Perovskite Strontium Titanate Research Articles

Perovskite ceramic nanoparticles in polymer composites for augmenting bone tissue regeneration

There is increasing interest in the use of nanoparticles as fillers in polymer matrices to develop biomaterials which mimic the mechanical, chemical and electrical properties of bone tissue for orthopaedic applications. The objective of this study was to prepare poly(ϵ-caprolactone) (PCL) nanocomposites incorporating three different perovskite ceramic nanoparticles, namely, calcium titanate (CT), strontium titanate (ST) and barium titanate (BT). The tensile strength and modulus of the composites increased with the addition of nanoparticles. Scanning electron microscopy indicated that dispersion of the nanoparticles scaled with the density of the ceramics, which in turn played an important role in determining the enhancement in mechanical properties of the composite. Dielectric spectroscopy revealed improved permittivity and reduced losses in the composites when compared to neat PCL. Nanofibrous scaffolds were fabricated via electrospinning. Induction coupled plasma-optical emission spectroscopy indicated the release of small quantities of Ca+2, Sr+2, Ba+2 ions from the scaffolds. Piezo-force microscopy revealed that BT nanoparticles imparted piezoelectric properties to the scaffolds. In vitro studies revealed that all composites support osteoblast proliferation. Expression of osteogenic genes was enhanced on the nanocomposites in the following order: PCL/CT > PCL/ST > PCL/BT > PCL. This study demonstrates that the use of perovskite nanoparticles could be a promising technique to engineer better polymeric scaffolds for bone tissue engineering.

Electric field induced pyroelectricity in strontium titanate

Pyroelectric materials have a broad spectrum for practical application. Apart from the established infrared sensor technology, recently the pyroelectric effect has been employed unconventionally in waste heat recovery, X-ray generation or water disinfection. This coupling phenomenon is the temperature dependence of a ferroelectric's spontaneous polarisation. A crystal structure that allows pyroelectricity cannot have an inversion centre, if it had a polar axis would not exist. Hence the well-known perovskite strontium titanate, crystallizing in the space group Pm-3m, is known to be dielectric. Nonetheless, under an external electric field of 1MV/m charged defects like oxygen vacancies redistribute in a strontium titanate single crystal, leading to a distortion of the unit cell and subsequently to the formation of a defect structure called the migration-induced field-stabilized polar (MFP) phase [1]. Raman scattering shows that the MFP phase of strontium titanate may exhibit broken centrosymmetry, suggesting the existence of a polar axis. Here, we investigate the pyroelectric properties of strontium titanate single crystals at room temperature during these electroformation cycles with a modified Sharp-Garn method [2]. Our frequency and field dependent measurements indicate the pyroelectricity of the MFP phase. Additionally the measurement method elucidates the kinetics of the oxygen vacancy migration as well as electric properties during electroformation. Inducing pyroelectricity in a centro-symmetric crystal structure opens the scope for a new class of pyroelectric materials.

Antibacterial activities of mechanochemically synthesized perovskite strontium titanate ferrite metal oxide

This work explored strontium titanate ferrite (SrTi1−xFexO3−δ or STFx in short) metal oxide as an effective antibacterial agent and investigated its bactericidal mechanism. The perovskite STFx nanoparticles (x=0, 0.2, 0.4, 0.6, 0.8 and 1) were successfully synthesized with high energy ball milling approach. The feasibility of utilizing this material for antibacterial application was studied on Escherichia coli (E. coli) in the presence of dispersed STF0.8 nanoparticles in water. Excellent bactericidal effect has been observed by killing all the E. coli (∼105CFU/mL) within 15min in both light and dark conditions, excluding photocatalysis as the major contributing mean of bactericidal effect. Mechanism study via surface charge characterization, fluorescence microscope observation, inductively coupled plasma measurement and SEM examination has revealed that the positive surface charge, high pH environment, Sr2+ dissociation and nano-size of STF0.8 metal oxide could have collectively contributed to its excellent bactericidal effect. These results have increased the potential to apply STFx in water purification for microorganism destruction.

