Doped Strontium Titanate Research Articles

Grain boundary segregation in iron doped strontium titanate: From dilute to concentrated solid solutions

Strontium titanate, a perovskite oxide, is a frequently studied material for a large variety of applications. When acceptor-doped (with Fe, for example), the material is useful for its mixed oxygen and electronic conductivity, with potential use in oxygen transport membranes or as a cathode for solid oxide fuel cells. A barrier to conductivity in perovskites is the presence of space charge regions at the grain boundaries, which form due to the segregation of charged point defects. Typically, space charge theory assumes bulk dopant concentrations beneath the dilute limit, however concentrated solid-solutions are often utilized in applications. The current work aims to address this disparity: grain boundary segregation in strontium ferrite-strontium titanate solid-solutions is analyzed at three compositions, with Fe contents ranging from near the dilute limit to well above the dilute limit (Fe contents of 2 %, 5 %, and 25 % on the B-site of the perovskite). Electrochemical impedance spectroscopy shows an increase in material conductivity as Fe is added. High-resolution STEM imaging and spectral mapping is utilized, showing that Fe segregates to the grain boundary core, contrary to what is expected from space charge theory. As the Fe content is increased, the amount of Fe segregated to the boundary increases significantly, but the segregation width of Fe at the boundary remains consistent.

Effect of graphene oxide and carbon black on the thermoelectric performance of niobium doped strontium titanate

Strontium titanate-based ceramics are promising n-type thermoelectrics due to their low cost and high thermal and chemical stability. Here, SrTi0.85Nb0.15O3 was prepared with carbon additions of electrochemically produced graphene oxide (eGO) and commercially available carbon black (CB). Ceramic samples were sintered at 1700 K under a reducing atmosphere. XRD, HR-TEM and Raman spectra confirmed the matrix phase was cubic perovskite; there were no carbon residues. By incorporating graphene oxide, the electrical conductivity increased nine-fold to 2818 S cm−1 at 300 K as a result of enhanced carrier mobility. In contrast, the carbon black samples exhibited low density and a small average grain size of ∼1 μm. High-resolution X-ray photoelectron spectroscopy revealed the presence of a large number of ionised impurities in the carbon black samples, which significantly enhanced scattering effects; low thermal conductivities of 1.7 W m−1 K−1 were achieved at 873 K. The work reveals that eGO promotes charge transport in SrTiO3, while CB significantly suppresses phonon transport. Both effects are relevant to the development of other thermoelectrics.

Investigating the Interplay of Polar Nanodomains and Superconductivity in Doped Strontium Titanate through Transmission Electron Microscopy

Investigating the Interplay of Polar Nanodomains and Superconductivity in Doped Strontium Titanate through Transmission Electron Microscopy

Comparison study of aluminum (Al)-doped strontium titanate (SrAlxTi1-xO3; x = 3 % and 5 %) photocatalyst for Methylene blue degradation

One famous photocatalyst to degrade methylene blue (MB) dye wastewater is SrTiO3 (strontium titanate or STO), whose performance can be enhanced by doping Aluminum (Al). This study aimed to fabricate Al-doped STO (SrTi1-xAlxO3; x = 3 % and 5 %) photocatalysts and compare the effects of low Al concentrations on photocatalytic performance. The photocatalysts were fabricated using a coprecipitation route and confirmed by XRD and FTIR instruments. The photocatalytic performance of Al-doped STO against MB was tested under varied UV light exposure hours and examined using a UV–Vis Spectrophotometer. In conclusion, Al-doped STO 3 % demonstrated better photocatalytic performance with a higher %degradation and faster degradation rate.

