Layered Perovskite Structure Research Articles

Structural Features in Some Layered Hybrid Copper Chloride Perovskites: ACuCl4 or A2CuCl4.

We present three new hybrid copper(II) chloride layered perovskites of generic composition ACuCl4 or A2CuCl4, which exhibit three distinct structure types. (m-PdH2)CuCl4 (m-PdH22+ = protonated m-phenylenediamine) adopts a Dion-Jacobson (DJ)-like layered perovskite structure type and exhibits a very large axial thermal contraction effect upon heating, as revealed via variable-temperature synchrotron X-ray powder diffraction (SXRD). This can be attributed to the contraction of an interlayer block, via a slight repositioning of the m-PdH22+ moiety. (3-AbaH)2CuCl4 (3-AbaH+ = protonated 3-aminobenzoic acid) and (4-AbaH)2CuCl4 (4-AbaH+ = protonated 4-aminobenzoic acid) possess the same generic formula as Ruddlesden-Popper (RP) layered perovskites, A2BX4, but adopt different structures. (4-AbaH)2CuCl4 adopts a near-staggered structure type, whereas (3-AbaH)2CuCl4 adopts a near-eclipsed structure type, which resembles the DJ rather than the RP family. (3-AbaH)2CuCl4 also displays static disorder of the [CuCl4]∞ layers. The crystal structures of each are discussed in terms of the differing nature of the templating molecular species, and these are compared to related layered perovskites. Preliminary magnetic measurements are reported, suggesting dominant ferromagnetic interactions.

Antiferromagnetic Order and Spin-Canting Transition in the Corrugated Square Net Compound Cu3(TeO4)(SO4)·H2O.

Strongly correlated electrons in layered perovskite structures have been the birthplace of high-temperature superconductivity, spin liquids, and quantum criticality. Specifically, the cuprate materials with layered structures made of corner-sharing square-planar CuO4 units have been intensely studied due to their Mott insulating ground state, which leads to high-temperature superconductivity upon doping. Identifying new compounds with similar lattice and electronic structures has become a challenge in solid-state chemistry. Here, we report the hydrothermal crystal growth of a new copper tellurite sulfate, Cu3(TeO4)(SO4)·H2O, a promising alternative to layered perovskites. The orthorhombic phase (space group Pnma) is made of corrugated layers of corner-sharing CuO4 square-planar units that are edge-shared with TeO4 units. The layers are linked by slabs of corner-sharing CuO4 and SO4. Using both the bond valence sum analysis and magnetization data, we find purely Cu2+ ions within the layers but a mixed valence of Cu2+/Cu+ between the layers. Cu3(TeO4)(SO4)·H2O undergoes an antiferromagnetic transition at TN = 67 K marked by a peak in the magnetic susceptibility. Upon further cooling, a spin-canting transition occurs at T* = 12 K, evidenced by a kink in the heat capacity. The spin-canting transition is explained on the basis of a J1-J2 model of magnetic interactions, which is consistent with the slightly different in-plane superexchange paths. We present Cu3(TeO4)(SO4)·H2O as a promising platform for the future doping and strain experiments that could tune the Mott insulating ground state into superconducting or spin liquid states.

Layered perovskite oxides Lan+1NinO3n+1 (n = 1, 2, and 3) for detecting ammonia under high temperature

A series of impedancemetric sensors for ammonia detection were fabricated using yttrium stabilized zirconia (YSZ) electrolyte and Lan+1NinO3n+1 (n = 1, 2, and 3) sensing electrodes. The sensing materials with layered perovskite structure were prepared using in-situ impregnation method and well-dispersed in YSZ porous skeleton after calcination at 900 °C. The sensing performances of the sensors with Lan+1NinO3n+1 sensing electrodes were investigated using the impedancemetric modulus |Z| and phase angle Θ as response signals, respectively. The results show that the sensor with La2NiO4+δ sensing electrode exhibits the higher response values and sensitivity compared to the sensor using La3Ni2O7-δ or La4Ni3O10-δ sensing electrodes, which is attributed to the largest NH3 adsorption capacity of La2NiO4+δ. The response signals |Z| or Θ of the La2NiO4+δ based sensor linearly depend on NH3 concentrations. The sensor hardly is insensitive to co-existing gases such as CO2, CH4, H2 and relative humidity, but NO or NO2 causes a positive error.