Insight into the Effects of Fe Addition on the Local Structure and Electronic Properties of SrTiO3

This paper reports an experimental and theoretical investigation of the effects of adding Fe to the perovskite strontium titanate SrTiO3. The effects include changes in the short-order range structure as well as in the electronic and electrical properties. X-ray diffraction analysis reveals that the SrTi1–xFexO3 network shrinks with increasing Fe content, while X-ray absorption spectroscopy measurements of the Ti and Fe K-edge revealed the presence of some under-coordinated TiO5 units created because of the partial replacement of Fe3+ ions in the Ti4+ site. UV–visible absorption spectra indicated a reduction in optical gap with increasing Fe content. The electronic structure and spin densities of STFO with x = 0, 0.0625, 0.125, 0.5, and 1 are calculated by the DFT method at the B3LYP computational level, showing a Jahn–Teller distortion of O atoms surrounding the Fe as well as the formation of under-coordinated TiO5 units. From the electrical viewpoint, the results show that STFO is a mixed (ionic and electronic) conductor and that the electronic contribution becomes dominant with increasing Fe content.

Strontium Titanate Perovskite SrTiO3 as a Promising Ideal Material for MEMS Applications : First-Principles FP-LMTO + LSDA Study

Strontium titanate perovskite oxide materials offer a number of advantages in microelectromechanical systems (MEMS) due to the micro-structural, electronic, magnetic and mechanical properties. In this paper, we report theoretical study on structural, electronic, magnetic and mechanical properties of strontium titanate perovskite oxide SrTiO3. This material selected as energetic substrate primarily for its dimensional stability that is relatively insensitive to environment conditions. The calculations performed using the first-principles full-potential linear muffin-tin orbital (FP-LMTO) method, under the local spin density approximation (LSDA) and plus the on-site Coulomb interaction (LSDA+U) scheme. The analysis of densities of states, exchange interactions and magnetic moments reveals that SrTiO3 exhibits a semiconductor character with an energy gap of Eg = 2.68 eV, in excellent agreement with the previous experimental results. Keywords: MEMS material; Perovskite; Electronic properties; FP-LMTO method.

Virus-templated visible spectrum active perovskite photocatalyst

In this study, photocatalytically active perovskite strontium titanate (SrTiO3) nanowires are fabricated for the first time using genetically engineered AEEE-M13 phage and metal alkoxide precursors. One newly developed doping approach with an ammonia gas treatment efficiently produced strontium titanate nanowires, which split water and produce hydrogen under visible-light irradiation. The optical absorption of nitrogen-doped strontium titanate can be tuned by varying the processing conditions and lies in the visible spectrum range when treated at 625°C–650°C. The excellent hydrogen evolution rate of these nanomaterials is correlated with both optical absorption and nitrogen doping level.

Electrochemical Performance of YST Infiltrated and Fe Doped YST Infiltrated YSZ Anodes for IT-SOFC

Donor doped and donor-acceptor co-doped strontium titanate perovskite are investigated for intermediate temperature solid oxide fuel cells (IT-SOFCs) anodes. Y0.08Sr0.88TiO3-δ and Y0.08Sr0.92Ti1-xFexO3-δ (x = 0.2, 0.4) anodes were prepared by infiltration in 65% porous yttria stabilized zirconia (YSZ) scaffolds. The microstructure and electrical conductivity of Y0.08Sr0.88TiO3-δ and Y0.08Sr0.92Ti1-xFexO3-δ stronglydependsonFecontent.TheconductivityofY0.08Sr0.88TiO3-δ andY0.08Sr0.92Ti1-xFexO3-δ;decreases with increasing Fe content in humidified H2 .Y 0.08Sr0.88TiO3-δ ,Y 0.08Sr0.92Ti0.8Fe0.2O3-δ ,a nd Y0.08Sr0.92Ti0.6Fe0.4O3-δ, anodes with aP d/CeO2 catalyst show peak power density of 298, 421, and 321 mW cm −2 , respectively, in wet H2 at 1073 K.

