacted with Si₃N₄, resulting in the formation of ZrN. The introduction of ZrN enhanced the high‐temperature mechanical properties of the composite, and its hardness and fracture toughness reached 13.4 GPa and 6.1 MPa·m¹/² at 900°C, respectively. The oxidation experiment was carried out in air at 1000°C, 1300°C, and 1500°C for 5 h. It was shown that high‐temperature oxidation promoted the formation and growth of porous oxide layers. The microstructure and phase composition of the formed oxide layers were investigated in detail. Finally, it was identified that the obtained composite exhibited a higher thermal diffusivity than that of monolithic Si₃N₄ in the temperature range of 100°C–1000°C

SiOC-based strain gauge with ultrahigh piezoresistivity at high temperatures

The nonlinear response of strain gauges at high temperatures has restricted their applications despite their high-precision and real-time measurement capability. This work addresses this limitation by utilizing the easy preparative access and versatility of silicon oxycarbide-based (SiOC) thin films as strain gauges offering outstanding high-temperature robustness and giant piezoresistive response. The sensitivity of the strain gauge is assessed with continuous cyclic loads, tensile and compressive, resulting in gauge factors of ca. 2000–5000. The linearity of the response is preserved up to 700 °C with a shift in the electrical response occurring at temperatures beyond 500 °C, switching the SiOC film from semiconducting to conducting behavior. This change causes a drop in the gauge factor of the SiOC-based thin films; nevertheless, it is still significantly higher than that of metallic and Si-based commercial strain gauges. Notably, the studied thin films can regulate the effect of temperature enabling them to be a highly sensitive device with good reversibility and replicability in high-temperature environments. Furthermore, the electrical shift at 460 °C broadens the application of the SiOC film as a current-limiting device and temperature sensor

Hierarchical microstructure growth in a precursor‐derived SiOC thin film prepared on silicon substrate

Silicon oxycarbide film deposited on a silicon substrate has shown superior electrical conductivity relative to its monolithic counterpart. In this work, the evolution of different microstructures detected on the SiOC film reveals its hierarchical microstructure. The existence of sp(2)-hybridized carbon domains has been unambiguously confirmed by means of Raman spectroscopy and transmission electron microscopy corroborated with electron energy loss spectroscopy. The diffusion coefficient of carbon in silica and its dependence on temperature were studied by assessing energy-dispersive X-ray spectroscopy profiles taken from the cross-sections of samples annealed at temperatures in the range from 1100 degrees C to 1400 degrees C. The activation energy for diffusion of carbon in silica was determined to be approximately 3.05 eV, which is significantly lower than the values related to the self-diffusion of silicon and oxygen. The microstructural evolution of precursor to SiCnO4-n and SiC serves as migration path of sp(2)-hybridized carbon to the SiOx layer. With increasing temperature, the formation of microscale carbon-rich segregation is promoted while the SiOC film becomes thinner

Structure and Electrical Properties of Carbon-Rich Polymer Derived Silicon Carbonitride (SiCN)

This article reports on the structure and electronic properties of carbon-rich polysilazane polymer-derived silicon carbonitride (C/SiCN) corresponding to pyrolysis temperatures between 1100 and 1600 degrees C in an argon atmosphere. Raman spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), Scanning Electron Microscopy (SEM) and Hall measurements were used to support the structural and electronic properties characterization of the prepared C/SiCN nanocomposites. A structural analysis using Raman spectroscopy showed the evolution of sp(2) hybridized carbon phase that resulted from the growth in the lateral crystallite size (L-a), average continuous graphene length including tortuosity (L-eq) and inter-defects distance (L-D) with an increase in pyrolysis temperature. The prepared C/SiCN monoliths showed a record high room temperature (RT) electrical conductivity of 9.6 S/cm for the sample prepared at 1600 degrees C. The electronic properties of the nanocomposites determined using Hall measurement revealed an anomalous change in the predominant charge carriers from n-type in the samples pyrolyzed at 1100 degrees C to predominantly p-type in the samples prepared at 1400 and 1600 degrees C. According to this outcome, tailor-made carbon-rich SiCN polymer-derived ceramics could be developed to produce n-type and p-type semiconductors for development of the next generation of electronic systems for applications in extreme temperature environments

SiCO ceramics as storage materials for alkali metals/ions: insights on structure moieties from solid‐state NMR and DFT calculations

Polymer-derived silicon oxycarbide ceramics (SiCO) have been considered as potential anode materials for lithium- and sodium-ion batteries. To understand their electrochemical storage behavior, detailed insights into structural sites present in SiCO are required. In this work, the study of local structures in SiCO ceramics containing different amounts of carbon is presented. 13C and 29Si solid-state MAS NMR spectroscopy combined with DFT calculations, atomistic modeling, and EPR investigations, suggest significant changes in the local structures of SiCO ceramics even by small changes in the material composition. The provided findings on SiCO structures will contribute to the research field of polymer-derived ceramics, especially to understand electrochemical storage processes of alkali metal/ions such as Na/Na+ inside such networks in the future

Temperature‐dependent mechanical and oxidation behavior of in situ formed ZrN/ZrO2‐containing Si3N4‐based composite

In this work, Si3N4 and Zr(NO3)(4) were used as raw materials to prepare ZrN/ZrO2-containing Si3N4-based ceramic composite. The processing, phase composition, and microstructure of the composite were investigated. Hardness and fracture toughness of the ceramics were evaluated via Vickers indentation in Ar at 25 degrees C, 300 degrees C, 600 degrees C, and 900 degrees C. During spark plasma sintering, Zr(NO3)(4) was transformed into tetragonal ZrO2, which further reacted with Si3N4, resulting in the formation of ZrN. The introduction of ZrN enhanced the high-temperature mechanical properties of the composite, and its hardness and fracture toughness reached 13.4 GPa and 6.1MPa center dot m(1/2) at 900 degrees C, respectively. The oxidation experiment was carried out in air at 1000 degrees C, 1300 degrees C, and 1500 degrees C for 5 h. It was shown that high-temperature oxidation promoted the formation and growth of porous oxide layers. The microstructure and phase composition of the formed oxide layers were investigated in detail. Finally, it was identified that the obtained composite exhibited a higher thermal diffusivity than that ofmonolithic Si3N4 in the temperature range of 100 degrees C-1000 degrees C

Polymer-derived SiOC ceramics: A potential catalyst support controlled by the sintering temperature and carbon content

A series of silicon oxycarbide ceramics with varying carbon content from ca. 10 wt% to ca. 40 wt% were prepared by thermal pyrolysis of four commercially available polysiloxanes and subsequent spark plasma sintering (SPS) at 1200 degrees C, 1400 degrees C, and 1600 degrees C. The results showed that the high carbon content led to a porous microstructure, and for SiOC with ca. 40 wt% carbon content, its porosity and specific surface area at 1600 degrees C reached 34% and 262 m(2)/g, respectively. The electrochemical behavior of materials was evaluated. It was shown that SiOC has a certain degree of electrocatalytic activity, and the sample with 10 wt% carbon content obtained at 1200 degrees C exhibited an overpotential of 450 mV vs. RHE at 10 mA.cm(-2) in acid medium. Finally, it was analyzed that the electrochemical behavior of SiOC is closely related to the phase composition and microstructure of the resulting ceramics