Double Perovskite System Research Articles

Optimizing Reversible Exsolution and Phase Transformation in Double Perovskite Sr2Fe1.5-xCoxMo0.5O6-δ Electrodes for High-Performance Symmetric Solid Oxide Cells.

Double perovskite (DP) oxides are promising electrode materials for symmetric solid oxide cells (SSOCs) due to their excellent electrochemical activity and stability. B-site cation doping in DP oxides affects the reversibility ofphase transformation and exsolution, which plays a crucial role in the catalyst recovery. Yet, few studies have been conducted on this topic. In this study, the Sr2Fe1.5-xCoxMo0.5O6-δ (CSFM, x = 0, 0.1, 0.3, 0.5) DP system demonstrates modulated exsolution and phase transformation reversibility by manipulating the oxygen vacancy concentration. The correlation between Co-doping level and oxygen vacancy concentration is investigated to optimize the exsolution and phase transformation properties. Sr2Fe1.2Co0.3Mo0.5O6-δ (3CSFM) exhibits reversible transformation between DP and Ruddlesden-Popper phases with a high density of exsolved CoFe nanoparticles under redox atmospheres. The quasi-symmetric cell with 3CSFM shows a peak power density of 1.27Wcm-2 at 850°C in H2 fuel cell mode and a current density of 2.33Acm-2 at 1.6V and 800°C in H2O electrolysis mode. The 3CSFM electrode exhibits robust stability during continuous operation for ≈700h. These results demonstrate the significant role of B-site doping in designing DP materials capable of dynamic phase transformation in diverse environments.

Investigations on structural and magnetic behavior of LaPrCo1-xFexMnO6 double perovskite system

Investigations on structural and magnetic behavior of LaPrCo1-xFexMnO6 double perovskite system

Achieving multi-excitation in lanthanide-based Cs2NaTbCl6:Ce/Yb double perovskite single crystals for anti-counterfeiting

Lanthanide-doped inorganic perovskite luminescent materials have always been regarded as a good platform for multi-functional applications such as anti-counterfeiting and information encryption, owing to their good visibility, diverse colors and simple design. In this study, we design the Cs2NaTbCl6: Ce/Yb double perovskite single crystals, achieving visible green luminescence under various excitation sources such as ultraviolet, near-infrared (980 nm) and X-ray. The possible emission and energy transfer mechanisms between Tb3+ ions and Ce3+, Ce4+, Yb3+ ions under different excitations are discussed in detail. Our work skillfully takes advantage of the Tb3+ ions acquiring the transferred energy from non-luminescent Ce4+ ions and luminescent Ce3+ ions, broadening the ultraviolet response and improving its stability. The luminescence intensity of Cs2NaTbCl6 double perovskite single crystal was increased about 40 times under 343 nm excitation by doping Ce4+ and Ce3+ ions, which shows that Ce4+ and Ce3+ ions doping effectively introduces a new excitation band. Furthermore, diversified anti-counterfeiting modes are fabricated to highlight the promising applications of Cs2NaTbCl6 double perovskite systems with tunable luminescence in advanced anti-counterfeiting, paving the way for future research on the multi-light sources luminescent materials.

Role of Fe supplantation in tailoring structural, electrical conductivity, and magnetic properties in La2Ni1-xFexMnO6 double perovskites

Double perovskite system La2Ni1-xFexMnO6 (x = 0, 0.2, 0.5, 0.8 & 1.0) were developed using sol-gel method. Rietveld refinement revealed monoclinic structure (ordered) along with occurrence of rhombohedral and orthorhombic structures suggesting antisite cationic disorder. Crystallite size and average grain size of samples varied between 454 and 1058 Å and 0.774–1.429 μm respectively. XPS revealed the dual oxidation states of Ni, Fe, and Mn ions. La2NiMnO6 attained the highest DC conductivity among all compositions. The increase in DC conductivity with temperature suggested the semiconducting behavior of the samples, that explained by Thermal Activation (TA) and Variable Range Hopping (VRH) conduction mechanisms. Obtained activation energy(Edc) showed increasing trend with temperature. M-H loops exhibit a ferromagnetic nature accompanied by antiferromagnetic interactions as suggested by exchange bias and partially saturated loops. La2NiMnO6 attained the highest saturation magnetization (29.81emu/g) and decreased with Fe supplantation. The possible mechanism of tuning conductivity and magnetic properties of La2Ni1-xFexMnO6 has been discussed in detail.

