Complex Perovskite Research Articles

Machine learning-enhanced band gaps prediction for low-symmetry double and layered perovskites.

Density functional theory (DFT) calculations are widely used for material property prediction, but their computational cost can hinder the discovery of novel perovskites. This work explores machine learning (ML) as a faster alternative for predicting band gaps in complex perovskites, focusing on low-symmetry double and layered structures. We employ Support Vector Regression (SVR), Random Forest Regression (RFR), Gradient Boosting Regression (GBR), and Extreme Gradient Boosting (XGBoost) to predict both direct and indirect band gaps. Model performance is evaluated using Mean Absolute Error (MAE), Mean Squared Error (MSE), and R-squared (R²) metrics. Our results reveal SVR as the most effective general model for predicting band gaps in both double and layered perovskites. Interestingly, for double perovskites specifically, XGBoost achieves even higher accuracy when incorporating derivative discontinuity as a feature. Feature importance analysis identifies the standard deviation of valence charges ("Valence (std)") as the most critical factor for band gap prediction across all studied perovskites. This research demonstrates the potential of ML for efficient and accurate band gap prediction in complex perovskites, accelerating material discovery efforts.

Investigation of Sr-substituted Ba1-xSrx(Zn1/3Nb2/3)O3 complex perovskites: structural, electrical and electrochemical properties

Herein we report the structural, dielectric and electrochemical properties of Ba1-xSrx(Zn1/3Nb2/3)O3 (BSZN, 0 ≤ x ≤1) solid solution synthesised by solid-state reaction. A complete substitutional solid solution was obtained, wherein the BSZN cubic perovskites of the space group of Pmm were obtained at x ≤ 0.6 while the pseudo-cubic phases were discernible at x > 0.6. The nano-sized crystallites, as determined by both Scherrer and Williamson-Hall analyses, supported the claim of large polyhedral grains of 0.1 to 0.3 μm by FE-SEM. Both ε′ and tan δ were found to vary consistently with increasing dopant concentration, except for an anomalous observation for the composition, x = 0.6 with the lowest tan δ of 0.0783 and the highest ε′ of 27.5. Such phenomenon could be attributed to the combined effects of larger grain size, higher relative density and stronger polarisation per molar volume. The impedance analysis revealed that these BSZN perovskites were of the negative temperature coefficient of resistance (NTCR) type. The combined plots of imaginary modulus (M″) and impedance (Z″) against frequency showed the short-range movement of localised charge carriers, suggesting a non-Debye-type relaxation process.

Disentangling the Optoelectronic Behavior of Lead Iodide Governed by Two-Dimensional Electron Confinement.

We present a joint experimental and theoretical study for complete spectroscopic characterization and optoelectronic properties of lead iodide. Experimentally, we combine X-ray diffraction experiments to elucidate the structure with photoelectron spectroscopy to explore its electronic structure. Computationally, simulations are performed in the frame of density functional theory. We show that PbI2 presents a two-dimensional layered structure and exhibits a large transient photocurrent effect under visible light illumination, which are compatible with the surface photovoltage scenario. The transient photocurrent has an extremely long lifetime: when the sample is lightened with visible light, it shows very long relaxation times and, consequently, huge charge carrier diffusion lengths. We explain this anomalous behavior with the slow carrier mobility of holes and electrons caused by the 2D electron confinement in the layered material. Our results can be used as a simple model for understanding the optoelectronic properties of more complex 2D hybrid perovskites.

