A-site Perovskite Research Articles

Elucidation of amphoteric nature of Pr2O3 using XPS and conductivity measurement in lead-free NKBT host lattice

The study of the piezoelectric response in praseodymium-doped (Na0.41K0.09Bi0.5)TiO3 (NKBT) revealed an unusual behaviour at doping level near 0.5 and 1.0 at%. Although there is a marginal increment in the piezoelectric charge coefficients for samples with praseodymium doping of 0.5–1.0 at% compared to undoped NKBT, importantly, the response drastically diminishes for doping concentrations exceeding 1.0 at%. To comprehend the observed anomaly, X-ray photoelectron spectroscopy (XPS) and temperature dependent conductivity measurement was carried out. These investigations provided critical insights into the role of oxygen vacancy and the behaviour of praseodymium ions in the NKBT matrix. The XPS analysis revealed the presence of core level peak corresponding to O-1s with asymmetric broadening at higher energy side implying the presence of oxygen bound to the perovskite lattice (binding energy: 529.2±0.3 eV) along with oxygen vacancy (binding energy: 531.5±0.4 eV). The XPS study further revealed that the concentration of the oxygen vacancy is lowest around 0.5 at% of praseodymium doping and beyond this the oxygen vacancy increases. The high temperature conductivity measurement supported these findings by showing similar trends in the electrical conductivity. Both the XPS and conductivity measurements further corroborate the conjecture that praseodymium behaves as amphoteric ion. The praseodymium occupies the A-site of perovskite (Na0.41K0.09Bi0.5)TiO3 for lower praseodymium concentration (<1.0 at%), whereas for higher doping concentration (>1.0 at%) it occupies the B-site exhibiting acceptor like behavior that deteriorates the piezoelectric response.

Evolution of conduction mechanism in Ca-doped YFe0.5Co0.5O3 compound by complex impedance spectroscopy

The ceramic samples of Y1-xCaxFe0.5Co0·5O3 (x = 0.15, 0.25, 0.35) has been synthesized using solid-state reaction method. These samples exhibited orthorhombic perovskite structure and belonged to the Pbnm space group. X-ray analysis confirmed that Ca2+ ions replaced Y3+ ions at the A-site of perovskite structured YFe0·5Co0·5O3 compound, while XPS studies confirmed the oxidation states of the constituent atoms. SEM micrographs and Williamson-Hall analysis showed that the crystallite size reduces with increasing Ca content, resulting in a strain-free, accommodated and stable microstructure. Complex impedance spectroscopic investigations established that the dispersion behaviors exhibited by the samples are due to Interfacial and Bulk polarizations. These phenomena are attributed to the accumulation of space charges and the hopping of electrons, respectively. Study further explore the semiconducting nature and negative temperature coefficient behavior of the material. Nyquist plots showed that grain interior is the major contributor to the conduction mechanism, while grain boundaries playing a secondary role. Correlated Barrier Hopping (CBH) has emerged as a suitable model to elucidate the conduction mechanism. The conduction process facilitated by CBH could potentially account for the observed negative permittivity in the material.

CO2/Cr-tolerance and oxygen reduction reaction of novel high-entropy perovskite cathode for intermediate temperature solid oxide fuel cell

The development and exploration of cathode oxides with outstanding electrocatalytic activity are critical processes aimed at achieving a decrease in the operation temperature of solid oxide fuel cells (SOFC). Herein, a novel high-entropy oxide, La0.2Pr0.2Nd0.2Sm0.2Gd0.2BaCoFeO5+δ (HEP), which incorporates five lanthanide species (La, Pr, Nd, Sm, and Gd) in the A-site of perovskite, has been specifically developed and assessed as selected cathode for intermediate-temperature SOFC. Investigations of phase structure, chemical compatibility, oxygen transport characteristics, oxygen reaction kinetic, thermal expansion, surface chemical state, conductivity, as well as CO2/Cr-durability are thoroughly performed to assess the basic physicochemical properties of the HEP cathodes. The HEP cathode possesses good operational stability, moderate thermal expansion behavior, fast oxygen transport dynamics, and superior chemical compatibility with the electrolyte. At 700 °C, the polarization resistance low to 0.072 Ω cm2 and output power density high to 332.2 mW cm−2 were obtained for the symmetrical and electrolyte-supported single cells. Furthermore, a stable current density is obtained for the single cell operating at 600 °C and 0.5 V for 100 h. Analysis of electrochemical impedance spectra (EIS) and distribution of relaxation time (DRT) data at different oxygen partial pressures reveal that the charge-transfer and oxygen ions ionization processes at intermediate frequencies present a significant limiting step in the rate of the oxygen reduction reaction. However, under realistic utilization conditions, cathodes of cells often endure irreversible performance degradation owing to the Cr deposition from interconnects or CO2 poisoning in air. Hence, the behavior of Cr and CO2 poisoning is also systematically investigated in symmetrical cell measurements; the results confirm that the HEP cathode displays good resistance to Cr and CO2 poisoning. Overall, our findings indicate that the HEP material is regarded as a favored ceramic cathode for SOFC.

