Perovskite Compounds Research Articles

Structural and optoelectronic properties of the Cs2InMCl6 (M: Sb, Bi, Ag) double perovskite compounds: A first-principles study

In this work we implied density-functional theory (DFT) to study structural and optoelectronic properties of the double perovskite Cs2InSbCl6 (CISC), Cs2InBiCl6 (CIBC) and Cs2InAgCl6 (CIAC) compounds. We found that structural parameters such as lattice constant and bulk modules are in close agreement with other computational and experimental results. Bandstructure calculations with norm-conserving pseudopotentials show that these compounds are semiconductors with a direct band gap that stay at the Gamma point of the first Brillouin zone. Their band gap values vary from 1.47 to- 3.16 eV. The valence band maximum (VBM) is primarily composed of the Cl-p, In-s, Sb/Bi-s, and Ag-s states, and the conduction band minimum (CBM) is composed of the Cl-s/p, In/Sb/Bi-p orbitals. Optical studies include dielectric function, absorption, optical conductivity, reflectivity, and refractive and extinction indexes were performed in the photon energy range 0.0 up to 14.0 eV to investigate the optical response of these structures. These compounds have large optical absorption of incident radiation in the range of about 2–14 eV. Therefore, they can potentially be promising candidates for use in optoelectronic devices.

Chemistry, Structure, and Function of Lone Pairs in Extended Solids.

ConspectusThe lone pair has been a known feature of the electronic structure of molecules for over 100 years. Beginning with the pioneering work of Lewis and others that was later developed into useful guidelines for predicting molecular structure, lone pairs and their steric consequences are now taught at the very earliest stages of a chemistry education. In the crystalline solid state, lone pairs have perhaps had a less visible yet equally consequential role, with a significant impact on a range of properties and functionalities. Important properties associated with s2 electron-derived lone pairs include their role in creating conditions favorable for ion transport, in the formation and correlation of local dipoles and the resulting polar behavior leading to ferroics and multiferroics, in increasing the refractive index of glass, in reducing the thermal conductivity of thermoelectric materials, and in breaking local symmetry permitting second-harmonic light generation.. In recent years, the role of the lone pair in developing the electronic structure of some topological quantum materials has also been recognized. While structural distortions due to lone pairs have traditionally been characterized through their crystallography, recent advances in scattering and spectroscopy have revealed the presence of local lone pair-driven distortions that do not correlate over long length scales. The role of these crystallographically "hidden" lone pairs, their detection, and their impact on properties have become a growing body of work in the literature. Hidden lone pairs are an effective argument for considering a role for lone pairs that goes beyond their being objects that occupy space in the coordination polyhedra of cations. This Account introduces the chemistry of lone pairs in extended crystalline solids, including a discussion of when they are stereochemically active, how they manifest in the structure, and how their chemistry can be tuned by the chemical environment around them. Eventually, all of these factors work in unison to help develop and tune properties of interest. Certain specific examples of structure-property relationships in materials that are driven by lone pair behavior are described here, including the potential impact of lone pairs on the optical and electronic properties of hybrid halide perovskite compounds that are relevant to their photovoltaic applications. We highlight the role of lone pairs in the dielectric behavior of geometrically frustrated pyrochlores, the temperature-dependent optoelectronic behavior of halide perovskites, the polar phase transitions in lead-free ferroelectric perovskites, and the compositional insulator-to-metal transition in ruthenium pyrochlores. The theme underpinning this Account is that the lone pair can be considered to be a powerful design element for a broad range of material function.