Structural, dielectric, impedance, ferroelectric, piezoelectric, energy harvesting, and optical properties of Ca1-xZnx(Fe0.5V0.5)O3 ceramics

The present work mainly describes the fabrication and characterization (structural, micro-structural, dielectric, piezoelectric, optical, and energy-harvesting) of Ca1-xZnx(Fe0.5V0.5)O3 with x = 0, 0.05, 0.10, and 0.15 complex perovskite. All four compounds are prepared by using the solid-state reaction method (calcination temperature = 1100 °C (6 h) and sintering temperature = 1150 °C (7 h)). The room temperature XRD data analysis confirms all four compounds' single-phase orthorhombic structures. Different modes of vibrations are confirmed by Raman spectroscopy. The grain size increases from 1.09 μm to 2.53 μm with increased zinc concentration. The variation of dielectric constant with frequency has been explained based on Maxwell-Wagner polarization. The effects of grain and grain boundary have been confirmed by impedance spectroscopy, which contributes to the conduction and relaxation mechanism of the compounds. The d33, g33, and energy harvesting performance gradually increase with an increase in zinc concentration, confirming the enhancement of the compounds' piezoelectric properties. The decrease in the band gap from 3.58 eV (x = 0) to 3.00 eV (x = 0.15) confirms the enhancement of optical properties.

Dft-based nano architectonics: Exploring Structural, Mechanical, and optoelectronic properties of halide double perovskites K2ScAgX6 (X=Cl, Br and I)

This report details a computational analysis of the various characteristics of newly developed double perovskites (DPs) K2ScAgX6 (where X =Br, Cl, and I), with an emphasis on their potential uses in energy storage and solar energy sector. Through the application of Density Functional Theory (DFT); the structural, mechanical and optoelectronic properties of these DPs materials have been investigated. The cubic phase of K2ScAgX6 DPs was confirmed, with tolerance factor (τ) values of 0.818, 0.812, and 0.804 for X =Cl, Br and I, respectively. Elastic parameters were used to determine the ductility, anisotropic features and mechanical stability of these materials. The presence of an indirect bandgap (Eg) has been determined via density of states and electronic bandgap computations, yielding values of 2.14 eV for K2ScAgCl6, 2.05 eV for K2ScAgBr6, and 1.98 eV for K2ScAgI6 using the modified Becke–Johnson (mBJ) potential within the Generalized Gradient Approximation (GGA). This research also investigated the absorption of light energy, polarization, optical loss, refractive index across the energy spectral range from 0 to 8 eV. These results indicate that these compounds have significant absorbance and conductivity in the visible and ultraviolet (UV) energy ranges, while remaining transparent to lower-energy photons. This computational study suggest that these complex perovskite materials are highly suitable for energy related applications, and offering significant potential for future experimental investigation.

Formation of Ruddlesden-Popper Faults in Complex Perovskite Oxides

Formation of Ruddlesden-Popper Faults in Complex Perovskite Oxides

CaTiO3 nanoparticles as functional additives for the BaTiO3-based X8R type dielectric ceramics

This research investigates the potential of Calcium titanate (CaTiO3 or CT) nanoparticles as functional additives to enhance the dielectric properties of Barium titanate (BaTiO3 or BT)-based ceramic dielectrics. To address the need for high-temperature stability in MLCC (multilayer ceramic capacitor) applications, especially within the automotive and aerospace sectors, we have explored BT-based complex perovskite solid solutions comprising various cation substitutions, including Ca2+ and Yb3+, into barium titanate (BT) as a method to suppress the dielectric property anomaly near the Curie temperature effectively. The focus is on the impact of the application of CT nanoparticles as additive materials on phase formation, microstructure development, and dielectric behavior of the resulting ceramics to align with the Extended 'Temperature Coefficient of Capacitance (TCC)' criteria defined by the EIA X8R specification. When the hydrothermally synthesized CT nanopowder was applied in the Ca-doped BT ceramics fabrications as source material of the Ca dopants, it was beneficial to achieve both temperature stability and high dielectric constant. The CT nanoparticles are believed to play multiple roles during the solid-state reaction with BT and rare earth dopant (Yb). Since the Yb3+ ions can be more easily dissolved into the CT lattice than BT with their amphoteric character, the CT nanoparticles in the BT-CT-Yb2O3 mixture can act as an intermediary, dissolving the Yb3+ first in its A- or B-site before the final solid-solution formation with the BT. The sequential substitutions of the Yb3+ and Ca2+ into BT via CT nanoparticles could affect the site occupancy of Ca2+ in the BT lattice, which is very important in determining the dielectric properties of the Ca-doped BT processed in reducing atmospheres. Through a comprehensive experimental approach, including phase composition analysis via X-ray diffraction (XRD) and microstructural examination using Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM), this work reveals the significance of synthetic methodology and dopant incorporation strategy on achieving a desired core-shell microstructure and improved dielectric performance. This research underscores the efficacy of CT nanoparticles as a promising route towards the development of BT-based dielectric ceramics with superior temperature stability, offering valuable insights for the advancement of MLCC technology to cater to high-temperature applications.

