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K 3 CrO 8 in K 3 NbO 8 as a Proposed Standard for g -Factor, Spin Concentration, and Field Calibration in High-Field EPR Spectroscopy

1999; American Chemical Society; Volume: 71; Issue: 10 Linguagem: Inglês

10.1021/ac9812330

1520-6882

Brant Cage, April Weekley, Louis‐Claude Brunel, Naresh S. Dalal,

Electrocatalysts for Energy Conversion

Currently there is a lack of an internal standard for EPR spectroscopy employing magnetic fields higher than about 3 T. It is here suggested that the solid solution of 0.5% K3CrO8 into K3NbO8 fulfills many of the requirements of such a standard. Its main EPR signal is due to a 3d1 electron and consists of a single sharp peak for single-crystal samples. The peak width ranges from 1.5 G (0.15 mT) at the X-band (Bo = 0.34 T) to 4 G (0.4 mT) at 330 GHz (Bo = 11.8 T). The g-values have been determined as g⊥ = 1.98508 ± 0.00005 and g∥ = 1.94272 ± 0.00005. This high degree of precision is necessary because EPR work at high frequencies can resolve g-tensors to six or seven significant figures. Additionally, K3CrO8 in K3NbO8 provides a field calibration standard via a weak but well-resolved hyperfine structure from its 53Cr isotope (I = 3/2, natural abundance 9.5%): A∥ = 39.55 ± 0.08 G, A⊥ = 11.49 ± 0.05 G. Variable-temperature and variable-frequency studies demonstrate that this sample can serve as a reliable standard for EPR measurements over the range of at least 5−300 K and 9−330 GHz. The sample can be prepared in a simple, reproducible way and can serve also as a standard for absolute spin count, thus making it unique among the other standards in current usage.