Electronic surface properties of SrTiO3 derived from a surface photovoltage study

In the past, surface photovoltage (SPV) analysis has been successfully applied to derive the electronic defect status of a number of wide-bandgap semiconductor surfaces. Here, the method is applied to the model perovskite strontium titanate, whose SPV phenomena are comprehensively studied over seven decades of excitation-light intensity. The SPV was recorded by a Kelvin probe setup as a function of wavelength in order to extract the energetic positions of electronic surface states within the bandgap. At selected wavelengths addressing distinct surface states, SPV transients were measured as a function of light intensity and temperature. Several models known from the literature were used to estimate and cross check surface state parameters such as surface state densities, capture cross sections for photons and electrons, and the surface band bending in the dark and under illumination. In contrast to other wide-bandgap materials, SPV transients of SrTiO3 exhibit highly complex shapes, i.e. they (i) show signatures of multiple carrier transitions, (ii) mixtures of surface and bulk contributions, as well as (iii) both ex- and intrinsic SPV processes.

Molecular dynamics simulations of oxygen vacancy diffusion in SrTiO3

A classical force-field model with partial ionic charges was applied to study the behaviour of oxygen vacancies in the perovskite oxide strontium titanate (SrTiO3). The dynamical behaviour of these point defects was investigated as a function of temperature and defect concentration by means of molecular dynamics (MD) simulations. The interaction between oxygen vacancies and an extended defect, here a Σ3(111) grain boundary, was also examined by means of MD simulations. Analysis of the vacancy distribution revealed considerable accumulation of vacancies in the envelope of the grain boundary. The possible clustering of oxygen vacancies in bulk SrTiO3 was studied by means of static lattice calculations within the Mott–Littleton approach. All binary vacancy–vacancy configurations were found to be energetically unfavourable.

Study of Impedance Spectroscopy of Ferroelectric (Pb Sr)TiO3 Glass Ceramic System with Addition of La2O3

Various composition of glasses were prepared by melt-quenched method in the glass ceramic system 64[(PbxSr1-x)⋅OTiO2]-25[(2SiO2⋅B2O3)]-7[BaO]-3[K2O] doped with 1 mole % La2O3 (0.0≤x≤0.4). Solid solution of perovskite lead strontium titanate (PST) phase was crystallized in borosilicate glassy matrix with controlled heat treatment schedule. X-ray diffraction analysis of these glass ceramic samples revealed that major crystalline phase of the entire glass ceramic samples bears cubic structure similar to SrTiO3 ceramic. Impedance spectroscopy studies were done in the frequency range 0.01 Hz to 3.0 MHz and in the temperature range 50 to 275°C. Impedance and complex modulus spectroscopic techniques were used to find out the various contributions to the polarization process. Resistive and capacitive contributions of the processes relaxing in the highest frequency range were found to have low values in comparison to the resistive and capacitive contributions for the processes relaxing in lower and intermediate frequencies ranges.

Mapping the Density of Scattering Centers Limiting the Electron Mean Free Path in Graphene

