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High‐pressure Raman study on two modifications of BaAl 2 Si 2
Author(s) -
Shimizu H.,
Kume T.,
Narita Y.,
Sasaki S.,
Kikudome T.,
Yamanaka S.
Publication year - 2007
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.200672520
Subject(s) - raman spectroscopy , bar (unit) , raman scattering , chemistry , ambient pressure , phase (matter) , clathrate hydrate , analytical chemistry (journal) , high pressure , molecular vibration , crystallography , thermodynamics , optics , physics , hydrate , organic chemistry , chromatography , meteorology
The new compound BaAl 2 Si 2 exists in two structural modifications at ambient condition; a clathrate‐like low‐pressure phase α‐BaAl 2 Si 2 and a layered high‐pressure phase β‐BaAl 2 Si 2 . Raman scattering of α‐BaAl 2 Si 2 and β‐BaAl 2 Si 2 has been measured at 1 bar and room temperature, and that of α‐BaAl 2 Si 2 under high pressures up to 20 GPa. For α‐BaAl 2 Si 2 , 17 Raman vibrational modes were observed at frequency of 40–450 cm –1 , which is almost consistent with the group theoretical analysis. Low‐frequency vibrational modes associated with Ba atoms in the polyhedrons were found around 65–80 cm –1 compa‐ rable to the typical clathrate Ba 8 Si 46 . The 4 Raman bands predicted by the group theory were found for β‐BaAl 2 Si 2 . Pressure dependence of Raman modes for α‐BaAl 2 Si 2 indicates the existence of phase transformation at about 20 GPa, which was irreversible with decreasing pressure. The decompressed α‐BaAl 2 Si 2 from 20 GPa to 1 bar shows Raman spectrum close to that of β‐BaAl 2 Si 2 at ambient pressure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)