Electrical and structural characteristics of lanthanum-doped barium titanate ceramics
17 Nov 1999-Journal of Applied Physics (American Institute of Physics)-Vol. 86, Iss: 11, pp 6355-6366
TL;DR: The single phase La-doped BaTiO3 with the formula Ba 1−xLaxTi1−x/4O3: 0.20 was prepared by solid state reaction of oxide mixtures at 1350°C, 3 days, in O2.
Abstract: Single phase La-doped BaTiO3 with the formula Ba1−xLaxTi1−x/4O3: 0⩽x⩽0.20 was prepared by solid state reaction of oxide mixtures at 1350 °C, 3 days, in O2. The tetragonal distortion in undoped BaTiO3 decreased with x and samples were cubic for x⩾0.05. Both the tetragonal/cubic and orthorhombic/tetragonal transition temperatures decreased with x, but at different rates, and appeared to coalesce at x∼0.08. The value of the permittivity maximum at the tetragonal/cubic phase transition in ceramic samples increased from ∼10 000 for x=0 at 130 °C to ∼25 000 for x=0.06 at ∼−9 °C. At larger x, the permittivity maximum broadened, showed “relaxor”-type frequency dependent permittivity characteristics and continued to move to lower temperatures. Samples fired in O2 were insulating and showed no signs of donor doping whereas air-fired samples were semiconducting, attributable to oxygen loss.
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TL;DR: In this article, the electrical properties of two single phase, lanthanum-doped BaTiO3 compositions, x= 0.03 and x = 0.20, were investigated by impedance spectroscopy after heat treatment in oxygen, argon, and air at 1350°C.
Abstract: The electrical properties of two single-phase, lanthanum-doped BaTiO3 compositions, x= 0.03 and x= 0.20, in Ba1–xLaxTi1–x/4O3 were investigated by impedance spectroscopy after heat treatment in oxygen, argon, and air at 1350°C. Samples heated in oxygen were electrically insulating, whereas those heated in argon lost oxygen and were semiconducting at room temperature, irrespective of x. Samples heated in air showed intermediate electrical properties and also were electrically inhomogeneous; the two compositions showed different electrical behaviors, and a model for each, based on oxygen nonstoichiometry within the ceramics, is proposed. Oxygen deficiency in samples sintered in air was avoided by heating at 1200°C, instead of 1350°C. Alternatively, oxygen lost from ceramics heated in air at 1350°C was regained by postannealing in oxygen at 1350°C.
266 citations
TL;DR: In this paper, a review of the origins of high permittivity in two groups of materials, La-doped BaTiO3 and a new barrier layer capacitor material, CaCu3Ti4O12, is given.
Abstract: A review is given of the origins of high permittivity in two groups of materials, La-doped BaTiO3 and a new barrier layer capacitor material, CaCu3Ti4O12. Factors that influence permittivity include: dopant, doping mechanism, processing conditions and grain size. La-doped BaTiO3 has high permittivity due to its ferroelectric nature at low temperatures and a novel doping mechanism: A-site substitution linked to the creation of B-site vacancies for charge compensation. Permittivities of 25,000 have been achieved, which can be increased further to ∼36,000 by additional doping with Zr. The value of impedance spectroscopy to characterize materials that have heterogeneous electrical microstructures is illustrated with the example of CaCu3Ti4O12; the high permittivity is not a bulk effect, as widely stated in the literature, but is a thin layer effect typical of a barrier layer capacitor. By attention to processing conditions to achieve large grain sizes, effective permittivities as high as 300,000 have been obtained.
244 citations
TL;DR: In this paper, the presence of Fe2+, detrimental to the ferroelectric and magnetic performance, was evaluated by x-ray photoelectron spectroscopy, showing no structural differences, uniformly distributed grains, a ferro-paraelectric transition temperature at 110°C and a normal diffuse phase transition (nonrelaxor behavior).
