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 article, the dependence of the lattice and charge excitations in compounds on doping and temperature has been studied using inelastic light scattering to analyze the properties of the materials.
Abstract: We employ inelastic light scattering to study the dependence of the lattice and charge excitations in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ compounds on doping and temperature. The phonons reveal strong local lattice distortions in the paramagnetic state, which gradually vanish below the ferromagnetic transition. We identify charge excitations in the metallic state. They exhibit a dependence on the doping level and symmetry selection rules typical for a plasmonlike excitation. Their energy scale of 100 meV requires a low-carrier-density component of the plasma outlining the importance of electronic interactions in ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}.$
37 citations
TL;DR: The high-temperature phase of Pb(Mg 1/2W1/2)O3, PbZrO3 and PbYb1/1Nb 1/1/3 O3 were studied in this paper, where a diffraction pattern detrimental to the crystal structure determination was presented.
Abstract: The high-temperature phase of Pb(Mg1/2W1/2)O3, Pb(Co1/2W1/2)O3 and Pb(Yb1/2Nb1/2)O3 belongs to the space group Fm3m with the unit cell size of 2ac×2ac×2ac where ac is the lattice parameter of the cubic perovskite unit cell. All these complex perovskites undergo phase transition into low-temperature orthorhombic structures with a shrunken lattice parameter along the c-axis and the approximate √2a lattice parameters along the a0- and b0-axes, which are, respectively, parallel to the prototype [110]c and [10]c directions. The symmetry along the b0-axis of the perovskites is most prominently distinguished from that along the a0-axis in that the low-temperature structure is modulated in the b0-axis direction. For Pb(Mg1/2W1/2)O3, a diffraction pattern detrimental to the crystal structure determination well below the Curie temperature is presented. At the same time, the crystal structures of lock-in phases of the aforementioned oxides are compared with the well-known structure of PbZrO3.
35 citations
TL;DR: In this paper, a cubic-tetragonal transition in some ordered Ba(B′ 1 2 B″ 1 2 )O 3 perovskite ceramics was shown to have a soft phonon mode in the tetragonal phase.
34 citations
TL;DR: In this paper, planewave pseudopotential calculations of formation energies (ΔE) were performed for ordered supercells in the perovskite based system (1−X)·PbNbO3−(X) ·PbMgO3, including six different supercells at the X=1/3 composition [Pb(Mg 1/3 Nb 2/3 )O 3 ; PMN].
28 citations
TL;DR: In this paper, the authors investigated the properties of the complex perovskite in terms of Raman scattering from 10 K up to 956 K and showed the existence of an additional intermediate phase I between the low-temperature antiferroelectric phase A and the hightemperature paraelectric phase P.
Abstract: The complex perovskite , exhibiting a long-range B-site cation ordering, has been investigated by Raman scattering from 10 K up to 956 K. The Raman results are systematically treated, and analysed through the characteristic parameters of phonon peaks. The existence of an additional intermediate phase I between the low-temperature antiferroelectric phase A and the high-temperature paraelectric phase P has been demonstrated (, ). These results were compared with dielectric measurements. The disappearance of the first-order Raman structures near 1000 K in the paraelectric phase is discussed in terms of dynamic disorder in the Pb and O sublattices.
21 citations