Layered Perovskite Compounds Research Articles

Investigation of structural, dielectric, impedance, and conductivity properties of layered perovskite type compound; NaYSnO4

In this paper, the structural study of NaYSnO4 (NYSO), a layered perovskite ceramic oxide, was done using an X-ray diffractometer (XRD) to identify the phase and determine the composition of NYSO. The microscopic structure of the sample seen by Scanning Electron Microscopy (SEM) was found to be polycrystalline and a mixture of large and small grains, which indicate the anisotropic nature of the sample. A FTIR spectroscopic behaviour of the material was used to identify the formation of different bonds in the material, and the XPS study gives an idea of the binding energy of each element in NYSO. A thorough analysis of the impedance, dielectric constant, dielectric loss, modulus and AC conductivity properties concerning temperature and frequency displays the electronic device characteristics. The complex impedance spectra were studied at temperatures range between 25 and 500˚C and frequency of 100 Hz to 1 MHz range. Nyquist plots reveal the charge conduction mechanism of the grain and well-defined grain boundaries that correspond to the resistive and capacitive phenomena of the material. Furthermore, the activation energy has been estimated to investigate the charge transportation mechanism. This article concludes by discussing future possibilities and scientific challenges in NTCR thermistors using NYSO.

Energetic Stability and Band-Edge Orbitals of Layered Inorganic Perovskite Compounds for Solar Energy Applications.

Halide and oxide perovskite semiconductors (e.g., CsPbI3 and SrTiO3) have been widely studied for solar energy conversion applications. The optoelectronic properties and performance of these compounds can be tuned through the growth of layered perovskite superstructures. While oxides are quite varied in the compositions and geometries taken up by layered perovskites, halides have proven much more limited. In this paper, we use density functional theory calculations and chemical intuition to explore why this is the case. We show that, in general, the thermodynamic stability or instability of layered perovskite superstructures depends on the interplay of their ionic and covalent character and, just as importantly, on the features of other competing phases.

Heat Capacity of Layered Perovskite Compounds: EsBaCuFeO 5 (Es = Ho, Gd, and Yb)

The layered perovskite compounds, which show multiferroic properties, have attracted interest due to their interesting magnetic and electronic properties. In this study, we have investigated the heat capacity of EsBaCuFeO5 (Es = Ho, Gd and Yb) as a function of the temperature by using the overall equation of fitting. The Debye temperature, Einstein temperature, the coefficients m and γ have been derived by fitting experimental heat capacity data with the overall equation of fitting that consist of the contribution from electronic, Debye and Einstein terms. The values of the fitting parameters obtained are in good agreement with the results in the literature. The results display that the method can be used for calculation of the heat capacity of the layered perovskite compounds over the entire range of temperature. This article is protected by copyright. All rights reserved.

Synthesis, structure, and properties of new Dion-Jacobson compounds A’LnNaNb3O10 (A’ = Cs, Rb, H; Ln = Nd, Pr)

A new series of Dion-Jacobson layered perovskite compounds A’LnNaNb3O10 (A’ = Cs, Rb, H; Ln = Nd, Pr) was synthesized for the first time. Phase and chemical purity of compounds were proved using XRD, SEM, and EDX. Compounds RbNdNaNb3O10, RbPrNaNb3O10, CsNdNaNb3O10 and CsPrNaNb3O10 were synthesized using solid-state reaction, whereas HNdNaNb3O10, HPrNaNb3O10 were obtained by ion-exchange reaction. Crystal structures of solid-state reaction products were refined using the Rietveld method. The plausibility of obtained crystal structures was studied using the bond valence sum (BVS) method. The thermal behavior of compounds was established using DTA. Ion-exchange products were found to be metastable hydrates. The presence of the crystallization water was confirmed by DTA and IR spectroscopy. Optical band gap, electronegativity, valence band (EVB), and conduction band (ECB) potentials of obtained compounds were calculated from diffuse reflectance spectroscopy data. A previously proposed correlation between band gap and structural distortions was confirmed.

