Structure Of Titanate Research Articles

The behavior of rare-earth pyrochlores and perovskites under ion irradiation

The behavior of samples of A2B2O7 composition under irradiation with 1-MeV Kr2+ ions was studied (A is a simulator of the REE-actinide fraction of the wastes of the treatment of used nuclear fuel and B is a quadrivalent cation of Zr, Sn, or Ti). Depending on the B elements, the samples are crystallized either in pyrochlore (Zr and Sn) or in the perovskite structural type (Ti). The matrices of the pyrochlore structure are radiation-resistant, which is shown by their high critical doses and low critical temperatures of amorphization. The phases of monocline REE titanate structure are characterized by low irradiation resistance and should be amorphized even within centuries of storage. To characterize the possibilities of their usage as matrices for waste immobilization, synthesis of materials containing short-living actinides and studies of the degree of the amorphization effect on their stability in aqueous solutions are required.

Effect of stoichiometry on the atomic and electronic structure of BaTiO3 nanoparticles: a first-principles study

We have used density functional theory calculations to investigate the atomic and electronic structure of barium titanate (BaTiO3) nanoparticles. We studied the local atomic structure of different-sized stoichiometric and nonstoichiometric nanoparticle models in detail. Our results showed that all the stoichiometric BaTiO3 clusters exhibit dielectric properties and form rhombohedral and monoclinic structures. However, oxygen deficient nonstoichiometric clusters show metallic behaviour and form cubic and tetragonal structures.

Photoelectrochemical Properties of Alkali-treated Sodium Titanate Nanorods

ABSTRACTThe band gap energy of the TiO2 photocatalytic is high at 3.2 eV. Ultraviolet (UV) light irradiation (<388nm) is required for the photocatalytic application. The lowering the band gap energy of TiO2 and enlarging light absorbing area are effective ways to enhance the efficiency of photocatalytic activity. Furthermore, the morphology and crystal structure of nanosized TiO2 considerably influences its photocatalytic behavior.In this study, sodium titanate nanorods were formed using an alkali-treatment and were heat treated at different temperatures. The photoelectrochemical properties of sodium titanate nanorods was measured as a function of heat treatment temperature. The nanorods were prepared on the surface of Ti disk with a diameter of 15mm and a thickness of 3mm. Ti disk was immersed in 5 M NaOH aqueous solution at a temperature of 60 °C for 24 h. Morphology of sodium titanate nanorods was observed using FE-SEM. Crystal structure of sodium titanate nanorods was analyzed using X-ray diffractometer. Photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) was used to evaluate photoelectrochemical properties of sodium titanate nanorods. The thin amorphous sodium titanate layer was formed during alkali-treatment. The sodium titanate layer was changed to nanorods after heat treatment at a temperature of 700 °C. The thickness and length of sodium titanate nanorods obtained at 700 °C were around 100 nm and 1μm, respectively. The crystal structure of sodium titanate was identified with Na2Ti6O13. Above 900 °C, the morphology of nanorods changed to agglomerated shape and the thickness of nanorods increased to 1 μm. The lowest value of PL was obtained at a temperature of 700 °C, while nonalkali treated specimen showed the highest value of PL. EIS revealed that polarization resistance at interface between sodium titanate nanorods and electrolyte was increased with increasing heat treatment temperature.

Mapping of ferroelectric domain structure using angle-resolved piezoresponse force microscopy.

Angle-resolved piezoresponse force microscopy (AR-PFM) was used in conjunction with electron backscatter diffraction (EBSD) to study ferroelectric domain structure in polycrystalline near-morphotropic lead zirconate titanate (PZT). We introduce the details of AR-PFM including experimental method, the process to generate AR-PFM maps, and the interpretation of AR-PFM map, using domain patterns observed in bulk PZT. The spatial distortion caused by scanner creep and non-linearity in scanning probe microscopy was corrected through image registration, taking advantage of the features present in topography images. Domain structures were mapped using AR-PFM data, and the maps consistently show alternating piezoresponse axes in a lamellar pattern of non-180° domain structure. Comparison of AR-PFM and EBSD data showed a discrepancy between the direction of lateral surface displacement and the in-plane polarization direction. Additionally, using suitable domain patterns, AR-PFM enabled discrimination between the tetragonal and rhombohedral phases at the sub-grain scale.