Ce-doped promotes the phase stability and electrochemical performance of SrCoO3-δ cathode for intermediate-temperature solid oxide fuel cells

The development of cathode with high oxygen reduction reaction (ORR) activity is crucial for intermediate-temperature solid oxide fuel cells (IT-SOFCs). SrCoO3-δ oxides, a mixed ion-electron conductivity (MIEC), are promising cathode materials. However, pure SrCoO3-δ exhibits a hexagonal or rhombohedral structure with poor electrical properties, limiting its application in IT-SOFCs. In this work, high-valence Ce4+ is doped at the A-site of SrCoO3-δ perovskite to improve the phase structural stability and electrochemical activity of SrCoO3-δ. The findings reveal that Ce4+ doping in small amounts significantly advances the conductivity and ORR activity due to enhanced structural stability. Among the series of samples, Sr0.95Ce0.05Co3-δ (SCC005) presents the best electrochemical performance. Moreover, the addition of Ce0.8Gd0.2O2-δ (GDC) further reduces polarization resistance by about ∼7 times. The peak power density of 1.3 W cm−2 is obtained at 750 °C for the SCC05-30%GDC cathode. The results indicate that A-site Ce doping is a promising strategy to enhance the ORR activity of SrCoO3-δ oxides.

Room temperature polar and weak-ferromagnetic oxide with low dielectric loss

Single-phase materials that are simultaneously ferroelectric and ferromagnetic at room temperature are promising for devices such as non-volatile random-access memory. Perovskite BiFeO3 which crystallizes in the polar rhombohedral structure (R3c) is ferroelectric and antiferromagnetic at room temperature. Here, we report a family of perovskite oxides in the BiFeO3 – Bi2/3TiO3 – ATiO3 (where A2+ is divalent alkaline earth metal ions e.g., Ca2+, Sr2+, Ba2+) ternary phase diagram that is polar as well as weak ferromagnetic above room temperature. The composition (Bi0.9167A0.075)(Fe0.9Ti0.1)O3 crystallizes in the polar rhombohedral structure space group R3c as corroborated by powder X-ray and neutron diffraction analysis. The nearly pure A-site perovskite possesses a long-range magnetic ordering above room temperature. These perovskites show a low dielectric loss, and the electrical response is dominated by grain contributions below 723 K.

La1.33-xNa3xTi2O6/Na3La2(BO3)3 heterostructure transformed from La2Ti2O7 plates for enhanced photocatalytic H2 evolution

Perovskite-type oxide semiconductors, as promising photocatalysts, possess flexible structures with corner-shared BO6 octahedrons and A cations, but are limited by the broad band gaps and severe photo-induced carrier recombination. Herein, a series of La1.33-xNa3xTi2O6/Na3La2(BO3)3 composites were synthesized by annealing the layered La2Ti2O7 with NaBH4. The doping of Na+ ions in perovskite's A-site promotes the transformation of La2Ti2O7 into La1.33-xNa3xTi2O6 phase, meanwhile, substituted La species turn into Na3La2(BO3)3 phase. The crystalline degree of perovskite structure evolves with the ratio of Na+ ions in the A site, and La2Ti2O7 undergoes amorphization, recrystallization, and further decomposition as the Na species increases. In well-crystallized La1.17Na0.48Ti2O6/Na3La2(BO3)3, intimate interfacial contacts induce extended optical absorption and optimized charge transfer. Under visible light irradiation, the sample exhibits significantly enhanced photocatalytic H2 evolution activity, with hydrogen production rate reaching 660 μmol∙g−1·h−1, whereas La2Ti2O7 has almost no catalytic activity. This work presents a novel strategy to transform the perovskite oxides at a relatively low temperature by exchanging cations with reductive NaBH4. It demonstrates applications in the development of visible light-driven perovskite-based heterogeneous photocatalysts.