Effect of lattice defects on crystal structure and microwave properties of Ba(Ga1/2Ta1/2)O3 doped Ba(Zn1/3Nb2/3)O3 ceramics

Traditionally, B-site cation ordering structure in Ba(B′1/3B″2/3)O3 based ceramics with complex perovskite structure is considered to be the dominant factor in determining the dielectric loss. The crystal structure of BZN-BGT ceramics changes to the B-site disordering from B-site 1:2 ordering accompanying with remarkably reduced dielectric loss. Ba(Ga1/2Ta1/2)O3 doping also inhibits the formation of Nb-rich secondary phases induced by Zn volatilization on the surface of BZN-BGT ceramics as well. The conductive activation energy Ea, an energy required for electrons to escape from the traps, increases to 0.55 eV from 0.40 eV, indicating the decrease of lattice defects concentration. As Ba(Ga1/2Ta1/2)O3 doping concentration increases, the dielectric thermal relaxation process of BZN-BGT ceramics weakens and the electrical conductivity decreases. These results indicate that the dielectric loss of BZN-BGT ceramics containing volatile Zn could be controlled by the lattice defects and secondary phases rather than B-site 1:2 ordering structure.

Advances in Functional Ceramics for Water Splitting: A Comprehensive Review

The global demand for sustainable energy sources has led to extensive research regarding (green) hydrogen production technologies, with water splitting emerging as a promising avenue. In the near future the calculated hydrogen demand is expected to be 2.3 Gt per year. For green hydrogen production, 1.5 ppm of Earth’s freshwater, or 30 ppb of saltwater, is required each year, which is less than that currently consumed by fossil fuel-based energy. Functional ceramics, known for their stability and tunable properties, have garnered attention in the field of water splitting. This review provides an in-depth analysis of recent advancements in functional ceramics for water splitting, addressing key mechanisms, challenges, and prospects. Theoretical aspects, including electronic structure and crystallography, are explored to understand the catalytic behavior of these materials. Hematite photoanodes, vital for solar-driven water splitting, are discussed alongside strategies to enhance their performance, such as heterojunction structures and cocatalyst integration. Compositionally complex perovskite oxides and high-entropy alloys/ceramics are investigated for their potential for use in solar thermochemical water splitting, highlighting innovative approaches and challenges. Further exploration encompasses inorganic materials like metal oxides, molybdates, and rare earth compounds, revealing their catalytic activity and potential for water-splitting applications. Despite progress, challenges persist, indicating the need for continued research in the fields of material design and synthesis to advance sustainable hydrogen production.

Effects of B′‐site configurational entropy on structure and microwave dielectric characteristics in Ba(B′1/3Nb″2/3)O3 complex perovskite ceramics