Recently, giant carrier mobility μ (>10(5) cm(2) V(-1) s(-1)) and micrometer electron mean free path (l) have been measured in suspended graphene or in graphene encapsulated between inert and ultraflat BN layers. Much lower μ values (10000-20000 cm(2) V(-1) s(-1)) are typically reported in graphene on common substrates (SiO(2), SiC) used for device fabrication. The debate on the factors limiting graphene electron mean free path is still open with charged impurities (CI) and resonant scatterers (RS) indicated as the most probable candidates. As a matter of fact, the inhomogeneous distribution of such scattering sources in graphene is responsible of nanoscale lateral inhomogeneities in the electronic properties, which could affect the behavior of graphene nanodevices. Hence, high resolution two-dimensional (2D) mapping of their density is very important. Here, we used scanning capacitance microscopy/spectroscopy to obtain 2D maps of l in graphene on substrates with different dielectric permittivities, that is, SiO(2) (κ(SiO2) = 3.9), 4H-SiC (0001) (κ(SiC) = 9.7) and the very-high-κ perovskite strontium titanate, SrTiO(3) (001), briefly STO (κ(STO) = 330). After measuring l versus the gate bias V(g) on an array of points on graphene, maps of the CI density (N(CI)) have been determined by the neutrality point shift from V(g) = 0 V in each curve, whereas maps of the RS density (N(RS)) have been extracted by fitting the dependence of l on the carrier density (n). Laterally inhomogeneous densities of CI and RS have been found. The RS distribution exhibits an average value ∼3 × 10(10) cm(-2) independently on the substrate. For the first time, a clear correlation between the minima in the l map and the maxima in the N(CI) map is obtained for graphene on SiO(2) and 4H-SiC, indicating that CI are the main source of the lateral inhomogeneity of l. On the contrary, the l and N(CI) maps are uncorrelated in graphene on STO, while a clear correlation is found between l and N(RS) maps. This demonstrates a very efficient dielectric screening of CI in graphene on STO and the role of RS as limiting factor for electron mean free path.

Preparation of Porous Nano-Strontium Titanate and its Application in Removal of Heavy Metals from Environmental Water

Porous nano-strontium titanate (PST) was successfully prepared by the reversed-phase suspension polymerization and sol-gel method using reversed-phase suspension droplets as the template, and characterized by XRD and SEM. The ability of the new adsorption to remove lead, cadmium, zinc, copper and nickel ions from water samples was assessed. The results showed that the sorbents were porous, perovskite strontium titanate, and the average particle diameter of crystalloid was 30 nm. The lead, cadmium, zinc, copper and nickel ions were quantitatively retained at pH 5-8; their adsorption capacities of PST for lead, cadmium, zinc, copper and nickel ions were 145.9 mg•g-1, 4.3 mg•g-1, 25.2 mg•g-1, 19.6 mg•g-1and 3.7 mg•g-1, respectively. The adsorbent can be regenerated completely by elution with 0.5 mol•L-1 HNO3. The adsorbent has a promising prospect in removal or enriching of lead, cadmium, zinc, copper and nickel in water.

Dielectric investigation of lead‐free perovskite strontium titanate with 25% bismuth ceramics

AbstractIn this work lead‐free 0.75SrTiO3‐0.25BiTiO3 ceramics have been investigated in broad frequency range. Obtained results showed pronounced dispersion below room temperature typical for the dipolar glasses. The calculated relaxation time distribution function broadens toward longest relaxation times part on cooling. The obtained most probable relaxation time diverges according to the Vogel‐Fulcher relationship with the following parameters: dipole activation energy EA=2123 K, glassy state temperature T0=52.7 K, shortest relaxation time, referring to dipole relaxations at very high temperatures, τ0=2.1·10–14 s. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Multipod Crystals of Perovskite SrTiO3

We use our designed self-propagating high-temperature synthesis (SHS) method for the synthesis of the multipod crystals of cubic perovskite strontium titanate (SrTiO3), which has a scale of about 5 μm in length and 200 nm in the cross section of legs. Electron microscopy and diffraction measurements show that the formation mechanism of these multipod crystals is not the same as previous reports of hexapod and tetrapod crystals but fairly similar to snow crystals, in which multi-needle-like crystals lie a on two-dimensional plate and two needle-like crystals grow perpendicular to them. These SrTiO3 multipod shaped crystals should provide promising materials for fundamental investigations on nanomicro-scale shape dependent unique properties such as piezoelectricity, opt-electricity, catalyticity, superconductivity, and so on. As the first success of synthesis of multipod-shaped perovskite crystals, our method shows a possibility that any materials would form the multipod shapes.

