Samples of SiCN ceramics were synthesized by thermal treatment of commercially available CERASET™ polyureasilazane, used as liquid-polymer precursor, at pyrolysis temperatures of 1000, 1050, 1100, 1150, and $1200°\mathrm{C}$ . Electron paramagnetic resonance (EPR) signals due to $s{p}^2$ -hybridized carbon-related dangling bonds were recorded over the $4–300\mathrm{K}$ temperature range at $X$ band $\left(9.6\mathrm{GHz}\right)$ , and the spectra showed the presence of an intense EPR line with $g=2.0027$ at room temperature for all samples; at liquid helium temperature an additional line was seen present as a shoulder to main line. These two signals are due to carbon-related dangling bonds present as (i) defects on the free-carbon phase and (ii) within the bulk of SiCN ceramic network. The value of the antiferromagnetic exchange constant between dangling bonds in the various samples, not hitherto available in the literature, was estimated from the temperature variation of the EPR linewidth to be anywhere from $J=-12$ to $J=-15\mathrm{K}$ in the samples synthesized at 1000, 1100, and $1150°\mathrm{C}$ . The EPR linewidth of the samples decreased with increasing pyrolysis temperature of a sample, being $0.07\mathrm{mT}$ at $X$ band at room temperature for the samples synthesized at 1150 and $1200°\mathrm{C}$ , which can be used potentially as stable $g$ markers, due to their very narrow linewidth. The $W$ -band $\left(95\mathrm{GHz}\right)$ room-temperature spectrum of the sample pyrolyzed at $1100°\mathrm{C}$ exhibited only one line consistent with the $X$ -band spectrum. At higher frequency of $G$ band $\left(170\mathrm{GHz}\right)$ the EPR spectra are better resolved, clearly showing the presence of a strong $(g=2.0027)$ and a weak $(g=2.0032)$ EPR line at room temperature, and the latter corresponds to the line present at $X$ band as shoulder at liquid-helium temperature. In addition, nuclear magnetic resonance measurements were carried out to confirm the existence of free-carbon phase and oxygen atoms in the samples.

Cobalt doping $(⩽1\%)$ produces ferromagnetism at room temperature in semiconducting $\mathrm{Sn}{\mathrm{O}}_2$ , presumably due to oxygen vacancies and/or changes in carrier concentration. Electron paramagnetic resonance (EPR) is a sensitive technique to investigate the Co ionic states and their local environments and/or interactions. This paper reports EPR studies of ${\mathrm{Co}}^{2+}$ ions doped in chemically synthesized nanoparticles of $\mathrm{Sn}{\mathrm{O}}_2$ carried out at $5\mathrm{K}$ . EPR spectra were recorded from $600°\mathrm{C}$ prepared $\mathrm{Sn}{\mathrm{O}}_2$ with Co concentrations of 0.5%, 1%, 3%, 5%, 8%, and 12% and from 1% Co-doped $\mathrm{Sn}{\mathrm{O}}_2$ prepared at temperatures of 150, 250, 350, 450, 600, and $830°\mathrm{C}$ . Each EPR spectrum in samples with cobalt doping can be simulated as an overlap of spectra due to two broad ferromagnetic resonance lines and those due to interstitially and substitutionally incorporated ${\mathrm{Co}}^{2+}$ ions with effective spin $S=1∕2$ characterized by their particular $\mathbf{g}$ and $\mathbf{A}$ tensors. It is concluded that the ${\mathrm{Co}}^{2+}$ ions occupy substitutional as well as interstitial sites of $\mathrm{Sn}{\mathrm{O}}_2$ and that a fraction, albeit small, of the doped ${\mathrm{Co}}^{2+}$ spins contribute to the ordered ferromagnetic state. The relative concentrations of these different components depend on the annealing temperature and Co concentration of the samples.

Pressure measurement in high temperature environments is important in many applications to provide valuable information for performance studies. Information on pressure patterns is highly desirable for improving performance, condition monitoring and accurate prediction of the remaining life of systems that operate in extremely high temperature environments, such as gas turbine engines. A number of technologies have been recently investigated, however these technologies target specific applications and they are limited by the maximum operating temperature. Thick and thin films of SiCN can withstand high temperatures. SiCN is a polymer-derived ceramic with liquid phase polymer as its starting material. This provides the advantage that it can be molded to any shape. CERASET™ also yields itself for photolithography, with the addition of photo initiator 2, 2-Dimethoxy-2-phenyl-acetophenone (DMPA), thereby enabling photolithographical patterning of the pre-ceramic polymer using UV lithography. SiCN fabrication includes thermosetting, crosslinking and pyrolysis. The technology is still under investigation for stability and improved performance. This work presents the preparation of SiCN films to be used as the body of a sensor for pressure measurements in high temperature environments. The sensor employs the phenomenon of drag effect. The pressure sensor consists of a slender sensitive element and a thick blocking element. The dimensions and thickness of the films depend on the intended application of the sensors. Fabrication methods of SiCN ceramics both as thin (about 40–60 µm) and thick (about 2–3 mm) films for high temperature applications are discussed. In addition, the influence of thermosetting and annealing processes on mechanical properties is investigated.

X -band (∼9.5GHz) electron paramagnetic resonance (EPR) studies of Fe3+ ions in Sn1−xFexO2 powders with 0.00⩽x⩽0.05 at various temperatures (5–300K) are reported. These samples are interesting to investigate as Fe doping (⩽5%) produces ferromagnetism in SnO2 [A. Punnooose et al., Phys. Rev. B 72, 054402 (2005)], making it a promising ferromagnetic semiconductor at room temperature. The EPR spectrum at 5K can be simulated reasonably well as the overlap of spectra due to seven magnetically inequivalent Fe3+ ions: four low-spin (S=1∕2) and three high-spin (S=5∕2) ions, characterized by different spin-Hamiltonian parameters, overlapped by three broad ferromagnetic resonance spectra. The three high-spin ions, situated substitutionally in the interior of nanodomains, are characterized by smaller zero-field splitting (ZFS) parameters D and E, so that all their energy levels are populated at 5K. On the other hand, the four low-spin ions are situated interstitially at the surfaces of nanodomains. They are characterized by much larger ZFS, so that only their lowest Kramers doublets are occupied at 5K. Based on this simulation, it is concluded that the observed spectra at different temperatures can be reproduced by changing appropriately the relative overlaps of the various paramagnetic and ferromagnetic characters, which remain present over the temperature range studied.