Structural, electronic and optical studies of Sr2NiTeO6 double perovskite by first-principle DFT–LDA + U calculation

The structural, electronic and optical properties of monoclinic Sr2NiTeO6 double perovskite have been studied using corrected density functional theory–local density approximation with applying of Hubbard U corrected energy (DFT–LDA + U) method in plane-wave pseudopotential basis. The influence of on-site Coulomb interaction on structural, electronic and optical properties of Sr2NiTeO6 double perovskite compound, which consists of strongly localized Ni 3d electrons, were investigated. The highly Coulomb repulsion between electrons was corrected using Hubbard U parameter, varying from 0 to 8 eV for Ni 3d orbitals. The calculated results demonstrated that Sr2NiTeO6 double perovskite was sensitive to the change in U values. The optimized structural properties give a good agreement with experiment and other calculation data with lattice parameters a = 5.673 Å, b = 5.565 Å, c = 7.847 Å, α = 89.999°, β = 90.257° and γ = 90.000°. The DFT–LDA + U predicted the calculated electronic band structure of Sr2NiTeO6 was showed metallic behaviour (0 and 2 eV) and insulator behaviour (4, 6 and 8 eV). The density of state (DOS) shows that there was a significant effect on hybridization of Ni 3d and O 2p states at the conduction and valence band, respectively. Moreover, the results of optical studies such as dielectric function, absorption and reflectivity were found significant to the variation of U values applied indicates that the U values give a better description on the electronic localization of Ni 3d states.

Molten Salt Flux Synthesis, Structure determination, Optical, Impedance and Modulus Spectroscopy Characterization of perovskite compound

The chemical Molten Salt Flux process was used for the synthesis of Ba0.97La0.02Ti1-xNb4x/5O3 polycrystalline sample (well-known as BLTi0.93Nb0.056). Doping with Niobium caused significant alterations in the physical properties of BLT ceramic. The XRD analysis revealed that Nb introduction forms a pure perovskite phase and crystallize in the P4/mmm-tetragonal symmetry. The average crystallite size was proven to decrease with the increase in Nb concentration. TEM image showed the formation of particles, where the average grain size decreased with Nb doping. The Nb incorporation into the BLT host lattice was also confirmed by the optical band gap (Eg) value. The optical properties were strongly influenced by Nb doping. The dielectric parameters were subsequently investigated as a function of frequency and d.c bias voltage. The observed dielectric dispersion was interpreted on the basis of Maxwell-Wagner interfacial model and Koop's phenomenological theory. Overall, Nyquist plot shows both bulk and grain boundary effect. The electrical relaxation process occurring in the material has been found to be d.c bias voltage dependent. Modulus analysis has established the possibility of hopping mechanism for electrical transport processes in the system.

Resistive switching and photovoltaic response characteristics for the BaTiO3/Nb:SrTiO3 heterostructure

Recently, perovskite compounds with ABX3 structures have been attracting increasing attention because of their excellent properties and their potential for applications in fields such as optoelectronics and memory devices. In this Letter, we introduce a BaTiO3/Nb:SrTiO3 (BTO/NSTO) heterostructure that displays both resistive switching and photovoltaic response characteristics. As a dual-function device, our heterostructure device not only exhibits bipolar resistive switching behavior with a switching ratio of up to 103 without any forming process but also shows a tunable photovoltage effect with an open-circuit voltage (Voc) of approximately 0.38 V. In addition, a high-resistance state and a low-resistance state of the device can be modulated by light illumination. This photo-modulation mechanism is revealed and shows that resistive switching can be attributed to migration of photogenerated carriers and charge trapping/detrapping caused by ferroelectric polarization reversal, which changes depletion layer characteristics at the BTO/NSTO interface. This work may help to provide an understanding of multifunctional characteristics of the BTO/NSTO heterostructure and will pave the way toward practical applications of this heterostructure in memory and optoelectronic devices.