Impact of Biofield Treatment on Atomic and Structural Characteristics of Barium Titanate Powder

Barium titanate, perovskite structure is known for its high dielectric constant and piezoelectric properties, which makes it interesting material for fabricating capacitors, transducer, actuator, and sensors. The perovskite crystal structure and lattice vibrations play a crucial role in its piezoelectric and ferroelectric behavior. In the present study, the barium titanate powder was subjected to biofield treatment. Further, the control and treated samples were characterized using X-ray diffraction (XRD) and Fourier transform infrared spectrometer (FT-IR) and Electron spin resonance (ESR). The XRD analysis showed the permanent compressive strain of 0.45% in treated barium titanate powder as compared to control. Furthermore, the biofield treatment had enhanced the density upto 1.38% in barium titanate as compared to control. The FT-IR spectra showed that the stretching and bending vibrations of Ti-O bond in treated BaTiO3 were shifted towards lower frequency as compared to control. The bond length was substantially increased by 0.72 % in treated BaTiO3 as compared to control. The ESR spectra of control and treated BaTiO3 sample showed the g-factor of 2.0; and biofield treatment has substantially changed the width and height of ESR signal in treated BaTiO3 as compared to control. These observations revealed that biofield treatment has significantly altered the crystal structure, lattice strain, and bond vibration of barium titanate.

Tuning the electronic band structure of microporous titanates with the hollandite structure

We present the electronic band structures of microporous titanates with the hollandite-type structure.

Synthesis of [111]- and {010}-faceted anatase TiO2 nanocrystals from tri-titanate nanosheets and their photocatalytic and DSSC performances.

[111]- and {010}-faceted anatase nanocrystals with controllable crystal size and morphology were synthesized from tri-titanate H2Ti3O7 nanosheets by hydrothermal reaction. The nanostructures and the formation reaction mechanism of the obtained TiO2 nanocrystals were investigated using XRD, FE-SEM, and TEM. Furthermore, the photocatalytic and dye-sensitized solar cell (DSSC) performances of the synthesized anatase nanocrystals were also characterized. Two types of reactions occur in the formation process of the anatase nanocrystals. One is an in situ topochemical conversion reaction of the layered titanate structure to an anatase structure, and another is the dissolution-deposition reaction on the particle surface, which splits the formed nanosheet-like particles into small TiO2 nanocrystals. The surface photocatalytic activity and the DSSC performance of the anatase nanocrystals are dependent on the crystal facet exposed on the particle surface, which increases in the order of non-facet < [111]-facet < {010}-facet. The increasing order corresponds to the increasing order of the bandgap and energy level of the lowest valence band of the anatase nanocrystals. Furthermore, the facet of the anatase also affects the DSSC performance, which is enhanced in the order of non-facet < [111]-facet < {010}-facet.

Phase relations and formation of chromium-rich phases in the system Mg4Si4O12–Mg3Cr2Si3O12 at 10–24 GPa and 1,600 °C

Phase relations in the system Mg4Si4O12–Mg3Cr2Si3O12 were studied at 10–24 GPa and 1,600 °C using a high-pressure Kawai-type multi-anvil apparatus. We investigated the full range of starting compositions for the knorringite–majorite system to derive a P–X phase diagram and synthesize garnets of a wide compositional range. Samples synthesized in the pressure range 10–14 GPa contain knorringite–majorite garnet and Cr-bearing pyroxene. With increasing Cr content in the starting materials, an association of knorringite–majorite garnet and eskolaite is formed. Garnets contain a significant portion of majorite (>10 mol%) even for a pure Mg3Cr2Si3O12 starting composition. Knorringite–majorite garnets were obtained in the pressure range from 10 to 20 GPa. With increasing pressure, the phase assemblages include Cr-bearing MgSiO3 akimotoite and MgSiO3 bridgmanite, as well as MgCr2O4 with calcium titanate structure, and stishovite. Single-crystal X-ray diffraction shows that the incorporation of Cr into the structure of garnet, as well as MgSiO3 akimotoite, and bridgmanite results in an increase in their unit cell parameters. Results of the experimental high-pressure investigation of the pseudo-binary system Mg4Si4O12–Mg3Cr2Si3O12 (SiO2–MgO–Cr2O3) may be applied to the origin of high chromium phases (mostly garnet) found as inclusions in peridotitic diamonds and formed in bulk rock compositions with high Cr/Al ratios in relation to the primitive mantle.

