Perovskite SrTiO3 Research Articles

Ideal two-dimensional electronic structure in bulk lead titanate for superior thermoelectrics

An ideal two-dimensional (2D) electronic structure is revealed in n-type tetragonal perovskite PbTiO3 through first-principle calculations. This opens exciting prospects for its applications in thermal-to-electrical energy conversion. The electronic structure is regarded as ideally 2D when it is highly dispersive only along two axes, while along the remaining axis, it is nearly non-dispersive with a bandwidth smaller than 1 meV – insignificant when compared to thermal energy above room temperature (i.e., kBT ≥ 25.9 meV). As a basis for comparison, the electronic structure of the cubic perovskite SrTiO3 is calculated. It is nonideal 2D with the bandwidth along the less dispersive axis larger than the thermal energy. The ideal 2D electronic structure in PbTiO3 leads to a 2D-like density of states, resembling a step function around the conduction minimum while for SrTiO3, the density of states remains 3D-like with a square-root energy dependence. Consequently, n-type PbTiO3 exhibits superior effective band degeneracy within the Fermi window compared to SrTiO3, even though PbTiO3 is nondegenerate at the conduction band minimum, while cubic SrTiO3 is three-fold degenerate. This demonstrates the important role of the ideality in the 2D electronic structure. The ab-initio results demonstrate the potential of PbTiO3 as a promising thermoelectric material.

Investigations of crystallographic, magnetic, optical and photoluminescence nature of Sm2O3 doped SrTiO3 nanomaterials for LED

We used the solid-state reaction (SSR) method to make samarium oxide-doped SrTiO3 perovskite ceramic. We then put the synthesized samples through PXRD analysis to look at their structural properties. It is observed that the Sm-doped SrTiO3 exhibited a cubic phase, with no secondary phase resulting from Sm-doping. For a higher doping concentration (at 5 %) of Sm2O3, we slightly increased the particle size (from 30 nm to 33 nm). HR-SEM is used to study the morphology and nature of each sample. We examined the component composition of Sr, Ti, O, and Sm using the EDAX spectra and matched it with the stoichiometry ratio. FT-IR spectroscopy was carried out to analyze the presence of functional groups and chemical bonding in the samples. We studied the magnetic properties of the synthesized samples at room temperature using the VSM technique. The coercivity, retentivity, and saturation magnetization of SrTiO3 considerably increased with a higher doping concentration of Sm. We used UV diffuse reflectance spectroscopy to record the reflectance spectra and calculate the optical energy values. An increase in Sm-doping concentration red-shifted the absorption peaks. The photoluminescence spectra revealed that the samples exhibited a wide spectrum of colours. The proposed combination of nanomaterials is suitable to become an appropriate candidate for white LED applications.

Enhancing the piezoelectric coefficient of SrTiO3 nanocubes and PVDF film deposited by supersonic spraying for energy-harvesting nanogenerators

Many perovskites and their piezoelectric composites have been investigated for harvesting ambient mechanical energy over the past two decades; however, the prospects for their commercialization appear remote because of several practical challenges. Therefore, highly scalable supersonic cold-spraying technology was used to fabricate flexible piezoelectric films of poly(vinylidene fluoride) (PVDF) and a novel perovskite SrTiO3 (ST). Substantial shear stress was exerted on PVDF during cold spraying owing to the hydrothermally synthesized SrTiO3 nanocubes and supersonic velocity, and the resulting film delivered an effective piezoelectric coefficient (69.6 pm·V−1) as confirmed by piezo-response force microscopy. As a result, the piezoelectric nanogenerator yields a maximum power of 130 µW at a load resistance of 0.9 MΩ. The composite film exhibited durability for 21,000 tapping cycles with 20 N applied force and 7 Hz frequency. The flexibility endurance was confirmed from 3000 bending cycles. PENG attached to knee delivered 1 and 2.3 V on bending to 45 and 90°, respectively. After electrical poling, the PENG was subjected to a 20 N tapping force that yielded a piezopotential of 31 V. To the best of our knowledge, this is the first time piezoelectricity was obtained using an ST/PVDF composite via mechanical energy harvesting. The flexible PENG film deposited by cold-spraying shows good potential for wearable self-powered devices.

