ANALYSIS OF ASYMMETRY OF THE MOSSBAUER BANDS OF FEXZN1-X(4-AMINO-1,2,4-TRIAZOLE)(3)(NO3)(2) COMPLEXES WITH THE SPIN TRANSITION (1)A(1)REVERSIBLE-ARROW-T-5(2) - PROOF OF ANISOTROPY OF IRON ATOM VIBRATIONS

This paper analyzes the nature of asymmetry of quadrupole doublets in the Mossbauer spectra of the high-spin (HS) and low-spin (LS) forms of FexZn1-x(ATr)(3)(NO3)(2) complexes possessing a polynuclear chain str ucture. It is assumed that the quantization axis z is directed along t he polymer chain. The asymmetric character of bands in the spectra is explained by the anisotropy of iron atom vibrations along the z axis o r perpendicular to it, i.e., by Goldanskii-Karyagin's effect. The quad rupole splitting is theoretically analyzed and compared with experimen t; the electric field gradient on the iron nuclei is negative for the HS form and positive for the LS form. The standard deviations of iron atoms are [x(2)] = 2.78 . 10(-18) cm(2), [z(2)] = 0.72 . 10(-18) cm(2) for the HS form and [x(2)] = 1.63 . 10(-18) cm(2), [z(2)] = 0.72 . 10 (-18) cm(2) for the LS form at 295 K; [x(2)] approximate to [z(2)] = 0 .26 . 10(-18) cm(2) for the LS form at 78 K.