3D to 2D Magnetic Ordering of Fe3+ Oxides Induced by Their Layered Perovskite Structure

The antiferromagnetic behavior of Fe3+ oxides of composition RE1.2Ba1.2Ca0.6Fe3O8, RE2.2Ba3.2Ca2.6Fe8O21, and REBa2Ca2Fe5O13 (RE = Gd, Tb) is highly influenced by the type of oxygen polyhedron around the Fe3+ cations and their ordering, which is coupled with the layered RE/Ba/Ca arrangement within the perovskite-related structure. Determination of the magnetic structures reveals different magnetic moments associated with Fe3+ spins in the different oxygen polyhedra (octahedron, tetrahedron, and square pyramid). The structural aspects impact on the strength of the Fe-O-Fe superexchange interactions and, therefore, on the Néel temperature (TN) of the compounds. The oxides present an interesting transition from three-dimensional (3D) to two-dimensional (2D) magnetic behavior above TN. The 2D magnetic interactions are stronger within the FeO6 octahedra layers than in the FeO4 tetrahedra layers.

Ni/YMnO3 perovskite catalyst for CO2 methanation

This work proposes an innovative Ni catalyst supported over YMnO3 perovskite as a promising catalytic system for CO2 methanation reaction. Under reductive conditions, the attendance of Mn redox couples within the layered perovskite structure promotes the constitution of sub-stoichiometric YMnO3-x units which, by means of the flexible YMnO3-x reorganization capacity, results in boosted anionic mobility's. The competitive turnover frequencies (20.1 and 17.0 s−1 at 400 °C under dry- and steamed- CO2 methanation conditions) displayed by Ni/YMnO3 system were related to the synergism between strongly interacting Ni particles with partially reduced YMnO3-x perovskites. The optimal Ni dispersions, for which no relevant signs of sintering issues were discerned, combined to effective role of oxygen vacancies towards the dissociative activation of CO2 molecules enabled highly active and stable catalytic behaviours with no evidence of cooking phenomena. On evaluating the water presence within CO2 methanation feedstock's, the deprived catalytic behaviour was fundamentally associated to depleted oxygen vacancies concentrations and promoted WGS side reactions.

Iron oxidation state in La0.7Sr1.3Fe0.7Ti0.3O4 and La0.5Sr1.5Fe0.5Ti0.5O4 layered perovskites: Magnetic properties

La0.5Sr1.5Fe0.5Ti0.5O4 and La0.7Sr1.3Fe0.7Ti0.3O4 solid solutions with the layered perovskite structure were synthesized using a solid state method. Structural properties of obtained samples were characterized using X-ray diffraction and X-ray fluorescence analyses. Magnetic properties were investigated using magnetometry, electron spin resonance (ESR) and Mössbauer spectroscopy methods. Based on magnetization and ESR measurements it was suggested the presence of Fe4+ ions in addition to trivalent iron ions that was exactly confirmed by Mössbauer spectroscopy investigations. Based on all experimental results one can suggest the presence of the electronic phase separation in the investigated samples – the simultaneous existence of the paramagnetic phase and magnetically correlated regions, which form due to the mixed-valence iron ions. So the paramagnetic phase with strong antiferromagnetic correlation exists in both samples, while the second phase is ferromagnetically and ferrimagnetically correlated regions in La0.5Sr1.5Fe0.5Ti0.5O4 and La0.7Sr1.3Fe0.7Ti0.3O4, respectively.

Tailoring the optical properties of SrBi4Ti4O15 thin films by RF sputtering process parameters

SrBi4Ti4O15 is a bismuth layered perovskite structure material, its thin film form gained much interest due to their geometrical flexibility and thickness. In the present study, SrBi4Ti4O15 thin films are deposited on amorphous substrate using radio frequency sputtering technique. SrBi4Ti4O15 thin films found to be single phase orthorhombic structure by using X-ray diffraction technique. Surface morphology studies such as grain size, shape and roughness were explored through atomic force microscopy. EDX analysis identified the individual elements and its percentage in the compound. Optical properties (refractive index and bandgap) were determined with varying the oxygen mixing percentage (OMP). The best optical properties (refractive index ~ 2.35 and bandgap ~ 3.4 eV) were obtained for films deposited at 50% OMP. These results shows the potential of using SrBi4Ti4O15 thin films in electro-optic devices.