Fe-doped nanostructured titanates synthesized in a single step route

In this research nanostructured titanates, containing iron in the structure, were obtained through a single-step alkaline hydrothermal route aiming at reduction of band-gap energy. In the process, a Fe–Ti rich Brazilian mineral sand was mixed with 10M of NaOH and then submitted to isothermal treatments at temperatures ranging from 110 to 190°C in an autoclave. The as-obtained products were water-washed and then characterized by transmission electron and scanning transmission electron microscopies, X-ray photoelectron, Mössbauer and diffuse reflectance spectroscopies. Transmission electron microscopy analyses showed a morphological dependence of the product as a function of the temperature, i.e., titanate nanosheets were predominantly formed at lower temperatures (110°C–150°C), while nanoribbons, with some nanosheets and nanoparticles, were the main products at higher temperatures (>150°C). Using energy dispersive X-ray it was determined that iron was incorporated into nanosheets. On the other hand, the as-obtained nanoribbons were Fe-free, while iron was principally associated with nanoparticles attached to the nanoribbons. By means of X-ray photoelectron and Mössbauer spectroscopies, it was elucidated that iron adopted Fe3+ form in the as-prepared nanosheets, occupying octahedral sites inside the titanate lepidocrocite-like structure. Diffuse reflectance spectroscopy showed a change of absorption pattern from nanosheets to nanoribbon/nanoparticle assembly: nanosheets exhibited high absorption from ultraviolet up to the visible light range, while the nanoribbon/nanoparticle assembly demonstrated a drop in absorption in the visible light range. These results suggest that Fe3+ incorporation inside the titanate structure is responsible for enhancing the visible light absorption, making these nanosheets potentially suitable for applications in photoinduced processes.

Structural studies of BaTiO3:Er3+ and BaTiO3:Yb3+ powders synthesized by hydrothermal method

Erbium and ytterbium doped barium titanate nanopowders were prepared using the hydrothermal method. A barium titanate structure doped with rare earth ions manifested new characteristics and improved the field of application of optical devices such as trichromatic tubes, LCD displays, lamps, and infrared lasers. In this work, BaTiO3:Er3+ and BaTiO3:Yb3+ were prepared using barium chloride [BaCl2], titanium butoxide [C16H36O4Ti], erbium chloride [ErCl3] and ytterbium chloride [YbCl3] as precursors. Anhydrous methanol was employed as a solvent. Metallic potassium was used to promote solubility in the system and increase the pH to 13. This method yielded the formation of a predominantly cubic structure in both Er3+ and Yb3+ doped BaTiO3 powders. Characteristic bondings of BaTiO3 were observed with FT-IR spectroscopy. The predominantly cubic structure was confirmed by X-ray diffraction and micro-Raman analyses. The particle size (∼30 nm) was estimated using the Scherrer equation and X-ray diffraction data. The results were presented and discussed.

