Showing papers on "Tetragonal crystal system published in 2006"
TL;DR: In this article, the authors have processed high-quality films of VO2 by pulsed laser deposition, which were grown epitaxially on (0001) sapphire substrate via domain matching epitaxy, involving matching of integral multiples of lattice planes between the film of monoclinic structure and the substrate.
Abstract: Vanadium oxide (VO2) exhibits a very interesting semiconductor to metal transition as the crystal structure changes from tetragonal or rutile to monoclinic upon cooling close to 68°C The characteristics of this transition are very interesting scientifically and are of immense technological importance due to a variety of sensor- and memory-type applications We have processed high-quality films of VO2 by pulsed laser deposition, which were grown epitaxially on (0001) sapphire substrate via domain matching epitaxy, involving matching of integral multiples of lattice planes between the film of monoclinic structure and the sapphire substrate These films exhibit a sharp transition near 68°C, large amplitude, and very small hysteresis, similar to bulk single crystal of VO2 The sharpness and amplitude of the transition and the hysteresis upon heating and cooling are found to be a strong function of crystal structure and microstructure (grain size, characteristics of grain boundaries, and defect content) Here
227 citations
TL;DR: It is observed here, for the first time, 3D oxygen ordering during an oxygen intercalation reaction, as established for SrCoO(2.82)(+/-)(0.07), which can be described as a tetragonal unit cell, related to the perovskite cell by a approximately 2(a radical2) and c approximately 2a.
Abstract: Electrochemical oxidation of the antiferromagnetically ordered SrCoO2.5, with brownmillerite-type structure, to the cubic ferromagnet SrCoO3, with perovskite structure, has been investigated in situ by neutron diffraction as well as by X-ray absorption fine structure (XAFS) spectroscopy in specially designed electrochemical cells. The neutron diffraction experiments were performed twice, using two different wavelengths (λ = 1.2921(2) and 4.74 A) in order to better discriminate structural and magnetic changes as functions of the charge transfer. From the neutron diffraction experiments, two intermediate phases, SrCoO2.75 and SrCoO2.82±0.07, were characterized. No superstructure reflections were observed for the corresponding SrCoO2.75 phase. Instead we observed here, for the first time, 3D oxygen ordering during an oxygen intercalation reaction, as established for SrCoO2.82±0.07, which can be described as a tetragonal unit cell, related to the perovskite cell by a ≈ 2(a√2) and c ≈ 2a. The structure of this...
198 citations
TL;DR: In this article, a lead-free analogue of PbTiO3, Bi2ZnTiO6, has been prepared by high-pressure solid-state synthesis methods and the tetragonal distortion (c/a ratio = 1.21) was reported for any d0 B site Pb or Bi based perovskite.
Abstract: Bi2ZnTiO6, a lead-free analogue of PbTiO3, has been prepared by high-pressure solid-state synthesis methods. Structural analysis reveals that the tetragonal distortion (c/a ratio = 1.21) of Bi2ZnTiO6 is the largest reported for any d0 B site Pb or Bi based perovskite. Significant cation displacements result in a point-charge calculated polarization of 150 μC cm-2.
180 citations
TL;DR: Barium titanate nanowires synthesized with a surfactant-free hydrothermal method have been characterized by various techniques and the Raman spectra confirm the tetragonal phase of the BaTiO3 Nanowires.
Abstract: Barium titanate nanowires synthesized with a surfactant-free hydrothermal method have been characterized by various techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), synchrotron X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The TEM and SEM analyses show the uniform cylindrical nanowires. The Rietveld refinement with synchrotron X-ray powder diffraction showed that the lattice parameters of cubic and tetragonal phases were a (= b = c) = 4.0134 A and a (= b) = 3.9998 A, c = 4.0303 A, respectively. The final weighted R-factor, Rwp, was 6.75% and the goodness of fit indicator was 1.30. The mass fraction of tetragonal and cubic phases based on the refined scale factor for the two phases were 98.4% and 1.6%, respectively, which clearly show the nanowires are tetragonal. The XPS analysis has shown that as-obtained BaTiO3 nanowires were phase pure. The Raman spectra confirm the tetragonal phase of the BaTiO3 nanowires. The dielectri...