Accelerated Exploration of Stability between Layered and Complex Structures in PrBa1-XSrxCo2-YFeyO5.5

Layered perovskite structures show high performance as an air electrode in solid oxide fuel cells and proton ceramic fuel cells. Radii difference among metal elements at site A of ABO3 is a prerequisite for conversion of perovskite structures from complex to layered. In this study, we study energetically favorable structures according to change in composition of site A (Pr, Ba, Sr) and site B elements (Co, Fe). 25 compositions were determined by changing x and y in PrBa1-xSrxCo2-yFeyO5.5 (x = 0, 0.25, 0.5, 0.75, 1, and y = 0, 0.5, 1, 1.5, 2). The 2×2×2 supercells with these compositions were studied using DFT. Since the number of possible atomic arrangements for each composition is very large, however, a genetic algorithm was used to search energetically favorable structure efficiently. The highest energy difference between complex and layered structures among the 25 compositions was obtained at x=0 and y=1.

Hetero-valent substitution strategy toward orange-red luminescence in Bi3+ doped layered perovskite oxide phosphors for high color rendering index white light-emitting diodes

Controllable efficient emission tuning from 553 nm (yellow) to 609 nm (orange-red) in novel Sr 1- x La 1+ x ZnO 3.5+ x /2 :Bi 3+ (0 ≤ x ≤ 0.4) phosphors with layered perovskite structure is first designed for high color rendering index pc-WLEDs via a hetero-valent cation substitution and controlling over site selective excitation strategies. • Hetero-valent substitution strategy is designed in novel yellow SrLaZnO 3.5 :Bi 3+ . • Luminescence tuning from 558 nm (yellow) to 585 nm (orange) is achieved. • Orange-red luminescence (609 nm) is achieved by site-selective excitation strategy. • White LED shows a superior color rendering index (Ra = 97.1, R9 = 98). The equivalent or hetero-valent substitution strategy is an efficient method for stimulating photoluminescence tuning or optimizing the photoluminescence performances of phosphor materials. A new K 2 NiF 4 -type layered perovskite SrLaZnO 3.5 :Bi 3+ phosphor with broad-band yellow emission (558 nm) is first explored. Based on an efficient hetero-valent substitution strategy, a series of Sr 1- x La 1+ x ZnO 3.5+ x /2 :Bi 3+ (0 ≤ x ≤ 0.4) solid solution phases are successfully constructed. The different Bi 3+ local environments at two crystallographic sites and vacancy oxygen make the various distributions of emission and excitation spectra. Consecutive emission tuning from yellow (558 nm) to orange (585 nm), and improvement of emission intensity and internal quantum efficiency (IQE = 45%-64%) are achieved through La 3+ hetero-valent substitution for Sr 2+ in Sr 1- x La 1+ x ZnO 3.5+ x /2 :Bi 3+ (0 ≤ x ≤ 0.4). The structural stability and Bi 3+ occupation distribution in solid solution have been revealed by structural elaboration and crystal field regulation. Based on the both hetero-valent substitution and site-selective excitation strategies, a novel orange-red luminescence can be observed peaking at ~609 nm under near-ultraviolet light (~390 nm) excitation without visible absorption. The fabricated full-spectrum phosphor-converted white light-emitting diodes (pc-WLEDs) show outstanding warm white light, and a high color rendering index (Ra = 97.1, R9 = 98) is achieved, implying that the as-prepared Sr 1- x La 1+ x ZnO 3.5+ x /2 :Bi 3+ (0 ≤ x ≤ 0.4) phosphors can used as yellow/orange-red components in pc-WLED lighting. These results indicate that hetero-valent substitution can predict and control site preference of luminescent centers, providing a new way for optimizing phosphor materials for solid-state lighting.

Defect Structure and Oxide-ion Conduction in (La, Sr)2NiO4+δ with Layered Perovskite Structure

Atomic configuration of La2−xSrxNiO4+δ (x = 1/4) with a layered perovskite structure was investigated by a molecular dynamics simulation and a reverse Monte Carlo modelling using a Faber-Ziman stru...

Domain observation in the visible-light photocatalyst Bi4NbO8Br with the layered perovskite structure

Layered perovskite oxyhalides Bi4MO8X (M = Nb, Ta; X = Cl, Br) are promising visible-light photocatalysts for water splitting, where the polar structure may enhance the conductivity of photocarriers. In this study, the domain structure of Bi4NbO8Br single crystal was investigated using piezoresponse force microscopy and transmission electron microscope. We observed a rare domain structure with a ferroelectric 180° domain in the nanoscale ferroelastic 90° domains developed in the ab plane. We also discuss the effect of these domain structures on the dynamics of photocarriers, which may provide new ideas for the design of highly active photocatalyst.