Emerging silver-doped strontium titanate nanostructures as photocatalysts for the degradation of organic pollutants under visible light

The primary objective of this research is to explore a novel and straightforward method, known as one-pot hydrothermal synthesis, for producing photocatalyst nanocomposite materials consisting of perovskite-based silver doped strontium titanate (Ag–SrTiO3). The investigation focused on assessing the photocatalytic effectiveness and recyclability of these nanocomposites when employed to eliminate ciprofloxacin (CIP) antibiotics under visible-light exposure. The XRD of the Ag–SrTiO3 exhibited a highly crystalline nature with stacked cube morphology, which was also revealed through the SEM technique. The TEM analysis showed the characteristics of the materials such as particle shape, and the SAED pattern confirmed the crystalline phases. The essential reaction parameters, including the amount of catalyst used, the solution's pH level, and the initial pollutant concentration, were altered to identify the most favorable conditions for photodegradation. Furthermore, this composite catalyst displayed excellent stability and could be reused, achieving an 84.5 % removal of CIP after five consecutive cycles. Through scavenger tests, it was determined that photogenerated holes (h+) and superoxide free radicals (•O2) played key roles in the degradation process. This research offers valuable insights into designing highly efficient nanomaterials for the removal of antibiotic degradation from wastewater, and it proposes a possible reaction mechanism.

Effect of vacuum sintering on the microstructure and spectroscopic properties of Eu doped strontium titanate ceramics

In this work, we report on the optical properties of europium-doped SrTiO3, synthesized in situ via the sol-gel method as nanopowders and sintered ceramic bulks by heat treatment in vacuum. The structure and morphology of the Sr1-3x/2EuxTiO3 (x = 0.01–0.07) nanopowders and ceramics, concerning to the europium concentration, were characterized by X-ray powder diffraction, field emission scanning electron microscopy, and transmission electron microscopy. The optical properties of as-prepared materials were also investigated. These analyses demonstrated that a temperature of 1425 °C in a vacuum of 10−4 Pa and a plateau of 4h are the optimal sintering conditions for Sr1-3x/2EuxTiO3 ceramics. Eu3+ doped SrTiO3 ceramics exhibit visible red photoluminescence characteristics. The emission of SrTiO3:Eu3+ phosphor with different amounts of Eu3+, excited by 395 nm and 465 nm light, was studied. The emission spectra exhibit characteristic luminescence from 5D0 → 7Fj (j = 0, 1, 2, 3, 4) intra-4f shell Eu3+ ion transitions. The most intense transitions are 5D0 → 7F1 (591 nm) for pumping at 395 nm and, 5D0 → 7F2 (615 nm) at 465 nm. The corresponding coordinates CIE for the Eu-doped SrTiO3 samples were calculated from the emission spectra obtained at 395 nm and 465 nm excitation wavelengths. This study demonstrates that the original protocol of materials engineering used is a simple and efficient method for manufacturing novel nanophosphors with enhanced reddish-orange emission. The as-obtained results indicated that the sol-gel synthesis combined with the sintering process in a vacuum at an appropriate temperature, plateau, could be a novel way to fabricate materials based on strontium titanate with reasonable optical properties.

Ni and Fe Doped (La,Sr)TiO3 Fuel Electrodes for Solid Oxide Cells – Electrical and Electrochemical Properties

Development of robust and impurity tolerant solid oxide cells (SOCs) has attracted a significant R&D-effort in recent years. The shortcomings of Ni-YSZ fuel electrodes in terms of redox stability, carbon and sulfur tolerance and long-term durability under strong polarization has spurred the search for alternative fuel electrode materials. Among them, doped strontium titanate materials has shown promising performance due to their good electrical transport properties, chemical and redox stability and tolerance towards impurities.In the present study, the electrical properties of the La0.477Sr0.33Ni0.03Fe0.03Ti0.94O3- δ (LSFNT) material, which is designed with the potential for exsoluting Ni and Fe nanoparticles, is investigated in detail. In addition, the performance of LSFNT based fuel electrodes is characterized in a symmetrical cell configuration. The electrical conductivity measurements are performed on both dense and porous LSFNT layers, as a function of temperature and pO2. The pre-reduced (1100oC, 24 hours, dry 5%H2/N2) dense LSFNT sample showed an electrical conductivity of ca. 10 S/cm at 850 oC in dry 5%H2/N2. The “in-situ reduced” (850oC, 700 hours) porous LSFNT layer showed a conductivity 10 times smaller. The conductivity was tracked as a function of pO2 showing an approximate pO2 -1/6 dependence. Also the ionic conductivity of the material was determined using an electron blocking method. At 850oC at a pO2 of 10-20 bar the ionic conductivity is ca. 0.05 S/cm at which is similar to that of Y2O3 doped ZrO2 electrolytes demonstrating that LSFNT is indeed a very good mixed ion- and electron-conducting material.Motivated by the observed conductivities SOC fuel electrodes of LSFNT were prepared by incorporating Gd-doped CeO2 electrocatalyst into LSFNT porous backbones and their electrochemical performance was measured in 50% H2 / 50% H2O at OCV. An electrode polarization resistance of 0.05 Ω cm2 at 850oC and 0.26 Ω cm2 at 650 oC is measured for these electrodes. The polarization resistance at 850 oC is comparable to that of Ni-YSZ fuel electrodes; while at 650oC it is significantly lower in similar atmospheres. This promising electrochemical performance shows the potential of the LSFNT fuel electrodes, as an alternative to Ni-YSZ fuel electrodes, in solid oxide cell applications.