Zn-doped Pb/Sn hybrid perovskite solar cells: Towards high photovoltaic performance

Achieving a low-toxicity mixed Sn/Pb halide perovskite solar cell with the higher performance and lower cost is still a major challenge. Furthermore, the element Zn was incorporated as a substitute cation for the toxic element Pb into the CH3NH3Sn0.25Pb0.75I3 perovskite compound, as a result of its significant properties such as non-toxic nature, inability to oxidize, and abundance on earth. Thus, the structures of Zn-doped Pb/Sn hybrid perovskite solar cells (PSCs) were introduced and studied. The results showed that 3% Zn-doping improved the crystal quality and surface coverage, increased the grain size (up to about 1 µm), and reduced the non-radiative recombination mechanism by increasing the lifetime of carriers. In general, it significantly improved the photovoltaic performance of this type of solar cell. In particular, CH3NH3Pb0.72Sn0.25 Zn0.03I2.94Cl0.06 compound with a yield of 11.68% showed the highest photovoltaic performance with the lowest Pb compared to the sample without Zn-doping (Zn-0%) with a yield of 4.30%. The findings provide a new area for further research on lead-reduced hybrid perovskite solar cells.

Prediction of structural, electronic, mechanical, thermal, and thermoelectric properties in PbMO3 (M = Sb, Bi) perovskite compounds: a DFT study

Prediction of structural, electronic, mechanical, thermal, and thermoelectric properties in PbMO3 (M = Sb, Bi) perovskite compounds: a DFT study

Electronic defect passivation of FASnI3 films by simultaneous Hydrogen-bonding and chlorine co-ordination for highly efficient and stable perovskite solar cells

• Hydroxylamine Hydrochloride (HaHc) was added to FASnI 3 precursor solution. • H-I bonding amid HaHc and FASnI 3 was confirmed by first principle calculation. • Concurrently Cl - interaction with Sn 2+ ions were observed. • The bifunctional effects reduced the electronic defects of FASnI 3 film. • Light soaking stability of 500 h was observed for the respective PSCs. Tin based perovskite solar cells (Sn-PSCs) has emerged as a viable solution for the fabrication of low toxic PSCs. However, the rapid crystallization process of tin halide perovskite compounds often result in severe elctronic defects which limits the open circuit voltage (V OC ) of the overall PSC. In this work, we report on the successful implementation of a bifunctional compound- Hydroxylamine Hydrochloride (HaHc) with FASnI 3 perovksite to reduce the electronic defects. The hydroxyl group in the HaHc formed a hydrogen bond with iodide ion in FASnI 3 perovskite system and stabilizes the overall structure, which is evidenced by nuclear magnetic resonance spectroscopy and first-principle calculations. Additionally, the Cl - ion of the HaHc co-ordinates with the under coordinated Sn 2+ ions of the FASnI 3 perovskite and induces crystal growth along the < h 00 > direction with enhanced crystallinity. Collectively with these dual aspects, the HaHc reduces the electronic defects of the FASnI 3 perovskite film. With an optimized concentration of HaHc added with the FASnI 3 , the corresponding Sn-PSCs showed improved V OC up to 0.676 V and power conversion efficiency of 9.18%. Additionaly, the bi-functional HaHc is effective to stabilize the FASnI 3 system and exhibited light soaking stablity up to 500 h for the respective Sn-PSCs.

Giant dielectric behavior in NdCrO3 perovskite nanoparticles

NdCrO3 perovskite compound synthesized via sol-gel process. Impedance spectroscopic data have been studied in the wide frequency range (0.1Hz-10MHz), at various temperatures (RT-500°C). Structural analysis have done by X-ray diffractometer, it indicates single-phase orthorhombic structure. Particle size is found to be 32nm. Microstructure seems to be uniform distribution of grains throughout the surface. This material showed the giant dielectric behaviour (ε1 > 104). Impedance studies of NdCrO3 noticed that it is negative temperature coefficient of resistance type semiconductor. The dc conductivity and relaxation plots were followed by Arrhenius law. Frequency reliant ac conductivity plots followed Jonscher’s power law. These results suggesting that NdCrO3 is suitable for gaint capacitors applications.