Colossal Ferroelectric Photovoltaic Effect in Inequivalent Double-Perovskite Bi2FeMnO6 Thin Films.

Double perovskite films have been extensively studied for ferroelectric order, ferromagnetic order, and photovoltaic effects. The customized ion combinations and ordered ionic arrangements provide unique opportunities for bandgap engineering. Here, a synergistic strategy to induce chemical strain and charge compensation through inequivalent element substitution is proposed. A-site substitution of the barium ion is used to modify the chemical valence and defect density of the two B-site elements in Bi2FeMnO6 double perovskite epitaxial thin films. We dramatically increased the ferroelectric photovoltaic effect to ∼135.67 μA/cm2 from 30.62 μA/cm2, which is the highest in ferroelectric thin films with a thickness of less than 100 nm under white-light LED irradiation. More importantly, the ferroelectric polarization can effectively improve the photovoltaic efficiency of more than 5 times. High-resolution HAADF-STEM, synchrotron-based X-ray diffraction and absorption spectroscopy, and DFT calculations collectively demonstrate that inequivalent ion plays a dual role of chemical strain (+1.92 and -1.04 GPa) and charge balance, thereby introducing lattice distortion effects. The reduction of the oxygen vacancy density and the competing Jahn-Teller distortion of the oxygen octahedron are the main phenomena of the change in electron-orbital hybridization, which also leads to enhanced ferroelectric polarization values and optical absorption. The inequivalent strategy can be extended to other double perovskite systems and applied to other functional materials, such as photocatalysis for efficient defect control.

Doping effects of Ho3+ on structural, magnetic and magnetocaloric properties of La2NiMnO6

The magnetic and magnetocaloric properties of the double perovskite system La2-xHoxNiMnO6 (x = 0.0, 0.1, and 0.2) have been studied with different Ho doping concentrations. Rietveld refined X-ray diffraction patterns of La2-xHoxNiMnO6 (x = 0.0, 0.1, and 0.2) compounds confirm the monoclinic phase with P21/n space group. A small amount of orthorhombic phase with pbnm space group was observed in the La2NiMnO6 (LNMO) phase. Zero Field Cooled magnetic measurements carried out at various temperatures indicate the Curie temperature (TC1) of 270 K for x = 0.0 due to the Ni2+-Mn4+ FM coupling. TC1 further decreases to 255 K for x = 0.2. At low temperatures ∼ 140 K, the La2NiMnO6 sample shows another ferromagnetic (TC2) coupling of Ni3+-Mn3+ ions. The change in magnetic entropy values for La2-xHoxNiMnO6 are found to be 1.248 J/K-kg, 1.925 J/K-kg, and 1.622 J/K-kg respectively for x = 0.0, 0.1, and 0.2 under a magnetic field of 5 T.

Centrosymmetric to non-centrosymmetric transition in the Ca2-xMnxTi2O6 double perovskite system studied through structural analysis and dielectric properties.

We have used high-pressure synthesis to synthesize samples of Ca2-xMnxTi2O6 double perovskite, where x varies between 0.2 and 1. The synthesized materials were structurally characterized with powder X-ray diffraction (XRD). Rietveld refinement of the XRD patterns was used to study the change from CaTiO3 (x = 0) to the composition CaMnTi2O6 (x = 1) where half of the Ca(II) ions are replaced by smaller Mn(II) ions. We analyzed the peak shapes in the XRD patterns, as well as lattice parameters, and it appears that smooth symmetry change from the centrosymmetric space group Pbnm to the non-centrosymmetric space group P42mc occurs between x = 0.3 and x = 0.5. We also confirmed the centrosymmetric to non-centrosymmetric transition by characterizing the dielectric properties of the materials with ferroelectric measurements.