159 citations
TL;DR: The phases of ceria-zirconia nanoparticles observed in air are studied as a function of particle size and composition by X-ray diffraction, transmission electron microscopy, and Raman spectroscopy as discussed by the authors.
Abstract: The phases of ceria-zirconia nanoparticles observed in air are studied as a function of particle size and composition by X-ray diffraction, transmission electron microscopy, and Raman spectroscopy The emergence of two tetragonal phases t{prime}{prime} and t monotonically moves toward higher zirconia concentrations with decreasing particle size A smaller particle size increases the solubility of zirconia in cubic ceria, while higher zirconia content in ceria stabilizes against coarsening In particular, the cubic Ce{sub 1-x}Zr{sub x}O{sub 2-y} is persistent and is 8% in phase amount even at 90% zirconia with 33 nm crystal size Neither the monoclinic phase m nor the tetragonal phase t{prime} is observed in the present nanoparticles (<40 nm) The effectiveness of these nanoparticles as oxygen source-and-sink in catalytic support is largely due to the persistence of the cubic and the t{prime}{prime} phases
158 citations
TL;DR: In this article, Li intercalation of Nb 2 O 5 has been shown to cause a significant rearrangement of the Nb-O octahedra accompanied by the change in Nb O and Nb Nb interactions.
Abstract: Nb 2 O 5 exhibits various crystal systems, such as orthorhombic (o), tetragonal (t), and monoclinic (m), among which Nb 2 O 5 synthesized at 900-1000°C is commercially used as a cathode material of the 2-V lithium ion battery. The battery performances depended on the structure of Nb 2 O 5 , and the t-Nb 2 O 5 synthesized at 1000°C exhibited an excellent cycling performance with a large discharge capacity of 190 mAh (g oxide) -1 . The structural variations of Nb 2 O 5 during electrochemical reaction were examined. The in situ synchrotron radiation-X-ray diffraction (XRD) measurement indicated that o- and t-Nb 2 O 5 maintain their original crystal lattices, accompanying a small change in the cell volume even after the Li intercalation. The in situ X-ray absorption fine structure (XAFS) analysis of o- and t-Nb 2 O 5 revealed that the continuous variation from Nb 5+ to Nb 4+ took place during the intercalation process. A significant rearrangement of the Nb-O octahedra accompanied by the change of Nb-O and Nb-Nb interactions occurred in both structures with Li intercalation. XRD and XAFS data suggests that the two-dimensional layer structure of t-Nb 2 O 5 seems to be more flexible regarding the Li intercalation compared with the three-dimensional structure of o-Nb 2 O 5 . This may account for the better cyclic performance of the former material as the electrode material.
153 citations
TL;DR: In this article, the phase transformation of tetragonal to monoclinic phase of zirconia with increasing calcination temperature was observed to be related to the critical crystallite size and lattice strain.
Abstract: Nanocrystalline zirconia samples having predominantly tetragonal crystalline phase were synthesized using sol−gel and conventional precipitation techniques from zirconium hydroxide obtained by the hydrolysis of both zirconium propoxide and zirconium oxychloride precursors. Thermal drying of zirconium hydroxide gel in an oven (110 °C, 12 h) results in lower crystallite size (11−13 nm) as compared to drying under vacuum (50 mbar, 70 °C), which shows higher crystallite size (20−21 nm) during both sol−gel and conventional precipitation synthesis. The progressive transformation of tetragonal to monoclinic phase of zirconia with increasing calcination temperature was observed to be related to the critical crystallite size and lattice strain. Sol−gel synthesis was found to be advantageous because of the stabilization of tetragonal phase at higher temperature, whereas complete phase transformation was observed in the samples prepared by precipitation method at 600−700 °C temperature. Sol−gel synthesis resulted in...
152 citations
TL;DR: In this article, the perovskite single phase of the BiFeO3 thin film was analyzed, and the crystal structure showed the tetragonal structure with a space group P4mm.
