Family Of Perovskite Materials Research Articles

Understanding secondary order parameters in perovskites with tilted octahedra

In the family of perovskite materials, the tilts of BX 6 octahedra are the most common type of structural distortion. Conventionally, the formation of low-symmetry perovskite phases with tilted octahedra is analyzed by considering only primary order parameters. However, octahedral tilting also gives rise to secondary order parameters which contribute to additional atomic displacements, ordering and lattice distortions. Our study highlights the significant impact of secondary order parameters on the structural formation and emergent physical properties of perovskites. Through group-theoretical and crystallographic analyses, we have identified all secondary order parameters within Glazer-type tilt systems and clarified their physical manifestations. We explore the fundamental symmetry relationships among various structural degrees of freedom in perovskites, including tilt-induced ferroelasticity, correlations between displacements and ordering of atoms occupying different positions, and the potential for rigid unit rotations and unconventional octahedral tilts. Particular emphasis is placed on the emergence of secondary order parameters and their coupling with primary order parameters, as well as their symmetry-based hierarchy, illustrated through a modified Bärnighausen tree. We applied our theoretical insights to elucidate phase transitions in well known perovskites such as CaTiO3 and RMnO3 (where R = La and lanthanide ions), thereby demonstrating the significant influence of secondary order parameters on crystal structure formation. Our results serve as a symmetry-based guide for the design, identification and structural characterization of perovskites with tilted octahedra, and for understanding tilt-induced physical properties.

Analysis of cubic perovskite oxide AgNbO3 under stress conditions: Potential for photovoltaic and high-temperature applications - A DFT study

In the family of perovskite materials, perovskite oxide gained considerable attention from researchers in diverse fields, due to their flexible chemistry. Here, cubic perovskite oxide AgNbO3 was studied using DFT via CASTEP code, to explore the key properties under varying stress conditions ranging from 0 to 100 GPa. Phase stability was confirmed by XRD analysis. Electronic properties confirmed the increasing trend in the band gap from 1.422 eV to 1.722 eV, with increasing stress. Optical characteristics reveal high absorption, conductivity, and lower loss function. Significantly, the elastic constants (C11, C12, and C44) satisfy the Born-stability criteria, ensuring the mechanical stability of the considered compound. Moreover, the Poisson ratio, Pugh's ratio (B/G), Frantsevich ratio, Cauchy pressure (PC), and anisotropic factor ensure the ductile nature as well as an anisotropic character over the entire stress range. The positive trajectory in phonon density confirms the thermal stability. Thermodynamically, the studied material shows high-temperature stability with a higher value of applied stress as confirmed by Debye temperature (θD). Furthermore, an inverse association of enthalpy and total entropy with free energy was observed. Based on these findings, confidently suggested that the considered cubic perovskite oxide, AgNbO3, can be efficiently used for photovoltaic and high-temperature applications.

Colloidal synthesis and charge carrier dynamics of Cs4Cd1−xCuxSb2Cl12 (0 ≤ x ≤ 1) layered double perovskite nanocrystals

<h2>Summary</h2> The toxicity and instability of lead-based metal halide perovskites are the two main obstacles that prevent perovskite materials from implementation in applications. Recently, layered double perovskites (LDPs) have emerged as a new family of perovskite materials, which provide a new route to solve these problems by lead-component replacement and reduction of crystal structure dimensionality. However, LDP nanocrystals (NCs) have been rarely studied, limiting the further property exploration and application realization. Here, we report the colloidal synthesis of a series of Cs₄Cd_1−xCu_xSb₂Cl₁₂ (0 ≤ <i>x</i> ≤ 1) LDP NCs by tuning the stoichiometry of metal precursors. The composition-structure-property relationships of the resulting LDP NCs are studied through material characterizations, density functional theory calculations, and transient-absorption spectroscopy. In addition, we demonstrate that high-performance high-speed photodetectors can be fabricated using the colloidal LDP NCs through solution processing. This work premises further expansion of such LDP-based materials for both fundamental studies and application integrations.

Transport Modeling of Locally Photogenerated Excitons in Halide Perovskites.