Intercalating Helium into A-Site Vacant Perovskites

Evolutionary searches were employed to predict the most stable structures of perovskites with helium atoms on their A-sites up to a pressure of 10 GPa. The thermodynamics associated with helium intercalation into [CaZr]F6 under pressure, and the mechanical properties of the parent perovskite and helium-bearing phase were studied via density functional theory (DFT) calculations. The pressure–temperature conditions where the formation of HeAlF3, HeGaF3, HeInF3, HeScF3, and HeReO3 is favored from elemental helium and the vacant A-site perovskites were found. Our DFT calculations show that entropy can stabilize the helium-filled perovskites because the volume that the highly compressible noble gas atom occupies within the perovskite pores may be larger than the volume it adopts in its elemental form under pressure. We find that helium incorporation will increase the bulk modulus of AlF3 from a value characteristic of tin (∼50 GPa) to one characteristic of stainless-steel (∼160 GPa) and hinders the pressure-induced rotation of its octahedra.

Enhanced energy storage performance and temperature stability achieved by a synergic effect in Nd3+/Ga3+ co-doped (Na0.5Bi0.5)TiO3 -based ceramics

(1-x)(0.75(Na0.5Bi0.5)TiO3-0.25SrTiO3)-xNdGaO3 ceramics (NBST-xNG, x = 0–0.06) were fabricated through a solid-state reaction method. High-valent Nd3+ ions enter the perovskite A-site to occupy Bi vacancies resulting from the volatilization of Bi, inhibiting the formation of oxygen vacancies and contributing to an enhanced breakdown electric field (Eb). Low-valent Ga3+ ions enter the B-site to substitute for Ti4+ ions, resulting in the formation of random electric fields (REFs) at the B-site due to co-occupying hetero-valence ions of Ga3+/Ti4+, which significantly reduces ferroelectric hysteresis. Therefore, a synergic effect of A- and B-sites co-doping was realized in NBST-xNG ceramics. Benefitting from this synergic effect, an enhanced recoverable energy storage density (Wrec) of 2.88 J/cm3 and an efficiency (η) of 83% are simultaneously obtained in NBST-0.04NG ceramics under a moderate electric field (E) of 200 kV/cm. Compared with most NBT-based ceramics, the values of (η vs Wrec/E2) for NBST-0.04NG ceramics show an obvious advantage, indicating excellent potential for application as an energy storage material. Moreover, Wrec and η of NBST-0.04NG ceramics exhibit excellent temperature stability from 30 °C to 200 °C due to the enhanced correlation strength of polar nanoregions (PNRs) and local structural stability. This work provides a potential strategy to improve the energy storage performance of NBT-based ceramics via the synergic effect of A- and B-site co-doping.

Lead-Free Aurivillius Phase Bi2LaNb1.5Mn0.5O9: Structure, Ferroelectric, Magnetic, and Magnetodielectric Effects.

Aurivillius phase Bi2LaNb1.5Mn0.5O9, derived from ferroelectric PbBi2Nb2O9 by simultaneous substitution of the A-site and B-site cations, was synthesized using a molten-salt method. Here, we discuss the structure-property relationships in detail. X-ray and neutron diffraction show that Bi2LaNb1.5Mn0.5O9 adopts an A21am orthorhombic crystal structure. Rietveld refinement analysis, supported by Raman spectroscopy, indicates that the Bi3+ ions occupy the bismuth oxide blocks, La3+ ions occupy the perovskite A-site, and Nb5+/Mn3+ ions occupy the perovskite B-site. Ferroelectric ordering takes place at 535 K, which coexists with local ferromagnetic order below 65 K. The cation disorder on the B-site results in relaxor-ferroelectric behavior, and the short-range ferromagnetic order can be attributed to Mn3+/Mn4+ double-exchange. Magnetodielectric coupling measured at 5 K and 100 kHz in a field of 5 T suggests the existence of intrinsic spin-lattice coupling with a magnetodielectric coefficient of 0.20%. These findings will provide significant impetus for further research into potential devices based on the magnetodielectric effect in Aurivillius materials.