Abstract: Ferroelectric BiFeO3 thin films were grown on Pt∕TiO2∕SiO2∕Si substrates by pulsed-laser deposition. From the x-ray diffraction analysis, the BiFeO3 thin films consist of perovskite single phase, and the crystal structure shows the tetragonal structure with a space group P4mm. The BiFeO3 thin films show enhanced electrical properties with low leakage current density value of ∼10−4A∕cm2 at a maximum applied voltage of 31V. This enhanced electrical resistivity allowed the authors to obtain giant ferroelectric polarization values such as saturation polarizations of 110 and 166μC∕cm2 at room temperature and 80K, respectively.
148 citations
TL;DR: In this article, microstructural instabilities associated with the precipitation of refractory-rich topologically close-packed (TCP) phases within the microstructure of advanced Ni-base single-crystal superalloys were quantified in two nominally identical alloys with and without additions of Ru.
Abstract: Microstructural instabilities associated with the precipitation of refractory-rich topologically-close-packed (TCP) phases within the microstructure of advanced Ni-base single-crystal superalloys were quantified in two nominally identical alloys with and without additions of Ru. Differences in the microstructural kinetics associated with the formation of TCP precipitates in these experimental single-crystal superalloys enabled the influence of Ru to be assessed. Detailed microstructural investigations were carried out on specimens subjected to prolonged isothermal exposures at elevated temperature. Even after 1000 hours at temperatures in excess of 1100 °C, the microstructure of the Ru-bearing alloy was highly resistant to the formation of TCP phases. Transmission electron micro-analysis (TEM) coupled with X-ray diffraction (XRD) was used to identify the characteristic crystal structures of the TCP precipitates in both alloys as being primarily the orthorhombic P and tetragonal σ phase. The sluggish precipitation kinetics of TCP phases in the Ru-bearing single-crystal Ni-base superalloy prevents the breakdown of the parent γ-γ′ microstructure and greatly enhances the high-temperature creep characteristics.
123 citations
TL;DR: In this paper, the influence of the ZrO2 phase on the catalytic activity for CO2 methanation has been investigated by TPD and TPR measurements, and the tetragonal zirconia-supported nickel catalysts showed a higher turnover frequency for the CO2 reaction and a greater CO2 adsorption than the monoclinic ZIR-supported catalysts.
121 citations
TL;DR: In this article, a strong coupling between local polar displacements and a commensurate octahedral tilting is proposed to explain the onset of classic ferroelectric behavior in tetragonal tungsten bronzelike dielectrics Ba2LaxNd1−xNb3Ti2O15.
Abstract: Strong coupling between local polar displacements and a commensurate octahedral tilting is proposed to explain the onset of classic ferroelectric behavior in tetragonal tungsten bronzelike dielectrics Ba2LaxNd1−xNb3Ti2O15. The ferroelectric phase transition is associated with a discontinuous non-lock-in transformation of an incommensurate tilted structure to a commensurate superstructure. In a manner reminiscent of perovskitelike oxides, the driving force for commensurate tilting increases as the average ionic radius of the rare-earth ion decreases; no classical ferroelectric transition is observed for compositions with x>0.75, which remain incommensurate and exhibit only relaxor behavior below room temperature.
TL;DR: HfO2 films with an enhanced dielectric constant, prepared through phase transition engineering by the addition of Al2O3, were deposited by plasma-enhanced atomic layer deposition adopting a supercycle concept as mentioned in this paper.
Abstract: HfO2 films with an enhanced dielectric constant, prepared through phase transition engineering by the addition of Al2O3, were deposited by plasma-enhanced atomic layer deposition adopting a supercycle concept After an annealing step at 700°C, the tetragonal phase, which is a high-temperature phase of HfO2, was stabilized completely at room temperature and the crystallographic direction was changed to the preferred (002) orientation As a result, Hf aluminate film with a (002)-oriented tetragonal phase had a dielectric constant of 47, approximately twice as large as the reported value of HfO2 film with a monoclinic phase
TL;DR: In this article, a nanocrystalline tetragonal Li2ZrO3 was prepared by a novel soft-chemistry route, resulting in powders with good properties for CO2 capture at high temperatures.