AbstractBa[(Ca0.2Mg0.2Zn0.2Co0.2Ni0.2)1/3Nb2/3]O3 and Ba[(Mg0.25Zn0.25Co0.25Ni0.25)1/3Nb2/3]O3 perovskite single‐phase ceramics were synthesized by a solid‐state reaction method, and they were annealed at different temperatures in order to investigate the effect of B′‐site configurational entropy on phase stability, ordered domain structure and microwave dielectric characteristics. By comparing the B′‐site high‐entropy composition with B′‐site medium‐entropy and low‐entropy compositions, the entropy‐dominated phase‐stabilization effect and sluggish diffusion effect were observed in Ba[(Ca0.2Mg0.2Zn0.2Co0.2Ni0.2)1/3Nb2/3]O3. These effects enhanced the temperature stability of the B‐site 1:2 ordered structure. Ba[(Ca0.2Mg0.2Zn0.2Co0.2Ni0.2)1/3Nb2/3]O3 even reached a higher Qf value after annealing above the order‐disorder transition temperature (To‐d). This research extends the entropy regulation to ordered complex perovskite and provides a promising way to modify the performances of complex perovskite dielectric ceramics.

Investigation of electrical and dielectric properties of complex perovskite Gd2/3Cu3Ti4O12 and Gd2/3Cu3Ti3.95Co0.025V0.025O12 ceramic synthesized via novel semi-wet route

Investigation of electrical and dielectric properties of complex perovskite Gd2/3Cu3Ti4O12 and Gd2/3Cu3Ti3.95Co0.025V0.025O12 ceramic synthesized via novel semi-wet route

Local Ordering, Distortion, and Redox Activity in (La0.75Sr0.25)(Mn0.25Fe0.25Co0.25Al0.25)O3 Investigated by a Computational Workflow for Compositionally Complex Perovskite Oxides.

Mixing multiple cations can result in a significant configurational entropy, offer a new compositional space with vast tunability, and introduce new computational challenges. For applications such as the two-step solar thermochemical hydrogen (STCH) generation techniques, we demonstrate that using density functional theory (DFT) combined with Metropolis Monte Carlo method (DFT-MC) can efficiently sample the possible cation configurations in compositionally complex perovskite oxide (CCPO) materials, with (La0.75Sr0.25)(Mn0.25Fe0.25Co0.25Al0.25)O3 as an example. In the presence of oxygen vacancies (VO), DFT-MC simulations reveal a significant increase of the local site preference of the cations (short-range ordering), compared to a more random mixing without VO. Co is found to be the redox-active element and the VO is the preferentially generated next to Co due to the stretched Co-O bonds. A clear definition of the vacancy formation energy (Evf) is proposed for CCPO in an ensemble of structures evolved in parallel from independent DFT-MC paths. By combining the distribution of Evf with VO interactions into a statistical model, the oxygen nonstoichiometry (δ), under the STCH thermal reduction and oxidation conditions, is predicted and compared with the experiments. Similar to the experiments, the predicted δ can be used to extract the enthalpy and entropy of reduction using the van't Hoff method, providing direct comparisons with the experimental results. This procedure provides a full predictive workflow for using DFT-MC to obtain possible local ordering or fully random structures, understand the redox activity of each element, and predict the thermodynamic properties of CCPOs, for computational screening and design of these CCPO materials at STCH conditions.

Enhanced ferroelectric and piezoelectric properties of Sb/Nb co‐doped BiScO3-PbTiO3-based ceramics via relaxation regulation near morphotropic phase boundary

Here, novel ferroelectric ceramics of Sb/Nb co-doped 0.36BiScO3-0.64PbTiO3 (BS-PT-Sb2O5-xNb2O5) of complex perovskite structure are reported with compositions near the morphotropic phase boundary (MPB) where the dominant monoclinic and tetragonal phases coexist. Excitingly, the incorporation of Sb/Nb dopants leads to a remarkable enhancement in both ferroelectric and piezoelectric properties. Notably, the sample with x = 1.0 demonstrates the optimal properties, boasting a giant piezoelectric coefficient (d33) of 498 pC/N (10.7 % higher than pure BS-PT ceramics), a high Curie temperature (Tc) of 392 °C, a high depolarization temperature of 362 °C and a large remanent polarization of 52.7 μC/cm2 (55.9 % higher than pure BS-PT ceramics). The enhanced ferroelectric and piezoelectric properties are ascribed to a relaxation behavior originating from the formation of polar nanoregions (PNRs) and reduced concentration of oxygen vacancy. The result provides an opportunity to elucidate the relationship between relaxation behavior and electrical properties, offering prospects for substantially improving the performance of piezoelectric ceramics.

