ABO3 Perovskite Research Articles

Perovskite Crystals: Unique Pseudo-Jahn–Teller Origin of Ferroelectricity, Multiferroicity, Permittivity, Flexoelectricity, and Polar Nanoregions

In a semi-review paper, we show that the local pseudo-Jahn–Teller effect (PJTE) in transition metal B ion center of ABO3 perovskite crystals, notably BaTiO3, is the basis of all their main properties. The vibronic coupling between the ground and excited electronic states of the local BO6 center results in dipolar distortions, leading to an eight-well adiabatic potential energy surface with local tunneling or over-the-barrier transitions between them. The intercenter interaction between these dipolar dynamic units results in the formation of the temperature-dependent three ferroelectric and one paraelectric phases with order–disorder phase transitions. The local PJTE dipolar distortion is subject to the presence of sufficiently close in energy local electronic states with opposite parity but the same spin multiplicity, thus limiting the electronic structure and spin of the B(dn) ions that can trigger ferroelectricity. This allowed us to formulate the necessary conditions for the transition metal perovskites to possess both ferroelectric and magnetic (multiferroic) properties simultaneously. It clarifies the role of spin in the spontaneous polarization. We also show that the interaction between the independently rotating dipoles in the paraelectric phase may lead to a self-assembly process resulting in polar nanoregions and relaxor properties. Exploring interactions of PJTE ferroelectrics with external perturbations, we revealed a completely novel property—orientational polarization in solids—a phenomenon first noticed by P. Debye in 1912 as a possibility, which was never found till now. The hindered rotation of the local dipole moments and their ordering along an external field is qualitatively similar to the behavior of polar molecules in liquids, thus adding a new dimension to the properties of solids—notably, the perovskite ferroelectrics. We estimated the contribution of the orientational polarization to the permittivity and flexoelectricity of perovskite crystals in different limiting conditions.

Strain induced Co/Mn ionization and magnetic properties in double-perovskite Nd2CoMnO6 thin films

The double-perovskite Nd2CoMnO6 (NCMO) thin films were epitaxially grown on LaAlO3 and SrTiO3 substrates with different orientations by the polymer-assisted deposition technique. A well crystallization quality of the films is confirmed by x-ray diffraction. The magnetism measurement suggests that all the films have a single ferromagnetic (FM) transition, but its substrate-orientational dependence is different from those in normal perovskite ABO3. By the analysis of the valence states of cations combining with the single FM transition, we suggest that the ionization degree of Co and Mn can be stimulated under both tensile and compressive strain, which can weaken the magnetic interaction. Thus, there are two aspects that competitively affect the magnetism [M(T) and Tc] of the NCMO film, i.e., the variation of oxygen octahedron similar to that in the normal perovskite ABO3 film and the degree of Co/Mn ionization, without changing the order of Co–O–Mn chain arrangement, resulting in the different orientation-dependent magnetism in NCMO films from that normally observed in ABO3 films. Our results give a systematic understanding of the substrate-induced-strain influence on the magnetic interaction in NCMO thin films and widen its practical application.

Observation of fault-free coherent layer during Ruddlesden–Popper faults generation in LaNiO3 thin films

Two-dimensional lattice defects, including surface and grain boundaries, in various perovskite oxides have garnered considerable attention, as the overall physical properties of the oxides can significantly vary depending on the atomic and electronic structure of the defects. In particular, because Ruddlesden–Popper (RP) planar faults have a unique lattice structure with [AO] monolayers being inserted in an ABO3 perovskite framework, they have attracted considerable attention, resulting in various relevant studies being conducted. This study focuses on the effect of lattice strain on formation of RP faults and on critical thickness in (001) epitaxial LaNiO3 thin-film fabrication through a sol–gel process. Atomic-scale direct observations identifies that a fault-free coherent buffer layer forms during the RP fault generation and its thickness varies depending on the strain exerted from the substrate. When DyScO3, the lattice mismatch of which is the largest, is used as a substrate, the critical thickness of the fault-free buffer layer remarkably reduces to a few unit cells. This work highlights the significance of direct observation to understand the defect formation in perovskite oxides.

