Premium
Observation of an incommensurate structure by optical spectroscopy with a 5f ion as an internal probe. U 4+ –ThCl 4 System
Author(s) -
Krupa J. C.,
Malek C. Khan,
Delamoye P.,
Moine B.,
Pedrini C.
Publication year - 1987
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2221400130
Subject(s) - tetragonal crystal system , ion , symmetry (geometry) , spectroscopy , chemistry , absorption spectroscopy , absorption (acoustics) , phase (matter) , phase transition , excitation , spectral line , atomic physics , crystal (programming language) , molecular physics , crystal structure , physics , crystallography , optics , condensed matter physics , programming language , geometry , mathematics , organic chemistry , quantum mechanics , astronomy , computer science
The second order phase transition in β‐ThCl 4 ( T c = 70 K) leads to an incommensurate tetragonal structure modulated along the fourfold symmetry axis. This is due to the freezing of an optical soft mode which induces a modulation of the chlorine ion positions in a plan perpendicular to this axis. Consequently in neighbouring unit cells the crystal field strength acting on the U 4+ ion is slightly different. Then the line shape in the optical spectra shows a continuous variation which reflects the shift of the energy as the symmetry changes. Selective excitation of the resulting different classes of sites, S 4 , D 2 , and various C 2 p ermits one to establish a correlation between absorption and emission profiles of U 4+ ions. The green and the red observed fluorescences of U 4+ in ThCl 4 are assigned in the different symmetries and the energy level mapped out as a function of a phase angle φ l related to the distortion according to the Delamoye and Currat model.