Abstract: Nanocrystalline tetragonal Li2ZrO3 was prepared by a novel soft-chemistry route, resulting in powders with good properties for CO2 capture at high temperatures. The CO2 capture and regeneration properties of the material were investigated by a tapered element oscillating microbalance (TEOM) in a wide range of temperatures and partial pressures of CO2. The nanocrystalline tetragonal Li2ZrO3 has superior CO2 capture and regeneration properties compared to monoclinic Li2ZrO3 prepared by solid-state synthesis. Moreover, the regeneration could be performed at a lower temperature, and a high stability of the CO2 capture/regeneration capacity was observed. The nanocrystalline tetragonal Li2ZrO3 opens new opportunities for the application of solid acceptors in CO2 capture in both post- and precombustion processes in power generation.
TL;DR: In this paper, the X-ray diffraction (XRD) patterns indicate that the films exhibited some pattern similar to that of bulk crystals of tetragonal chalcopyrite, predominantly oriented.
TL;DR: In this article, the equilibrium temperature at which the tetragonal and monoclinic phases of either ZrO2 or HfO2 coexist is defined by the middle temperature of As and Ms.
Abstract: The equilibrium temperature (T0) at which the tetragonal and monoclinic phases of either ZrO2 or HfO2 coexist is generally defined by the middle temperature of As (the onset transformation temperature on heating) and Ms (the onset transformation temperature on cooling). It cannot be directly determined due to the athermal nature of the martensitic transformation. Practically, the determination of T0 is important for the prediction of As and Ms in ZrO2 or HfO2-based materials. In this work, the ZrO2–HfO2 system was studied experimentally by differential thermal analysis (DTA) to obtain the martensitic tetragonal ⇔ monoclinic transformation temperatures in the temperature range of 1273–1973 K. The T0 temperatures obtained for ZrO2 and HfO2 are 1367±5 and 2052±5 K, respectively. They are adopted for the assessments of the Gibbs energy parameters of these two oxides. A reasonably calculated ZrO2−HfO2 phase diagram is presented.
TL;DR: In this paper, a hierarchical micro-/nanoscale domain structure is revealed in MC phase of (1−x)Pb(Mg1∕3Nb2∕ 3)O3-xPbTiO3 single crystal near the morphotropic phase boundary by combination of analytical electron microscopy and polarized light microscopy.
Abstract: A hierarchical micro-/nanoscale domain structure is revealed in MC phase of (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 single crystal near the morphotropic phase boundary by combination of analytical electron microscopy and polarized light microscopy. The hierarchical domain structure is a self-assembling of nanodomains with tetragonal structure, submicrodomains appearing as monoclinic, and microdomains exhibiting the same monoclinic state due to an average effect. The outstanding piezoelectric properties may result from the cooperative response of the hierarchical micro-/nanoscale domain structure.
TL;DR: In this article, a splitting shift between Fe and Ti atoms was found along the c axis in 0.7PbTiO3−0.3BiFeO3; however, this splitting does not appear in the tetragonal phase.
Abstract: The structures of (1−x)PbTiO3–xBiFeO3 (x=0.3 and 0.6) were investigated by means of the neutron powder diffraction. A splitting shift between Fe and Ti atoms was found along the c axis in 0.7PbTiO3–0.3BiFeO3; however, this splitting does not appear in 0.4PbTiO3–0.6BiFeO3. The tetragonal phase of PbTiO3–BiFeO3 exhibits a large spontaneous polarization. The negative thermal expansion of PbTiO3 is significantly enhanced in a wide temperature range by the BiFeO3 substitution. The average bulk thermal expansion coefficient of 0.4PbTiO3–0.6BiFeO3 is a¯v=−3.92×10−5°C−1, which is much strong in the known negative thermal expansion oxides.
TL;DR: Accounting for this FE–AFE nature of these phases is expected to be important in accurately simulating the domain wall structures, energetics, and dynamics, which in turn may lead to the design of improved materials.
