Dielectric and Raman studies of (BaxPb1−x)(Yb0.5Nb0.5)O3
TL;DR: In this article, Raman spectra of the solid solution series (BaxPb1−x)(Yb0.5Nb 0.5)O3 from x = 0.0 to 0.3 have been analyzed and a new mode at 420 cm−1 is observed for the compounds with Ba2+ substitution.
Abstract: Dielectric dispersion and Raman studies are carried out on the solid solution series (BaxPb1−x)(Yb0.5Nb0.5)O3 from x = 0.0 to 0.3. The x-ray diffraction analysis indicates that with the substitution of Ba2+, the intensity of the peaks corresponding to antiparallel displacement of Pb2+ decreases and the structure becomes cubic. The low frequency dielectric dispersion studies indicate that the series undergoes a transition from an antiferroelectric to a relaxor ferroelectric with variation of x. Raman spectra of the compositions indicate the presence of a greater number of modes for the compounds with cubic structure (). A new mode at 420 cm−1 is observed for the compounds with Ba2+ substitution. The intensity of this mode increases monotonically with increase in Ba2+ substitution and this has been attributed to the commencement of local distortion. This could be responsible for the appearance and increase in the diffuseness around Tmax, the temperature corresponding to .
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TL;DR: In this paper, a qualitative analysis of various modes suggests that 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.
Abstract: 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(Yb0.5Ta0.5)O3 disappear and an additional mode appears at 420cm−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.
20 citations
TL;DR: In this paper, a lead-free perovskite BaY 0.5 Nb 0.3 O 3 was prepared by conventional ceramic technique at 1375°C/7h in air atmosphere.
Abstract: Lead-free perovskite BaY 0.5 Nb 0.5 O 3 was prepared by conventional ceramic technique at 1375 °C/7 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were derived from the experimental results using FullProf software. XRD analysis of the compound indicated the formation of a single-phase cubic structure with the space group Pm3m. EDAX, X-ray mapping and SEM studies were carried to study the quality and purity of the compound. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were presented using the impedance data. Electric modulus studies supported the hopping type of conduction in BaY 0.5 Nb 0.5 O 3 . The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in BaY 0.5 Nb 0.5 O 3 . The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and apparent activation energy of the compound.
13 citations
TL;DR: A comparative study of the properties of two highly ordered lead based complex perovskites Pb(Y b1/2Ta1/ 2)O3 and Pb (Y b 1/2Nb 1 /2 )O3 has been carried out through x-ray diffraction, dielectric and Raman scattering measurements as mentioned in this paper.
12 citations
TL;DR: In this paper, pristine and Ba{sup 2+} substituted MgFe{sub 2}O{sub 4} are prepared and the relaxor-like behavior observed in the dielectric dispersion indicates the existence of B-site short-range ordering with the local P4{sub 1}22/P4{ sub 3}22 symmetry which is confirmed by the Raman spectroscopy.
9 citations
TL;DR: In this paper, a density functional theory calculation of double perovskite oxides was performed with the Vienna ab initio Simulation Package to understand the electronic structure of the systems.
6 citations
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TL;DR: In this paper, EXAFS data are presented to provide evidence that Pb is actually attracted to the larger B′ cations which are usually ferroelectrically inactive, leaving the smaller B″ cations relatively free of Pb-OB coupling.
129 citations
TL;DR: In this article, the phase transition in the relaxor ferroelectric lead scandium tantalate, Pb(Sc0.5Ta 0.5)O3, is investigated in both ordered and partly disordered (Sc, Ta disorder) modifications through the technique of hardmode Raman spectroscopy.
Abstract: The phase transition in the relaxor ferroelectric lead scandium tantalate, Pb(Sc0.5Ta0.5)O3, is investigated in both ordered and partly disordered (Sc, Ta disorder) modifications through the technique of hard-mode Raman spectroscopy. The vibrational modes for ordered para phase, ordered ferroelectric phase, disordered para phase and disordered ferroelectric phase are assigned to different representations of the respective groups (Fm3m (Z=2), R3m (Z=2), Pm3m (Z=1) and R3m (Z=1)) using the usual group-theoretical methods. The temperature evolution of the strong Raman band at 61cm-1 (hard mode) is investigated from 102 K to 873 K, for both phase transitions, namely ordered para to ordered ferro and disordered para to disordered ferro phases. The temperature variations of integrated intensity, full width at half maximum and square of the frequency of the 61cm-1 band are discussed in the light of phase transition mechanisms involved in relaxor ferroelectrics for both cases.