Structural phase transition and suppressed Griffiths-like phase induced by Sr2+-doping in LaCr0.5Mn0.5O3 compound

We have investigated the influence of heat treatment and Sr-doping on the structural and magnetic properties of the LaCr0.5Mn0.5O3 compound produced by the modified combustion method using urea as fuel. It was shown that the undoped sample can be produced with heat treatment at a temperature as low as 300 °C. However, the addition of 10% Sr makes it difficult to be obtained at low temperatures, and hence, the desired phase was reached with a heat treatment above 800 °C. Moreover, the Sr-doping induced a structural phase transition from orthorhombic to rhombohedral, which is attributed to an increase of the ionic radius on the perovskite A-site. The observed deviation of the Curie-Weiss (C-W) law adjusted above the magnetic ordering temperature of the LaCr0.5Mn0.5O3 sample was attributed to the presence of Griffiths-like phase (GP) with Griffiths temperature at TG = 280 K, nevertheless, this deviation was suppressed with the Sr-doping. Finally, Sr-doping induces an increase of Cr4+ and Mn4+ valence states, enabling the existence of more double-exchange interactions, which is responsible for the increase of the magnetization and magnetic ordering temperature.

Determination of the Crystal Structures in the A-Site-Ordered YBaMn2O6 Perovskite

We present a complete structural study of the successive phase transitions observed in the YBaMn2O6 compound with the layered ordering of cations on the perovskite A-site. We have combined synchrotron radiation X-ray powder diffraction and symmetry-adapted mode analysis to describe the distorted structures as pseudosymmetric with respect to the parent tetragonal structure. The YBaMn2O6 compound shows three consecutive phase transitions on cooling from 603 K down to 100 K. It undergoes a first-order structural transition at T1 ≈ 512 K from a C2/m cell with a single Mn site to a P21/c cell with two nonequivalent Mn sites. No checkerboard ordering of the two types of MnO6 octahedra is revealed, and there is no significant charge segregation. A second transition is observed below T2 ≈ 460 K giving rise to a duplication of the c-axis and the occurrence of four nonequivalent Mn sites. These sites are grouped in two pairs, producing, in this case, a checkerboard arrangement in the ab-plane with an average charge segregation of Δq ≈ 0.4 e–. The observed distortions in this phase disagree with the formation of an orbital-ordered phase. Finally, another structural transition is observed coupled to the magnetic transition at TN ≈ 200 K and the c-axis is no longer duplicated. The low-temperature phase is polar with SG P21. It also contains four nonequivalent Mn sites grouped in two pairs. The charge difference between these pairs is increased, achieving a value of Δq ≈ 0.7 e–. In this phase, an asymmetric stretching mode favors a Jahn–Teller-like distortion in the expanded MnO6 octahedra that could be associated with an ordering of eg (3dx2–z2/3dy2–z2) orbitals. Our refinements disclose that this phase is ferroelectric with significant polar displacements of the Mn and Obasal atoms along the b-axis. The simultaneous occurrence of ferroelectricity and magnetic ordering indicates that YBaMn2O6 can be considered as a type II multiferroic compound and can present magnetoelectric coupling.