Influence of A-site non-stoichiometry on electromechanical properties of Sr(Hf0.5Zr0.5)O3-modified Bi0.5(Na0.8K0.2)0.5TiO3 piezoelectric ceramics

Effect of Na non-stoichiometry in Sr(Hf0.5Zr0.5)O3-modified Bi0.5(Na(0.8+x)K0.2)0.5TiO3 ceramics was examined in the range of − 0.04 ≤ x ≤ 0.04. The effect of Na non-stoichiometry on microstructure, ferroelectric, piezoelectric, dielectric properties and high-temperature impedance was explored. Compared to the stoichiometric compositions, Na excess and deficiency exhibit the same effect as observed for the acceptor and donor doping, respectively. All non-stoichiometric and stoichiometric compositions exhibit a pure ABO3 perovskite phase with pseudocubic symmetry. The deficiency of Na in ceramics decreases the grain size and drives the system towards ergodic relaxor as evident by pinched ferroelectric loop and the negligible negative strain along with an increase in maximum strain (Sm). The corresponding normalized strain (Sm/Emax.) increased from 275 to 800 pm/V when Na content decreased from x = + 0.04 to − 0.04. In contrast, excess Na exhibits the converse effect and drives the system towards ferroelectricity. Composition with deficient Na also exhibits lower dielectric loss and increase in resistivity by an order of magnitude compared to excess Na as observed from the high-temperature dielectric and impedance measurements. The results of this study demonstrate that Na non-stoichiometry significantly affects the electric properties of the studied system and thus can be effectively modulated to achieve improved electromechanical properties for materials having actuator-based applications.

Polar Metal Phase Induced by Oxygen Octahedral Network Relaxation in Oxide Thin Films

ABO3 perovskite materials and their derivatives have inherent structural flexibility due to the corner sharing network of the BO6 octahedron, and the large variety of possible structural distortions and strong coupling between lattice and charge/spin degrees of freedom have led to the emergence of intriguing properties, such as high-temperature superconductivity, colossal magnetoresistance, and improper ferroelectricity. Here, an unprecedented polar ferromagnetic metal phase in SrRuO3 (SRO) thin films is presented, arising from the strain-controlled oxygen octahedral rotation (OOR) pattern. For compressively strained SRO films grown on SrTiO3 substrate, oxygen octahedral network relaxation is accompanied by structural phase separation into strained tetragonal and bulk-like orthorhombic phases, and the asymmetric OOR evolution across the phase boundary allows formation of the polar phase, while bulk metallic and ferromagnetic properties are maintained. From the results, it is expected that other oxide perovskite thin films will also yield similar structural environments with variation of OOR patterns, and thereby provide promising opportunities for atomic scale control of material properties through strain engineering.

Orthorhombically distorted perovskite SeZnO3 nanosheets as an electrocatalyst for lithium-oxygen batteries

Perovskite ABO3 provides higher catalytic activity than binary metal oxides owing to crystallographic defects and oxygen vacancies due to the multivalence of the A and B cations. In this study, perovskite SeZnO3 nanosheets were synthesized via a simple wet chemistry method with sodium dodecyl sulfate as the surfactant. Material surface analysis using O 1s X-ray photo-electron spectroscopy confirmed an Ovacancy concentration of 50%, confirming the presence of large amounts of defects on the surface of the SeZnO3 nanosheets. The lithium-oxygen batteries with SeZnO3 nanosheet as an oxygen-electrode electrocatalyst exhibited a high reversibility (140 cycles) and a stable rate capability (50–500 mA g−1). Additionally, electrochemical impedance spectroscopy measurements indicated that the electronic conductivity of a SeZnO3 nanosheet was higher than that of ZnO. Therefore, we propose that the unique SeZnO3 structure exhibits excellent catalytic activity and electrical conductivity and can serve as a route towards improved lithium-oxygen batteries.

Perspective on the pressure-driven evolution of the lattice and electronic structure in perovskite and double perovskite

Perovskite ABO3 as one of the most common structures has demonstrated great structural flexibility and electronic applications. Evolving from perovskite, the typical double perovskite A2BB′O6 has two element species (B/B′), where the ordered arrangements of BO6 and B′O6 octahedron provide much more tunability. Especially, by applying external pressure, the energetic order between different phases in perovskite and double perovskite materials can be notably modified with more fascinating physical properties. However, it is still a challenge to propose a general model to explain and predict the high-pressure structures and properties of various perovskites and double perovskites due to their flexibility and complexity. In this perspective, we will discuss pressure effects on the crystalline structure and electronic configurations in some perovskites and double perovskites. We then focus on a prediction method for the evolution of the lattice and electronic structure for such materials with pressure. Finally, we will give a perspective on current challenges and opportunities for controlling and optimizing structural and electronic states of a given material for optimized functionalities.

