PHASE TRANSITIONS AND EXCITONSRaman and infrared studies of librational-translational modes in stress-aligned ferroelastic KCN

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PHASE TRANSITIONS AND EXCITONSRaman and infrared studies of librational-translational modes in

stress-aligned ferroelastic KCN

Denys Durand, L. C. Scavarda Do Carmo, F. Luty

To cite this version:

Denys Durand, L. C. Scavarda Do Carmo, F. Luty. PHASE TRANSITIONS AND EXCITONSRaman

and infrared studies of librational-translational modes in stress-aligned ferroelastic KCN. Journal de

Physique Colloques, 1980, 41 (C6), pp.C6-437-C6-437. �10.1051/jphyscol:19806112�. �jpa-00220019�

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JOURNAL DE PHYSIQUE Colloque C6, supplgment au no 7 , Tome 41, Juillet 1980, page C6-437

PHASE TRANSITIONS AND EXCITONS.

Raman and infrared studies of librational-translational modes in stress-aligned ferroelastic KCN (*)

D.

Durand

(**),

L. C. Scavarda

do

Carmo

(***)

and F. Luty

Physics Department, University of Utah, Salt Lake City, Utah 84112, U.S.A.

Abstract. - KCN crystals, when cooled from the pseudo-cubic disordered phase into the low temperature phase of parallel CN- order, break up into a multi-domain structure with strong light scattering. As this prevents any measurements of polarized Raman or IR spectra, the assignment of bands to particular librational and/or translational modes has been highly speculative and controversial in previous works. By application of uniaxial stress in the ferroelastic phase, we have succeeded to align a large fraction of the ortho-rhombic domains and to reduce the light scattering. This enabled us, for the first time, to measure polarized spectra of the librational/translational modes, the CN- stretching and combinations of both, using Raman and IR techniques. From experiments with various stress-and light-geometries, the symmetry properties of all observed Raman and IR transition are deter- mined. Definite assignments of these bands to particular librational and translational modes will be presented and discussed.

(*) Supported by NSF Grant # DMR 12675 and NATO (***) On leave from Pontificia Universidad Catolica do Rio de Grant f 1500. Janeiro, and supported by a fellowship from PUC and CNPg

(**) Permanent address ^:Physics Department, Universite de (Brazil).

Metz. France.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19806112