Excitons have fundamental impacts on optoelectronic properties of semiconductors. Halide perovskites, with long carrier lifetimes and ionic crystal structures, may support highly mobile excitons because the dipolar nature of excitons suppresses phonon scattering. Inspired by recent experimental progress, we perform device modeling to rigorously analyze exciton formation and transport in methylammonium lead triiodide under local photoexcitation by using a finite element method. Mobile excitons, coexisting with free carriers, can dominate photocurrent generation at low temperatures. The simulation results are in excellent agreement with the experimentally observed strong temperature and gate dependence of carrier diffusion. This work signifies that efficient exciton transport can substantially influence charge transport in the family of perovskite materials.

Disentangling the Luminescent Mechanism of Cs4PbBr6 Single Crystals from an Ultrafast Dynamics Perspective.

New all-inorganic perovskites like Cs4PbBr6 provide rich luminescent tools and particularly novel physical insights, including their zero-dimensional structure and controversial emitting mechanism. The ensuing debate over the origin of the luminescence of Cs4PbBr6 inspired us to tackle the issue through fabricating high-quality Cs4PbBr6 single crystals and employing ultrafast dynamics study. Upon photoexcitation, Cs4PbBr6 underwent dynamics steps distinct from that of CsPbBr3, including exciton migration to the defect level on a time scale of several hundred femtoseconds, exciton relaxation within the defect states on the picosecond time scale, and exciton recombination from the subnanosecond to nanosecond time scale. The observation disclosed that crystal defects of Cs4PbBr6 induced green emission while CsPbBr3 mainly relied on quantum confinement to emit at room temperature. The study provides an in-depth understanding of the photoinduced multistep dynamics steps of Cs4PbBr6 associated with display and photovoltaic applications, establishing Cs4PbBr6 as a new candidate for uses associated with the perovskite family of materials.

Optical Characterization of CaCu3Ti4O12 thin Films

CaCu3Ti4O12 is in the family of perovskite materials that may have potential electrical as well as optical applications. In this study, we have focused on the optical properties of the films. These films are deposited by RF magnetron sputtering process using CaCu3Ti4O12target. The films are deposited under varies deposition conditions that include argon gas flow ratios, process pressures and substrate temperature. The transmission and reflection properties are performed using the UV-Visible spectrophotometer to extract the bandgap and refractive index of these films.

Air-Stable Surface-Passivated Perovskite Quantum Dots for Ultra-Robust, Single- and Two-Photon-Induced Amplified Spontaneous Emission

We demonstrate ultra-air- and photostable CsPbBr3 quantum dots (QDs) by using an inorganic-organic hybrid ion pair as the capping ligand. This passivation approach to perovskite QDs yields high photoluminescence quantum yield with unprecedented operational stability in ambient conditions (60 ± 5% lab humidity) and high pump fluences, thus overcoming one of the greatest challenges impeding the development of perovskite-based applications. Due to the robustness of passivated perovskite QDs, we were able to induce ultrastable amplified spontaneous emission (ASE) in solution processed QD films not only through one photon but also through two-photon absorption processes. The latter has not been observed before in the family of perovskite materials. More importantly, passivated perovskite QD films showed remarkable photostability under continuous pulsed laser excitation in ambient conditions for at least 34 h (corresponds to 1.2 × 10(8) laser shots), substantially exceeding the stability of other colloidal QD systems in which ASE has been observed.

Why Are There So Few Perovskite Ferroelectrics?

We use a combination of symmetry arguments and first-principles calculations to explore the connection between structural distortions and ferroelectricity in the perovskite family of materials. We explain the role of octahedral rotations in suppressing ferroelectricity in these materials and show that, as the tolerance factor decreases, rotations alone cannot fully suppress ferroelectricity. Our results show that it is cation displacements (“hidden” in Glazer notation) that accompany the rotations, rather than the rotations themselves, that play the decisive role in suppressing ferroelectricity in these cases. We use the knowledge gained in our analysis of this problem to explain the origin of ferroelectricity in R3c materials such as FeTiO3 and ZnSnO3 and to suggest strategies for the design and synthesis of new perovskite ferroelectrics. Our results have implications not only for the fundamental crystal chemistry of the perovskites but also for the discovery of new functional materials.