Magnetocaloric effect in PrGd1-xBaxMn2O6 (0.0 ≤ x ≤ 1.0) double perovskite manganite system

Magnetocaloric effect in PrGd1-xBaxMn2O6 (0.0 ≤ x ≤ 1.0) double perovskite manganite system

Extrinsic electronic states to tune the luminescence and bonding nature of Cs2NaInCl6 double perovskite

Halide double perovskites have been extensively investigated in recent years as more stable and environmentally friendly materials with significant optoelectronic properties. Herein, we introduce Mn2+ ions in the Cs2NaInCl6 lattice to impart new electronic pathways to the otherwise weak optically active double perovskite for tuning its luminescent behaviour. X-ray diffraction, Raman, UV–visible, Photoluminescence (PL), and time–resolved PL (TRPL) spectroscopy are used to investigate the effect of Mn 2+ feed ratio on structural, vibrational, and optical properties. The chemical environment and surface morphology of the Mn2+ ions doped Cs2NaInCl6 double perovskite were investigated using X-ray photoelectron (XPS), energy dispersive X-ray (EDS) spectroscopies, and scanning electron microscopy. Results of the Rietveld refinement and Raman spectra divulge a decrease in In-Cl and Na-Cl bond length upon Mn2+ incorporation. The microstructure of the Cs2NaInCl6 double perovskite system was also studied using HRTEM analysis. UV–visible studies demonstrated a tremendous increase in absorption and a slight increase in band gap upon Mn2+ doping. PL and TRPL measurements of Mn2+: Cs2NaInCl6 discloses its red luminescence at 614 nm corresponding to the d-d atomic transition of Mn2+ with a long lifetime of 2.1 ms. Electron density investigations using maximum entropy method (MEM) demonstrate clear evolution of In-Cl and Na-Cl bonds from a highly ionic nature in pure Cs2NaInCl6 to strong covalent nature in Mn2+: Cs2NaInCl6 double perovskites. This affirms the simultaneous replacement of In, Na ions by Mn2+ to maintain charge neutrality in the compound and tune the electronic states of the Cs2NaInCl6 system.

Structural, electronic and magnetic properties of Fe-doped strontium ruthenates

By employing a combined approach of density-functional theory (DFT) and dynamical mean-field theory (DMFT) calculations, we examine the structural, electronic, and magnetic characteristics of two distinct strontium ruthenates: Sr2RuO4, an unconventional superconductor, and the correlated metal SrRuO3, both at 50% Fe-doping level. In both Sr2Fe0.5Ru0.5O4 and SrFe0.5Ru0.5O3, the original ruthenium (Ru) and the dopant iron (Fe) atoms adopt 3-dimensional and 2-dimensional G-type structures, respectively. The hybridization between Fe-3d and Ru-4d is comparatively weaker than in other double perovskite systems. The interplay between strong correlations and reduced itinerancy results in significant spin splitting at Fe and Ru sites. Consequently, a charge transfer process, along with the super-exchange effect, leads to antiferromagnetically coupled Fe3+ and Ru5+ ions and establishes a semiconducting ferrimagnetic order. Subsequent DMFT calculations demonstrate the persistence of the ferrimagnetic order even at room temperature (300 K). These findings align with prior reports on SrFe0.5Ru0.5O3, thus reinforcing the notion that 3d–4d transition metal oxides hold considerable promise as candidates for high-performance spintronic devices, such as spin-valve sensors and spintronic giant magnetoresistance devices.

Role of structural, morphological, and electronic characteristics in investigating the low temperature transport and magnetic behavior of Sr doped Sm2NiMnO6

Oxide double perovskites of the form R2NiMnO6 (R= rare-earth) are known to possess the multifunctional behavior. Herein, we have induced structural and electronic modifications in Sm2NiMnO6 system by Sr doping to form Sm2−xSrxNiMnO6 (x = 0.0, 0.2, and 0.4) and accordingly investigated the structural, morphological, electronic, dielectric, magnetic and magnetoresistance properties. Sm2NiMnO6 has monoclinic structure with P21/n space group and doping with Sr does not change the phase of compound. Microstructure studies suggest a decrease in the grain size with increase in Sr doping while elemental overlay and analysis suggest the presence of known elements in uniformity. Chemical valency indicates the existence of mixed valence of Ni and Mn cations along with presence of oxygen vacancies in all the sample of Sm2−xSrxNiMnO6 (x = 0.0, 0.2, and 0.4). Frequency (200 Hz to 2 MHz) and low temperature (100–320 K) dependence of dielectric measurements have been carried out to observe the behavior of dielectric constant and dielectric loss. With increase in concentration of Sr, the dielectric constant decreases while the dielectric loss increases. Temperature variation of ac conductivity as well as resistivity suggests the negative temperature coefficient of resistance, depicting the semiconducting behavior of all the samples. Temperature variation of magnetization in terms of field cooled (FC) and zero field cooled (ZFC) curves shows the presence of two magnetic transitions in all the three samples. One pertains to paramagnetic to ferromagnetic transition temperature and another is due to downturn in magnetization at lower temperature. Sr doping also causes an increase in the magnetic ordering temperature. Field variation of magnetization shows the ferromagnetic nature of all the three samples, where the saturation magnetization decreases with increase in temperature as well as increase in Sr concentration. Temperature dependence of resistivity at different magnetic fields indicates the presence of magnetoresistance effect in all the three samples. These studies highlight the role of Sr doping in determining and influencing the various physical properties discussed in this paper and the importance of these double perovskite systems for future material design and various technological applications.