Abstract: With the purpose of fabricating ceramics where ferroelectric and magnetic order coexist, ceramics of Pb(Fe1∕2Nb1∕2)O3 have been prepared using the traditional ceramic method following three different routes. The first is a direct via starting from oxide reagents and the other two use different kinds of FeNbO4 precursors with either monoclinic or orthorhombic structures. Crystallographic and surface morphological studies were carried out by the powder x-ray diffraction and scanning microscopy techniques. The presence of Fe2+, detrimental to the ferroelectric and magnetic performance, was evaluated by x-ray photoelectron spectroscopy. The samples showed no structural differences, uniformly distributed grains, a ferro-paraelectric transition temperature at 110°C and a normal diffuse phase transition (nonrelaxor behavior). Differences in the degree of diffuseness, densities and grain size were observed depending on the kind of precursor. Measurements of dc and ac electrical resistivity, dielectric constant an...
229 citations
TL;DR: In this article, rare-earth ions with various ionic radii enter the unit cell to substitute for A-site Ba2+ ions and inhibit the grain growth in (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 (Ln=La,Sm,Eu,Dy,Y) ceramics.
Abstract: Based on the Ti-vacancy defect compensation model, (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 (Ln=La,Sm,Eu,Dy,Y) ceramics have been fabricated via the conventional solid-state reaction method. The microstructures, dielectric properties, and ferroelectric relaxor behavior of (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 ceramics have been investigated. The results indicate that rare-earth ions with various ionic radii enter the unit cell to substitute for A-site Ba2+ ions and inhibit the grain growth. The typical ferroelectric relaxor behavior is induced due to the rare-earth ions substitution. The diffuseness of the phase transition and the degree of ferroelectric relaxor behavior are enhanced, the TC is remarkably shifted to lower temperature, and the tunability is suppressed with the increase of x value and substituted ionic radius for (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 (x=0.005–0.04, Ln=La,Sm,Eu,Dy,Y) ceramics. Tunable ferroelectric materials with moderate dielectric constant and low dielectric loss can be obtained by manipulating the doping am...
209 citations
TL;DR: Recent advances in the synthesis of high-quality BaTiO3 NCs via a variety of chemical approaches including organometallic, solvothermal/hydrothermal, templating, molten salt, and sol-gel methods are highlighted.
Abstract: The current trend in the miniaturization of electronic devices has driven the investigation into many nanostructured materials. The ferroelectric material barium titanate (BaTiO3) has garnered considerable attention over the past decade owing to its excellent dielectric and ferroelectric properties. This has led to significant progress in synthetic techniques that yield high quality BaTiO3 nanocrystals (NCs) with well-defined morphologies (e.g., nanoparticles, nanorods, nanocubes and nanowires) and controlled crystal phases (e.g., cubic, tetragonal and multi-phase). The ability to produce nanoscale BaTiO3 with controlled properties enables theoretical and experimental studies on the intriguing yet complex dielectric properties of individual BaTiO3 NCs as well as BaTiO3/polymer nanocomposites. Compared with polymer-free individual BaTiO3 NCs, BaTiO3/polymer nanocomposites possess several advantages. The polymeric component enables simple solution processibility, high breakdown strength and light weight for device scalability. The BaTiO3 component enables a high dielectric constant. In this review, we highlight recent advances in the synthesis of high-quality BaTiO3 NCs via a variety of chemical approaches including organometallic, solvothermal/hydrothermal, templating, molten salt, and sol-gel methods. We also summarize the dielectric and ferroelectric properties of individual BaTiO3 NCs and devices based on BaTiO3 NCs via theoretical modeling and experimental piezoresponse force microscopy (PFM) studies. In addition, viable synthetic strategies for novel BaTiO3/polymer nanocomposites and their structure-composition-performance relationship are discussed. Lastly, a perspective on the future direction of nanostructured BaTiO3-based materials is presented.
204 citations
References
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TL;DR: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations as mentioned in this paper.
