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Spectroscopy at very high pressures: 45—structural phase transitions in A 2 HgI 4 , (A = Ag, Cu, Tl, 1/2Pb), investigated by Raman scattering
Author(s) -
Adams David M.,
Hatton Peter D.
Publication year - 1983
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250140306
Subject(s) - raman spectroscopy , chemistry , phase transition , diamond anvil cell , spinel , raman scattering , analytical chemistry (journal) , phonon , phase (matter) , space group , high pressure , spectral line , crystallography , condensed matter physics , x ray crystallography , materials science , diffraction , optics , physics , thermodynamics , organic chemistry , chromatography , metallurgy , astronomy
Raman spectra and phonon pressure dependencies are reported for the spinel‐related iodides A 2 HgI 4 , (A = Ag, Cu, Tl and 1/2Pb) at high pressures in a diamond anvil cell. In each case the upper pressure limit of observation was set by changes in band gap which caused darkening and photodecomposition. New phase transitions were found for Cu 2 HgI 4 (8 and 25 kbar), Tl 2 HgI 4 (11.5 kbar) and PbHgI 4 (7 and 14 kbar). Transitions in Ag 2 HgI 4 were located at 3.3, 5.9 and 8.1 kbar, confirming and extending earlier evidence. The β‐Ag 2 HgI 4 to phase II transition at 3.3 kbar appears to be second‐order in type. Using Landau's theory, Ag 2 HgI 4 II was shown to adopt space group C 2 3 . Similarly, at the I/II transition in Cu 2 HgI 4 , the new phase (II) can have either D 2 8or C 2ν 18symmetry.