Experimental and Theoretical Studies of SASeD Doped with Cr³⁺

Abstract

The results of optic and EPR measurements are presented. The transmition bands observed during optic measurements (above and below T c ) have been identified. It is shown that the phase transition, taking place at 180 K reflects itself only in a small parallel shift of the whole spectrum towards higher frequencies. Temperature dependence of the EPR spectrum reveals not only the transition at 176 K but two other anomalies detected at T 1 = 156 K and T 2 = 285 K. An outline of the theory predicting the existence of these anomalies is discussed in terms of the so-called cluster model.

On a correlation between EPR data for SASeD doped with Cr^{3+} and soft modes

“…In our previous paper [7] we studied in detail the contribution of two active groups SO 4 (I) and SO 4 (II) to both the phase transition and to two experimentally observed anomalies for SASD.…”

“…The following designations were used in (5)- (8): i is the lattice cell number; f is the number of sublattice (in every cell); a is the number of the branch of lattice vibration; Γ is the tunnelling constant for motion of SeO 4 group through a potential barrier; ∆ f is the height of this barrier; p 0 is the dipole momentum of the active groups; E is the external electric field; J ij , K ij are constants of interaction for particles from the same sublattice (J ij ) and from different sublattices (K ij ), K = K 11 = K 22 , ω a ( k) is the cyclic frequency of a-branch of lattice vibration with a fixed wave vector k; S x f i , S z f i are spin operators, β ka , β + ka are phonon operators. The potential barrier ∆ f for the crystal structure of SASeD can be taken in the form (see [3,7]):…”