Terahertz electric-field-driven dynamical multiferroicity in SrTiO3

The emergence of collective order in matter is among the most fundamental and intriguing phenomena in physics. In recent years, the dynamical control and creation of novel ordered states of matter not accessible in thermodynamic equilibrium is receiving much attention1–6. The theoretical concept of dynamical multiferroicity has been introduced to describe the emergence of magnetization due to time-dependent electric polarization in non-ferromagnetic materials7,8. In simple terms, the coherent rotating motion of the ions in a crystal induces a magnetic moment along the axis of rotation. Here we provide experimental evidence of room-temperature magnetization in the archetypal paraelectric perovskite SrTiO3 due to this mechanism. We resonantly drive the infrared-active soft phonon mode with an intense circularly polarized terahertz electric field and detect the time-resolved magneto-optical Kerr effect. A simple model, which includes two coupled nonlinear oscillators whose forces and couplings are derived with ab initio calculations using self-consistent phonon theory at a finite temperature9, reproduces qualitatively our experimental observations. A quantitatively correct magnitude was obtained for the effect by also considering the phonon analogue of the reciprocal of the Einstein–de Haas effect, which is also called the Barnett effect, in which the total angular momentum from the phonon order is transferred to the electronic one. Our findings show a new path for the control of magnetism, for example, for ultrafast magnetic switches, by coherently controlling the lattice vibrations with light.

Investigation of perovskite catalysts BaTiO3 and SrTiO3 for the oxidative coupling of methane

Investigation of perovskite catalysts BaTiO3 and SrTiO3 for the oxidative coupling of methane

Enhancement of SrTiO3 photocatalytic efficiency by Al doping: Answers from the structure, morphology and electronic properties contributions

Our study focuses on disclosing the mechanisms standing behind the improved photocatalytic performance of SrTiO3, where Al modification of the perovskite structure boosts the photocatalytic O2 evolution activity of the Al:SrTiO3 system. By adapting the synthesis method that produces well-crystallized materials with low defect density and employing surface modification techniques, we aim to enhance the photocatalytic efficiency of SrTiO3via Al2O3 nanoceramic oxide doping at concentrations ranging from 0 to 10% and further examining of the relationship between doping process and the changes in the electronic and crystalline structure of SrTiO3. The prepared Al-based SrTiO3 perovskite samples (Al3%:SrTiO3, Al7%:SrTiO3, Al10%:SrTiO3) were thoroughly characterized to understand their structural, electronic, and morphological properties. Complementary X-ray techniques were employed to assess the stoichiometry (X-ray photoelectron spectroscopy - XPS), local environment, and chemical state (X-ray absorption spectroscopy - XAS in both total electron yield (TEY) and fluorescence yield (TFY). The comprehensive characterization enables us to understand the changes in the electronic properties and morphological features of the modified samples elucidating the surface formation mechanism while providing insights into the structural modifications induced by Al doping in the SrTiO3 perovskite lattice. Our findings give new perspectives for the development of Al-modified SrTiO3 perovskite materials with enhanced photocatalytic performance providing rich insights into the optimization of photocatalytic processes for applications in environmental remediation and sustainable energy production.

First-principles calculations to investigate impact of doping by chalcogen elements on the electronic, structural, and optical properties of SrTiO3 compounds

Doping techniques are commonly utilized to effectively modify the physical properties of a desired compound. In this study, we employed the first-principles DFT calculations with a GGA + TB-mBJ approach as implemented by the Wien2k code, by investigating the effects of oxygen group element concentrations on the structural, electronic, and optical properties of the perovskite substance SrTiO3. We calculated the formation energies of each doped structure to assess the viability of synthesis. The band gap is equal to 1.355 eV, 0.653 eV, and 0.632 eV for 12.5 % S, Se, and Te doped SrTiO3, respectively. For the pure SrTiO3, the band gap is 2.584 eV. According to our findings, raising the chalcogen concentrations resulted in a considerable decrease in band gaps and an improvement in the ability to absorb light in the visible range (380–790 nm), exceeding 105 cm−1 for Te doped SrTiO3 (STO). At zero frequency, the dielectric constant was found (ε1 (0)) to be 4.432 for SrTiO3 pure and 6.332 for SrTiO3 doped with Te (12.5 %) in GGA-PBE and (ε1 (0)) = 4.432 and 12.217 for GGA + mBJ. The optical conductivity of SrTO3 doped with Te is determined to be 0.322 * 104 /Ω.cm, in comparison to a value of 0.377 * 104/Ω.cm for mBJ. Our research revealed that raising the chalcogen concentrations significantly enhanced the electrical conductivity, as predicted, along with improvements in optical conductivity and reflectivity. SrTiO3-xYx (Y = S, Se, or Te) represents one of our quaternary alloys, demonstrating substantial potential as a promising material for advanced photovoltaic and solar cell applications. Our findings revealed that the doped materials exhibited significantly high absorption rates and productivity. We also examined additional optical parameters, including optical band gap, Urbach energy, and optical conductivity.

