Double Perovskite Layers Research Articles

Achieving Over 30% Efficiency Employing a Novel Double Absorber Solar Cell Configuration Integrating Ca3NCl3 and Ca3SbI3 Perovskites

Perovskites are particularly appealing solar absorber materials in the realm of photovoltaic (PV) technology due to their remarkable optical properties, low cost, increased efficiency, and lightweight design. This study proposes a structure that combines a double perovskite absorber layer (DPAL) of Ca3NCl3 and Ca3SbI3 with an electron transport layer (ETL) and hole transport layer (HTL) of CdS and CBTS via SCAPS-1D. Our research also demonstrated that the perovskite solar cell (PSC) with DPAL performs much better with the addition of HTL and is more efficient than single-layer PSCs. This paper thoroughly examines the effect of thickness, doping levels, and defect densities of each layer on electrical parameters like VOC, JSC, FF, and PCE. Additionally, it shows the J-V and QE characteristics and thoroughly examines the effects of temperature. With a DPAL of 24.43%, two solar cells built around a single absorber have achieved their maximum efficiency of 17.19% and 18.07%, respectively. Using CBTS HTL with Al/FTO/CdS/dual absorber (Ca3SbI3/Ca3NCl3)/CBTS/Ni structure, this study achieves an optimized efficiency of up to 30.22% with VOC of 1.39 V, FF of 88%, and JSC of 24.75 mAcm-2. This research may offer crucial information and a practical plan for creating an affordable Ca3SbI3/Ca3NCl3 thin-film solar cell.

Achieving 34 % efficiency with a dual-absorber solar cell design using CaRbCl3 and Ca3NCl3 perovskites

This study’s DFT calculations show that the direct bandgaps of perovskite CaRbCl3 and Ca3NCl3 are 1.386 eV and 1.430 eV, respectively, confirming their semiconducting nature. The study also provides density of states and dielectric constant data for these materials. In photovoltaic (PV) technology, perovskites are highly valued as solar absorber materials for their exceptional optical properties, low cost, high efficiency, and lightweight design. This study presents a structure (Al/FTO/CdS/dual absorber (CaRbCl3/Ca3NCl3)/V2O5/Au) incorporating a CdS electron transport layer (ETL) and a V2O5 hole transport layer (HTL) with a double perovskite absorber layer (DPAL) of CaRbCl3 and Ca3NCl3 using SCAPS-1D. The results show that the DPAL-based perovskite solar cell (PSC) outperforms single-layer PSCs, with significant efficiency gains when HTL is included. The study thoroughly examines the effects of layer thickness, doping levels, and defect densities on key electrical parameters such as VOC, JSC, FF, and PCE. It also explores J-V and QE characteristics and the impact of temperature. The ideal absorber thickness for achieving the highest PCE is 500 nm for CaRbCl3 and 600 nm for Ca3NCl3, combined with a doping density of 1 × 1017 cm−3, a defect density of 1 × 1011 cm−3 and interface defect density of 1 × 1010 cm−2. While single-absorber solar cells achieve maximum efficiencies of 24.40 % (CaRbCl3) and 24.02 % (Ca3NCl3), the DPAL setup reaches an optimized efficiency of 27.66 %, further increasing to 34.39 % with a VOC of 1.295 V, FF of 83.95 %, and JSC of 31.63 mA/cm2 when using V2O5 HTL. This research provides valuable insights and a practical strategy for developing cost-effective CaRbCl3/Ca3NCl3 thin-film solar cells.

Enhancing the efficiency of lead-free Cs2AgBiBr6 based double perovskite solar cells with optimizing ETLs and HTLs using SCAPS-1D

This study introduces a tin-free, stable, lead-free, double perovskite solar cell device with improved power conversion efficiency (PCE). Different electron transporting layers (ETLs) including IGZO, AZO, LBSO, and TiO2 and hole transporting layers (HTLs) as Cu2O, CNTS, ZnTe, and P3HT are considered for optimization with Cs2AgBiBr6 and fluorine-doped tin oxide as double perovskite layer and substrate respectively. The effect of various device parameters on the device performance has been studied. The device configuration of FTO/AZO/Cs2AgBiBr6/ZnTe achieves a PCE of 26.89 %, fill factor (FF) of 83.87 %, open-circuit voltage (VOC) of 1.50 V, and short-circuit current (JSC) of 21.35 mA/cm2.