Lattice dynamics of the BaMg1/3Ta2/3O3 complex perovskite: DFT calculation and Raman spectroscopy

The article presents the results of studies of theBaMg1/3Ta2/3O3 (BMT) complex perovskite crystal using Raman spectroscopy and density functional theory (DFT) calculation. The polarized Raman spectra of a cubic BMT single crystal are obtained in two different geometries in a broad temperature range (5–580 K). The density functional theory calculations of the lattice dynamics and vibrational spectra of the BMT crystal in the Г point of the trigonal phase are carried out. The simulated Raman spectra are analyzed in comparison with the experimental spectra of cubic single crystals and those of ceramics in the trigonal phase. The Raman spectra peculiarities are observed and explained.

Electronic properties of the barium magnesium tantalate

BaMg1/3Ta2/3O3 (BMT) crystals belong to the family of complex perovskites and are well known for their excellent microwave dielectric properties. In this work, structural optimization of the lattice parameters was performed. Electron density functional theory calculations of the electronic band structure of BMT crystal of the trigonal phase were carried out along Г–A–K–M–L directions of the Brillouin zone. The calculated band gap energy was 3.554 eV. The partial density of states of BMT crystal in P-3 m1 phase was simulated. Top of the valence band was formed by 2p-states of O and bottom of the conduction band – by 5d-states of Ta.

Development of ultra-high energy storage density and ultra-wide operating temperature behavior of a lead-free capacitor sensor; (Bi1/2 K1/2) (Fe1/3Mn1/3W1/3)O3

In the present report, attention has been focused on the development of electronic components of a high-energy storage density in small dimensions using ceramic technology and standard techniques. The detailed studies of electrical and dielectric properties of a potassium, manganese, and tungsten modified complex perovskite with a chemical composition: (Bi1/2K1/2) (Fe1/3Mn1/3W1/3)O3 (by solid-state reaction route) have been attempted for the purpose. Through the analysis of structural X-ray diffraction and micro-structural properties, the quality of the developed material has been verified. These methods have provided a crystallite size of 97 nm, and micro-strain (0.0027) and a grain size of 9.83 μm. Studies of frequency and temperature dependent dielectric and complex impedance support the divergence of dielectric dispersion and relaxation from Debye-type behavior. The nature of conductivity of the material of semiconductor type suggests its potential use in optoelectronic component. The temperature coefficient of resistance of −1.3491% confirms that it is a contender for thermistor devices applications. These findings indicate that material with high energy storage density and minimal energy loss could be used for energy storage devices. The dielectric constant and efficiency of 671 and 70.44%, respectively with a maximum power density (0.16 MW/cm3) at 1 kHz is achieved for the devices.

Method for bandgap interpolation of perovskite's spectral complex refractive index.

Lead halide perovskites are a promising class of materials for solar cell applications. The perovskite bandgap depends on the material composition and is highly tunable. Opto-electrical device modelling is commonly used to find the optimum perovskite bandgap that maximizes device efficiency or energy yield, either in single junction or multi-junction configuration. The first step in this calculation is the optical modelling of the spectral absorptance. This requires as input the perovskite's complex refractive index N as a function of wavelength λ. The complex refractive index consists of real part n(λ) and imaginary part k(λ). For the most commonly used perovskites, n and k curves are available from spectroscopic ellipsometry measurements, but usually only for a few discrete bandgap energies. For solar cell optimization, these curves are required for a continuous range of bandgap energies. We introduce new methods for generating the n and k curves for an arbitrary bandgap, based on interpolating measured complex refractive index data. First, different dispersion models (Cody-Lorentz, Ullrich-Lorentz and Forouhi-Bloomer) are used to fit the measured data. Then, a linear regression is applied to the fit parameters with respect to the bandgap energy. From the interpolated parameters, the refractive index curve of perovskite with any desired bandgap energy is finally reconstructed. To validate our method, we compare our results with methods from literature and then use it to simulate the absorptance of a single junction perovskite and a perovskite/silicon tandem cell. This shows that our method based on the Forouhi-Bloomer model is more accurate than existing methods in predicting the complex refractive index of perovskite for arbitrary bandgaps.

