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Anomalous pressure dependence of acoustic phonons of AgGaSe 2 investigated by inelastic neutron scattering to 4.3 GPa
Author(s) -
Klotz S.,
Derollez P.,
Fouret R.,
Braden M.,
Hennion B.,
Hubert Ch.,
Meducin F.,
Łażewski J.,
Gonzalez J.
Publication year - 2003
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.200301581
Subject(s) - inelastic neutron scattering , phonon , monoclinic crystal system , neutron diffraction , condensed matter physics , inelastic scattering , softening , materials science , neutron scattering , transverse plane , diffraction , phase transition , scattering , crystal structure , optics , crystallography , chemistry , physics , structural engineering , engineering , composite material
The pressure dependence of the transverse acoustic (TA) phonons along [100] and [001] and the low‐frequency optical Λ 3 modes of AgGaSe 2 has been measured at pressures to 4.3 GPa by inelastic neutron scattering. We find an exceptionally strong frequency decrease of the TA modes with Grüneisen parameters as low as –10 for wave vectors close to the zone centre. The associated elastic coefficient C 44 decreases by ∼50% between 0 and 2.6 GPa. The softening also affects the optical modes to a less extent. These lattice dynamical anomalies seem to be related to a continuous structural phase transition located at ∼2.6 GPa. Single crystal X‐ray diffraction results are consistent with a monoclinic lattice of the high pressure phase which can be regarded as a slightly distorted chalcopyrite structure, similar to AgGaS 2 .