Microwave-Assisted Topochemical Conversion of Layered Titanate Nanosheets to {010}-Faceted Anatase Nanocrystals for High Performance Photocatalysts and Dye-Sensitized Solar Cells

The {010}-faceted anatase nanocrystals with controllable crystal size and morphology were synthesized by microwave hydrothermal treatment of layered titanate nanosheet solutions. The nanostructures and formation reaction mechanism of TiO2 nanocrystals were investigated using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction. Their photocatalytic behavior and dye-sensitized solar cell (DSSC) performance were studied and compared with [111]-faceted anatase nanocrystals and anatase nanocrystals without a specific facet on the surface. There are two kinds of reactions in the formation process of the anatase nanocrystals. One is an in situ topochemical conversion reaction of layered titanate structure to anatase structure, and another is the dissolution–deposition reaction on the particle surface. The microwave hydrothermal process is suitable to control the structural conversion reaction for uniform the crystal size and morphology due to its uniform heating mechanism. The UV–visible spectrum results revealed that the bandgap of the TiO2 nanocrystals was enhanced in the order of nanocrystal without specific facet < [111]-faceted nanocrystal < {010}-faceted nanocrystal, which corresponded to their photocatalytic activities. The DSSC performance also was enhanced in the same order, suggesting that the {010}-faceted nanocrystals are promising for the high performance DSSCs.

Substitution Effects of Gd and Mg on Cubic Structure of Barium Titanate

Barium titanate BaTiO3 is a ferroelectric oxide with low dielectric loss and high permittivity, which makes it a good insulator for industrial uses. However, the pure barium titanate is not always used for electronic devices. Gd- and Mg-doping in barium titanate is effective for the dielectrics in multilayer ceramic capacitors MLCCs, for example, to attain the uniform temperature-variation of dielectric constants in the wide temperature-range where MLCCs are practically used, while the Curie temperature is significantly decreased [1]. In this study, the structural characteristics of Gd- and Mg-substituted barium titanate (Ba,Gd)(Ti,Mg)O3 (BGTM) in the cubic phase were investigated to clarify the effects of Gd- and Mg-substitution on the crystal structure and the chemical bonding. Synchrotron radiation x-ray powder diffraction measurements were carried out using the BGTM samples with the Mg content of x = 0 ~ 0.1. Lattice parameters, substitution sites of the Gd and Mg ions, thermal parameters, and electron charge density distributions in the crystals were analyzed by using the maximum entropy method (MEM)/Rietveld method. The Curie temperature decreased with increasing x. The phase transition did not take place in BGTM with x &gt; 0.05. The Gd ion was confirmed to be substituted for the Ba ion with larger thermal vibration amplitude than that of the Ba ion. The amplitude was almost independent of the Gd content. It was revealed that the Gd ion occupied the off-centered positions slightly form the Ba-site along the &lt;100&gt; directions at lower temperatures. Difference in thermal behaviors of the Gd and Ba ions can be attributed to the size difference between the smaller Gd ion and the larger Ba ion. The Mg ion was observed on the Ti-site. The substitution of the Mg ion for the Ti ion suppresses the ferroactivity of the Ti ion, which causes the lowering of the Curie temperature.

Generation of reactive oxygen species in titanates nanotubes induced by hydrogen peroxide and their application in catalytic degradation of methylene blue dye

The present work describes the application of sodium (Na-) and hydrogen (H-) titanate nanotubes (TiNTs) as catalysts in oxidation reactions with aqueous hydrogen peroxide. By applying a combination of characterization techniques, it is shown that the interaction of TiNTs with H2O2 leads to a modification in the color and vibrational structure of the TNT, which can be attributed to the formation of superoxide radicals. Electron paramagnetic resonance measurements reveal that fraction of generated radicals increases asymptotically with H2O2 concentration. Catalytic tests of methylene blue discoloration revealed that TiNTs are very active in the discoloration of the dye, being the catalytic activity dependent on the concentration of H2O2. The analysis of the reaction products by electrospray ionization mass spectrometry showed that the dye was successively oxidized in different intermediate compounds. The effects of previous thermal treatment of the TiNTs were also investigated, and it was found that the active catalytic sites are progressively deactivated as the treatment temperature is increased. The overall results suggest that terminal groups present in the titanate structure, such as TiO:− are active catalytic sites that convert into highly reactive superoxide radicals upon interaction with H2O2 molecules.