Atomic‐Scale Engineering for New Generation Air Electrode Materials of Solid Oxide Cells: Quintuple Perovskite Sm2Ba3Co2Fe3O15‐δ with Twinned Crystal Structure

AbstractThe catalytic activity and thermomechanical stability of electrode materials are crucial for the efficient operation of reversible solid oxide cell (rSOC). However, these two traits often impose limitations on one another. In this work, a unique quintuple perovskite Sm2Ba3Co2Fe3O15‐δ (SBCF‐5L), comprising of A‐site ordered double perovskite layers and disordered simple perovskite layers, is reported as a high‐performance air electrode material for rSOC. The designed SBCF‐5L material exhibits a highly symmetrical tetragonal structure (pseudo‐cubic) with an isotropic thermal expansion and a limited chemical expansion. The formation barriers for oxygen vacancies are comparable between A‐site ordered layers and disordered simple perovskite layers, resulting in a high concentration of oxygen vacancies and 3D‐like bulk mobility of oxygen ions. Perpendicularly twinned nanodomains are developed in the particles, providing more active sites for surface electrode reaction. When applied in electrolyte‐supported cells, the SBCF‐5L electrode exhibits excellent electrochemical performance with low polarization resistance of 0.017 Ω cm−2, high power density of 1.01 W cm−2 and high electrolysis current density of 1.08 A cm−2 at 1.3 V at 800 °C in fuel cell and electrolysis modes, respectively. This study introduces a new approach of atomic‐scale engineering to rationally design a new generation of air electrodes for rSOC.

A theoretical study of all-inorganic perovskite solar cells: Computational modeling of the CsPbI[formula omitted]/RbGeI[formula omitted] bilayer absorber structure

All-inorganic perovskite solar cells (AI-PSCs) have garnered significant attention in the perovskite community due to their stability and efficient photogeneration and absorption capabilities. Despite the toxicity associated with all-inorganic CsPbI3 perovskites containing lead (Pb), its presence remains crucial for achieving excellent photovoltaic properties. However, the imperative shift towards AI-PSCs using less toxic materials with suitable photovoltaic properties is imperative. The incorporation of a double perovskite absorber layer allows for broadening the absorption spectrum of PSCs and enhancing cell stability. In this study, we propose a novel AI-PSC structure with CsPbI3 as the top absorber with a wide bandgap of 1.69 eV and a lead-free RbGeI3 perovskite as the bottom absorber layer with a low bandgap of 1.31 eV. Utilizing numerical simulations with the SCAPS-1D simulator, we analyze the photovoltaic parameters of AI-PSCs with single and double absorber layers. Our investigations reveal that a double absorber layer structure, comprising CsPbI3 and RbGeI3 materials, outperforms a single-junction PSC based on CsPbI3. By optimizing critical device parameters, we achieved an impressive efficiency of 31.91% in an AI-PSC device with a CsPbI3(0.6 μm)/RbGeI3(2 μm) bilayer configuration. This study positions lead-free RbGeI3 perovskite as a promising partner for CsPbI3, offering a potential pathway for the development of highly efficient AI-PSCs.

In-Depth Analysis on the Fabry-Perot Effect of Cs2AgBiBr6 Double Perovskite-Based Solar Cells via Optical Path Length Modulation