Abstract: Using quantum mechanics (QM, Density Functional Theory) we show that all four phases of barium titanate (BaTiO3) have local Ti distortions toward (an octahedral face). The stable rhombohedral phase has all distortions in phase (ferroelectric, FE), whereas higher temperature phases have antiferroelectric coupling (AFE) in one, two, or three dimensions (orthorhombic, tetragonal, cubic). This FE–AFE model from QM explains such puzzling aspects of these systems as the allowed Raman excitation observed for the cubic phase, the distortions toward observed in the cubic phase using x-ray fine structure, the small transition entropies, the heavily damped soft phonon modes, and the strong diffuse x-ray scattering in all but the rhombohedral phase. In addition, we expect to see additional weak Bragg peaks at the face centers of the reciprocal lattice for the cubic phase. Similar FE–AFE descriptions are expected to occur for other FE materials. Accounting for this FE–AFE nature of these phases is expected to be important in accurately simulating the domain wall structures, energetics, and dynamics, which in turn may lead to the design of improved materials.
TL;DR: The diffuse reflection spectra of the solid solutions shift monotonically to a long wavelength as the ratio of Bi (V) ions to Ca (Mo) ions increases in the solid solution, and the band structure and the dependence of the photocatalytic properties were discussed in relation to the solid-solution compositions and photophysical properties.
Abstract: New solid solutions with the composition of Ca1-xBixVxMo1-xO4 prepared by a solid-state method were found as novel photocatalysts with enhanced activity for O2 evolution from aqueous solutions containing sacrificial regent AgNO3 under visible-light irradiation (>420 nm). The obtained solid solutions crystallized in tetragonal crystal structures, except one of the end compounds, BiVO4, which crystallized in monoclinic structures. The diffuse reflection spectra of the solid solutions shift monotonically to a long wavelength as the ratio of Bi (V) ions to Ca (Mo) ions increases in the solid solution. The band structure and the dependence of the photocatalytic properties were discussed in relation to the solid-solution compositions and photophysical properties.
TL;DR: In this article, a multiscale thermomechanical model was developed to analyze martensitic phase transformations from a cubic crystalline lattice to a tetragonal crystalline structure.
TL;DR: In this article, Simon et al. describe non-linear properties of tetragonal tungsten bronze materials related to solid-state chemistry, with five different cationic or anionic crystallographic sites.
TL;DR: In this paper, electron-doped SrTiO3 single crystals at room temperature were observed, and the chemical substitution of La3+ for Sr2+ changes the temperature of the structural phase transition from cubic to tetragonal symmetry.
Abstract: Blue-light emissions from electron-doped SrTiO3 single crystals at room temperature were observed. Substituting La3+ for Sr2+ and Nb5+ for Ti4+ in SrTiO3 provides electron carriers in Ti 3d conduction bands; these carriers are responsible for the room-temperature blue-light emission. This blue-light emission is essentially the same as that observed in Ar+-irradiated oxygen-deficient SrTiO3. This blue luminescence is independent of the defect type. The chemical substitution of La3+ for Sr2+ changes the temperature of the structural phase transition from cubic to tetragonal symmetry. The relation between the photoluminescence properties and the structural phase transition is also discussed.
TL;DR: In this article, thin films of 9.5% yttria-doped zirconia in the range of 17-210nm thickness were deposited on MgO (100) substrates by electron beam evaporation.
Abstract: Thin films of 9.5% yttria-doped zirconia in the range of 17–210nm thickness were deposited on MgO (100) substrates by electron beam evaporation. The conductivity of the films was found to increase as the film thickness decreased. The films were found to be a mixture of both cubic and tetragonal phases. The impedance and electrical modulus parameters indicate that the relaxation process is due to ionic conduction. Enhancements in conductivity are attributed to the space charge effects that occur at the interface and grain boundaries as evidenced by the high activation energy observed in the conductivity relaxation process.
TL;DR: Barium titanate (BTO) ceramics with an average grain size of 8nm were fabricated and studied in this paper, where the temperature dependent Raman spectra revealed successive transitions from rhombohedral to orthorhombic, tetragonal, and cubic as the temperature increased from 87to673K.
