The lead-based complex perovskite Pb(Yb0.5Ta0.5)O3, exhibiting long-range B-site cation ordering has been studied by Raman spectroscopy. The investigation has been performed as a function of temperature ranging from 250 K to a lower temperature 10 K in the spectral range 1020-20 cm-1. The spectra are analyzed through the characteristic parameters: peak position and line width of phonon modes. Significant decrease in the asymmetric phonon line broadening with noticeable shift of the peak positions and appearance of new modes in the Raman spectra at low temperature have been observed. The local distortion in the lattice has been enhanced substantially at low temperature. The splitting of the F2g modes suggests that the orthorhombic phase is stabilized at low temperature. The two F2g modes (60 and 518 cm-1) show soft mode behavior. © 2007 Elsevier B.V. All rights reserved.

Venkatachalam Subramanian

Department Of Physics

ANTIFERROELECTRIC MATERIALS

Ceramic materials

Low temperature operations

Perovskite

Raman spectroscopy

LEAD-BASED COMPLEX PEROVSKITES

PHONON MODES

SPECTRAL RANGES

Crystal Structure

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IIT Madras

Vibrational Spectroscopy

Raman spectra of a complex perovskite system (Pb1−xBax)(Yb0.5Ta0.5)O3, x = 0.0; 0.1 and 0.2 have been studied at low temperature in the range of 10-250 K. The fascination of the system is that it undergoes a crossover from a highly ordered antiferroelectric (x = 0.0) to ferroelectric (x = 0.1) to disordered relaxor ferroelectric (x = 0.2). The nature of splitting that prevails in F2g (≈60 cm−1), F1g (≈538 cm−1) modes and their gradual merging and disappearance with x indicates an orthorhombic symmetry for x = 0.0 and a pseudo-cubic structure for x = 0.2. The mode at 420 cm−1 suggests the existence of rhombohedral distortion in all the compositions. The soft mode behavior of the F2g modes has been analyzed by fitting the data with the power law ωs = A(TC − T)β. © The Author(s).

Fulltext

Journal of Advanced Dielectrics

Low temperature Raman scattering study of barium doped lead ytterbium tantalate ceramics

A comparative study of the properties of two highly ordered lead based complex perovskites Pb(Y b1/2Ta1/2)O3 and Pb(Y b1/2Nb1/2)O3 has been carried out through x-ray diffraction, dielectric and Raman scattering measurements. These two compounds differ significantly in their structure, dielectric response and phonon vibration although the ionic radii and valencies are same for Ta and Nb. The room temperature x-ray diffraction pattern and Raman spectra show that the symmetry of lead ytterbium tantalate is lower than that of lead ytterbium niobate. The Raman spectra of Pb(Y b1/2Ta1/2)O3 also indicates the presence of local distortion in the lattice which may be one of the factors responsible for the existence of a secondary transition. © 2006 Elsevier Ltd. All rights reserved.

Solid State Communications

A comparative study of dielectric and Raman spectroscopy of Pb(Y b1/2Ta1/2)O3 and Pb(Y b1/2Nb1/2)O3

The ordered complex perovskite lead ytterbium tantalate undergoes a change in structural and dielectric properties as the concentration of Ba increases. The x-ray diffraction patterns show a decrease in the intensity of superlattice reflections due to Pb-antiparallel displacement as well as to B -site ordering. The structure approaches cubic symmetry with increase in Ba content. The dielectric response shows a gradual change from antiferroelectric to relaxor ferroelectric and then the relaxor behavior starts decreasing as Ba content increases. Raman-scattering study of the samples shows that some of the modes seen for Pb (Yb0.5 Ta0.5) O3 disappear and an additional mode appears at 420 cm-1 with increase in Ba concentration. A qualitative analysis of various modes suggests that the substitution of Ba for Pb leads to a decrease in the degree of ordering and occurrence of local distortions in the lattice as evidenced by the broadening of certain peaks in the Raman spectra. © 2005 American Institute of Physics.

Journal of Applied Physics

Raman spectroscopic study of (Pb 1-x Ba x) (Yb 1/2 Ta 1/2) O 3 ceramics

The structure and low frequency dielectric properties of Pb 1 - x Ba x (Yb 1/2 Ta 1/2 )O 3 solid solutions with x=0.00, 0.10, 0.15, 0.20 and 0.30 have been investigated usingX-raydiffraction and dielectric constant measurements. As Ba 2+ concentration increases beyond x=0.15, the crystal structure changes from monoclinic to pseudocubic at room temperature. The sharp paraelectric- antiferroelectric phase occuring in pure Pb(Yb 1/2 Ta 1/2 )O 3 , remarkably decreases and simultaneously the weak ferroelectric phase gets enhanced with increase in x. The maximum value of the dielectric constant (K max ) varies with x, showing a peak value at x=0.20 whereas dielectric maximum temperature (T max ) continuously decreases with increase in x. The diffuseness exponent and degree of diffuseness are calculated for x=0.15, 0.20 and 0.30 by fitting the dielectric data to the modified Curie-Weiss law and the values indicate that the compounds exhibit diffuse phase transition. The paper also discusses the influence of calcination and sintering temperature on the dielectric properties of pure Pb(Yb 1/2 Ta 1/2 )O 3.

Ferroelectrics

Dielectric study of the phase transitions in Pb1-xBa x(Yb1/2Ta1/2)O3 ceramics

Ceramics International

Soft optical phonon in Ba-doped Sr2Nb2O7 ceramics

Journal of Molecular Structure

Local phenomena in relaxor-ferroelectric PbSc0.5B″0.5O3 (B″=Nb, Ta) studied by Raman spectroscopy

Temperature dependence Raman spectroscopic studies of Pb(Yb0.5Ta0.5)O3

Journal	Vibrational Spectroscopy
ISSN	09242031
Open Access	No