Protonic Conduction in the BaNdInO4 Structure Achieved by Acceptor Doping.

The potential of calcium-doped layered perovskite compounds, BaNd1–xCaxInO4–x/2 (where x is the excess Ca content), as protonic conductors was experimentally investigated. The acceptor-doped ceramics exhibit improved total conductivities that were 1–2 orders of magnitude higher than those of the pristine material, BaNdInO4. The highest total conductivity of 2.6 × 10–3 S cm–1 was obtained in the BaNd0.8Ca0.2InO3.90 sample at a temperature of 750 °C in air. Electrochemical impedance spectroscopy measurements of the x = 0.1 and x = 0.2 substituted samples showed higher total conductivity under humid environments than those measured in a dry environment over a large temperature range (250–750 °C). At 500 °C, the total conductivity of the 20% substituted sample in humid air (∼3% H2O) was 1.3 × 10–4 S cm–1. The incorporation of water vapor decreased the activation energies of the bulk conductivity of the BaNd0.8Ca0.2InO3.90 sample from 0.755(2) to 0.678(2) eV in air. The saturated BaNd0.8Ca0.2InO3.90 sample contained 2.2 mol % protonic defects, which caused an expansion in the lattice according to the high-temperature X-ray diffraction data. Combining the studies of the impedance behavior with four-probe DC conductivity measurements obtained in humid air, which showed a decrease in the resistance of the x = 0.2 sample, we conclude that experimental evidence indicates that BaNd1–xCaxInO4–x/2 is a fast proton conductor.

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...

New layered perovskite family built from [CeTa2O7]- layers: coloring mechanism from unique multi-transitions.

A Ce3+-based layered perovskite compound, Dion-Jacobson type RbCeTa2O7, has been discovered for the first time by introducing only a trivalent cerium ion to form [CeTa2O7]- layers. The unique green color was experimentally and theoretically ascribed to two charge transfer transitions of ligand-to-metal O2p → Ce4f and metal-to-metal Ce4f → Ta5d.

Effect of doping of Co, Ni and Ga on magnetic and dielectric properties of layered perovskite multiferroic YBaCuFeO5

YBaCuFeO5 is one of the interesting multiferroic compounds, which exhibits magnetic ordering and dielectric anomaly above 200 K. Partial substitution of Fe with other magnetic and non-magnetic ion affects the magnetic and the structural properties of the system. We report detailed investigation of structural, magnetic and dielectric properties of YBaCuFe0.85M0.15O5 (M = Co, Ni and Ga). We observed that the partial replacement of Ni and Co in place of Fe, results in magnetic dilution and broadening of the magnetic transition and shifting towards lower temperature. The replacement of Fe with non-magnetic Ga also results in shifting of the magnetic transition to the lower temperature side. The observed dielectric relaxation behavior in these compounds is due to the charge carrier hoping. This study highlights the impacts of magnetic and non-magnetic doping at the magnetic site on magnetic and dielectric properties in layered perovskite compound YBaCuFeO5.

Low temperature magnetic and dielectric properties of LnBaCuFeO5 (Ln =Nd, Eu, Gd, Ho and Yb)

The layered perovskite compounds are interesting due to their intriguing physical properties. In this article we report the structural, magnetic and dielectric properties of LnBaCuFeO5 (Ln = Nd, Eu, Gd, Ho and Yb). The structural parameters decrease from Nd to Yb due to the decrease in the ionic radii. An antiferromagnetic transition is observed for EuBaCuFeO5 near 120 K along with glassy dynamics of the electric dipoles below 100 K. The magnetic transition is absent in other compounds, which may be due to dominance of the magnetic moment of the rare earth ions. The dielectric constant does not show any anomaly, except in the case of HoBaCuFeO5 where it shows a weak frequency dependence around 54 K. These compounds show a significant enhancement of dielectric constant at high temperatures which have been attributed to Maxwell-Wagner effect. Our results highlight the impact of rare earth ion on the properties of layered perovskite compounds.