The effect of Strontium contents on novel MIEC1-MIEC2 dual-phase ceramic-based oxygen transport membranes

Although ceramic-based oxygen transport membranes (OTMs) have irreplaceable advantages over traditional oxygen production technologies, their oxygen permeability and stability need to be further improved. Based on the theoretical starting point of increasing the three-boundary reaction zone and reducing blocking effect, a set of new dual-phase membranes 75wt%Ce0.8Sm0.1Cu0.1O2-δ-25wt%-Sm0.8Sr0.2Co0.8Fe0.2O3-δ (CSC-8282) and 75wt%Ce0.8Sm0.1Cu0.1O2-δ-25wt%Sm0.3Sr0.7Co0.8Fe0.2O3-δ (CSC-3782) with different strontium contents were prepared by a one-pot sol-gel method ensuring that each element has the same chemical potential. The surface morphology, crystal structure and element distribution are systematically studied by SEM, XRD and EDS, which confirms that the synthesized membranes have an obvious dual-phase structure and excellent compactness. The results of the oxygen permeability experiment show that the oxygen permeability of CSC-3782 is always higher than that of CSC-8282 under any conditions due to the inducing effect of strontium on oxygen vacancies, and flow rate of CSC-3782 at 960°C reached 0.64 and 0.22mL⋅cm-2⋅min-1 for He and CO2 as a sweep gas, respectively. The final long-term stability test confirmed that the dual-phase composite membrane with great prospects for development has high temperature stability and CO2-tolerant property, and the doping of strontium to A-site of perovskite contributes to the improvement of its performance.

Synergy of NTP-La1-xAgxMn1-yCoyO3-δ Hybrid for Soot Catalytic Combustion at Low Temperature

Ag and Co co-doped La1-xAgxMn1-yCoyO3-δ perovskites were prepared by the citric acid sol–gel method. The maximum solubility of Ag+ in LaMnO3 decreased with the increase of Co doped in B-site, which lead to the exsolution of excess Ag+ from A-site of perovskite. The exsolution progress is more favorable to the formation of uniform and stable Ag nanoparticles on the perovskite substrate. The non-thermal plasma (NTP) assisted La1-xAgxMn1-yCoyO3-δ for soot catalytic combustion had been investigated under diesel exhaust gas conditions. When La1-xAgxMn1-yCoyO3-δ was utilized as the catalyst without NTP, the soot could hardly be oxidized at 200 °C. However, when La1-xAgxMn1-yCoyO3-δ was combined with NTP, the efficiency of soot removal was dramatically improved. The NTP-La0.5Ag0.5Mn0.8Co0.2O3-δ hybrid had the highest soot removal efficiency and CO2 selectivity. The combination of NTP and La1-xAgxMn1-yCoyO3-δ could form a synergistic catalytic effect, which significantly promoted the combustion of soot at low temperature. The results of characterization and experiments indicated that the synergistic catalytic performance depended on the coordination of short-living species in plasma, adsorbed oxygen and Ag nanoparticles on surface of La1-xAgxMn1-yCoyO3-δ. Based on these results, the reaction mechanism of plasma-catalyst hybrid for soot catalytic combustion was proposed.

A-site perovskite oxides: an emerging functional material for electrocatalysis and photocatalysis

This review summarizes the recent progress of A-site perovskite oxides as an emerging functional material for electrocatalysis and photocatalysis applications.

Structure-property relationships in the lanthanide-substituted PbBi2Nb2O9 Aurivillius phase synthesized by the molten salt method

Samples of PbBi2Nb2O9, PbBi1.5La0.5Nb2O9, and PbBi1.5Nd0.5Nb2O9 have been prepared by the molten salt method. The structure, morphology, and electrical properties were investigated. All samples are single-phase and crystallize in an orthorhombic structure with A21am symmetry. Neutron diffraction data indicate that the Ln3+ cations prefer to occupy the perovskite A-site, whereas Pb/Bi occupy the perovskite A-site and the Bi2O2 layer. Changes in unit cell volume are observed on substitution and are attributed to the ionic radii of the Ln3+ cations and also correlated to changes in the B-O bond distances in the BO6 octahedra, which are also observed in IR spectra. SEM images reveal anisotropic plate-like grains, which increase in size with the presence of Ln3+ ions. The ferroelectric transition temperature (Tc) decreases with decreasing degree of BO6 distortion as the influence of the 6s2 lone pair of Bi3+ is diminished. Relaxor ferroelectric behavior is observed with Ln3+ substitution, driven by the disorder of the A-site cations. The room temperature ferroelectric polarization increases with Ln3+ substitution, ascribed to the decreased dielectric loss.