79 citations
TL;DR: In this paper, the multiband Raman spectra were measured on lead magnesium niobate (PMN) and lead titanate (PT) solid solutions at various temperatures.
Abstract: Precision Raman spectra have been measured on lead magnesium niobate (PMN)–lead titanate (PT) solid solution at various temperatures. The multiband Raman spectra are inconsistent with Pm3m symmetry but can be accommodated within a model of ordered nanodomains of rhombohedral symmetry. Raman band widths are large and nearly independent of temperature indicating a static structural disorder rather than a dynamic dipolar disorder. Abrupt changes in wave number and widths of certain bending modes at 200 K are interpreted as evidence for a reversible phase transition at this temperature. All of the spectroscopic properties are largely independent of the titanium concentration in the PMN–PT solid solutions.
74 citations
TL;DR: In this paper, the effect of small structural deviations on the atomic vibrations is analyzed by calculating the modes of structural units at various atomic positions, and it is shown that doubling the structural unit is always possible on a local scale of a few unit cells.
Abstract: Local structural arrangements and corresponding dynamical effects in relaxor ferroelectrics PbSc1/2Nb1/2O3 and PbSc1/2Ta1/2O3 were studied by Raman spectroscopy. Polarized Raman spectra of single crystals were measured at different temperatures in several scattering configurations. The peaks observed are assigned on the basis of normal-mode calculations. The effect of small structural deviations on the atomic vibrations is analysed by calculating the modes of structural units at various atomic positions. It is shown that doubling the structural unit is always possible on a local scale of a few unit cells. The presence of two Raman peaks originating from the F2u mode shows that electron-phonon coupling occurs in PbSc1/2B''1/2O3, thus leading to dynamical off-centre-symmetrical structural fluctuations. The structural perturbation consists of the non-coplanarity of Pb and O atoms in the planes perpendicular to the body diagonal and deviations of B cations from the centre of BO6 octahedra. The intensity ratio of the two peaks is sensitive to the degree of orientational ordering of the lone pairs of Pb atoms within the Pb-O planes, which is related to the degree of compositional B'/B'' ordering. The temperature dependence of the peaks arising from asymmetrical O-B-O bending, BO3 translation and Pb-localized modes shows that on cooling different structural changes are preferential in the two materials studied. In PbSc1/2Nb1/2O3 the lowering of the temperature favours the off-centre deviations of the B cations. In PbSc1/2Ta1/2O3 the temperature decrease stabilizes the non-coplanarity of the Pb and O atoms in the planes perpendicular to the body diagonal and enhances the correlation between the electronic lone pairs of Pb.
65 citations
TL;DR: In this article, the effect of A-site substitution on the B-site order of Pb(Mg1/3Nb2/3)O3 was studied by partial substitution at the A site by both donor La3+/Bi3+ and acceptor K+1.
Abstract: The control of the B-site order of Pb(Mg1/3Nb2/3)O3 was studied by the partial substitution at the A site by both donor La3+/Bi3+ and acceptor K+1. Different A-site cations and their concentrations were chosen to modify the chemical order at the B site. The Raman scattering results over a wide temperature range (−190–300 °C) confirm that the first order scattering is dominant in phonon bands resulting from both ordered regions and disordered matrix. The degree of the B-site order is estimated by the full width at half maximum of the phonon bands associated with the ordered regions, specifically, the highest frequency breath-type A1g mode of the BO6. It is concluded that the order is enhanced with the donor La3+/Bi3+ doping, while with the acceptor K+1 doping, the order is suppressed. The effect of A-site substitution on the B-site order has thus been elucidated.
62 citations