Raman spectra of Cs₂CdBr₄single crystals

Abstract

Polarized Raman spectra of Cs2CdBr4 single crystals were measured in the frequency range 0-350 cm-' at 100-290 K. The spectra are analysed within the framework of the Landau theory of stmctural phase transitions; the analysis indicates that the transition to the triclinic phase with P i symmetry is accompanied by unit-cell volume multiplication.

Soft-mode-driven lattice instabilities in Cs2HgCl4crystal: phenomenological treatment and far-infrared spectroscopy of the structurally modulated phases

“…Thirty one IR-active optic phonon modes are classified in high temperature phase I (space group Pnma) according to irreducible representations in the -point as follows [37]:…”

Far-infrared spectroscopy investigation of commensurate and incommensurate Cs2CdBr4crystal

“…For the mode classification (3), we have taken into account external and internal vibrations together, because all of the observed modes lie in the low-frequency region below 230 cm −1 due to the large mass of structural units of this crystal. According to references [11,[13][14][15], the CdBr 2− 4 groups have very low-frequency bending vibrations in the regions 49-53 cm −1 (ν 2 ) and 61-75 cm −1 (ν 4 ) and stretching vibrations in the regions 161-166 cm −1 (ν 1 ) and 177-181 cm −1 (ν 3 ). Analogously to the case for other representatives of the A 2 BX 4 family (e.g.…”

“…According to the factor-group analysis, in the high-temperature phase I [11] the 84 vibrational modes of Cs 2 CdBr 4 crystal at the Brillouin zone centre are classified in terms of irreducible representations as follows:…”

“…The amplitudon should be active in the totally symmetric A g spectra and the phason in the A g , B 1g and B 2g spectra for propagation along the x-, y-and z-axes, respectively [17,18]. However, no significant changes in the Raman spectra were seen at the I-II transition, and neither of these modes were detected, from which it was concluded that the transition is of the order-disorder type [10,11].…”

“…Although the acoustic properties and optical birefringence were studied in detail as functions of temperature and hydrostatic pressure [8,9], and recently the temperature dependences of Raman [10,11] and Brillouin [9] spectra were reported, infrared (IR) data and other lattice dynamics studies are lacking for Cs 2 CdBr 4 .…”