resonance measurement; paramagnetic; high pressure; low temperature; EPR
Major improvements have been made on the sensitive high pressure electron paramagnetic resonance (EPR) system developed previously in 1978 at this laboratory. These changes allow low temperature measurements and provide a more stable signal. The high pressure EPR cell is placed inside a vacuum chamber to provide thermal isolation, so that the system may be cooled by a closed cycle refrigerator to temperatures between 45 and 60 K, depending on the energy input to the modulation coil. The combination of high pressure and low temperature greatly expands the thermodynamic range over which EPR measurements can be made. An improved and effective method of forming a conductive surface to define the microwave cavity is presented. This method successfully avoids the deterioration of the sapphire's polished surface which causes premature breaking of the sapphire high pressure anvil, and therefore significantly improves the reliability of the system at high pressure. Other modifications to the system, such as the microwave coupling method, the modulation coil, and selecting of a hydrostatic pressure fluid, are discussed. EPR measurements on BaTiO3 have been made at temperatures ranging from 233 to 353 K and pressures from 0 to 4.4 GPa. High quality signals can be realized in the entire pressure and temperature range.
(c) 1997 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in The Journal of Chemical Physics and may be found at http://link.aip.org/link/?RSINAK/68/3877/1;