Quartic anisotropy of the recoilless fractions in NaCl

Abstract

Previously obtained data on the recoilless fractions in single crystals of sodium chloride have been reanalyzed in terms of the general formalism conforming to the crystal symmetry. The original data were obtained by using Rayleigh scattering of the Mössbauer radiation. It was found that above the quantum region and at a temperature high enough to neglect anisotropy of the ionic form factors there is some anisotropy of the thermal motion of the entirely quartic character. On the other hand, quadratic terms in the wave-vector transfer are completely quasiharmonic. A departure from the Gaussian thermal distribution is quite significant for both cations and anions. The anisotropy tends to diminish at high temperatures.

Emission Mössbauer spectroscopy in the Co–O system under high oxygen pressure

“…In the high temperature limit, i.e. for TOT A [1], the MSD can be approximated by the relationship ATCBT 3 [16][17][18][19]. The above expression can be expanded around T A to the second order approximation, leading to the high temperature limit of Eq.…”

“…Anions are divalent, while cations are either divalent or trivalent. Therefore, the chemical unit cell of the normal spinel contains four divalent cations in the tetrahedral T1 sites constituting FCC sub-lattice, four divalent cations in the tetrahedral T2 sites, and 16 [4][5][6][7]. Tetrahedrally coordinated divalent Co ions (by oxygen anions) become antiferromagnetically ordered at about 40 K [4,7].…”