Investigations on tuning the band gaps of Al doped SrTiO3

Electronic structures of pure and Al-doped SrTiO3 (STO) were investigated by first-principles calculations based on the density functional theory. For Sr1−xAlxTiO3 (x = 0.125, 0.25), Al impurity bands were observed at the Fermi level and the band gap of SrTiO3was effectively tuned. According to the calculated densities of states, there was obvious hybridization between O-2p and Ti-3d orbitals. The A-site ions in the ABO3 perovskite structure played a key role in the tuning of the band gaps. When Sr was replaced by Al, the covalent bond of Ti-O was strengthened. The results had implications for the experimentally observed photocatalytic functionalities of SrTiO3.

Electronic and optical properties of group IIA-IVB cubic perovskite oxides: Improved TB-mBJ study

The recently developed improved Tran and Blaha modified Becke-Johnson exchange potential (TB-mBJ) approach within the framework of DFT is used to calculate band gaps and optical properties of cubic perovskites ABO3 (A = Ca, Sr, Ba and B = Ti, Zr, Hf). The bonding nature and electronegativity difference between B-cation and O atoms are considerably influencing the electronic band gaps of these compounds. Improved TB-mBJ treats the electronic density appropriately between them, producing accurate band gaps. The optical response shows wide range of light absorption, from visible to ultraviolet, in these compounds expecting their possible applications in various optoelectronic devices.

150 KeV Cu− ion- implantation in SrVO3 thin films: A study of Cu induced defect states

Investigations on the extrinsic defects induced alteration in B–O6 octahedra, energy band-structure amendments and physical assets of ABO3 perovskites are technologically important and require modest approaches for the defect creation and their investigations. In this study, Cu defects have been assimilated in SrVO3 films using 150 KeV Cu ion-implantation with two different ion fluences; 1.63 × 1015 ion/cm2 and 8.15 × 1015 ion/cm2. The implanted Cu ions do not make metallic/oxide clusters in SrVO3 films, as confirmed by XRD studies, but have facilitated the lattice parameter enlargement and energy band-gap narrowing by creating their defect states and V–O6 octahedra distortion. NEXAFS spectra at Cu L-edge have confirmed the Cu2+ ions in low/high Cu doses implanted SrVO3 films. Cu defects induced V–O6 octahedra distortion has manifested a diverse ligand field interaction between V 3 d and O 2p orbitals and has narrowed the; (i) energy gap of V 2p3/2 and V 2p1/2 transitions and (ii) energy gap between t2g/eg and the O 2p and metal (n+1)sp hybridized orbitals, leading to the band-structure alteration of SrVO3 films. Mechanistic understanding of band-structure perturbation is discussed in the light of ion-solid interaction induced defect formation in SrVO3 thin films.

Effect of preparation method and B-side metal type on the physicochemical properties of LaBO3 perovskite catalyst and its catalytic behaviour in the biomass pyrolysis

Although perovskites are extensively investigated in many areas, studies using perovskites as catalysts for biomass pyrolysis are still quite limited. While various transition metals can be inserted into perovskites to form different perovskites, it is critical to investigate the effects of various transition metallic substituents on the characterization of catalysts. This work involves the evaluation of nine perovskite-type catalysts in terms of their effectiveness and suitability for pyrolysis of date stone biomass. LaCoO3, LaMnO3 and LaNiO3 perovskite catalysts were prepared by sol-gel, hydrothermal and microwave methods and characterized by X-ray powder diffraction, scanning electron microscopy and surface area measurement. Pyrolysis of date stones has been performed in tubular reactor at 520 °C with 100 °C/min and a nitrogen gas flow rate of 100 cm3/min. The influences of catalyst preparation method on catalytic cracking of pyrolysis vapours in terms of bio-oil yields were examined. Additionally, the effect of B metal in ABO3 perovskite structure on catalyst character and pyrolysis yields were examined in detail. According to results, highest bio-oil yield was achieved as 23.4% with LaMnO3 catalyst synthesized with sol-gel method. All perovskite-type catalysts have reduced the bio-oil yield and improved the water and gaseous yield as expected. This study paves the way for developing more challenging perovskite catalysts for the renewable energy sources.

