Soft Modes and Local Structural Transitions in Pb-free Ba(Ti0.8Zr0.2)O3-x(Ba0.7Ca0.3)TiO3 (x = 0.5): Pressure- and Temperature-dependent Raman Studies
TL;DR: In this article, the Raman studies of a new lead-free relaxor ferroelectrics, Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCTZO), are compared with the eigenmodes of BTO calculated by using an ab-initio quantum-mechanical frozen-phonon method.
Abstract: We report our Raman studies of a new lead-free relaxor ferroelectrics, Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCTZO). The Raman modes of BCTZO are compared with those of BaTi0.8Zr0.2O3 (BTZO), and BaTiO3 (BTO). Also, they are compared with the eigenmodes of BTO calculated by using an ab-initio quantum-mechanical frozen-phonon method. The sharp mode at 321 cm-1 of BTO, reported as a coupled mode showing an interference effect, becomes progressively broader in BTZO and BCTZO. This behavior, together with a broadening of the 527-cm-1 mode, suggests that the mode-coupling is weakened in BTZO and BCTZO. The structural transitions of BCTZO were investigated as functions of pressure at pressures below 20 GPa and of temperature at temperatures below 600 K. Three characteristic pressure-induced transitions, on each at 2.5, 5.0, and 13.0 GPa, were found. The transitions are suggested by the drastic changes in phonon modes (two softening modes, one each at ~ 300 and ~ 530 cm-1) and by the transformation of the intensity profile. A temperature-induced transition was found at a Curie temperature of ~ 380 K, where the average structure changes from tetragonal to cubic. It is accompanied by a softening mode at ~ 530 cm-1. The phonon spectrum of BCTZO suggests that its local environment is close to that of BTZO. However, the characteristic pressures of BCTZO are close to those of BTO. The sequence of pressure-induced transitions in both BCTZO and BTZO illustrate rich interplay between the long-range averaged structure and the short-range local order such that four distinguishable phases are suggested: tetragonal, locally ordered but compensated cubic, disordered cubic, and ideal cubic. We found that the critical pressures are plausibly related to the average crystal lattice.
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TL;DR: In this article, a single-crystal epitaxial thin films of a high entropy perovskite oxide are synthesized using Pulsed laser deposition to grow the configurationally disordered $AB{\mathrm{O}}_{3}$ pervskite on MgO substrates.
Abstract: Examples of single-crystal epitaxial thin films of a high entropy perovskite oxide are synthesized. Pulsed laser deposition is used to grow the configurationally disordered $AB{\mathrm{O}}_{3}$ perovskite $\mathrm{Ba}(\mathrm{Z}{\mathrm{r}}_{0.2}\mathrm{S}{\mathrm{n}}_{0.2}\mathrm{T}{\mathrm{i}}_{0.2}\mathrm{H}{\mathrm{f}}_{0.2}\mathrm{N}{\mathrm{b}}_{0.2}){\mathrm{O}}_{3}$ epitaxially on $\mathrm{SrTi}{\mathrm{O}}_{3}$ and MgO substrates. X-ray diffraction and scanning transmission electron microscopy demonstrate that the films are single phase with excellent crystallinity and atomically abrupt interfaces to the underlying substrates. Atomically resolved electron-energy-loss spectroscopy mapping shows a uniform and random distribution of all $B$-site cations. The ability to stabilize perovskites with this level of configurational disorder offers new possibilities for designing materials from a much broader combinatorial cation pallet while providing a fresh avenue for fundamental studies in strongly correlated quantum materials where local disorder can play a critical role in determining macroscopic properties.
112 citations
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TL;DR: In this paper, the first examples of single crystal epitaxial thin films of a high entropy perovskite oxide are synthesized using Pulsed Laser Deposition (PLD) and X-ray diffraction and scanning transmission electron microscopy demonstrate that the films are single phase with excellent crystallinity and atomically abrupt interfaces to the underlying substrates.
Abstract: The first examples of single crystal epitaxial thin films of a high entropy perovskite oxide are synthesized. Pulsed laser deposition is used to grow the configurationally disordered ABO3 perovskite, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, epitaxially on SrTiO3 and MgO substrates. X-ray diffraction and scanning transmission electron microscopy demonstrate that the films are single phase with excellent crystallinity and atomically abrupt interfaces to the underlying substrates. Atomically-resolved electron energy loss spectroscopy mapping shows a uniform and random distribution of all B-site cations. The ability to stabilize perovskites with this level of configurational disorder offers new possibilities for designing materials from a much broader combinatorial cation pallet while providing a fresh avenue for fundamental studies in strongly correlated quantum materials where local disorder can play a critical role in determining macroscopic properties.