Color tunable Eu-doped CaSrNb2O7 phosphors for white light-emitting diodes and optical thermometers

Herein, Eu-doped CaSrNb2O7 perovskites are synthesized by using the high-temperature solid-phase method, resulting in layered perovskite structure, with the space group of Cmc21 and a strong luminescence response under excitation wavelength of 314 nm. Moreover, these as-prepared CaSrNb2O7:xEu3+ (x = 0–0.15) phosphors are color-tunable. Specifically, the color changes from white to blue with raising temperature. After thermal stability testing, the fluorescence intensity ratio, maximum absolute and relative sensor sensitivity of CaSrNb2O7:xEu3+ are calculated to evaluate the thermal properties of materials. It turned out that the maximum absolute and relative sensor sensitivity are 0.043 K-1 and 0.0105 K-1, and the temperature resolution is as low as 0.0286K, respectively. It suggests that the high sensitivity and excellent resolution of CaSrNb2O7:xEu3+ make it a promising candidate for optical thermometers.

Layered Perovskite Compound NaLaTiO4 Modified by Nitrogen Doping as a Visible Light Active Photocatalyst for Water Splitting

Sr2TiO4 and NaLaTiO4 are structural congeners with K2NiF4-type layered perovskite structure. However, nitrogen doping results in distinct modifications to their visible light absorption. Na/La orde...

Enhanced Visible Light Absorption in Layered Cs3Bi2Br9 Halide Perovskites: Heterovalent Pb2+ Substitution-Induced Defect Band Formation

We have successfully substituted trivalent Bi3+ with divalent Pb2+ in Cs3Bi2Br9-layered perovskites. Controlled heterovalent Pb substitution in these Cs3Bi2Br9-layered perovskites reduces the band gap because of the emergence of defect states in between the bands. These heterovalent Pb-substituted Cs3Bi2Br9 bulk perovskite compounds are successfully synthesized for the first time by chemical reprecipitation method. X-ray photoelectron spectroscopy analysis indicate that lead substitution in the structure is in Pb2+ form, which creates a charge imbalance in the compound as it replaces Bi3+ from the layered perovskite structure. Such charge imbalance is compensated either by bromine vacancies (VBr) or interstitial cesium (Csi) additions. VBr or Csi in Cs3Bi2Br9 along with PbBi creates defect states in between the bands, which results in redshift in the layered perovskite band. Band structure calculations indeed confirm the onset of such defect states, responsible for the redshift. A more detailed defect physics simulation indicates that the defect complex PbBi + VBr is more probable to form if Pb is rich in the environment, which consequently introduces a few deep level defects responsible for the reduction of the band gap. Understanding of the electronic structure and defect physics of such heterovalent Pb-substituted Cs3Bi2Br9 will strengthen the future photovoltaic and optoelectronic applications.

Lead-Free Cs4CuSb2Cl12 Layered Double Perovskite Nanocrystals.

Concerns about the toxicity of lead-based perovskites have aroused great interest for the development of alternative lead-free perovskite-type materials. Recently, theoretical calculations predict that Pb2+ cations can be substituted by a combination of Cu2+ and Sb3+ cations to form a vacancy-ordered layered double perovskite structure with superior optoelectronic properties. However, accessibilities to this class of perovskite-type materials remain inadequate, hindering their practical implementations in various applications. Here, we report the first colloidal synthesis of Cs4CuSb2Cl12 perovskite-type nanocrystals (NCs). The resulting NCs exhibit a layered double perovskite structure with ordered vacancies and a direct band gap of 1.79 eV. A composition-structure-property relationship has been established by investigating a series of Cs4CuxAg2-2xSb2Cl12 perovskite-type NCs (0 ≤ x ≤ 1). The composition induced crystal structure transformation, and thus, the electronic band gap evolution has been explored by experimental observations and further confirmed by theoretical calculations. Taking advantage of both the unique electronic structure and solution processability, we demonstrate that the Cs4CuSb2Cl12 NCs can be solution-processed as high-speed photodetectors with ultrafast photoresponse and narrow bandwidth. We anticipate that our study will prompt future research to design and fabricate novel and high-performance lead-free perovskite-type NCs for a range of applications.