Herein, the Fabry-Perot (F-P) interference of cesium silver bismuth bromide (Cs2AgBiBr6) double perovskite solar cells has been analyzed by modulating the optical path length of each layer step by step using the finite-difference time-domain (FDTD) method. The study was performed pass through three main steps. In step 1, for the fluorine-doped tin oxide (FTO)/Cs2AgBiBr6 double perovskite/gold (Au) architecture, we increased the absorption layer thickness from 150 to 600 nm at intervals of 150 nm and then predicted the optical performance including the absorption and reflection. In step 2, titanium dioxide (TiO2) layer was added between FTO electrode and Cs2AgBiBr6 double perovskite and then scaled from 20 to 200 nm at intervals of 20 nm. In the analysis process, short-circuit current density (Jsc) repeatedly fell and rose as the TiO2 layer thickness increased, and when TiO2 layer thickness is 100 nm, Jsc showed the highest value of 13.91 mA/cm2. In step 3, by applying a spiro-OMeTAD layer between the Cs2AgBiBr6 double perovskite absorption layer and Au electrode, the Jsc showed a continuous increase with slight decrease as the spiro-OMeTAD layer thickness increased from 110 to 200 nm, and when the spiro-OMeTAD layer thickness was 200 nm, Jscwas calculated as 14.57 mA/cm2, which is the highest value in the range. In the case of the optimal condition of full structure device, the Fabry-Perot resonance peaks were discovered at 477, 520, 572, 659, and 778 nm five wavelength regions, and the influence of the Fabry-Perot resonance on the generation rate inside the absorption layer on the 520, 572, and 659 nm monochromatic wavelength light was analyzed according to the position in the device. Our study approaches the Cs2AgBiBr6 double perovskite solar cell from an F-P cavity perspective and shows the light trapping phenomenon of the device according to the optical path length modulation.

Design, optimization and enhancement of power conversion efficiency exceeding 30% for lead-free all-inorganic double perovskite-based solar cells using dual active layers

Here, we present a comprehensive simulation study focused on the design and optimization of power conversion efficiency (η) for lead-free, all-inorganic double perovskite-based solar cell (DPSC) device using SCAPS 1D. A non-toxic halide double perovskite layer, Cs2AgSb0.25Bi0.75Br6 is employed as absorber layer in designed solar cell along with various electron transport layers like ZnO, TiO2, C60, PCBM, IGZO and hole transport layers including NiO, Cu2O, MoO3, CuI, spiro-OMeTAD in n-i-p heterostructure configuration, aiming to achieve eco-friendly device with optimized efficiency and enhanced stability. The optimal configuration, FTO/C60/ Cs2AgSb0.25Bi0.75Br6/Cu2O/C, achieves a η ∼ 25.32% with Voc ∼ 1.58 V, Jsc ∼ 17.48 mA/cm2 and FF ∼ 91.4%. To further enhance the device performance, double active layers combining CsSnCl3 (band gap ∼ 1.52 eV) and Cs2AgSb0.25Bi0.75Br6 (band gap ∼ 1.80 eV) are introduced into the optimized device to leverage optical absorption for wide range of solar spectrum due to the graded optical band gap. Consequently, the power conversion efficiency of the cell elevated to ∼ 32.23% accompanied by Voc ∼ 1.36 V, Jsc ∼ 26.34 mA/cm2 and FF ∼ 90.3%, with a promise of creating high-efficiency solar cell devices, driving substantial progress in green energy technology.

Formation of Low-Dimensional Double Perovskite Layers by ABS and PEAI Sequential Treatment for Achieving High-Performance CsPbI3 Solar Cells

Formation of Low-Dimensional Double Perovskite Layers by ABS and PEAI Sequential Treatment for Achieving High-Performance CsPbI₃ Solar Cells

Performance Improvement of Perovskite Solar Cell Design with Double Active Layer to Achieve an Efficiency of over 31%