“Perovskite SrTiO3 for photo catalytic and optoelectronic applications”

In this work, we report the synthesis of SrTiO3(STO) nanoparticles by solid-state method for photocatalytic applications. The samples were calcinated at different temperatures to obtain a single phase. The prepared samples were studied using various analytical techniques such as XRD, DRS, SEM/EDAX, and FTIR. XRD analysis before and after high-temperature calcination indicates eliminating impurities from the sample. FTIR spectroscopy also correlates with the formation of pure SrTiO3. SEM analysis shows the formation of cube-like nanostructures and a bandgap of 3.2 eV was observed from Diffuse Reflectance Spectroscopy studies. The photocatalytic activity of SrTiO3 towards methylene blue was studied for various catalyst concentrations. The SrTiO3 catalyst attained a degradation efficiency reaching up to 83 % in 120 min. IV measurements of the SrTiO3 thin films reveal the potential optoelectronic applications.

Flexophotovoltaic Effect and Above-Band-Gap Photovoltage Induced by Strain Gradients in Halide Perovskites.

We have measured the flexophotovoltaic effect of single crystals of halide perovskites MAPbBr_{3} and MAPbI_{3}, as well as the benchmark oxide perovskite SrTiO_{3}. For halide perovskites, the flexophotovoltaic effect is found to be orders of magnitude larger than for SrTiO_{3}, and indeed large enough to induce photovoltages bigger than the band gap. Moreover, we find that in MAPbI_{3} the flexophotovoltaic effect is additional to a native bulk photovoltaic response that is switchable and ferroelectric-like. The results suggest that strain gradient engineering can be a powerful tool to modify the photovoltaic output even in already well-established photovoltaic materials.

Flame Spray Pyrolysis Synthesis of Vo-Rich Nano-SrTiO3-x.

Engineering of oxygen vacancies (Vo) in nanomaterials allows diligent control of their physicochemical properties. SrTiO3 possesses the typical ABO3 structure and has attracted considerable attention among the titanates due to its chemical stability and its high conduction band energy. This has resulted in its extensive use in photocatalytic energy-related processes, among others. Herein, we introduce the use of Flame Spray Pyrolysis (FSP); an industrial and scalable process to produce Vo-rich SrTiO3 perovskites. We present two types of Anoxic Flame Spray Pyrolysis (A-FSP) technologies using CH4 gas as a reducing source: Radial A-FSP (RA-FSP); and Axial A-FSP (AA-FSP). These are used for the control engineering of oxygen vacancies in the SrTiO3-x nanolattice. Based on X-ray photoelectron spectroscopy, Raman and thermogravimetry-differential thermal analysis, we discuss the role and the amount of the Vos in the so-produced nano-SrTiO3-x, correlating the properties of the nanolattice and energy-band structure of the SrTiO3-x. The present work further corroborates the versatility of FSP as a synthetic process and the potential future application of this process to engineer photocatalysts with oxygen vacancies in quantities that can be measured in kilograms.

Experimental investigation of structural, morphological, and optical characteristics of SrTiO3 nanoparticles using a shock tube for photocatalytic applications

Abstract We investigated the role of dynamic shock waves in perovskite SrTiO3 (STO) material. XRD, FE-SEM, EDAX, FTIR, UV-DRS, XPS, and Raman spectroscopy were all used to examine the title material. When perovskite sample was loaded with shocks, its diffraction pattern did not show any crystal structure changes. The FE-SEM results suggest that the grain size increased linearly with the number of shocks. We used energy-dispersive X-ray spectroscopy to perform elemental analysis; results confirmed that SrTiO3 NPs were indeed present. Although the impulse of the shock wave changed the optical characteristics, it did not affect the molecular structure. To find the optical band gap energies of untreated and shocked NPs, Tauc plot relationships were used. The band-gap energies got smaller as the shock pulse became more substantial. The impact of shock waves caused oxygen vacancies and surface defects, lowering band gap energy. The test for photocatalytic testing showed that SrTiO3 NPs that are loaded with shock waves worked much better when they were exposed to visible light. The characteristics, including stress, strain, and bond length, were found to significantly influence photocatalytic applications. In addition, attempts were made to provide a viewpoint for future study. Overall, the objective of this research was to provide valuable insights for experts engaged in the field of SrTiO3.

Hybrid Molecular Beam Epitaxy for Single-Crystalline Oxide Membranes with Binary Oxide Sacrificial Layers.