Atomic‐Scale Control of Electronic Structure and Ferromagnetic Insulating State in Perovskite Oxide Superlattices by Long‐Range Tuning of BO6 Octahedra

AbstractControl of BO6 octahedral rotations at the heterointerfaces of dissimilar ABO3 perovskites has emerged as a powerful route for engineering novel physical properties. However, its impact length scale is constrained at 2–6 unit cells close to the interface and the octahedral rotations relax quickly into bulk tilt angles away from interface. Here, a long‐range (up to 12 unit cells) suppression of MnO6 octahedral rotations in La0.9Ba0.1MnO3 through the formation of superlattices with SrTiO3 can be achieved. The suppressed MnO6 octahedral rotations strongly modify the magnetic and electronic properties of La0.9Ba0.1MnO3 and hence create a new ferromagnetic insulating state with enhanced Curie temperature of 235 K. The emergent properties in La0.9Ba0.1MnO3 arise from a preferential occupation of the out‐of‐plane Mn d3z2−r2 orbital and a reduced Mn eg bandwidth, induced by the suppressed octahedral rotations. The realization of long‐range tuning of BO6 octahedra via superlattices can be applicable to other strongly correlated perovskites for exploring new emergent quantum phenomena.

Stability and amphotericity analysis in rhombohedral ABO3 perovskites

Perovskite structures (ABO3) exhibit several desirable physical properties. These properties relate closely to composition and structure. For instance, structural distortions such as off-centering of B-site cation and/or tilting of BO6 polyhedra allow tuning of properties. Notably, the tilting of BO6 polyhedra yields a rhombohedral structure. This structure is increasingly relevant for functional perovskites. However, there exists no predictive approach thus far that allows for stability analysis in rhombohedral perovskites, and the determination of amphotericity domains for dopants. Here, we derive a tolerance factor equation (tR) that works well for the rhombohedral ABO3 perovskites. The predictive capability of the equation is benchmarked using sodium bismuth titanate (NBT), as a case in point. Using tR, we determined the following rare-earth doping trends in NBT: La to Nd occupy A-site; Tm to Lu go to B-site; and intermediate ions (Sm to Er) occupy both the sites (i.e., show amphotericity). The approach is consistent with experimental literature and hence benchmarked duly. The tolerance factor based analysis described here is hence plausibly relevant for the broader category of rhombohedral perovskites. In fact, it would be useful for accelerated prediction and determination of (a) stable rhombohedral structures, and (b) amphoteric dopants.

Effect of Lattice Strain on the Formation of Ruddlesden-Popper Faults in Heteroepitaxial LaNiO3 for Oxygen Evolution Electrocatalysis.

A great deal of research has recently been focused on Ruddlesden-Popper (RP) two-dimensional planar faults consisting of intervened [AO] monolayers in an ABO3 perovskite framework due to the structurally peculiar shear configuration. In this work, we scrutinize the effect of elastic strain on the generation behavior of RP faults, which are electrocatalytically very active sites for the oxygen evolution reaction (OER), in (001) epitaxial LaNiO3 thin films through by using two distinct single-crystal substrates with different cubic lattice parameters. Atomic-scale direct observations reveal that RP faults can be more favorably created when tensile misfit strain is exerted. Furthermore, we demonstrate that the controlled growth of thin films show notably enhanced OER activity by the RP faults. The findings in this study highlight the impact of symmetry-breaking defect formation for better oxygen electrocatalysis in perovskite oxides.

Machine learning substitutional defect formation energies in ABO3 perovskites

Perovskite oxides are a promising material platform for use in a wide range of technological applications including electronics, sensors, fuel cells, and catalysis. This is owing to the extraordinary tunability of their physical and chemical properties via defect engineering. The feasibility and the stability of a defect, such as a substitutional dopant, in the host lattice is usually obtained via experiments and/or through detailed quantum mechanical calculations. Both of these conventional routes are expensive and time consuming. An alternative is a data-driven machine learning (ML)-based approach. In this work, we have applied ML techniques to identify the factors that influence defect formation energy, which is an important measure of the stability of the defects, in perovskite oxides. Using 13 elemental properties as features and random forest regression, we demonstrate a systematic approach to down-selecting from the larger set of features to those that are important, establishing a framework for accurate predictions of the defect formation energy. We quantitatively show that the most important factors that control the dopant stability are the dopant ionic size, heat of formation, effective tolerance factor, and oxidation state. Our work reveals previously unknown correlations, chemical trends, and the interplay between stability and underlying chemistries. Hence, these results showcase the efficacy of ML tools in identifying and quantifying different feature-dependencies and provide a promising route toward dopant selection in the perovskites. We have developed a framework that itself is general and can be potentially applied to other material classes.

