Irradiated cubic single crystal SiC as a high temperature sensor
Radiation is known to cause point defects formation in different materials. In the case of cubic SiC single crystal radiation flux on the order of 2⋅10 20 neutrons/cm 2 at 0.18 MeV causes over 3% volume lattice expansion. Radiation-induced strain (measurable by X-Ray diffraction) can be relieved when the annealing temperature exceeds the temperature of irradiation. Based on this effect the original technology of maximum temperature measurement was developed a while ago. Single crystal SiC sensor small size (200-500 microns), wide temperature range (150-1450 °C), “no-lead” installation, and exceptional accuracy make it very attractive for use in small, rotating and “hard-to-access” parts, including, but not limited to gas turbine blades, space shuttle ceramic tiles, automobile engines, etc. With the advances in X-Ray diffraction measurements, crystal and thin film growth techniques, it is the time to revise and update this technology. Modeling radiation damage, as well as annealing effects are also beneficial.
Research on neutron-irradiated 6H-SiC crystals by x-ray diffraction
Single crystal SiC has become more and more important semiconductor material due to its excellent physical and chemical properties. The present paper reports a study of characteristics of unirradiated and irradiated SiC. 6H-SiC single crystals were irradiated at approximately 60-80oC to a neutron fluence of 5.74×1018 n/cm2.The radiation damage and the defect recovery in the single crystals were investigated by X-ray diffraction meter. The experimental observation on diffraction peaks of different crystal faces shows that there are serious damages in the neutron-irradiated 6H-SiC crystals and amorphization appears at one of the measured planes. The restoration of radiation damage occurred during the isochronal annealing process, and the recovery feature is depended on annealing temperature. The X-ray diffraction data show that the radiation damages remained almost unchanged below the temperature of 600oC, and the healing process got more and more obvious while the annealing temperature is beyond 600oC. It is found that beyond 600oC the crystal structure gradually reordered and the FWHM of face (006) peak reveals a linear recovery behavior with increasing annealing temperature. High-temperature detector can be made according to the linear recovery law in order to achieve the measurement of the high-temperature environment.
Photoinduced spin-state transition of Co3+ in the layered perovskite manganite thin film
The photoinduced effect, at different temperatures, on layered perovskite manganite La1.2Sr1.8Mn1.8Co0.2O7 thin film deposited on a SrTiO3(100) substrate has been studied using a He–Ne laser (632.8 nm) with the power of output 25 mW at low temperatures. The electrical transport and magnetic properties of the film are investigated systematically in the temperature region from 20 to 300 K. The resistance shows a significant decrease at low temperatures (T<90 K) under laser irradiation, which can be interpreted in terms of the spin-state transition of Co3+ ions. The magnetic field combined with the laser is also used to detect the photoinduced effect of the spin-glass state. The time dependence of the metastable system under several applied fields was also discussed. The system has the ability to keep a persistent memory of the magnetic history imprinted in its zero-field resistance.