This research aims to optimize the efficiency of the device structures by introducing the novel double perovskite absorber layer (PAL). The perovskite solar cell (PSC) has higher efficiency with both lead perovskite (PVK), i.e., methylammonium tin iodide (MASnI3) and Caseium tin germanium iodide (CsSnGeI3). The current simulation uses Spiro-OMeTAD as the hole transport layer (HTL) and TiO2 as an electron transport layer (ETL) to sandwich the PVK layers of MASnI3 and CsSnGeI3, which have precise bandgaps of 1.3 eV and 1.5 eV. The exclusive results of the precise modeling technique for organic/inorganic PVK-based photovoltaic solar cells under the illumination of AM1.5 for distinctive device architectures are shown in the present work. Influence of defect density (DD) is also considered during simulation that revealed the best PSC parameters with JSC of 31.41 mA/cm2, VOC of 1.215 V, FF of nearly 82.62% and the highest efficiency of 31.53% at the combined DD of 1.0 × 1014 cm−3. The influence of temperature on device performance, which showed a reduction in PV parameters at elevated temperature, is also evaluated. A steeper temperature gradient with an average efficiency of −0.0265%/K for the optimized PSC is observed. The novel grading technique helps in achieving efficiency of more than 31% for the optimized device. As a result of the detailed examination of the total DD and temperature dependency of the simulated device, structures are also studied simultaneously.

Bandgap Engineering of Two-Dimensional Double Perovskite Cs4AgBiBr8/WSe2 Heterostructure from Indirect Bandgap to Direct Bandgap by Introducing Se Vacancy.

Heterostructures based on layered materials are considered next-generation photocatalysts due to their unique mechanical, physical, and chemical properties. In this work, we conducted a systematic first-principles study on the structure, stability, and electronic properties of a 2D monolayer WSe2/Cs4AgBiBr8 heterostructure. We found that the heterostructure is not only a type-II heterostructure with a high optical absorption coefficient, but also shows better optoelectronic properties, changing from an indirect bandgap semiconductor (about 1.70 eV) to a direct bandgap semiconductor (about 1.23 eV) by introducing an appropriate Se vacancy. Moreover, we investigated the stability of the heterostructure with Se atomic vacancy in different positions and found that the heterostructure was more stable when the Se vacancy is near the vertical direction of the upper Br atoms from the 2D double perovskite layer. The insightful understanding of WSe2/Cs4AgBiBr8 heterostructure and the defect engineering will offer useful strategies to design superior layered photodetectors.

Low-Temperature Exsolution of Ni-Ru Bimetallic Nanoparticles from A-Site Deficient Double Perovskites.

Exsolution of stable metallic nanoparticles for use as efficient electrocatalysts has been of increasing interest for a range of energy technologies. Typically, exsolved nanoparticles show higher thermal and coarsening stability compared to conventionally deposited catalysts. Here, A-site deficient double perovskite oxides, La2- x NiRuO6- δ (x=0.1and 0.15), are designed and subjected to low-temperature reduction leading to exsolution. The reduced double perovskite materials are shown to exsolve nanoparticles of 2-6nm diameter during the reduction in the low-temperature range of 350-450°C. The nanoparticle sizes are found to increase after reduction at the higher temperature (450°C),suggestingdiffusion-limited particle growth. Interestingly, both nickel and ruthenium are co-exsolved during the reduction process. The formation of bimetallic nanoparticles at such low temperatures is rare. From the insitu impedance spectroscopy measurements of the double perovskite electrode layers, the onset of the exsolution process is found to be within the first few minutes of the reduction reaction. In addition, the area-specific resistance of the electrode layers is found to decrease by 90% from 291to 29Ωcm2 , suggesting encouraging prospects for these low-temperature rapidly exsolved Ni/Ru alloy nanoparticles in a range of catalytic applications.