Process-Gas-Influenced Anti-Site Disorder and Its Effects on Magnetic and Electronic Properties of Half-Metallic Sr2FeMoO6 Thin Films

Anti-site disorder, arising due to the similar size of Fe and Mo ions in Sr2FeMoO6 (SFMO) double perovskites, hampers spintronic applicability by deteriorating the magnetic response of this double perovskite system. A higher degree of anti-site disorder can also completely destroy the half-metallicity of the SFMO system. To study the effects of different process gas conditions on the anti-site disorder, we have prepared a series of SFMO thin films on SrTiO3 (001) single-crystal substrate using a pulsed laser deposition (PLD) technique. The films are grown either under vacuum or under N2/O2 partial gas pressures. The vacuum-grown SFMO film shows the maximum value of saturation magnetization (MS) and Curie temperature (TC), signaling the lowest anti-site disorder in this series. In other words, there is a long-range Fe/Mo-O-Mo/Fe ferrimagnetic exchange in the vacuum-grown thin film, thereby enhancing the magnetization. Further, all the SFMO films show a semiconducting state with a systematic increase in overall resistivity with the increased anti-site disorder. The electrical conduction mechanism is defined by the variable-range hopping model at low temperatures. Raman spectra show a weak Fano peak, suggesting the presence of electron–phonon coupling in SFMO thin films. These results show the significance of the process gas in causing anti-site disorder, tuning the degree of this disorder and therefore its influence on the structural, magnetic, electrical, and vibrational properties of SFMO thin films.

Research progress of double perovskite ferroelectric thin films

Double perovskite ferroelectric thin films are completely new material systems derived from single perovskite. Their diversity of composition and structure and the tendency for spontaneous atomic ordering broaden the path for the development of ferroelectric thin films. The ordered double perovskite ferroelectric thin films lead to excellent ferroelectric, dielectric, magnetic, and optical properties, promising further applications in photovoltaic cells, information memory, and spintronic and photoelectric devices, where the intrinsic coupling and tuning of multiple properties could also push it into multifunctional intersecting devices. However, complex internal physical mechanisms and difficult preparation conditions have prevented its further development. Based on ordered/disordered ferroelectric thin films of double perovskites, this paper first discusses ordered characterization methods such as superstructure reflection/diffraction peaks, especially for epitaxial thin films, saturation magnetization (macroscopic), and scanning transmission electron microscopy (microscopic). In response to the generally poor ordering of present systems, the paper also reviews the internal structure of the material and the external synthesis conditions that affect the ordering, including the valence and radii of the cations, preparation methods, element substitution and strain engineering, in the hope of triggering further research into ordered double perovskite ferroelectrics. Combined with the current state of research on existing double perovskite ferroelectricity thin film systems, advances in the fields of ferroelectric photovoltaics, magnetoelectric coupling, dielectric tunability, resistive switching, and photoelectric coupling have been presented. Finally, the challenges facing the material system are discussed and an outlook is provided for the development of the field.