Modified Pechini synthesis and characterization of Y-doped strontium titanate perovskite

This work reports the modified Pechini preparation and properties of an A-site deficient perovskite Sr 0.86Y 0.08TiO 3− δ (SYT). Good chemical homogeneity and electrical conductivity were determined, making SYT a potential conductive component material in a composite anode for solid oxide fuel cells. As an oxide with inherent resistance to oxidation and hydroxylation, SYT could be a substitute for the metallic Ni component in composite anodes for solid oxide fuel cells, particularly for reversible solid oxide fuel cells with attendant high steam concentrations.

Capacitance thermometer made of oxygen isotope-exchanged strontium titanate perovskite

A thermometer comprising a parallel capacitor made from a single crystal of oxygen isotope-exchanged SrTi(Ox18O1−x16)3 showed a dimensionless temperature sensitivity Sd exceeding 0.123 at 2K in the quantum ferroelectric region. On the other hand, the value of Sd in the quantum paraelectric region was 0.022 at 2K. The thermometric properties of the capacitance sensor were significantly improved by the O18 oxygen isotope exchange. A capacitance thermometer made of O18 oxygen isotope-exchanged SrTi(Ox18O1−x16)3 is a candidate element for accurate monitoring of cryogenic temperatures.

Synthesis and UV−Visible-Light Photoactivity of Noble-Metal−SrTiO3 Composites

The photocatalytic activity of strontium titanate (SrTiO3) perovskite films has been examined and compared with that of commercially available titania (TiO2, Degussa P25) in the degradation of a model pollutant, Victoria Blue dye. The effects of pH, synthesis temperature, and Sr/Ti ratio in the synthesis of the perovskite were examined. SrTiO3 was prepared using Ag, Pt, or Au and characterized using optical and surface analysis methods. We found no clear evidence of substitution of the noble metal into the SrTiO3 lattice, and most metal existed as zerovalent metal deposits. Addition of Ag to SrTiO3 showed the most promising catalytic activity toward dye degradation. Degradation of the dye under UV−visible light was also observed to be enhanced only for Ag−SrTiO3.

Direct large-scale synthesis of perovskite barium strontium titanate nano-particles from solutions

This paper reports a wet chemical synthesis technique for large-scale fabrication of perovskite barium strontium titanate nano-particles near room temperature and under ambient pressure. The process employs titanium alkoxide and alkali earth hydroxides as starting materials and involves very simple operation steps. Particle size and crystallinity of the particles are controllable by changing the processing parameters. Observations by X-ray diffraction, scanning electron microscopy and transmission electron microscopy TEM indicate that the particles are well-crystallized, chemically stoichiometric and ∼50 nm in diameter. The nanoparticles can be sintered into ceramics at 1150 °C and show typical ferroelectric hysteresis loops.

Thin-film field-effect transistors based on La-doped SrTiO3 heterostructures

Field-effect transistors have been fabricated from epitaxial perovskite strontium titanate heterostructures. Lanthanum-doped SrTiO3 was used as the semiconducting channel while insulating SrTiO3 was used as a gate insulator. Both depletion and accumulation effects in the channel have been studied from 300 to 4 K. Hall effect measurements indicate a temperature independent n-type carrier density around 5×1019 cm−3. At 300 K, typical mobilities are 2–3 cm2 V−1 s−1 while low temperature mobilities are as high as 15 cm2 V−1 s−1.

Strontium titanate resistance modulation by ferroelectric field effect

Among perovskite oxides strontium titanate (STO) SrTiO3 undergoes a metal–insulator transition at very low carrier concentration and exhibits high mobility values at low temperature. We exploited such electrical properties and the structural compatibility of perovskite oxide materials in realizing ferroelectric field effect epitaxial heterostructures. By pulsed laser deposition, we grew patterned field effect devices, consisting of lanthanum doped STO and Pb(Zr,Ti)O3. Such devices showed a resistance modulation up to 20%, consistent with geometrical parameters and carrier concentration of the semiconducting channel.