Effects of A-site cations and the substitution site on the upconversion luminescence of Er3+ in the zirconate perovskite series

We investigated the upconversion luminescence (UCL) properties of AZrO3 (A = Ca, Sr, and Ba) perovskite compounds co-doped with Er3+ and Yb3+ in relation to the change in the crystal structure from orthorhombic to cubic. The dopants selectively substituted the A- and B-site ions in the ABO3-type perovskite structure. Upon excitation at 980 nm, we observed the two main UCL features at 545 nm and 660 nm, which depended strongly on the ion occupying the A-site and whether the dopant substituted the ion occupying the A- or the B-site. The intensity of the UCL was found to be maximized for A = Ca because this ion resulted in the lowest crystal symmetry of the host material. The dependence of the UCL on the substitution site (A or B) was significant for A = Sr, in accordance with the sizable difference in the lattice constants of host materials doped at either the A-site or B-site. Our results showed that the crystal symmetry of the host materials and the related local lattice symmetry could play an important role in determining the emission properties of Er3+ ions in perovskite crystals.

H/F Substitution Induced Large Increase of Tc in a 3D Hybrid Rare-Earth Double Perovskite Multifunctional Compound.

Invited for the cover of this issue are Le-Ping Miao, Chao Shi, Yi Zhang and co-workers at Jiangxi University of Science and Technology. The image depicts the structure diagrams of the 3D hybrid rare-earth double perovskite compounds. The phase transition temperatures of the two compounds were indicated by the "ice and fire", respectively. It implies the increase of the phase transition temperature of the compounds. Read the full text of the article at 10.1002/chem.202103913.

H/F Substitution Induced Large Increase of Tc in a 3D Hybrid Rare-Earth Double Perovskite Multifunctional Compound.

Increasing attention has been devoted to studying perovskite-type multifunctional stimuli-responsive materials with multiple channel physical characteristics. However, it remains challenging to simultaneously achieve multifunction and regulate structural phase transition temperature in hybrid perovskites. Here, we report two three-dimensional organic-inorganic hybrid rare-earth double perovskite compounds, (HQ)2 RbEu(NO3 )6 (1, HQ=quinuclidium) and (4FHQ)2 RbEu(NO3 )6 (2, 4FHQ=4-fluoro-quinuclidium), which exhibit ferroelasticity, dielectric switch, and excellent photoluminescence response. The phase transition temperature of 2 increases 169 K compared with 1 through H/F substitution. This result is attributed to the H/F substitution inducing the generation of the Rb-F coordination bond between cations and anions. Meanwhile, the photoluminescence emission intensity of 2 shows no quench with the increase of temperature, in particular, the emission spectrum achieves fine regulation at high temperatures. This work provides a new solution for the realization of multi-functions and regulations of the properties based on hybrid perovskite materials with high critical temperatures.

Structural, microstructural and electrical characteristics of Ca, Sn and Se modified Bi0.5Na0.5TiO3 ferroelectric ceramics

In this paper, studies of structural, microstructural and electrical properties of calcium, tin, and selenium modified bismuth sodium titanate (Bi0.5Na0.5TiO3) compound with a general chemical formula (Bi0.45Na0.45Ca0.1) (Ti0.9Sn0.05 Se0.05) O3, synthesized by a high-temperature mixed oxide reaction method, have been discussed. Analysis of room temperature X-ray diffraction data confirms the formation of perovskite single-phase compound with rhombohedral symmetry. The surface morphology of the sample exhibits the uniform distribution of grains of varying size. Studies of the electrical parameters (dielectric, impedance and conductivity) of the material, collected at various temperatures (75–375 °C) in a wide frequency range (1 kHz–1MHz) have provided its conduction and relaxation behavior. The electric field dependent current density (J-E) characteristics suggest the Ohmic behavior while the field dependent polarization (P-E loop) confirms the ferroelectric nature of the studied material.

Reversible Manipulation of Photoconductivity Caused by Surface Oxygen Vacancies in Perovskite Stannates with Ultraviolet Light (Adv. Mater. 5/2022)

2D Photoconductivity Light–matter interaction under different oxygen pressures can reversibly manipulate photoconductivity from surface oxygen vacancies of perovskite stannate semiconductors. In article number 2107650, utilizing a surface-selective photochemical reaction, Junwoo Son and co-workers report that ultraviolet-excited electron–hole pairs of a perovskite compound under low oxygen pressure accelerate the unprecedented formation of spatially confined and optically programmable in-gap states induced by oxygen vacancies at room temperature.