The role of ion‐molecule reactions in the growth of heavy ions in Titan's ionosphere

AbstractThe Ion and Neutral Mass Spectrometer (INMS) and Cassini Plasma Spectrometer (CAPS) have observed Titan's ionospheric composition and structure over several targeted flybys. In this work we study the altitude profiles of the heavy ion population observed by the Cassini Plasma Spectrometer‐Ion Beam Spectrometer (CAPS‐IBS) during the nightside T57 flyby. We produce altitude profiles of heavy ions from the C6–C13 group (Ci indicates the number, i, of heavy atoms in the molecule) using a CAPS‐IBS/INMS cross calibration. These altitude profiles reveal structure that indicates a region of initial formation and growth at altitudes below 1200 km followed by a stagnation and dropoff at the lowest altitudes (1050 km). We suggest that an ion‐molecule reaction pathway could be responsible for the production of the heavy ions, namely reactions that utilize abundant building blocks such as C2H2 and C2H4, which have been shown to be energetically favorable and that have already been identified as ion growth patterns for the lighter ions detected by the INMS. We contrast this growth scenario with alternative growth scenarios determining the implications for the densities of the source heavy neutrals in each scenario. We show that the high‐mass ion density profiles are consistent with ion‐molecule reactions as the primary mechanism for large ion growth. We derive a production rate for benzene from electron recombination of C6H7+ of 2.4 × 10−16 g cm−2 s−1 and a total production rate for large molecules of 7.1 × 10−16 g cm−2 s−1.

New clues on the interior of Titan from its rotation state

AbstractThe Saturnian satellite Titan is one of the main targets of the Cassini-Huygens mission, which revealed in particular Titan's shape, gravity field, and rotation state. The shape and gravity field suggest that Titan is not in hydrostatic equilibrium, that it has a global subsurface ocean, and that its ice shell is both rigid (at tidal periods) and of variable thickness. The rotational state of Titan consists of an expected synchronous rotation rate and an unexpectedly high obliquity (0.3○) explained by Baland et al. (2011) to be a resonant behavior. We here combine a realistic model of the ice shell and interior and a 6-degrees of freedom rotational model, in which the librations, obliquity and polar motion of the rigid core and of the shell are modelled, to constrain the structure of Titan from the observations. We consider the gravitational pull of Saturn on the 2 rigid layers, the gravitational coupling between them, and the pressure coupling at the liquid-solid interfaces.We confirm the influence of the resonance found by Baland et al., that affects between 10 and 13% of the possible Titans. It is due to the 29.5-year periodic annual forcing. The resonant Titans can be obtained in situations in which a mass anomaly at the shell-ocean boundary (bottom loading) is from 80 to 92% compensated. This suggests a 250 to 280 km thick ocean below a 130 to 140 km thick shell, and is consistent with the degree-3 analysis of Hemingway 26 et al. (2013).

Temperature dependence of flexoelectricity in BaTiO3 and SrTiO3 perovskite nanostructures

Abstract Piezoelectricity is a property of non-centrosymmetric crystals. In most typically used ferroelectrics, this property is lost as the temperature is increased beyond the Curie point thus strongly reducing the availability of efficient materials that can be used for high temperature energy harvesting. Flexoelectricity, as can be shown from simple symmetry arguments, is a universal and linear electromechanical coupling that dictates the development of polarization upon application of inhomogeneous strains. The implications of this phenomenon become amplified at the nanoscale. In this communication, we develop a molecular dynamics approach predicated on a specially tailored interatomic force-field to extract the temperature dependence of flexoelectricity. Surprisingly, we find that it, at least for Barium Titanate and Strontium Titanate nano structures, increases with temperature. Apart from cataloging this interesting observation for the future use in high temperature energy harvesting, we also examine the physical mechanisms that lead to the observed temperature dependence.

Nonlinear magnetoelectric effect in composite multiferroics

The theoretical and experimental studies of the nonlinear magnetoelectric effect in composite multiferroics in the low-frequency spectral region and in the electromechanical resonance region have been performed. It has been shown that such structures demonstrate a nonlinear magnetoelectric effect, which is quadratic in ac magnetic field strength at weak magnetic fields. In the region of the electromechanical resonance, the resonance excitation of an electric field occurs by means of ac magnetic field at a frequency lower than the resonance frequency by a factor of two. In the low-frequency spectral region, there is a difference of amplitude values of two neighboring voltage maxima due to the superposition of signals from the linear and nonlinear effects, and the difference is proportional to the dc magnetic field strength in weak fields. The results of the experimental study of the two-layer permendur-lead zirconate titanate structure are presented.