54 citations
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TL;DR: In this paper, the microstructure, phase composition, and local structure were investigated by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy, and the incorporation of Bi3+ into the B-site of the perovskite BCZT structure.
Abstract: Lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) piezoceramics with Bi2O3 additive were synthesized using solid-state ceramic processing. Various amounts of Bi2O3 (0.05, 0.1, 0.5, and 1.0 mol%) were added after calcination, milled, compacted, and sintered with no compensation at A- or B-sites. Addition of up to 0.5 mol% Bi2O3 was found to greatly enhance the densification and increase the piezoelectric properties, while higher amounts decreased the grain size and induced relaxor-like electrical behavior, obeying the Vogel-Fulcher model. The highest properties were obtained for the BCZT with 0.1 mol% Bi2O3 sintered at 1350 °C: d33 = 325 pC/m, d33* = 509 pm/V (at 3 kV/mm), kp = 0.42, and Pr = 10.4 μC/cm2. The microstructure, phase composition, and local structure were investigated by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The appearance of the A1g vibration mode in the Raman spectra and the shift of diffraction peaks to lower 2θ values indicate the incorporation of Bi3+ into the B-site of the perovskite BCZT structure.
43 citations
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TL;DR: In this paper, the photoferroic Cr3+-doped BaTiO3 nanoparticles with nominal Cr content ranging from 2-8 mol% were synthesized by a microwave-assisted hydrothermal method.
Abstract: We report on the synthesis of photoferroic Cr3+-doped BaTiO3 nanoparticles with nominal Cr content ranging from 2–8 mol% by a microwave-assisted hydrothermal method. The absorption properties of the doped systems are significantly enhanced due to the d–d band transition of Cr3+/4+. The structural properties of the materials are examined on the basis of lattice distortions given by the tolerance factor and microstrain. Raman scattering provides complementary information on the lattice vibrations indicating a softening of the longitudinal optic (LO) phonon mode located at 716 cm−1 with increasing Cr concentration. The charge transport properties investigated through electrochemical impedance spectroscopy (EIS) demonstrate that there is a reduction in the charge transfer resistance from 5.2 Ω to 4.3 Ω for the undoped and 4 mol% Cr3+-doped respectively, which favors the degradation kinetics. The photo-oxidation ability of the systems is evaluated by time evolution of photodegradation of methyl orange under standardized solar irradiation. The experimental results confirm that the best photocatalytic performance is achieved with the 4 mol% Cr3+-doped BaTiO3 nanoparticles, which is ∼2.7 times higher than for the undoped sample. Evidence of superoxide radical being the dominant active species is provided by in situ reactive oxide species (ROS) capture experiments.
39 citations
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TL;DR: In this article, an approach for reducing the sintering temperature and increasing the electromechanical strain response of (Ba, Ca, Zr, Ti)O3 piezoceramics by aliovalent doping with Ce is presented.
Abstract: Lead-free piezoceramics based on the (Ba, Ca)(Zr, Ti)O3 (BCZT) system exhibit excellent electromechanical properties for low-temperature actuation applications, but suffer from relatively high processing temperatures. Here we demonstrate an approach for the reduction of the sintering temperature and simultaneous increase of the electromechanical strain response of (Ba, Ca)(Zr, Ti)O3 piezoceramics by aliovalent doping with Ce. The samples were prepared by solid state synthesis and their crystallographic structure, dielectric, ferroelectric, and electromechanical properties were investigated. The highest d*33 value of 1189 pm/V was obtained for the sample with 0.05 mol% Ce, substituted on the A-site of the perovskite lattice. The results indicate a large potential of these materials for off-resonance piezoelectric actuators.
32 citations
References
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TL;DR: Ferroelectric ceramics have been the heart and soul of several multibillion dollar industries, ranging from high-dielectric-constant capacitors to later developments in piezoelectric transducers, positive temperature coefficient devices, and electrooptic light valves as mentioned in this paper.