Magnetic and magnetocaloric properties in Nd1-3xBax Cax SrxMnO3 (x=0.11and 0.133) perovskite manganites

A systematic investigation of structural, magnetic and magnetocaloric properties for Nd1-3xBax Cax SrxMnO3 (x ​= ​0.11 and 0.133) manganites is reported. X-ray powder diffraction (XRD) patterns suggest that our samples crystallize in the orthorhombic perovskite structure with a Pbnm space group. Magnetization temperature dependence under the field-cooled cooling (FCc), field-cooled warming (FCw) and zero-field-cooling (ZFC) modes exhibit a ferromagnetic(FM)- paramagnetic(PM) phase transition at TC temperature increasing from 120 ​K for x ​= ​0.11–145 ​K for x ​= ​0.133. An analysis using the Banerjee’s criterion curves near TC indicates that x ​= ​0.11 displays a second-order transition while x ​= ​0.133 displays a first order magnetic phase transition. The analysis is further confirmed by the phenomenological universal curves of the normalized entropy variation as a function of rescaled temperature. The maximum magnetic entropy change (−ΔSMmax) and relative cooling power (RCP) were estimated to 1.68 ​J /kg K and 89.45 ​J /kg for x ​= ​0.11 and 4.11 ​J/kg K and 132.45 ​J /kg for x ​= ​0.133 under 3T, respectively. The experimental approach mixing three different alkaline earth on the A-site perovskite significantly improves the broadening of the magnetic entropy change temperature dependence and then the relative cooling refrigerant capacity. Such approach can be transferred to manganite showing ferromagnetic to paramagnetic phase transition near room temperature for magnetic refrigeration application.

A novel facile strategy to suppress Sr segregation for high-entropy stabilized La0·8Sr0·2MnO3-δ cathode

Sr segregation on a perovskite oxide surface immensely affects the oxygen reduction activity and the durability of solid oxide fuel cells cathode. Herein, a facile strategy is proposed, which employs a high-entropy perovskite oxide as a cathode to suppress the Sr segregation during the long-term operation. The as-prepared high-entropy La0·8Sr0·2MnO3-δ (LSM) incorporates five components into A-site of LSM perovskite, including La, Pr, Nd, Sm and Sr (La0.2Pr0.2Nd0.2Sm0.2Sr0·2MnO3-δ, HE-LSM). The homogeneously dispersive multiple rare-earth metal species in A-site of perovskite are thermodynamically stable at high temperature. Besides, the lattice distortion of HE-LSM caused by the high dispersity of A-site cations will lead to the formation of disordered stress field around Sr, which can limit the transport rate of Sr. Further long-term stability test indicates that HE-LSM is rather stable under the operation condition, demonstrating that high-entropy perovskite oxide is a potential cathode material which can suppress the cation segregation for solid oxide fuel cell.

Silver-Modified Ba1-xCo0.7Fe0.2Nb0.1O3-δ Perovskite Performing as a Cathodic Catalyst of Intermediate-Temperature Solid Oxide Fuel Cells.

A series of silver (Ag)-modified barium cobalt ferrous niobate (Ba1-xCo0.7Fe0.2Nb0.1O3-δ, BCFN) materials were fabricated using a solid-state method by doping silver cations into the A-site of this perovskite matrix (Ag-BCFN). The electrochemical analyses indicated that the Ag-BCFN cathodic catalysts performed superior to the nonmodified catalysts when applied in intermediate-temperature solid oxide fuel cells (IT-SOFCs). These Ag-BCFN cathodic catalysts displayed a cubic perovskite structure (PDF 75-0227, Pm3̅m, α = 90°) with a high degree of crystallinity, as demonstrated by X-ray powder diffraction analyses. It was also found that the in situ exsolution of the silver ion (Ag+) occurred, where 57.9% of doped Ag+ was reduced into metallic Ag particles with size ranging from 5 to 10 nm, as shown by electron microscopic analyses. The cerium gadolinium oxide (Ce0.9Gd0.1O2-δ) electrolyte-supported symmetrical half cell using different Ag-BCFN formulations of Ba1-xAgxCo0.7Fe0.2Nb0.1O3-δ as electrodes showed a polarization resistance as low as 0.233 Ω·cm2 and an exchange current density of 85.336 mA·cm-2 at 650 °C under ambient pressure. The improved electrochemical kinetics is anticipated to be attributed to two reasons: doping of ions (Ag+) in the A-site of perovskite and in situ exsolved silver nanoparticles (Ag NPs) along the edge and on the surface of BCFNs improving the mobile charge and electrical properties of the material. The remaining Ag+ in the A-site induced the electron redistribution, whereas the Ag NPs were found to increase the electrochemically active sites and enable the formation of a triple-phase boundary. These explanations were confirmed by the density functional theory study, indicating that Ag-doping processes lead to a decrease in the formation energy of oxygen vacancies from 1.72 to 1.42 eV upon the partial substitution of Ba2+ by Ag+ cations.