Efficiency of volatile organic compound degradation in air using doped strontium titanate photocatalysts. Quenching experiments towards understanding of doping mechanisms

Efficiency of volatile organic compound degradation in air using doped strontium titanate photocatalysts. Quenching experiments towards understanding of doping mechanisms

Visible Light Photocatalysts: Studying Dopant Heterogeneity in Rhodium Doped Strontium Titanate.

Visible Light Photocatalysts: Studying Dopant Heterogeneity in Rhodium Doped Strontium Titanate.

T-Square Dependence of the Electronic Thermal Resistivity of Metallic Strontium Titanate.

The temperature dependence of the phase space for electron-electron (e-e) collisions leads to a T-square contribution to electrical resistivity of metals. Umklapp scattering is identified as the origin of momentum loss due to e-e scattering in dense metals. However, in dilute metals like lightly doped strontium titanate, the origin of T-square electrical resistivity in the absence of umklapp events is yet to be pinned down. Here, by separating electron and phonon contributions to heat transport, we extract the electronic thermal resistivity in niobium-doped strontium titanate and show that it also displays a T-square temperature dependence. Its amplitude correlates with the T-square electrical resistivity. The Wiedemann-Franz law strictly holds in the zero-temperature limit, but not at finite temperature, because the two T-square prefactors are different by a factor of ≈3, like in other Fermi liquids. Recalling the case of ^{3}He, we argue that T-square thermal resistivity does not require umklapp events. The approximate recovery of the Wiedemann-Franz law in the presence of disorder would account for a T-square electrical resistivity without umklapp.

Synthesis of Microcomponent Doped Strontium Titanate Single Crystal Special Raw Material Powder by Solid Phase Method

Synthesis of Microcomponent Doped Strontium Titanate Single Crystal Special Raw Material Powder by Solid Phase Method

Tailoring the magneto-electronic and optical properties of cobalt doped strontium titanate by first-principles calculations

Ferromagnetic semiconductors or half metals offer strategic advantage in spintronic applications due to their robust stray fields and ultrafast magnetic dynamics. Controlling their magnetization and readout of their magnetic state are essential for these applications but remain challenging. Herein, we present a density functional theory (DFT) based full potential linearized augmented plane wave (FP-LAPW) analysis of the magneto-optical properties of novel and most widely studied diamagnetic SrTiO3 (STO) doped with cobalt. Pure STO is non-magnetic wide band gap (3.25 eV) semiconductor. Our study shows that versatile transport and magnetic properties can be obtained in CoxSr1-xTiO3, ranging from magnetic semiconductor to half metallic ferromagnetic nature depending upon the dopant's concentration. Spin resolved electronic properties and non-zero values of calculated magnetic moments for doped supercells reveal that Co0·125Sr0·875TiO3 and Co0·25Sr0·75TiO3 are good DMSs while Co0·5Sr0·5TiO3 and Co0·75Sr0·25TiO3 are half metallic ferromagnets. The analysis of band structures and density of states reveal that partially filled Co-3d and O-2p states show hybridization. Moreover, calculated optical conductivity lie in the visible region of the order of 103 (Ω cm)−1 while reflectivity in this region is minimum. Our findings demonstrate Co doping as a powerful approach to control the magneto-optoelectronic physics in STO, which will stimulate further experimental research with promise for tailored magnetic and optoelectronic properties in Co doped STO systems.