Spin glass and exchange bias phenomena in NdSrNiMnO6 nanoparticles: Role of antiferromagnetic antisite disorders

We report the discovery of spin glass (SG) and exchange bias (EB) phenomena in NdSrNiMnO6 nanoparticles. Doping at Nd site in the double perovskite compound Nd2NiMnO6, induces antisite disorders leading to antiferromagnetic antiphase boundaries within the system, which are further responsible for the observed phenomena. The role of particle size on these effects has been discussed as the amount of antisite disorder may vary with particle size. We observed a high Curie temperature (TC ∼ 264 K) for small size samples. As the particle size increases, the ferromagnetic (FM) transition becomes indistinct and system transforms to a magnetically frustrated state containing co-existence of FM, antiferromagnetic (AFM) and SG phases. Meanwhile, TC decreases with increasing particle size and the FM ordering becomes unclear for largest particle size sample. The detail investigation of ac susceptibility, memory effect, DC magnetization and magnetic relaxation measurements exposes the SG behavior in the largest particle size sample. By varying the amount of antisite disorders in the NdSrNiMnO6 with increasing particle size, we obtained intrinsic EB effect with a large EB field (∼640 Oe). Further, the EB effect has also been explored by carrying out the cooling field dependent EB measurements in addition to training effect experiments. The exchange interaction between the AFM core and SG like shell of the system is explained through a phenomenological core shell model.

The effect of Sr substitution on the structural and physical properties of manganite perovskites Ca1-xSrxMnO3-δ (0 ≤ x ≤ 1).

Calcium manganite (CaMnO3-δ) has been extensively utilized in many applications due to its unique physical and chemical properties. In this study, the effect of Sr-substitution at the Ca-site on the structural, magnetic, electronic and electrical properties of CaMnO3 manganite perovskites is investigated in detail. The perovskite compounds Ca1-xSrxMnO3-δ (x = 0, 0.25, 0.5, 0.75 and 1) were synthesized through the sol-gel method at 1200 °C. From the patterns of X-ray diffraction, it was observed that all of the synthesized compounds show a pure perovskite phase at room temperature. The refinement results of the perovskite series suggest that a structural transformation from an orthorhombic (Pnma) to a hexagonal (P63/mmc) system occurred for 0.50 < x ≤ 0.75. We note however that the sample with the composition x = 0.50 showed a phase mixture of orthorhombic (Pnma) and hexagonal (P63/mmc). Based on DFT calculations, we have demonstrated the energetic stability of all compounds by negative formation energy and confirmed the semiconductor behavior by the presence of a band gap. The change in the band gap value with the Sr content suggests the potential tuning of the electronic behavior of CaMnO3-SrMnO3 solid solution. Furthermore, as the temperature increases from 300 to 1000 K, the electrical resistivity exhibits a reduction while the Seebeck coefficient (S) shows an augmentation. The negative values of S indicated the n-type-semiconductor nature of all compounds. The obtained values of the activation energy from thermal evolution of resistivity suggested that the electrical transport behavior of all the compounds followed the mechanism of small polaron hopping. Power factor is greatly affected by the Sr amount and reached a maximum value at x = 0.50. Overall, introducing Sr into the CaMnO3-δ matrix improved the power factor and reduced electrical resistivity. According to the obtained results, the studied manganite perovskites could be proposed as suitable materials for photocatalytic and thermoelectric applications.

Impact of rare earth (RE3+ = La3+, Sm3+) substitution in the A site perovskite on the structural, and electrical properties of Ba(Zr0.9Ti0.1)O3 ceramics.