Optical Properties, Electronic Structures, and Photocatalytic Performances of Bandgap-Tailored SrBi2Nb2−xVxO9 Compounds

Layered perovskite compounds of SrBi2Nb2−xVxO9 (x = 0.0, 0.02, 0.04, 0.06, and 0.08) were synthesized via a solid-state reaction method. Their optical properties, electronic band structures, and photocatalytic activities under visible light irradiation were investigated for the first time. The incorporation of vanadium into the SrBi2Nb2O9 lattice reduced the bandgap energies, allowing the compounds to effectively absorb visible light. Electronic band structure calculations revealed that the V 3d orbitals caused bandgap narrowing by forming an additional band below the conduction band, while the O 2p and Bi 6p orbitals dominantly contributed to the formation of the valence band. The photocatalytic activity tested under visible light irradiation (>420 nm) revealed that it increased linearly with the V content in the SrBi2Nb2−xVxO9 compounds until saturation at x = 0.06, which was attributed to improved visible light absorption originating from the reduced bandgap energies.

Atomic-Scale Tailoring of Organic Cation of Layered Ruddlesden-Popper Perovskite Compounds.

Layered Ruddlesden-Popper (RP) phase perovskite compounds have emerged as promising photovoltaic materials for solar cell applications, but they suffer from poor absorption and strong exciton-binding energy. Herein, fluoro-, chloro-, and bromo-substitutions on the 4-position of the phenyl group in the component C6H5CH2CH2NH3+ (PEA+) are designed and synthesized to investigate their effect on the layered RP type H-PEA2MA2Pb3I10 (MA = CH3NH3) perovskite as an example. Single-crystal X-ray diffraction and temperature-dependent photoluminescence spectroscopy characterization reveal the electron-withdrawing halogen in organic cations decreases the distortion of inorganic sheets and significantly reduces the impact of two-dimensional quantum and dielectric confinement. This is further verified with an increased visible absorption and lower exciton-binding energy for these new layered RP-type perovskite compounds. A planar structured perovskite solar cell using an F-PEA2MA2Pb3I10 layer achieves a power conversion efficiency of 5.8%, which is better than that of the reference H-PEA2MA2Pb3I10.

The Effect of Lanthanum Doping and Oxygen Vacancy on Perovskite, Pyrochlore Oxide and Lanthanide Titanates: A First Principle Study

AbstractThe effects of La-substitution into SrTiO3 (STO) perovskite oxides on their phase structure, formation enthalpy and electrical conductivity have been investigated. La substitution in STO has been reported to show a significant enhancement in electronic conductivity in a wide-band-gap layered perovskite compound STO. Mixture of Lanthanum and Titanium oxide may lead to various phases including La2/3TiO3, La2Ti2O7 and La2TiO5. In this work, more than 50 structural models have been constructed by considering ionic state substituents, distance between substituents and their concentrations. We investigated the formation enthalpy, elastic properties and band gap by density functional theory (DFT) calculations. We have also investigated the effect of reducing environment on La2/3TiO3. The computed bulk modulus (∼2.4 % deviation) and band gap (∼12% deviation) of STO are in good agreement with the literature. Our results indicate that La substitution into STO could significantly reduce the band gap. Reduction in band gap is maximum when the substituents is present at low concentrations. Internal position of La substituents in STO affects the band gap marginally while energy remains almost same. Formation enthalpy of La2/3TiO3 from LaTiO3 is around 2 eV. La2/3TiO3 acts as band insulator (band gap = 2.8 eV). In reducing environment, the band gap of La2/3TiO3 significantly reduces. Sr substitution in La2/3TiO3 lower the band gap and formation enthalpy. La2Ti2O7 and La2TiO5 have higher band gap and lower bulk modulus than STO. Sr substitution is not feasible in La2Ti2O7 and La2TiO5.