Abstract: Barium titanate (BTO) ceramics with an average grain size of 8nm were fabricated and studied The temperature dependent Raman spectra revealed successive transitions from rhombohedral to orthorhombic, tetragonal, and cubic as the temperature increased from 87to673K Local piezoresponse force measurements indicated that the ceramics had switchable polarization at room temperature Dielectric measurements showed a broad ferroelectric-to-paraelectric phase transition with a maximum permittivity of 1800 at 390K All these results suggest that ferroelectricity could remain in BTO ceramics with grain size as small as 8nm in diameter
TL;DR: In this paper, a single-phase compound was formed exhibiting a tetragonal system and the ac conductivity spectrum obeyed the Jonscher power law, which indicated the possibility of hopping mechanism for electrical processes in the system with a nonexponential type of conductivity relaxation.
Abstract: (Pb0.97Sr0.03)(Zr0.05Ti0.95)O3 nanocrystalline powder was prepared by a solution based chemical method. Preliminary x-ray diffractogram analysis of some aspects of crystal structure showed that a single-phase compound was formed exhibiting a tetragonal system. Impedance spectroscopy study showed the presence of both bulk and grain boundary effects in the material, which is also evident from the scanning electron microscope micrographs. The bulk conductivity indicates an Arrhenius-type thermally activated process. The ac conductivity spectrum obeyed the Jonscher power law. Modulus analysis indicated the possibility of hopping mechanism for electrical processes in the system with a nonexponential type of conductivity relaxation.
TL;DR: In this paper, a systematic exploration of the composition-structure relationship has been performed using X-ray diffraction on several single crystals having large composition gradients, and temperature-dependent magnetic measurements show the martensitic transition to orthorhombic martensite is broader than to tetragonal Martensite.
TL;DR: In this paper, the crystal structure and electromagnetic properties as well as thermal stability of the A-site ordered PrBaMn 2 O 6 manganites have been investigated using two-step synthesis mode.
TL;DR: A potential driven self-assembly of sodium dodecyl sulfate/tungsten oxide aggregates at the electrolyte-electrode interface followed by template extraction and annealing yielded mesoporous thin films of electrochromic tungstenoxide (WO(3).
Abstract: A potential driven self-assembly of sodium dodecyl sulfate/tungsten oxide aggregates at the electrolyte–electrode interface followed by template extraction and annealing yielded mesoporous thin films of electrochromic tungsten oxide (WO3). Electron microscopy images revealed that the films are characterized by a hitherto unreported hybrid structure comprising nanoparticles and nanorods with a tetragonal crystalline phase of WO3 with the measured lattice parameters: a = 0.53 nm and c = 0.37 nm. In addition to pentagonal voids characteristic of the tetragonal WO3 phase at the lattice scale, open channels and pores of 5–10 nm in diameter lie between the nanoparticles, which cumulatively promote rapid charge transport through the film. This resulted in colouration efficiency (ηmax~90 cm2 C−1 at λ = 900 nm) and switching kinetics (colouration time = 3 s and bleaching time = 2 s for a 50% change in transmittance) higher and faster than previously reported values for mesoporous WO3 films. Repetitive cycling between the clear and blue states has no deleterious effect on the electrochromic performance of the film, which is suggestive of its potential as a cathode in practical electrochromic windows.
TL;DR: The structure of the CuAl2 structure was analyzed by electron localization function (ELF), crystal orbital Hamiltonian population (COHP) analysis and Raman spectroscopy as mentioned in this paper.
TL;DR: In this article, the crystal structure and phonon modes of chemically substituted Ba(RE 1/2Nb1/2)O3 microwave ceramics (RE = La, Nd, Sm, Gd, Tb, and Y) were evaluated.
Abstract: Raman spectroscopy was employed to evaluate the crystal structure and phonon modes of chemically substituted Ba(RE1/2Nb1/2)O3 microwave ceramics (RE = La, Nd, Sm, Gd, Tb, and Y). It was verified that these materials could be divided into tetragonal (ceramics with RE = Y, Tb, and Gd) and orthorhombic (RE = Sm, Nd, and La) structures. Lorentzian lines were used to fit the spectra, which presented 9 bands for the first group and 23 bands for the second group of ceramics. The position and width of the phonon modes were determined, and were correlated to the ionic radii and tolerance factors for the different atoms substituted in the B‘-site. It is believed that simple rotational distortions of the oxygen octahedra led to the occurrence of structures other than cubic, which is very difficult to detect by X-ray diffraction or even spectroscopic techniques.