Performance evaluation of lead–free double-perovskite solar cell

This article presents the numerical simulation of lead–free (Pb-free) double–perovskite (Cs 2 AgBi 0.75 Sb 0.25 Br 6 , i.e., mixed antimony bismuth halide double-perovskite) solar cell (DPSC) using solar cell capacitance one dimensional simulator (SCAPS-1D). In this contribution, the hole transport layers (HTLs) and electron transport layers (ETLs) are optimized. The optimization is performed by correlating the open circuit voltage (V OC ) with the built-in potential (V bi ). It is disclosed from the simulation results, that higher V bi resulted higher V OC . Furthermore, it is also found that, for the proper selection of HTL, the E V_HTL (Valence band maximum of HTL) and φ BC (Work function of back contact) should not be much deeper than the E V_PVK (Valence band maximum of double–perovskite layer) to avoid V bi loss. Correspondingly, for proper selection of ETL, E C_ETL (Conduction band minimum of electron transport layer) and Φ FC (Work function of front contact), should not be much higher than E C_PVK to prevent V bi loss. The optimized HTL and ETL are found to be Cu 2 O (copper(I) oxide) and ZnOS (Zinc oxysulfide) respectively. Moreover, the device photovoltaic performance is further improved by optimizing the double-perovskite layer thickness which is found to be 400 nm. Under optimized condition, the device photovoltaic power conversion efficiency (η) improves to 18.18%. The optimized device photovoltaic performance are found to be, open –circuit voltage (Voc) = 1.39 V, short-circuit current density (J SC ) = 16.04 mA/cm 2 , and fill factor (FF) = 78.34% which indicates that double–perovskite absorber layer (Cs 2 AgBi 0.75 Sb 0.25 Br 6 ) is a suitable candidate for the development of highly efficient Pb-free DPSC. • The numerical simulation of lead-free double–perovskite is performed with-optimized device efficiency of 18.18%. • The electron transport layer and hole transport layer is optimized by co-orelating V OC with V bi . • The simulation study reveals that V OC is strongly dependent on V bi of lead-free double –perovskite absorber layer. • The optimized ETL and HTL found to be ZnOS and Cu 2 O respectively.

A new lead-free Sillén–Aurivillius oxychloride Bi5SrTi3O14Cl with triple-perovskite layers for photocatalytic water splitting under visible light

A series of Sillén–Aurivillius layered oxyhalides with a single- and double-perovskite layer, Bi4MO8X (M = Nb, Ta; X = Cl, Br) and AA′Bi3M2O11Cl (A, A′ = Sr, Ba, Pb, Bi; M = Ti, Nb, Ta), have been recently demonstrated as promising photocatalysts for visible-light-induced water splitting due to relatively high energy valence bands arising from strong interactions between Bi-6s and O-2p orbitals. Herein, we report the synthesis, characterization and photocatalytic property of Bi5SrTi3O14Cl with triple-perovskite layers. The combined use of synchrotron X-ray diffraction and scanning transmission electron microscopy allowed the precise determination of the crystal structure (space group: P2an), including site occupancies. The experimental results revealed that Bi5SrTi3O14Cl possesses a similar bandgap and valence band level as the previously reported Bi5PbTi3O14Cl, indicating that the presence of Pb-6s is not essential for the formation of a higher energy valence band maximum. Partial density of states for both materials obtained by DFT calculations suggested considerable interactions of the Bi-6s orbitals with the O-2p orbitals, in particular those in the perovskite layers, which is the key to the formation of the higher energy valence band. Bi5SrTi3O14Cl exhibited higher activity for O2 evolution than Bi5PbTi3O14Cl, suggesting the detrimental effect of Pb2+ on the photocatalytic activity, thereby allowing the construction of a Z-scheme water splitting system workable under visible light.

A Facile Way to Form a Graded Halide Layer in Perovskite Solar Cells.

A light harvest layer composed of gradual change from formamidinium lead triiodide (FAPbI₃) to methylammonium lead triiodide (MAPbI₃) was fabricated using a novel two-step process. That is, a graded halide layer structure without extra processing steps is demonstrated. Conventionally, in the fabrication of MAPbI₃ perovskite solar cells (PSCs) using two-step process, PbI₂ layer was the first deposited on a mesoporous TiO₂ coated substrate. The methylammonium iodide (MAI) solvent was then spin-coated on the surface of PbI₂ layer and heated to form the MAPbI₃ perovskite layer. Double perovskite layers such as FAPbI₃ plus MAPbI₃ requires twice of the second step which FAI and MAI should be spin-coated individually. This can be tedious and time consuming. We report here a facile way to form a graded perovskite layer, consisting FAPbI₃ to MAPbI₃, in a single step. FAI was first added into dimethylformamide (DMF) solution that was used to form PbI₂ layer, then MAI solution was dripped on top of the FAI/PbI₂ layer. The graded perovskite layer structure (FAPbI₃/MAPbI₃) in a gradient manner are readily formed, where the structure is confirmed by EDS to be FTO/compact TiO₂/mesoporous TiO₂/FAPbI₃(thin)/MAPbI₃/Spiro-OMeTAD/Ag. The Jsc, and Voc of solar cells with this graded perovskite layer are enhanced and the efficiency increases from 11.62% to 14.06%.