High-Performance Protonic Ceramic Electrochemical Cells for Hydrogen Production and Electricity Generation at Intermediate Temperatures

Achieving energy conversion between electricity power and hydrogen in protonic ceramic electrochemical cells (PCECs) is an emerging and attractive approach to store intermittent renewable energies which can be converted back to electricity in reversible operation. Economically competitive PCEC systems have distinct advantages over conventional oxygen-ion conducting counterpart (O-SOC), but further materials innovation is still needed to improve cell performance at reduced operating temperature (400~600○C), enhance system lifetime and reduce cost. To achieve efficient electrochemical hydrogen and power production with stable operation, highly robust and durable oxygen electrode is urgently desired to facilitate water oxidation and oxygen reduction reactions, which are the critical technical barriers for both electrolysis and fuel cell operation at reduced temperatures. The recent efforts in this study have been focused on developing new triple conducting electrode with perovskite or layered perovskite structure for high-performance and stable PCECs. The systematic material characterizations are carried out to evaluate the feasibility of activity, stability and interface compatibility, such as Fourier-transform infrared spectroscopy, high-temperature X-ray diffraction, hydrogen permeation and first-principal computation. The catalytic activity towards water splitting reaction is demonstrated in various electrochemical performance evaluation at 400~600○C. The long-term durability of the PCEC is examined to show the high resistance against transient current density change in reversible operation and high steam concentration.

Potassium Doping Effect on the Photovoltaic Performance of Perovskite Solar Cells

We have fabricated a series of potassium-doped (K-doped) perovskite solar cells (PSCs). Structural investigations of the developed PSCs have shown that alkai doping affects the perovskite layer structure and morphology with the increase of the crystallite size and surface uniformity. K-doped samples exhibite higher photovoltaic (PV) performance and improved operational stability compared to the control series of undoped PSCs, due to retarded recombination processes.

Tunable Perovskite-Derived Bismuth Halides: Cs3Bi2(Cl1-xIx)9.

Bismuth-based perovskites are of interest as safer alternatives to lead-based optoelectronic materials. Prior studies have reported on the compounds Cs3Bi2Cl9, Cs3Bi2I9, and Cs3Bi2Cl3I6. Here we examine a range of compounds of the formula Cs3Bi2(Cl1-xIx)9, where x takes values from 0.09 to 0.52. Powder and single-crystal X-ray diffraction were used to determine that all of these compounds adopt the layered vacancy-ordered perovskite structure observed for Cs3Bi2Cl3I6, which is also the high-temperature phase of Cs3Bi2Cl9. We find that, even with very small iodine incorporation, the structure is switched to that of Cs3Bi2Cl3I6, with I atoms displaying a distinct preference for the capping sites on the BiX6 octahedra. Optical absorption spectroscopy was employed to study the evolution of optical properties of these materials, and this is complemented by density functional theory electronic structure calculations. Three main absorption features were observed for these compounds, and with increasing x, the lowest-energy features are red-shifted.

Effect of the thickness of Sr2Bi4Ti5O18 transition layer on the properties of BiFeO3/Sr2Bi4Ti5O18 bilayer composite thin films

BiFeO3(BFO)/Sr2Bi4Ti5O18(SBT) bilayer composite thin films were prepared using the sol-gel method. The influence of the SBT transition layer thickness on the properties of BFO/SBT bilayer composite thin films was studied. The results showed that an SBT transition layer with the proper thickness can improve the BFO/SBT bilayer composite film performance. X-ray diffraction (XRD) analysis revealed that a bismuth layered perovskite structure is formed in all of the thin films. The scanning electron microscopy (SEM) result showed that the BFO/80 nmSBT sample exhibits good crystallization, an improved density and a uniform minimum grain size compared with the other samples. The X-ray photoelectron spectroscopy (XPS) result showed that the Fe2+ content and oxygen vacancy concentration are lowest in the BFO/80 nm SBT sample. This sample has good ferroelectric properties: the leakage current density has the lowest value of J = 5.21 × 10-5 A/cm2 among the samples at 350 kV/cm, 2Ec = 900 kV/cm, and 2Pr = 151 μC/cm2. At a low electric field (E<100 kV/cm), the leakage mechanism of the thin film is ohmic conduction, and the Fowler-Nordheim (F–N) tunneling effect is observed at a high electric field (E>100 kV/cm). The relative dielectric constant (εr) is 121, the dielectric loss (tanδ) is 0.024 at 105 Hz.

Изучение влияния допирования калием на характеристики перовскитного солнечного элемента

We have fabricated a series of potassium-doped (K-doped) perovskite solar cells (PSCs). Structural investigations of the developed PSCs have shown that alkai doping affects the perovskite layer structure and morphology with the increase of the crystallite size and surface uniformity. K-doped samples exhibite higher PV performance and improved operational stability compared to the control series of undoped PSCs, due to retarded recombination processes.