Multielement Doped Barium Strontium Titanate Nanomaterials as Capacitors

Due to the growing demand of energy and wastage of energy, there exists an interest of storing energy so that it could be utilized efficiently. Capacitors are materials designed for such an application. Ferroelectric materials are known for their application as capacitors. Of such materials, perovskites are the preferable classes of materials that have been used as capacitors. Barium strontium titanate nanomaterial is a member of perovskites which encompasses a smaller dielectric loss, elevated dielectric constant, and good thermal stability. Research studies also clarified that incorporating dopants into a barium strontium titanate nanomaterial of high dielectric materials including metal/metal oxides enhances their efficiency and effectiveness. Moreover, multielement doping or codoping has shown better dielectric properties as compared to the unidoping of BST. In this review, barium strontium titanate capacitors codoped with more than one metal/metal oxides have been studied most of which have shown that the codoped barium strontium titanate materials possess improved and sufficient dielectric properties to be utilized as capacitors. We believe that this work will have of its own contribution on understanding the doped barium strontium titanate nanomaterial by clarifying the most probable and detail reasons behind the enhancement of dielectric properties of codoped barium strontium titanate nanomaterials.

Comparison of structural and dielectric properties of doped (M, R and A) barium strontium Titanate: Review

Barium Strontium Titanate is lead -free, environment friendly compound having high dielectric constant, high dielectric tunability and low dielectric loss which make this perovskite material applicable for various industrial, electronic and microwave tunable device. Recent development in Barium Strontium Titanate by doping modification of (Alkali metal, Transition and Rare earth metal) are reviewed. The A site doping, B site doping and both site co-doping modification are analysed and summarized respectively. By using multiple manufacturing techniques, including the conventional method and sol–gel, the comparison of the dielectric and microstructure properties of barium strontium titanate with different dopants is critically examined. Out of these dopants, Transition metal doped Barium Strontium Titanate show more suitable properties for applications like storage capacitors and phase shifters etc. BST ceramics with transition metal doping shows low dielectric loss and high dielectric constant suitable for DRAM cell capacitor as well as for tunable antennas having large frequency domain, as well as for microwaves devices.

Terahertz time-domain spectroscopic ellipsometry of metallic strontium titanate

The coexistence of the polar instability and metallic conduction has attracted much attention. Ferroelectric soft optic modes and carrier electrons were investigated in A- and B-site heterovalent doped strontium titanate SrTiO3 crystals by the terahertz time-domain spectroscopic ellipsometry. The observed real and imaginary parts of a complex dielectric constant were fitted by the damped harmonic oscillator model for the ferroelectric soft optic mode and the Drude-Smith model for carrier electrons. The observed soft mode frequency increases as the La and Nb content increases. It is found that the square of the ferroelectric soft mode frequency linearly changes to the carrier electron concentration. This fact indicates that the carrier electrons suppress the ferroelectric instability and the ferroelectric soft mode frequency increases as the carrier concentration increases.

Photocatalytic water splitting of improved strontium titanate for simultaneous separation of H2 in a twin photoreactor

A core-shell structural Rh-CrOx loaded on Al3+ doped strontium titanate was used for photocatalytic water splitting. A specially designed twin photoreactor, which integrates the water splitting and the degradation of isopropanol, can simultaneously carry out the degradation of isopropanol and hydrogen production. A flux method was conducted to prepare Rh@CrO3 cocatalyst on Al3+ doped high-crystallinity strontium titanate for the photocatalyst of hydrogen evolution. Nearly 1200 μmole/g of hydrogen was evolved in photocatalytic whole water splitting in five hours under simulated AM 1.5 G sunlight. Pt-loaded WO3 was utilized to degrade 100 ppm isopropanol solution. The above photocatalysts were used in the twin reactor with electron-mediator I-/IO3- and a Neosepta anion-exchanged membrane. Hydrogen evolution of 1102 μmole/g and isopropanol removal of 10.1% were achieved in five hours, indicating the rate-limiting H2 rate was overcome. The quantum efficiencies on the hydrogen-evolution and degradation sides were estimated to be 0.102% and 0.123%, respectively.