Physisorption induced p-xylene gas-sensing performance of (C4H9NH3)2PbI4 layered perovskite

A novel organic-inorganic layered perovskite compound (C4H9NH3)2PbI4 has been synthesized through a simple and high-yield solution method. For the first time, this layered perovskite was used as a candidate material for gas sensors. Gas sensors based on (C4H9NH3)2PbI4 provided unique gas-sensing properties toward 1–800 ppm p-xylene (p-C8H10) at the working temperature of 140 °C, including fast response, quick response-recovery, good selectivity and repeatability. The as-prepared (C4H9NH3)2PbI4 gas sensor can detect as low as 1 ppm concentration of p-xylene with a response of 11.8 at 140 °C. In situ diffuse reflectance Fourier transform infrared (DRFTIR) measurement shows that the p-xylene sensing mechanism can be mainly attributed to physical adsorption, which is different from other common gas-sensing metal oxides that are based on adsorption-redox-desorption mechanism.

Photoluminescence Properties of Layered Perovskite-Type Strontium Scandium Oxyfluoride Activated With Mn4.

In this research, we have found that layered perovskite titanate Sr2TiO4 doped with Mn4+ exhibits photoluminescence even at room temperature despite no luminescence from Mn4+-doped SrTiO3 with a three-dimensional bulky perovskite structure. The relative position of t2g orbital of Mn to the valence band is a key factor for appearance of Mn4+-emission in Sr2TiO4:Mn. This result suggested usefulness of layered perovskite-type materials as hosts for Mn4+-activated phosphors than the bulky perovskite-type materials. Our investigation into photoluminescence of Mn4+-doped layered perovskite compounds has revealed that strontium scandium oxyfluoride Sr2ScO3F activated with Mn4+ exhibits Mn4+-emission with a peak at 697 nm under excitation at 300–600 nm and its emission intensity is much stronger than that of Sr2TiO4:Mn. The internal and external quantum yields of Sr2ScO3F:Mn were determined to be 50.5 and 43.5% under excitation at 345 nm, respectively.

Realization of a Hole-Doped Mott Insulator on a Triangular Silicon Lattice.

The physics of doped Mott insulators is at the heart of some of the most exotic physical phenomena in materials research including insulator-metal transitions, colossal magnetoresistance, and high-temperature superconductivity in layered perovskite compounds. Advances in this field would greatly benefit from the availability of new material systems with a similar richness of physical phenomena but with fewer chemical and structural complications in comparison to oxides. Using scanning tunneling microscopy and spectroscopy, we show that such a system can be realized on a silicon platform. The adsorption of one-third monolayer of Sn atoms on a Si(111) surface produces a triangular surface lattice with half filled dangling bond orbitals. Modulation hole doping of these dangling bonds unveils clear hallmarks of Mott physics, such as spectral weight transfer and the formation of quasiparticle states at the Fermi level, well-defined Fermi contour segments, and a sharp singularity in the density of states. These observations are remarkably similar to those made in complex oxide materials, including high-temperature superconductors, but highly extraordinary within the realm of conventional sp-bonded semiconductor materials. It suggests that exotic quantum matter phases can be realized and engineered on silicon-based materials platforms.

Effect of crystalline electric field on heat capacity of LnBaCuFeO5 (Ln = Gd, Ho, Yb)

Structural, magnetic and thermodynamic properties of layered perovskite compounds LnBaCuFeO5 (Ln = Ho, Gd, Yb) have been investigated. Unlike the iso-structural compound YBaCuFeO5, which shows commensurate antiferromagnetic to incommensurate antiferromagnetic ordering below ∼200 K, the studied compounds do not show any magnetic transition in measured temperature range of 2–350 K. The high temperature heat capacity of the compounds is understood by employing contributions from both optical and acoustic phonons. At low temperature, the observed upturn in the heat capacity is attributed to the Schottky anomaly. The magnetic field dependent heat capacity shows the variation in position of the anomaly with temperature, which appears due to the removal of ground state degeneracy of the rare earth ions, by the crystalline electric field.