A computational study of double perovskites A2BI6 (A = Cs, K, Rb; B = Pt, Sn) invoking density functional theory

AbstractLead‐free double perovskite materials A2BI6 (A = Cs, K, Rb; B = Pt and Sn) have been studied and analyzed invoking density functional theory (DFT). Computed values of the HOMO–LUMO gap for lead‐free double perovskites material A2BI6 are found in the range of 1.062–2.811 eV. The energy gaps of K2PtI6, K2SnI6, and Rb2SnI6 are in the optimal energy gap range (0.9 to 1.6 eV) required for a lead‐free double perovskite system. Conceptual DFT‐based descriptors, viz., molecular hardness, softness, electronegativity, electrophilicity index, dipole moment, and polarizability, are computed. The result reveals that K2PtI6 shows high efficacy towards electron injection and may show the maximum electron driving force. The optical properties—refractive index and dielectric constant—of these perovskites are also computed. The maximum value of refractive index and dielectric constant is found for K2PtI6. Our computed results are in good agreement with the available experimental and other theoretical data. Perovskite materials K2PtI6, K2SnI6, and Rb2SnI6 display a suitable energy gap as well as a high refractive index and dielectric constant, which makes them suitable for photovoltaic applications.

Discovering New Type of Lead‐Free Cluster‐Based Hybrid Double Perovskite Derivatives with Chiral Optical Activities and Low X‐Ray Detection Limit

Abstract2D chiral hybrid perovskites have recently emerged as outstanding semiconductor materials. However, most of the reported 2D chiral perovskites have limited structural types and contain high levels of toxic lead, which severely hinders their further applications. Herein, by using a mixed‐cation strategy, an unprecedented type of lead‐free cluster‐based 2D chiral hybrid double perovskite derivatives are successfully obtained, [(R/S‐PPA)4(IPA)6Ag2Bi4I24]·2H2O (1‐R and 1‐S), and [(R/S‐PPA)4(n‐BA)6Ag2Bi4I24]·2H2O (2‐R and 2‐S) (R/S‐PPA=R/S–1‐phenylpropylamine; IPA=isopentylamine; n‐BA=n‐butylamine). Their inorganic skeletons are linked by binuclear {Bi2I10} and infinite chain {Ag2Bi2I14}∞, in which bismuth clusters and multiple coordination modes (e.g., tetrahedral AgI4 and octahedral AgI6) are introduced into the double perovskite system for the first time. This introduction induces distortion of the inorganic layer, which may facilitate the transfer of chirality from the chiral cations into achiral double perovskite skeletons. Further, circular dichroism measurements and circularly polarized light detection confirm their inherent chiral optical activities. In addition, 1‐S exhibits an ultralow X‐ray detection limit of 129.5 nGy s−1, which is 42‐fold lower than that of demands in regular medical diagnosis (5.5 µGy s−1). This study provides a pathway to construct novel type of lead‐free cluster‐based double perovskite derivatives.

Formula omitted]-antisite disorder driven exchange bias effect and Griffiths-like phase in 25% Sr-doped [formula omitted

The unusual magnetic behaviour and multiple magnetic phases in double perovskite systems mainly originate from B-antisite disorder and various exchange couplings. Here we report the detailed exchange bias study in the hole doped Sm1.5Sr0.5CoMnO6 double perovskite system. The existence of structural antisite-disorder (Co-O-Co-O-Mn or Mn-O-Mn-O-Co) in the system is revealed. The ordering of Co2+ and Mn4+ gives rise to two ferromagnetic transitions, Tc1∼133 K and Tc2∼114 K. A Griffiths-like phase at ∼153 K is identified by the dc magnetization data above the ferromagnetic ordering temperature. The isothermal magnetization measurements further probe the exhibition of the conventional exchange bias effect and training effect phenomena in our sample. Maximum field shift ∼3.43 kOe in exchange bias effect is observed owing to the exchange couplings at the interfaces of FM/AFM at low temperature induced by B-antisite-disorder. In the 64–300 K temperature range, this disordered double perovskite exhibits insulating characteristics with a variable range hopping type of conduction mechanism. We also notice a negative magnetoresistance of −2.74% at 64 K and 60 kOe magnetic field.