Structural and multiferroic properties in double-layer Aurivillius phase Pb0.4Bi2.1La0.5Nb1.7Mn0.3O9 prepared by molten salt method

A single-phase sample of the Aurivillius compound Pb0.4Bi2.1La0.5Nb1.7Mn0.3O9 was prepared by a molten salt method using K2SO4/Na2SO4 as the flux. The crystal structure, morphology, ferroelectric, and magnetic properties were investigated. Neutron powder diffraction data confirmed a non-centrosymmetric orthorhombic crystal structure with space group A21am and Pb/Bi disorder in the bismuth oxide blocks, Bi/Pb/La disorder on the perovskite A-site, and Nb/Mn disorder on the perovskite B-site. The morphology of the sample showed anisotropic plate-like grains as probed by scanning electron microscopy. The dielectric constant exhibits a transition peak between 600 K and 640 K that depends on frequency, indicating relaxor ferroelectric behavior. Electrical polarization versus applied field loops are unsaturated, with a remnant polarization of 0.43 μC/cm2 at 40 Hz under the maximum electrical field applied of 160 kV/cm. The ferroelectricity originates from the displacement of oxygen atoms in the BO6 octahedra, resulting in a polar structural distortion. Magnetic susceptibility measurements showed the presence of mixed Mn3+ and Mn4+, resulting in short-range ferromagnetic order via double exchange interactions below 33 K. The remnant magnetization (Mr) is 0.01 emu/g at 5 K. This mixed valence of Mn cations is mainly responsible for the high electrical conductivity. Thus, Pb0.4Bi2.1La0.5Nb1.7Mn0.3O9 exhibits coexisting ferroelectric and ferromagnetic properties.

Amphotericity-spectroscopy correlations in Eu doped sodium bismuth titanate (Na0.5Bi0.5TiO3)

Optical characteristics of a doped material depend on the site wherein the dopant resides. In mixed A-site perovskites, the dopant has several possibilities. This, in turn, correlates with the emission spectrum of the doped material. Here we choose Eu3+ as the dopant since it is a well-known and efficient red-luminophore. Sodium bismuth titanate (NBT-Na0.5Bi0.5TiO3) is selected as a host due to its ability to accommodate Eu over large concentration windows while maintaining optical activity. For compositions x ≥ 0.04, we show that Eux:NBT has amphoteric behavior (i.e., simultaneous dopant substitution in two competing sites). Eu3+ occupancy in Bi and Ti-sites are quantitatively estimated using Rietveld refinement. Also, the appearance of A1g breathing vibrational mode (830–860 cm−1) in Raman spectra shows the presence of Eu3+ on the Ti-site. Photoluminescence (PL) emission shows sharp and intense bands at ∼592 nm, ∼615 nm, and ∼687 nm, and one weak band at ∼652 nm, corresponding to f–f transitions of Eu3+. To evaluate the optical characteristics with varying site-substitution of Eu3+; Judd–Ofelt parameters and radiative properties are calculated for the first time in this mixed A-site titanate system. From the values of asymmetric ratios; Eu3+ ion is shown to occupy the non-centrosymmetrical sites (Bi-sites) of NBT. However, at x = 0.04, Ω2 < Ω4, which indicates long-range effects and hence Eu occupancy in centrosymmetric sites (Ti-sites). This study opens up avenues for further exploration of correlations between dopant-concentration, amphotericity, and spectrochemical response in other systems. The amphoteric behavior of dopants can tune emission intensities and produce multi-emission colors using a single-dopant. This would have implications for luminescence-based applications.