Innovative complex perovskites for efficient hydrogen Evolution: A DFT-Based design strategy

Recently, hydrogen, a high-energy, non-polluting fuel, has attracted considerable attention. Perovskites are of great interest in the hydrogen energy field due to their attractive properties. Herein, first-time novel complex perovskites [K(Mg+2Nb+5)O3] were designed computationally. The DFT has been utilized to systematically examine structural, electronic, optical, elastic, and mechanical properties to explore their potential applications in producing solar-driven hydrogen. Complex compositions (varying Mg+2 and Nb+5 concentrations) likely to adopt cubic or pseudocubic (a≈b≈c) perovskite structures based on structural parameters and the Goldschmidt tolerance factor. Including Nb in the crystal structure plays a significant role in shaping the band gap energy. Formation enthalpies show that all compounds are dynamically stable and synthesizable. Absorption coefficients (∼105cm-1) and effective optical responsiveness in UV and visible range make them a potential candidate for light energy harvesting. The computed high dielectric constant, a declining trend in refractive index and reflectivity, and minimum energy loss characteristics are attractive and are suitable for optoelectronic applications. Mechanical elements, ductility, anisotropy, toughness, and crack resistance proposed that compounds are highly desirable for various applications. The proposed complex compositions could catalyze efficient hydrogen evolution reactions (HERs) due to their suitable bandgap energies, suitable absorption coefficients, and alignment of the band edges regarding the redox potential of water.

Growth and characterization of novel piezo-/ferroelectric single crystals from the PSN-BS-PT ternary system

Bismuth-based single crystals with the nominal composition of 0.1Pb(Sc1/2Nb1/2)O3-0.315BiScO3-0.585PbTiO3 (0.1PSN-0.315BS-0.585PT) ternary complex perovskite system were successfully grown using a high-temperature solution growth (HTSG) method. A mixture of PbO and Bi2O3 in a molar ratio of 73:27 was used as flux, and the flux to charge ratio was optimized to be 70:30 (wt%). The grown crystals, with dimensions up to 3 mm, exhibit a pseudo-cubic morphology. The XRD patterns of the ground powder and naturally formed pseudo-cubic facets confirm that the grown single crystals crystallize in the perovskite structure with the rhombohedral symmetry as the major phase, and the naturally grown pseudo-cubic facets are parallel to {100}C. The domain structures in the (001)-oriented single crystals examined by polarized light microscopy (PLM) and optical crystallography reveal the coexistence of rhombohedral and monoclinic phases in majority, with the presence of a minor tetragonal phase likely grown at the late stage of the growth, demonstrating the morphotropic phase boundary (MPB) characteristics for the grown crystals. Upon heating, phase transition from the major rhombohedral and monoclinic to the cubic phase take place at TC = 370 °C. The ferroelectric properties are displayed by polarization-electric field (P-E) hysteresis loops with a remanent polarization of 17 µC/cm2 and a high coercive field of 68 kV/cm. The piezoelectric coefficient (d33) is found to be 478 pC/N. The high Curie temperature and decent piezo- and ferroelectric performance of the PSN-BS-PT crystals make this ternary complex perovskite system a promising candidate for potential applications in high-temperature and high-power electromechanical transduction.

Magnetic structure and properties of the compositionally complex perovskite (Y0.2La0.2Pr0.2Nd0.2Tb0.2)MnO3

The magnetic structure and properties were measured in a compositionally complex perovskite manganite possessing local spin disorder on the A-site and found to be similar to an undisordered control.