STRUCTURE DISORDER AND RAMAN SCATTERING IN BaTiO3 AND KNbO3

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Submitted on 1 Jan 1972

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STRUCTURE DISORDER AND RAMAN SCATTERING IN BaTiO3 AND KNbO3

M. Fontana, M. Lambert, A. Quittet

To cite this version:

M. Fontana, M. Lambert, A. Quittet. STRUCTURE DISORDER AND RAMAN SCATTER- ING IN BaTiO3 AND KNbO3. Journal de Physique Colloques, 1972, 33 (C2), pp.C2-54-C2-54.

�10.1051/jphyscol:1972213�. �jpa-00214949�

M. P. FONTANA, M. LAMBERT AND A. M. QUITTET

STRUCTURE DISORDER

AND RAMAN SCATTERING IN BaTiQ3 AND KNb03

Abstract. - We have shown [I] that the Raman scattering spectra observed in the cubic para- electric phase of BaTi03 by different investigators 121, [3] cannot be due to either impurity related effects or to ordinary second order process even if one of the two phonons participating in such a process were soft.

The KNbO3 spectra are very similar. In particular, they also show prominent broad peaks at 260 and 560 cm-1 analogous to those found at about 270 and 530 cm-1 in BaTiO3. In both cases the spectrum does not disappear at the ferroelectric phase transition and its intensity begins only to decrease at quite higher temperatures (200 OC for BaTiO3 and 600 OC for KNbO3).

Such an effect can be related to the structure disorder which has been proposed on the basis of X Ray diffuse scattering experiments 141. This disorder can be described in terms of off-center atomic displacements : the structure has no local inversion symmetry center and thus Ramanscatter- ing can be observed even in the cubic phase. The Raman scattering can be interpreted as a second order process involving a phonon and a pseudo-spin excitation. The decrease with temperature of the Raman cross section must be correlated with the evolution of the disordered structure.

K N b 0 3

a, LOOT

, '..-, _,

----

O . . . ' . . . . .

0 200 LOO 600 800 ^'

STOKES SHIFT (CM)

Raman spectra of BaTiO3 and KNbO3 ; a) below the ferroelectric transition ; b) above the transition.

References

[I] FONTANA (M. P.) and LAMBERT (M.), Solid State [3] DIDOMENICO (M.), WEMPLE Jr (S. H.), PORTO (S. P. S.) Comm. (to be published). and BAUMAN (R. P.), Phys. Rev., 1968, 174, 522.

[2] RIMAI (L.) and PARSONS (J. L.), Solid State Comm., [4] LAMBERT (M.) and COMES (R.), Solid State Comm., 1967, 5, 381 and also RIMAI (L.) and PARSONS 1969, 7, 305.

( J . L.), Phys. Rev., 1968, 168, 623.

(*) Laboratoire associe au C. N. R. S.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972213