Ab initio calculations of ABO3 perovskite (001), (011) and (111) nano-surfaces, interfaces and defects

We carried out ab initio calculations for technologically important ABO3 perovskite, such as, SrTiO3, BaTiO3, SrZrO3 and PbZrO3 (001), (011) and (111) nano-surfaces, interfaces and bulk [Formula: see text]-centers. For SrTiO3, BaTiO3, SrZrO3 and PbZrO3 (001) nano-surfaces, as a rule, all first surface layer atoms relax inward, whereas all second layer atoms relax outward, and, typically, all third surface layer atoms, again, relax inward. Calculated (001) surface energies for SrTiO3, BaTiO3, SrZrO3 and PbZrO3 perovskites are almost equal for both BO2 and AO-terminations, and always smaller than the (011) and (111) surface energies. We discussed the results of our ab initio calculations dealing with BaTiO3/SrTiO3 and SrZrO3/PbZrO3 (001) interfaces. We analyzed systematic trends in ABO3 perovskite bulk [Formula: see text]-center ab initio calculations.

Effect of zirconium substitution on structural and optical properties of lanthanum orthoferrite

Lanthanum Orthoferrite (LaFeO3) is one of the perovskite oxide ABO3 materials. In this study, LaFe1-x Zr x O3 ( x = 0.01, 0.03 and 0.05) were synthesized by sol-gel method. Synthesized LaFeO3 with substituted Zr on Fe-site was characterized for crystal structures and optical properties. The X-ray diffraction (XRD) analysis confirms that the LaFe1-x Zr x O3 material has an orthorhombic structure with Pnma space group. The local structure of this sample was studied using Raman spectroscopy. Raman analysis shows, there are Zr4+ substituted effect on the tilt and stretching phonon modes of LaFeO3. Fourier Transform Infrared (FTIR) characterization test confirmed the effect of substitution on structural properties in terms of the upward shift of tilt, bending, and symmetric stretching of Fe-O-Fe bonds in FeO6. Optical bandgap has been determined using Kubelka-Munk function with the Tauc connection by the Uv-Vis Spectrophotometer which shows that the energy bands decrease (2.14–2.10 eV) with increased Zr-content.

Characteristics of Perovskites ReNiO₃ (Re = La and Nd) Prepared by Solid State Reaction in the Ambient of Oxygen.

In the proposed method, we could complete the synthesis with only 3 h of thermal treatment, which is relatively fast in comparison to the previously reported procedure, without an expensive gascontrolled chamber system. The compound comprises Re₂O₃ and NiO₃ powders that were mixed thoroughly in a stoichiometric ratio in a ball mill for 24 h and then dried in an oven at a 100 °C. The powder mixture was quickly calcined at various temperature for at least 3 h in an oxygen gas flow compared to conventional annealing method. After calcination at 1100 °C, the detected XRD peaks matched well with peaks of the standard ABO₃ perovskite structure. Moreover, EDX and FT-IR spectral analysis results confirmed that the mixture had formed stoichiometry ReNiO₃. All prepared samples comprised plate-like grains with a random orientation, and their average particle size was in the range of 1 to 3 μm calculated from FE-SEM images.

Stable electric polarization switching accompanied by magnetization reversal in B-site-substituted multiferroic BiFe0.9Co0.1O3 thin films

We report the substitution of manganese or scandium as a third element into the B-site of multiferroic BiFe0.9Co0.1O3 thin film in the ABO3 perovskite structure. Stable electric polarization switching via a biased cantilever was achieved multiple times in the BiFe0.892Co0.1Mn0.008O3 and BiFe0.87Co0.1Sc0.03O3 on SrTiO3 (001) while the piezoresponse force microscope image after the poling was inhomogeneous and was not reversible in BiFe0.9Co0.1O3 thin film on SrTiO3 (001). Although the electric domains are fragmented by Mn substitution, magnetization reversal by electric field was observed in the BiFe0.892Co0.1Mn0.008O3 thin film on SrTiO3 (001) as well as in the BiFe0.9Co0.1O3 on GdScO3 (110) studied previously.

Emerging Perovskite Electromagnetic Wave Absorbers from Bi-Metal–Organic Frameworks

Highly efficient electromagnetic wave absorbers are urgently demanded for the removal of electromagnetic pollution and interference in consumers’ electronics. ABO3 perovskite oxides with fascinatin...