Structure and dynamics of Titan’s outer icy shell constrained from Cassini data

The Cassini–Huygens mission has brought evidence for an internal ocean lying beneath an outer icy shell on Titan. The observed topography differs significantly from the reference hydrostatic shape, while the measured geoid anomalies (estimated up to degree three) remain weak. This suggests compensation either by deflections of the ocean/ice interface or by density variations in an upper crust. However, the observed degree-three gravity signal indicates either that the topography is not perfectly compensated, or that mass anomalies exist in the deep interior, or a combination of both. To investigate the compensation mechanisms, we developed an interior structure model satisfying simultaneously the surface gravity and long-wavelength topography. We quantified the excess deflection of ocean/ice I interface, the density anomalies in the upper crust, or the deflection of the ice/rock interface needed to explain the observed degree-three anomalies. Finally, we tested the long-term mechanical stability of the internal mass anomalies by computing the relaxation rate of each internal interface in response to interface mass load. We showed that the computed deflection of the ocean/ice I interface is stable only for a conductive highly viscous layer above a relatively cold ocean (T<250K). Solutions with a moderately convecting ice shell are possible only for models with crustal density variations. Due to fast relaxation, the high pressure ice layer cannot be the source of the degree three geoid anomalies. The existence of mass anomalies in the rocky core remains a possible explanation. Estimation of the degree-four gravity signal by future Cassini flybys will further constrain the compensation mechanism and the source of gravity anomalies.

Effect of reductant type on phase composition and ferroelectric behavior of combustion-synthesized BaTiO3 and Bi4Ti3O12

Finely dispersed BaTiO3 and Bi4Ti3O12 powders were prepared by solution-combustion synthesis using glycine, carbamide, and glycerol as reducing agents. The use of glycine as a reducing agent was found to yield single-phase BaTiO3 and Bi4Ti3O12 without additional heat treatment. Explored was the influence of reductant type and process parameters on the phase composition, crystal structure, and dielectric properties of combustion-synthesized barium and bismuth titanates.

Lepidocrocite-type Layered Titanate Structures: New Lithium and Sodium Ion Intercalation Anode Materials

The electrochemical characteristics of lepidocrocite-type titanates derived from K0.8Ti1.73Li0.27O4 are presented for the first time. By exchanging sodium ions for potassium, the practical specific capacity of the titanate in both sodium and lithium half cells is considerably enhanced. Although the gross structural features of the titanate framework are maintained during the ion exchange process, the symmetry changes because sodium occupies different sites from potassium. The smaller size of the sodium ion as compared to potassium and the change in site symmetry allow more alkali metal cations to be inserted reversibly into the structure during discharge in sodium and lithium cells than in the parent compound. Insertion of lithium cations takes place at an average of about 0.8 V vs Li+/Li while sodium intercalation occurs at 0.5 V vs Na+/Na, with sloping voltage profiles exhibited for both cell configurations, implying single-phase processes. Ex situ synchrotron X-ray diffraction measurements show that a lithiated lepidocrocite is formed during discharge in lithium cells, which undergoes further lithium insertion with almost no volume change. In sodium cells, insertion of sodium initially causes an overall expansion of about 12% in the b lattice parameter, but reversible uptake of solvent minimizes changes upon further cycling. In the case of the sodium cells, both the practical capacity and the cyclability are improved when a more compliant binder (polyacrylic acid) that can accommodate volume changes associated with insertion processes is used in place of the more common polyvinylidene fluoride. The ability to tune the electrochemical properties of lepidocrocite titanate structures by varying compositions and utilizing ion exchange processes make them especially versatile anode materials for both lithium and sodium ion battery configurations.