Dielectric response ofN2−Arsolid solutions in the audio frequency range

Abstract

High sensitivity dielectric measurements are reported for N 2-Ar solid mixtures for 49Ͻx(N 2) Ͻ100 mol%. The results show the onset of strong hysteresis effects for the temperature dependence of the dielectric constant on thermal cycling below 30 K. These onset temperatures are identified with transitions to a quadrupolar glass state. Samples cooled from high temperatures ͑above 50 K͒ in the presence of a small external ac electric field also show a characteristic field-cooled history dependence down to 50% dilution of N 2. The results presented are purely empirical, but qualitative estimates of the magnitude of the effects using a generalized fluctuation-dissipation argument are consistent with the observations.

Thermal hysteresis of the dielectric susceptibility of solid oxygen in the audio frequency range

“…22 Striking phenomena including strong hysteresis and field cooling memory effects have been observed for these systems. 21 Given the high degree of frustration of both the orientational and magnetic interactions in solid oxygen, similar hysteresis effects could be anticipated for solid O 2 .…”

“…21 In the latter studies, the variations were attributed to field-induced changes in a complex free-energy landscape of the frustrated electric-quadrupole interaction energies in the quadrupole glass region of the phase diagram. The case of solid O 2 is different.…”

“…The anisotropy is very high for O 2 molecules, ⌬␣ / ␣ 0 = 0.72, 26 and as a consequence, dielectric measurements can provide a powerful tool for probing local molecular ordering over a range of frequencies that are especially relevant to the dynamical time scale of the intermolecular correlations in solid O 2 and as was shown for solid N 2 -Ar mixtures. 21 The polarizability is determined from the observed dielectric constant using the Clausius-Mossotti relation ␣ = 3 4N ͑ −1͒ / ͑ −2͒. ␣ aniso depends directly on the local order parameters, the alignment i ͑T͒, and the eccentricity i ͑T͒ through the relation…”

“…The dielectric susceptibility 20,21 has been shown to be a very sensitive probe of the local ordering of molecular orientations in simple diatomic molecular solids such as N 2 where the ordering is driven by local electrostatic interac- tions that are highly frustrated. It is important to note that the dielectric measurements give the generalized susceptibility for applied electric fields that perturb the molecular axis alignments and in the absence of anisotropic magnetoelastic interactions would not be sensitive to the magnetic degrees of freedom.…”