The advancement in thin-film exfoliation for synthesizing oxide membranes has led to possibilities for creating artificially assembled heterostructures with structurally and chemically incompatible materials. The sacrificial layer method is a promising approach to exfoliate as-grown films from a compatible material system, allowing for their integration with dissimilar materials. Nonetheless, the conventional sacrificial layers often possess an intricate stoichiometry, thereby constraining their practicality and adaptability, particularly when considering techniques such as molecular beam epitaxy (MBE). This is where easy-to-grow binary alkaline-earth-metal oxides with a rock salt crystal structure are useful. These oxides, which include (Mg, Ca, Sr, Ba)O, can be used as a sacrificial layer covering a much broader range of lattice parameters compared to conventional sacrificial layers and are easily dissolvable in deionized water. In this study, we show the epitaxial growth of the single-crystalline perovskite SrTiO3 (STO) on sacrificial layers consisting of crystalline SrO, BaO, and Ba1-xCaxO films, employing a hybrid MBE method. Our results highlight the rapid (≤5 min) dissolution of the sacrificial layer when immersed in deionized water, facilitating the fabrication of millimeter-sized STO membranes. Using high-resolution X-ray diffraction, atomic-force microscopy, scanning transmission electron microscopy, impedance spectroscopy, and scattering-type near-field optical microscopy (SNOM), we demonstrate single-crystalline STO membranes with bulk-like intrinsic dielectric properties. The employment of alkaline earth metal oxides as sacrificial layers is likely to simplify membrane synthesis, particularly with MBE, thus expanding the research and application possibilities.

Time-resolved nonlinear optical spectroscopy of perovskites.

Ultrafast decay of optical phonons has been studied in wide-bandgap BaSnO3 and SrTiO3 perovskites using nonlinear spectroscopy with 120 femtosecond time resolution. The coherent Raman mode excitations have been selected and traced with tunable optical pulses. Decay of symmetry forbidden modes of vibrations have been detected directly in time. Phonon decay rates for the main LO- and TO- phonon modes have been found to be within 1.36-1.78 ps-1 and are explained in terms of parametric phonon interactions and pure dephasing mechanisms in the materials that are of interest in microelectronic applications.

Optimized thermoelectric performance driven by A‐site deficient in SrxLa0.1TiO3−δ/TiO2−y composites

AbstractFor thermoelectric applications at high temperatures, perovskite SrTiO3 is a promising contender as an n‐type oxide thermoelectric (TE) material. In this work, SrxLa0.1TiO3−δ/TiO2−y composite ceramics were successfully synthesized by solid state reaction, using a combination of A‐site cation vacancy and composite fabrication. Through X‐ray diffractometer and scanning electron microscopy analysis, a complex microstructure composed of two kinds of titanium oxides was formed after reductive sintering and annealing. In addition, controlling the content of Sr vacancies in the SrxLa0.1TiO3−δ matrix increased the thermoelectric power factor (PF) by optimizing the weighted mobility in the composite, resulting in the highest PF of 425.8 μW m−1 K−2 and the maximum ZT of 0.16 for the Sr0.875La0.1TiO3−δ/TiO2−y composite through the synergistic optimization of electrical and thermal transport properties. The strategy proposed in this study of design A‐site‐deficient composites with nano‐sized metal paved a new way to fabricate high performance oxide thermoelectric materials.

Synergy of oxygen vacancy and Mn-substitution on SrTiO3 perovskites supported copper nanocatalysts for enhanced cyclohexylbenzene oxidation

Aiming at the main challenge of poor atomic economy for selective oxidation of hydrocarbons, synergistic catalysis on heterogenous catalysts has been focused on precisely regulating oxidation of specific chemical bonds in organic substrates. Here, a series of copper nanocatalysts loaded on Mn-substituted SrTiO3 perovskite-type oxides with varying Mn/Ti ratios for cyclohexylbenzene (CHB) oxidation to form cyclohexylbenzene-1-hydroperoxide (CHBHP) were successfully synthesized by coprecipitation method assisted by a micro-liquid-film reactor. It was found that the introduction of manganese created numerous oxygen vacancies in nanocatalysts, promoting the activation of oxygen molecules. Moreover, both copper and manganese ions enhanced the activated adsorption of CHB substrate. In particular, as-constructed Cu-based nanocatalyst with a substitution of 15% Mn into Ti sites showed superior catalytic oxidation efficiency with a ∼30% yield of CHBHP product, which is at the highest level compared with previously reported heterogenous catalysts, mainly attributable to the favorable synergy between copper, manganese, and oxygen vacancies. This work sheds light on the importance of multi-active site synergistic catalysis in advanced alkane oxidation processes.