Abstract: The effective ionic radii of Shannon & Prewitt [Acta Cryst. (1969), B25, 925-945] are revised to include more unusual oxidation states and coordinations. Revisions are based on new structural data, empirical bond strength-bond length relationships, and plots of (1) radii vs volume, (2) radii vs coordination number, and (3) radii vs oxidation state. Factors which affect radii additivity are polyhedral distortion, partial occupancy of cation sites, covalence, and metallic character. Mean Nb5+-O and Mo6+-O octahedral distances are linearly dependent on distortion. A decrease in cation occupancy increases mean Li+-O, Na+-O, and Ag+-O distances in a predictable manner. Covalence strongly shortens Fe2+-X, Co2+-X, Ni2+-X, Mn2+-X, Cu+-X, Ag+-X, and M-H- bonds as the electronegativity of X or M decreases. Smaller effects are seen for Zn2+-X, Cd2+-X, In2+-X, pb2+-X, and TI+-X. Bonds with delocalized electrons and therefore metallic character, e.g. Sm-S, V-S, and Re-O, are significantly shorter than similar bonds with localized electrons.
51,997 citations
Book•
06 Oct 1977
TL;DR: In this paper, the theory of ferroelectricity in terms of soft modes and lattice dynamics is developed and modern techniques of measurement, including X-ray, optic, and neutron scattering, infra-red absorption, and magnetic resonance.
Abstract: The book develops the modern theory of ferroelectricity in terms of soft modes and lattice dynamics and also describes modern techniques of measurement, including X-ray, optic, and neutron scattering, infra-red absorption, and magnetic resonance. It includes a discussion of the related phenomena of antiferroelectricity, pyroelectricity, and ferroelasticity and seconds on domains, thin films, ceramics, and polymers, leading on to a comprehensive survey of potential and actual device capabilities for pyroelectric detection, memories, display, and modulation. It should provide an authoritative account for those engaged in research or graduate ferroelectric or pyroelectric devices.
4,931 citations
TL;DR: In this paper, the authors used impedance spectroscopy for unravelling the complexities of such materials, which functions by utilizing the different frequency dependences of the constituent components for their separation, and showed that electrical inhomogeneities in ceramic electrolytes, electrode/electrolyte interfaces, surface layers on glasses, ferroelectricity, positive temperature coefficient of resistance behavior and even ferrimagnetism can all be probed, successfully.
Abstract: Electroceramics are advanced materials whose properties and applications depend on the close control of structure, composition, ceramic texture, dopants and dopant (or defect) distribution. Impedance spectroscopy is a powerful technique for unravelling the complexities of such materials, which functions by utilizing the different frequency dependences of the constituent components for their separation. Thus, electrical inhomogeneities in ceramic electrolytes, electrode/electrolyte interfaces, surface layers on glasses, ferroelectricity, positive temperature coefficient of resistance behavior and even ferrimagnetism can all be probed, successfully, using this technique.
2,004 citations
TL;DR: In this article, the ferroelectric Curie point theory was extended with a ferro-electric effect to the case of semiconducting BaTiO 3 and showed an enormous increase in resistivity above the Curie points.
Abstract: Semiconducting BaTiO 3 can be prepared by substituting small amounts of ions of higher valency for Ba or Ti ions. At higher concentrations the foreign ions are compensated by metal ion vacancies. Polycrystalline samples prepared in air show an enormous increase in resistivity above the ferro-electric Curie point. According to Heywang this is a result of surface barriers which are very sensitive to the value of dielectric constant. This theory is extended with a ferro-electric effect.
577 citations
TL;DR: Very high and broad Curie maxima are observed in ceramic Ba(Ti1-yZry)O3 mixed crystals, which are often used for the preparation of ceramic dielectrics as discussed by the authors.
Abstract: Very high and broad Curie maxima are observed in ceramic Ba(Ti1-yZry)O3 mixed crystals, which are often used for the preparation of ceramic dielectrics The ferroelectric-to-paraelectric phase transition of ceramic Ba(Ti1-yZry)O3 was studied using dielectric measurements, quantitative DTA, X-ray diffraction, and determination of the remanent polarization At higher Zr concentrations, it was found that ferroelectric and paraelectric phases coexist in a wide temperature region Up toy =016, the phase transition remains first order The diffuse character is promoted by the small energy difference between the ferroelectric and paraelectric phases appearing at higher Zr content It can be best described by a normal distribution of Curie temperatures using the phenome-nological theory of Devonshire and the Newton-Raphson mathematical approximation
566 citations