Abstract: Ferroelectric ceramics were born in the early 1940s with the discovery of the phenomenon of ferroelectricity as the source of the unusually high dielectric constant in ceramic barium titanate capacitors. Since that time, they have been the heart and soul of several multibillion dollar industries, ranging from high-dielectric-constant capacitors to later developments in piezoelectric transducers, positive temperature coefficient devices, and electrooptic light valves. Materials based on two compositional systems, barium titanate and lead zirconate titanate, have dominated the field throughout their history. The more recent developments in the field of ferroelectric ceramics, such as medical ultrasonic composites, high-displacement piezoelectric actuators (Moonies, RAINBOWS), photostrictors, and thin and thick films for piezoelectric and integrated-circuit applications have served to keep the industry young amidst its growing maturity. Various ceramic formulations, their form (bulk, films), fabrication, function (properties), and future are described in relation to their ferroelectric nature and specific areas of application.
3,442 citations
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TL;DR: It is predicted that the single-crystal form of the MPB composition of the present system may reach a giant d(33) = 1500-2000 pC/N, which may provide a new recipe for designing highly piezoelectric materials (both Pb-free and P b-containing) by searching MPBs starting from a TCP.
Abstract: We report a non-Pb piezoelectric ceramic system Ba(Ti(0.8)Zr(0.2))O(3)-(Ba(0.7)Ca(0.3))TiO(3) which shows a surprisingly high piezoelectric coefficient of d(33) approximately 620 pC/N at optimal composition. Its phase diagram shows a morphotropic phase boundary (MPB) starting from a tricritical triple point of a cubic paraelectric phase (C), ferroelectric rhombohedral (R), and tetragonal (T) phases. The high piezoelectricity of the MPB compositions stems from the composition proximity of the MPB to the tricritical triple point, which leads to a nearly vanishing polarization anisotropy and thus facilitates polarization rotation between 001T and 111R states. We predict that the single-crystal form of the MPB composition of the present system may reach a giant d(33) = 1500-2000 pC/N. Our work may provide a new recipe for designing highly piezoelectric materials (both Pb-free and Pb-containing) by searching MPBs starting from a TCP.
2,197 citations
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TL;DR: In this article, the pressure dependence of the R1 ruby fluorescence line has been calibrated at 25°C against the compression of NaCl using the Decker equation of state for NaCl.
Abstract: The pressure dependence of the R1 ruby fluorescence line has been calibrated at 25 °C against the compression of NaCl. Pressures are determined using the Decker equation of state for NaCl. The dependence is linear to 195 kbar following the equation PNaCl=2.746(Δλ), where P is in kbar and Δλ in A. The uncertainty in the value of the slope, dp/dλ, expressed in terms of a 95% confidence interval is 2.746±0.014 kbar A−1. The coefficient of the quadratic term (Δλ)2 is not significantly different from zero; and the quadratic term makes indeed a negligible contribution to the fit. Taking into account the reported uncertainty associated with the Decker equation of state for NaCl, the value of the slope is 2.740±0.016 kbar A−1 within a 95% confidence interval.
1,681 citations
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TL;DR: The CRYSTAL program as discussed by the authors computes the electronic structure and properties of periodic systems (crystals, surfaces, polymers) within Hartree-Fock, Density Functional and various hybrid approximations.
Abstract: CRYSTAL [1] computes the electronic structure and properties of periodic systems (crystals, surfaces, polymers) within Hartree-Fock [2], Density Functional and various hybrid approximations. CRYSTAL was developed during nearly 30 years (since 1976) [3] by researchers of the Theoretical Chemistry Group in Torino (Italy), and the Computational Materials Science group in CLRC (Daresbury, UK), with important contributions from visiting researchers, as documented by the main authors list and the bibliography. The basic features of the program CRYSTAL are presented, with two examples of application in the field of crystallography [4, 5].
847 citations
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TL;DR: In this paper, an approach for computing all of these various response tensors in a unified and systematic fashion is presented for two materials, hexagonal ZnO and rhombohedral, at zero temperature.
Abstract: The methods of density-functional perturbation theory may be used to calculate various physical response properties of insulating crystals including elastic, dielectric, Born charge, and piezoelectric tensors. These and other important tensors may be defined as second derivatives of an appropriately defined energy functional with respect to atomic-displacement, electric-field, or strain perturbations, or as mixed derivatives with respect to two of these perturbations. The resulting tensor quantities tend to be coupled in complex ways in polar crystals, giving rise to a variety of variant definitions. For example, it is generally necessary to distinguish between elastic tensors defined under different electrostatic boundary conditions, and between dielectric tensors defined under different elastic boundary conditions. Here, we describe an approach for computing all of these various response tensors in a unified and systematic fashion. Applications are presented for two materials, hexagonal ZnO and rhombohedral $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_{3}$, at zero temperature.
649 citations