Experimental Investigation on Structural, Dielectric, and Transport Properties of Copper Doped SrTiO3

Copper -doped Strontium Titanate (STO) with Copper filler percentages of 5% and 10% was prepared through a solid-state reaction method at high temperatures. The structural study of the materials was characterized by the X-ray diffraction technique and confirmed to be in the Cubic phase. Also, the surface morphology of the samples was studied by scanning electron microscopy. The impedance study of the samples was characterized by an LCR meter between the frequencies ranges 102-106 Hz. The exponential dependence of ac conductivity on frequency was confirmed where the value of ac conductivity increases with the rise in filler concentration from 5% to 10%.

The study of nickel impurity segregation on LSNT perovskite open surfaces by means of ab initio molecular dynamics

In this paper, the segregation of the Ni impurity on open surfaces of the doped strontium titanate perovskite is investigated by means of ab initio molecular dynamics method based on the density functional theory and applied to a model periodic cell with stoichiometry La0.5Sr0.5TiO3 (LST).The performed studies are based on recent experimental observations on the segregation of Ni impurity atoms and their tendency to form clusters at the boundaries of defect structure of La0.2Sr0.7Ni0.1Ti0.9O3-δ (LSNT) perovskite. The results of the first-principles calculations of segregation energy showed that Ni does actively segregate toward the open surfaces. It was found that during segregation, nickel atoms leave the crystal volume to the perovskite surface and rise above its upper layer. Thus, the obtained results confirm the experimental data on the segregation and formation of nickel clusters on open LSNT surfaces.

Isotope tuning of the superconducting dome of strontium titanate

Doped strontium titanate SrTiO$_3$ (STO) is one of the most dilute superconductors known today. The fact that superconductivity occurs at very low carrier concentrations is one of the two reasons that the pairing mechanism is not yet understood, the other is the role played by the proximity to a ferroelectric instability. In undoped STO, ferroelectric order can in fact be stabilized by substituting $^{16}$O with its heavier isotope $^{18}$O. Here we explore the superconducting properties of doped and isotope-substituted SrTi$(^{18}$O$_{y}^{16}$O$_{1-y})_{3-\delta}$ for $0\le y \le 0.81$ and carrier concentrations between $6\times 10^{17}$ and $2\times 10^{20}$ cm$^{-3}$ ($\delta<0.02$). We show that the superconducting $T_c$ increases when the $^{18}$O concentration is increased. For carrier concentrations around $5\times 10^{19}$~cm$^{-3}$ this $T_c$ increase amounts to almost a factor $3$, with $T_c$ as high as 580~mK for $y=0.74$. When approaching SrTi$^{18}$O$_3$ the maximum $T_c$ occurs at a much smaller carrier densities than for pure SrTi$^{16}$O$_3$. Our observations agree qualitatively with a scenario where superconducting pairing is mediated by fluctuations of the ferroelectric soft mode.

Doped Strontium Titanate Anode for Solid Oxide Fuel Cells: Electrical and Sintering Behavior

When doped strontium titanate is used as anode material for solid oxide fuel cells, it demands good electron-ion mixed conductivity and proper sintering kinetics. In this work, La0.5Sr1.5Ti1.5Fe0.5O3-δ, La0.5Sr1.5Ti1.5Co0.5O3-δ, and La0.5Sr1.5Ti1.5Ni0.5O3-δ anodes with double perovskite structure were synthesized. The porosity of the anodes was between 38.5% and 18.7% after sintering at 1200 °C in air. The apparent electrical conductivity reached 500–600 S⋅cm−1 at 700 °C under H2 atmosphere and no pre-reduction process at high temperature was involved. La0.5Sr1.5Ti1.5Co0.5O3-δ anode showed the highest sintering activity and it reached the peak rate of sintering shrinkage at 1209 °C. The doping of Fe, Co and Ni elements into strontium titanate exhibited great potential to adjust the conductivity and sintering kinetics for anode materials.