Synthesis of Cs2AgSbCl6 and improved optoelectronic properties of Cs2AgSbCl6/TiO2 heterostructure driven by the interface effect for lead-free double perovskites solar cells

Double perovskites Cs2AgSbCl6 have been synthesized via the solution state for applications as a promising photovoltaic absorber. Considering TiO2 as an electron transport layer (ETL), Cs2AgSbCl6/TiO2 heterojunction nanoparticles have also been prepared by the hydrothermal process to study the interface effect. Experimental measurements show that Cs2AgSbCl6 has a cubic structure with the lattice constant of 10.699 Å. The absorption peaks in the optical spectrum of the Ag and Sb-based double perovskites agree well with our density functional theory calculations. The Cs2AgSbCl6/TiO2 heterostructure exhibits enhanced optical absorption in the visible-light region compared to that of Cs2AgSbCl6, which is caused by the formation of the interface states and the decreased bandgap, thus facilitating the photo-induced optical transition in the visible-light region. From the charge transfer analysis of two interfaces (Ag2Sb2Cl8/TiO2 and Cs4Cl4/TiO2 interfaces), we find that the efficient separation of photo-induced carriers can be achieved at the Cs4Cl4/TiO2 interface, with electron flowing from the double perovskite layer to the TiO2 ETL, which is beneficial for improving the power conversion efficiency of solar cells. The combined study of theory and experiments indicates that the double perovskites Cs2AgSbCl6 would be a promising light-absorbing material in contact with TiO2 for the lead-free perovskite-based solar cell devices.

Impact of Mn3+ upon Structure and Magnetism of the Perovskite Derivative Pb2–xBaxFeMnO5 (x ∼ 0.7)

On the basis of the Mn(3+) for Fe(3+) substitution in Pb(2-x)Ba(x)Fe2O5, a novel oxide Pb1.3Ba0.7MnFeO5 has been synthesized at normal pressure. Though it belongs to the same structural family, the mixed "MnFe" oxide exhibits a very different structural distortion of its framework compared to the pure "Fe2" oxide, due to the Jahn-Teller effect of Mn(3+). Combined neutron diffraction, high resolution electron microscopy/high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) investigations allow the origin of this difference to be determined. Here we show that the MO6 octahedra of the double perovskite layers in the "MnFe" structure exhibit a strong tetragonal pyramidal distortion "5 + 1", whereas the "Fe2" structure shows a tetrahedral distortion "4 + 2" of the FeO6 octahedra. Similarly, the MO5 polyhedra of the "MnFe" structure tend toward a tetragonal pyramid, whereas the FeO5 polyhedra of the "Fe2" structure are closer to a trigonal bipyramid. Differently from the oxide Pb(2-x)Ba(x)Fe2O5, which is antiferromagnetic, the oxide Pb1.3Ba0.7MnFeO5 exhibits a spin glass behavior with Tg ∼ 50 K in agreement with the disordered distribution of the Mn(3+) and Fe(3+) species.

Anisotropic Mechanical and Thermal Properties of Nd<sub>2</sub>SrAl<sub>2</sub>O<sub>7</sub>

For a long time since the anisotropy basically confined to a single crystal, used as a polycrystalline ceramic materials generally considered to be isotropic. In this paper, the anisotropic mechanical, thermal expansion coefficient and thermal conductivity of a double perovskite slab-rocksalt layer Nd2SrAl2O7 was studied by first principles as an example. The method is using density functional theory (DFT) and crystal parameters, which has been used to calculate the modulus of elasticity of anisotropic in a three-dimensional space. While combined with traditional thermal conductivity theory, we have obtained the tensor of thermal diffusion, thermal conductivity in 3D space for the first time in the world within no. The results are in good agreement with the experiment. The advantage of method is avoiding the difficulty of experimental measurement, reducing the time and obtaining relatively accurate results.