Effect of Fe supplantation on structural and dielectric properties of La2CoMnO6

Double Perovskite system La2Co1-xFexMnO6 (x = 0, 0.2, 0.5, 0.8 and 1.0) has been synthesized by sol-gel route. XRD profiles confirmed the absence of any external phase in pure La2CoMnO6 phase. Rietveld refinement analysis confirmed the existence of monoclinic (ordered) as well as rhombohedral and orthorhombic (disordered) structures. Lattice parameters and unit cell volume are found to increase with increase in Fe content. Morphological and compositional analysis was done using FESEM with EDS. Frequency and temperature dependent dielectric characterization revealed the dispersion of both dielectric constant as well as loss tangent at low frequency and high temperature. The Nyquist plot of impedance (cole-cole) revealed negative temperature coefficient of resistance (NTCR) behavior of prepared samples and suggest a non-Debye type relaxation in these samples. An increasing trend with increase in frequency and temperature was exhibited by ac conductivity. Variation of dc electrical conductivity with temperature suggested a semiconducting behavior which can be explained by both small polaron hopping (SPH) and variable range hopping (VRH) conduction mechanisms.

Coexistence and Coupling of Spin-Induced Ferroelectricity and Ferromagnetism in Perovskites.

Spin-induced ferroelectricity usually does not occur in perovskites with simple collinear magnetic structures. Here, we demonstrate that in even-layer perovskite systems, some common distortion modes involving octahedral rotation and Jahn-Teller distortion can break the inversion symmetry, allowing the emergence of spin-dependent out-of-plane polarization in a simple magnetic structure. Such spin-induced ferroelectricity is very common in double-perovskite systems and can coexist with ferromagnetism or ferrimagnetism above room temperature. We explain its origin by modifying the spin-dependent p-d hybridization mechanism. Our Letter provides a universal design for two-dimensional multiferroics and enables the control of polarization by means of a magnetic field.

An Effective Strategy of Introducing Chirality to Achieve Multifunctionality in Rare-Earth Double Perovskite Ferroelectrics.

The hybrid rare-earth double perovskite (HREDP) system provides great convenience for the construction of multifunctional materials. However, suffering from the high symmetry of their intrinsic structure, HREDPs face the challenges in the realization and optimization of ferroelectric and piezoelectric properties. For the first time, after a systematic investigation of the chirality transformation principle, it is found that the introduction of chirality is an efficient strategy for the targeted construction of multifunctionality, which simultaneously increases the possibility of obtaining multiaxial ferroelectricity and ferroelasticity, and effectively realizes a large piezoelectric response. Moreover, chirality induced ferroelasticity will also achieve excellent magnetic or optical response driven by pressure-sensitive. To verify the feasibility of the above ideas, by using rare-earth ions (Ce3+ ) and suitable chiral organic cations, a new HREDP, (R-N-methyl-3-hydroxylquinuclidinium)2 RbCe(NO3 )6 (R1) is successfully designed, in which ferroelasticity, multiaxial ferroelectricity, satisfactory piezoelectric response, and the pressure-driven single-ion magnetics switch are simultaneously achieved for the first time. This work shows that the induction of chirality and the HREDP system provide an effective strategy and ideal platform for the expansion and optimization of the functions in perovskite ferroelectrics.

Silver‐Bismuth Based 2D Double Perovskites (4FPEA)4AgBiX8 (X = Cl, Br, I): Highly Oriented Thin Films with Large Domain Sizes and Ultrafast Charge‐Carrier Localization

AbstractTwo‐dimensional (2D) hybrid double perovskites are a promising emerging class of materials featuring superior intrinsic and extrinsic stability over their 3D parent structures, while enabling additional structural diversity and tunability. Here, we expand the Ag–Bi‐based double perovskite system, comparing structures obtained with the halides chloride, bromide, and iodide and the organic spacer cation 4‐fluorophenethylammonium (4FPEA) to form the n = 1 Ruddlesden–Popper (RP) phases (4FPEA)4AgBiX8 (X = Cl, Br, I). We demonstrate access to the iodide RP‐phase through a simple organic spacer, analyze the different properties as a result of halide substitution and incorporate the materials into photodetectors. Highly oriented thin films with very large domain sizes are fabricated and investigated with grazing incidence wide angle X‐ray scattering, revealing a strong dependence of morphology on substrate choice and synthesis parameters. First‐principles calculations confirm a direct band gap and show type Ib and IIb band alignment between organic and inorganic quantum wells. Optical characterization, temperature‐dependent photoluminescence, and optical‐pump terahertz‐probe spectroscopy give insights into the absorption and emissive behavior of the materials as well as their charge‐carrier dynamics. Overall, we further elucidate the possible reasons for the electronic and emissive properties of these intriguing materials, dominated by phonon‐coupled and defect‐mediated polaronic states.