Impact of rare earth (La, Pr, Eu) impurities on the perovskite SrTiO3 for efficient photocatalytic activity

Owing to the growing demand for environmentally friendly technologies across a wide range of fields, including energy, environment and medicine, photocatalytic materials have gained a lot of interest in recent years. First-principles calculations were used in order to examine a variety of physical characteristics such as electronic density of states, structural, optical, and photocatalytic properties of pristine and rare-earth (RE = La, Pr, Eu) doped SrTiO3. The reported electronic band gap of pristine SrTiO3 is Eg = 3.03 eV, which is reasonably consistent with prior theoretical and experimental studies. On the other hand, related to Sr(1−x)RExTiO3, the obtained energy band gaps are 2.75 eV, 2.80 eV, and 2.90 eV associated with Eu-SrTiO3, Pr-SrTiO3, and La-SrTiO3 respectively. The narrowing of the electronic band gap of the studied systems is due to the incorporation of RE-doped SrTiO3, which greatly enhanced the visible light absorption spectra and photocatalytic properties. Thus, it can be concluded that adding RE elements to this kind of materials, is a suitable choice for optoelectronic and photocatalytic applications.

The spectroscopy of hydride in single crystals of SrTiO3 perovskite.

Under reducing conditions, SrTiO3 perovskite can exchange up to 20% of its O2- ions for H- (hydride), greatly influencing its material properties. This not only presents intriguing possibilities for material design, but also for hydrogen sequestration in the deep earth, where perovskite-structured minerals are abundant. However, uncertainties remain surrounding hydride incorporation in SrTiO3, including details of the hydride structural state, and how hydride interacts with the broader defect chemistry of SrTiO3. Additionally, experimental studies of hydride in SrTiO3 and other perovskites may face analytical limitations. The most common methods for characterizing hydride, namely 1H NMR, may not be suitable in all experimental contexts, including materials with relatively low hydride concentrations and in situ high-pressure, high-temperature experiments. Here, we present an investigation of hydride in single crystals of SrTiO3 focused on detailed spectroscopic measurements. Through a combination of density functional theory (DFT)-assisted Fourier transform infrared (FTIR) spectroscopy and UV-vis spectroscopy, we observe structural hydride and its effects on the electronic transitions in SrTiO3. These results are compared directly against 1H NMR. We find that, although hydride is sometimes difficult to identify via FTIR, infrared spectroscopy is significantly more sensitive to hydride than 1H NMR. We also find that DFT makes accurate predictions about the spectroscopic behavior of hydride in SrTiO3, pointing to the value of ab initio techniques in future studies.

Enhancing electrochemical methane coupling in solid oxide cells by tuning oxygen species in the catalyst

La-doped SrTiO3 perovskite was explored as anode for methane coupling in solid oxide cells. DFT showed methane coupling can achieve higher conversions when activated on surfaces with fewer oxygen vacancies and more lattice oxygen.

Structural, Optical and Photocatalytic Properties of SrTiO3 Perovskite obtained by Solvothermal Method

Structural, Optical and Photocatalytic Properties of SrTiO3 Perovskite obtained by Solvothermal Method

Review of Systematic Tendencies in (001), (011) and (111) Surfaces Using B3PW as Well as B3LYP Computations of BaTiO3, CaTiO3, PbTiO3, SrTiO3, BaZrO3, CaZrO3, PbZrO3 and SrZrO3 Perovskites.

We performed B3PW and B3LYP computations for BaTiO3 (BTO), CaTiO3 (CTO), PbTiO3 (PTO), SrTiO3 (STO), BaZrO3 (BZO), CaZrO3 (CZO), PbZrO3 (PZO) and SrZrO3 (SZO) perovskite neutral (001) along with polar (011) as well as (111) surfaces. For the neutral AO- as well as BO2-terminated (001) surfaces, in most cases, all upper-layer atoms relax inwards, although the second-layer atoms shift outwards. On the (001) BO2-terminated surface, the second-layer metal atoms, as a rule, exhibit larger atomic relaxations than the second-layer O atoms. For most ABO3 perovskites, the (001) surface rumpling s is bigger for the AO- than BO2-terminated surfaces. In contrast, the surface energies, for both (001) terminations, are practically identical. Conversely, different (011) surface terminations exhibit quite different surface energies for the O-terminated, A-terminated and BO-terminated surfaces. Our computed ABO3 perovskite (111) surface energies are always significantly larger than the neutral (001) as well as polar (011) surface energies. Our computed ABO3 perovskite bulk B-O chemical bond covalency increases near their neutral (001) and especially polar (011) surfaces.