Synthesis and characterization of La 1+ xSr 2− xCoMnO 7− δ ( x=0,0.2; δ=0,1)

The n=2 Ruddlesden–Popper phases LaSr 2CoMnO 7 and La 1.2Sr 1.8CoMnO 7 have been synthesized by a sol–gel method. The O6-type phases LaSr 2CoMnO 6 and La 1.2Sr 1.8CoMnO 6 were produced by reduction of the O7 phases under a hydrogen atmosphere. The materials crystallize in the tetragonal I4/ mmm space group with no evidence of long-range cation order in the neutron and electron diffraction data. Oxygen vacancies in the reduced materials are located primarily at the common apex of the double perovskite layers giving rise to square pyramidal coordination around cobalt and manganese ions. The oxidation states Co 3+/Mn 4+ and Co 2+/Mn 3+ predominate in the as-prepared and reduced materials, respectively. The materials are spin glasses at low temperature and the dominant magnetic interactions change from ferro- to antiferromagnetic following reduction.

Comparison of two- and three-layer restacked Dion–Jacobson phase niobate nanosheets as catalysts for photochemical hydrogen evolution

Restacked niobate nanosheets were prepared by exfoliation of the corresponding Dion–Jacobson type layered perovskites (HCa2Nb3O10, HSr2Nb3O10 and HLaNb2O7) with tetra(n-butyl)ammonium hydroxide and subsequent treatment with hydrochloric acid. The nanosheets were characterized by means of X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and diffuse reflectance spectroscopy. With modification by platinum nanoparticles as additional catalysts, these nanosheet materials were tested as photocatalysts for hydrogen evolution from water containing 2-propanol as an electron donor under ultraviolet irradiation (λ > 300 nm). The activity of a triple-layered nanosheet (HSr2Nb3O10) was an order of magnitude higher than that of the HLaNb2O7nanosheet with double perovskite layers, despite their physicochemical similarity. Physicochemical analyses suggested that in triple-layered perovskite nanosheets, photocatalytic activity is influenced by several factors including the conduction band potential and the band-gap energy (the number of available photons), which are derived from the distortion of perovskite blocks consisting of NbO6 octahedra.

Disordered commensurate structure of the 2212-related phase Fe 2(Bi 0.69Sr 2.31)Fe 2O 9.5±1/2δ and structural mechanism

The structure of the Fe 2(Bi 0.69Sr 2.31)Fe 2O 9.5−1/2 δ has been carried out by single crystal X-ray diffraction. Its structure can be considered as commensurately modulated with a basic structure of Fmmm symmetry and with a modulation vector q ⇒ = α a ⇒ * + γ c ⇒ * whose α and γ values are, respectively, equal to 1/3 and 1. The ferrite is described as a three-fold superstructure with a ≈ 3 a p 2 , b ≈ a p 2 and c ≈ 26 Å (space group Bbmb). It is described using a disorder model in agreement with diffuse scattering observations. The structure is built up from the intergrowth sequence between [(Bi, Sr)Fe 2O 3.5±1/2 δ ] ∞ complex layers, related to the rock salt (RS)-type blocks, and double perovskite layers. Large analogies are found between the present structure and the so-called 2212 modulated structures related to the high T c superconductor copper oxides or to the corresponding Fe or Co oxides; they are discussed here. A statistical disorder characterizes the [Fe 2O 2.5±1/2 δ ] ∞ double layer. Taking advantage of similar structural arrangements in related oxide compounds, a structural model is proposed. A description of this double layer is then given in terms of sequence of polyhedra (tetragonal pyramids, mono-caped tetrahedra and trigonal bi-pyramids), in comparison with other related modulated structures with different periodicities. The powder sample exhibits a statistical distribution of α around an average value of 0.35; the oxygen non-stoichiometry appears as the driving force for the α value, i.e. for the modulation, commensurate or incommensurate. The Mössbauer study has been performed and interpreted on the basis of the refined structure.