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.
16 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.
Abstract: 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.
11 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.
Abstract: Graphical abstract: - Highlights: • Mechanism driving polarization in MgFe{sub 2}O{sub 4} is the Maxwell–Wagner polarization. • But Raman studies confirm the existence of local P4{sub 1}22/P4{sub 3}22 symmetry in MgFe{sub 2}O{sub 4}. • Ba{sup 2+} substitution increases ferroelectric ordering, ΔT{sub m} span, and masks electronic contribution. - Abstract: Using the molten salt method, pristine and Ba{sup 2+} substituted MgFe{sub 2}O{sub 4} are prepared. The relaxor-like behaviour 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. The paper further analyses the origin of polarization using Maxwell–Wagner fit and Nyquist plot. This work suggests a possible way to increase the relaxor-like ferroelectric ordering, larger span of relaxation temperature (ΔT{sub m}) and the effective masking of electronic contribution by the substitution of Ba{sup 2+} ion.
7 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.
Abstract: X-ray photoemission spectroscopy (XPS) measurements of double perovskite oxides, Ba 2 GdTaO 6 and Sr 2 GdTaO 6 are performed in the energy window of 0–1300 eV. Density functional theory calculations are initiated with the Vienna ab initio Simulation Package to understand the electronic structure of the systems. The calculated DOS has been compared with the experimental valence band XPS spectra. It has been observed that the Ta-5 d and O-2 p states are hybridized in the valence band. The chemical shifts of these compounds suggest a mixed ionic and covalent character of the bonds, which has been used to explain the electrical conduction mechanism of the systems. The calculated ratio of the spin-orbit interaction energy for Ba 3 d and 4 d states matches well with the observed experimental results.
6 citations
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TL;DR: In this paper, it was shown that the degree of order in the B site Sc3+, Ta5+ cations can be controlled by suitable thermal annealing.
Abstract: In Pb(Sc0.5Ta0.5)O3 it has been shown that the degree of order in the B‐site Sc3+, Ta5+ cations can be controlled by suitable thermal annealing. For samples which have been well‐ordered by long annealing, dielectric measurements on single crystals show a normal first‐order ferroelectric phase change at 13 °C and a maximum low‐temperature spontaneous polarization of 23.0 μc/cm2. With increasing disorder, the crystals begin to exhibit the classical diffuse phase transition of a ferroelectric relaxor, with a broad Curie range and strong low‐frequency dielectric dispersion in the transition range. X‐ray diffraction measurements of the size of the ordered microregions suggest that ordering proceeds by different mechanisms in single‐crystal versus ceramic samples, though the resulting effects upon the dielectric behavior are very similar.
742 citations
TL;DR: In this paper, the perovskite structure of the relaxor PbMg1/3Nb2/3O3 (PMN) was studied using X-ray and neutron powder diffraction data.
Abstract: The perovskite structure of the relaxor PbMg1/3Nb2/3O3 (PMN) is studied using X-ray and neutron powder diffraction data. The static diffuse scattering (SDS) observed in the diffraction patterns at low temperatures is interpreted using a two-phase Rietveld analysis. The structural model is based on a long-range structure with an average cubic symmetry, and a short-range order due to atomic shifts involved by the formation of polar regions. The two-phase model provides a good improvement in reliability factors. The correlation length and the coexistence of different phases at low temperatures are discussed.
328 citations
TL;DR: In this paper, a correlation between the nanoscale B-site order and relaxor on glassy ferroelectric behavior is found in these lead perovskites, and a hypothesis is suggested which relates 0-3 polar connectivity to order-disorder connectivity.
Abstract: From transmission electron microscopy studies on several complex lead perovskite compounds Pb(B'B'')O3, and their solid solutions a classification can be obtained based on B-cation order. This classification divides the complex lead perovskites into three subgroups; random occupation or disordered, nanoscale or short coherent long-range order and long coherent long-range order of B-site cations. A correlation between the nanoscale B-site order and relaxor on glassy ferroelectric behavior is found in these lead perovskites. An hypothesis is suggested which relates 0-3 polar connectivity to 0-3 order-disorder connectivity. This hypothesis is discussed with relation to present theories [G. A. Smolenskii: J. Phys. Soc. Jpn. (1970) Suppl., p. 26, L. E. Cross: Ferroelectrics 76 (1987) 241, T. L. Renieke and K. L. Ngai: Solid State Commun. 18 (1973) 1543] and reported experimental results of the perovskite relaxor ferroelectrics.
308 citations
TL;DR: In this paper, a classification of complex lead perovskites is presented based on the relative scale of long-range cation order, and the implications of Cation order in relation to relaxor and normal ferroelectric behavior are discussed.
Abstract: From a number of studies on ferroelectric and related materials based on complex lead perovskites [Pb(Bx′B1−x″)O3], it is apparent that the B-site cation order influences the crystallography, phase transitions, and other physical properties. A classification of complex lead perovskites is presented based on the relative scale of long-range cation order. In particular, we discuss the implications of cation order in relation to relaxor and normal ferroelectric behavior.
290 citations
TL;DR: In this article, a zero-field spontaneous relaxor-ferroelectric transition is reported in Pb(Sc 0.5Ta0.5)O3 (PST), with and without defects.
Abstract: A zero-field spontaneous relaxor-ferroelectric transition is reported in Pb(Sc0.5Ta0.5)O3 (PST). This behavior is different from that of other relaxors, where such transitions occur only under the field. A highly disordered PST that has the wide relaxation spectrum typical of relaxors is shown to transform spontaneously into a macroscopic ferroelectric state. Introduction of defects (lead vacancies) into the material impedes the transition resulting in the usual relaxor behavior. Dielectric properties of PST, with and without defects, are analyzed. For the interpretation of the observed properties, a model invoking an additional nonpolar phase is proposed. This model does not imply a freezing in the system. At the low-frequency limit, it is possible to account for the Vogel-Fulcher (VF) law for the temperature of the maximum of the dielectric constant, using only the commonly accepted assumption of an exponentially wide relaxation time spectrum that shrinks on heating. The presented approach interprets the observed proximity between the ferroelectric phase transition temperature and that of the freezing temperature obtained from the VF relation.
264 citations