Measurements of polarization fluctuations at time scales longer than ${10}^{\mathrm{-}6}$ s have not been feasible via electron spin resonance techniques. Using partially deuterated ${\mathrm{KH}}_2$${\mathrm{PO}}_4$ (KDP) as an example, this study shows that the double-modulation electron spin resonance technique enables the detection of polarization fluctuations on the millisecond time scale. The measured correlation times for 73% deuterated KDP exhibit Vogel-Fulcher behavior, indicating that this lattice may exhibit structural glass behavior, with a glass formation temperature of 138±10 K.

• Received 6 December 1993

DOI:https://doi.org/10.1103/PhysRevB.49.13211