Time-of-Flight Elastic and Inelastic Neutron Scattering Studies on the Localized 4d Electron Layered Perovskite La5Mo4O16

The magnetic structure and spin-wave excitations in the quasi-square-lattice layered perovskite compound La$_5$Mo$_4$O$_{16}$ were studied by a combination of neutron diffraction and inelastic neutron scattering techniques using polycrystalline sample. Neutron powder diffraction refinement revealed that the magnetic structure is ferrimagnetic in the $ab$ plane with antiferromagnetic stacking along the $c$ axis where the magnetic propagation vector is $\mathbf{k}=\left(0,0,\frac{1}{2}\right)$. The ordered magnetic moments are estimated to be $0.54(2)\mu_\text{B}$ for Mo$^{5+}$ ($4d^1$) ions and $1.07(3)\mu_\text{B}$ for Mo$^{4+}$ ($4d^2$) ions at 4 K, which are about half of the expected values. The inelastic neutron scattering results display strong easy-axis magnetic anisotropy along the $c$ axis due to the spin-orbit interaction in Mo ions evidenced by the spin gap at the magnetic zone center. The model Hamiltonian consisting of in-plane anisotropic exchange interactions, the interlayer exchange interaction, and easy-axis single-ion anisotropy can explain our inelastic neutron scattering data well. Strong Ising-like anisotropy and weak interlayer coupling compared with the intralayer exchange interaction can explain both the high-temperature magnetoresistance and long-time magnetization decay recently observed in La$_5$Mo$_4$O$_{16}$.

(Invited) Energy and Information Conversion Assisted By Electric Double Layers at Liquid-Solid Nano-Interfaces

Electric double layers (EDLs) at liquid-solid interfaces have attracted much attention in soft-material electronics, because they can induce extremely large electric fields, through which effective carrier injection and charge separation can be realized. As representative EDL materials, ionic liquids possess excellent features for electronic application, such as a wide electrochemical window, low vapor pressure, and high chemical and physical stability. In this presentation, we describe our recent works on organic field-effect transistors with ionic liquids as gate dielectrics. Secondly, we describe the opto-electronic conversion in organic photocells with a [Metal | Semiconductor | Electrolyte | Metal] structure, which can be used to effectively produce a polarization current under modulated light stimulus. We discuss their application to the information conversion in the NIR light range, as biosensors, and as AC photovoltaic cells based on the layered Perovskite compounds.

Cupric bromide hybrid perovskite heterojunction solar cells

Currently, the hybrid perovskite solar cells were exclusively dominated by the Pb or Sn-based perovskite materials, and these materials, however, exhibit long term instabilities associated with ambient hydrolysis and oxidation, limiting their widespread applications. In this work, two layered cupric bromide hybrid perovskite compounds are prepared as light absorbers for application in heterojunction solar cells. The perovskite layers can be deposited from the solutions of the as-prepared perovskites or directly from their precursor solutions at ambient condition. Their preliminary phoyovoltaic performance was carried out in mesoporous TiO2 heterojunction solar cells.

Mechanism of enhanced photocatalytic activities on N-doped La2Ti2O7: An insight from density-functional calculations

Recently, a wide-band-gap layered perovskite compound La2Ti2O7 (LTO) has been reported to show a significant enhancement of both the visible and UV light photocatalytic activities after doping with N atoms. It is known that the doping sites often act as recombination centers of the photo-exited carriers and block the redox reactions. In this work, we investigated the origin of the enhancement in photocatalytic activity of N-doped LTO by using density functional theory (DFT) calculations. More than 40 models were constructed by considering ionic state of dopants, distance between dopants, doping concentrations, and formation of oxygen vacancy. The structure-properties relation of N-doped LTO was established. We found that the model of Sub3N–3Odv (with three dispersed substitutional N atoms at O sites and one oxygen vacancy in 87-atom LTO supercell) well explains both the shift-up of the valence bands and the narrowed band gap observed in experiment. The obtained band gap of 2.46 eV agrees well with the experimental value of 2.51 eV. For the models with interstitial N atoms, the impurity states are mainly localized at the higher-energy region of the band gap, which may trap the photo-excited carriers and decrease the photocatalytic activity. The work provides a potential implication for effective band-gap narrowing of wide-gap photocatalysts.