RAMAN-SPECTROSCOPIC STUDY OF FERROELASTIC PHASE TRANSITION IN LANTHANUM PENTAPHOSPHATES

1 January 1986

journal article
Published by Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences in Acta Physica Sinica

Vol. 35 (11) , 1521-1527
https://doi.org/10.7498/aps.35.1521

Abstract

The soft optic mode spectra of monoclinic I lanthanum pentaphosphates LnP5O14(Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb) are measured in the range of 20-300℃. The Ag-B2g and Ag-Ag soft modes in different LnP5O14 all soften to 20 cm-1 at ferroelastic transition temperature Tc. Another Bg-B3g soft mode softens to 38cm-1 at Tc. The coupling of Ag-B2gsoft mode with e5, plays an essential role in the phase trasition and the temperature dependence of soft-mode intensity can be described by means of the bilinear mode-coupling model. The increment of Tc from La to Tb in this system is owing to the lanthanum contraction.

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