Undoped Ba(Zr0.9Ti0.1)O3 and rare-earth-doped (Ba1−xRE2x/3)(Zr0.9Ti0.1)O3 (RE3+ = La3+, Sm3+) perovskite compounds were synthesized by the conventional solid-state reaction route. Both solubility of rare earth in Ba(Zr0.9Ti0.1)O3 and formation of perovskite structure with the Pm3̄m space group were verified by the Rietveld method using X-ray diffraction data. SEM micrographs of all ceramics revealed high densification, low porosity, and even homogeneous grain distribution of various dimensions over the total surface. The frequency-dependent electrical properties were analyzed by complex impedance spectroscopy. Different types of studies such as the Nyquist plot, real and imaginary part of impedance, conductivity, modulus formalism, and charge carriers activation energy were used to explain the microstructure–electrical property relationships.

Mechanism of Luminescence Enhancement in Eu3+ Activated Double Perovskite Phosphors Bi2-xEuxWO6 (x = 0-0.24) Prepared by Sol-Gel Method

A double perovskite structured series Bi2–xEuxWO6 (x = 0.03-0.24) was prepared by using simple citrate sol-gel method at 700 ºC for 5 h of sintering. The double perovskite structure and its lattice parameters were analyzed by the XRD technique and found to be pure orthorhombic phase. The concentrated sample of x = 0.12 exhibits more intensity than all other concentration in their emission spectra. Particle size, thickness of the particle, distance between particles and its surface morphology were identified by scanning electron microscopy. The size and distance between particles lies in between the range of 1-50 nm and 20-50 nm, respectively. In addition to this the absorption of light capacity for every sample was investigated through diffuse reflectance spectra method. All the samples of double perovskite structures exhibit a sharp cut-off of absorption light in the UV and visible regions of diffuse reflectance spectra. Predominantly, sample x = 0.12 shows very good charge transfer band in their excitation spectra that leads to more absorption of light correspondingly emits high intensity in emission spectra. All the samples of series emit main peaks in the range of 550-700 nm in their emission spectra. Out of all four main peaks, 614 nm peak represents the red phosphor with 5D0−7F2 transition in the emission spectra. The prepared double perovskite structure compound CRI co-ordinates (0.6254, 0. 3739) are almost close to commercially available red phosphor i.e. Y2O2S (0.67, 0.33) as per NTSC. Hence, the prepared red phosphors can be used in order to display devices, luminescent materials and WLEDs.

Two manganese chloride organic–inorganic hybrid compounds showing strong luminescence and switchable phase transition and dielectric anomaly

Two organic–inorganic hybrid manganese halide perovskite compounds [Me3NNH2]MnCl3 and [(CH3)3NCH2CH2F]2MnCl4 exhibit switchable phase transition and dielectric anomaly, and also emit strong red and green luminescence.

Study of inorganic lead halide perovskites properties using first-principles density functional theory for photovoltaic and optoelectronic devices

Cesium lead iodide perovskites have attracted significant interest due to their rapidly increasing efficiency when used in solar cells applications. Density functional theory was used to investigate the structural, electronic, elastic, and optical properties of CsPbI3, CsPbI2Br, CsPbBr2I and CsPbBr3 perovskite materials. The generalized gradient approximation, GGA-PBE was used to estimate the band gaps of these materials. There is gradual increase in the band gap values due to mixing composition of I and Br which may be attributed to the ionic radii differences between Br and I in the mixed halide compounds, and the hybridization tendency of the X-halide (I 5p and Br 4-p) state. Structural analysis shows that the calculated lattice parameters were consistent with experimental parameters reported in the literature. Also, mechanical properties including elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and anisotropy factor were computed. The calculated electronic properties showed that the energy band gap of CsPbI3 could be tuned by substituting iodine with bromine. All four compounds were found to be semiconductors with direct energy band gaps in R symmetry point between 1.466 and 2.494 eV as predicted by the GGA-PBE. The optical properties of these perovskite compounds against the incident photon energy radiation indicate that the materials could be good candidates for solar cells applications. The elastic constants were also determined, and they revealed the ductile nature of these compounds.