Distorted Perovskite Structure Research Articles

“Yb modification of bismuth Ferrite: Unveiling Optical, Dielectric, and electrochemical properties for advanced applications”

This study explores the detailed impact of Yb3+ substitutional doping on the structural, optical, dielectric, and electrochemical characteristics of bismuth ferrite. Rigorous structural analysis conducted via X-ray diffraction confirmed the formation of a rhombohedral distorted perovskite structure, within the R3C space group. The investigation of crystallite size showed a reducing trend as Yb3+ content increased. Morphological studies revealed the presence of finely dispersed nanocrystalline grains, exhibiting particle size within the range from 281 to 197 nm. Raman spectroscopy unveiled notable phonon mode shifts towards higher wavenumbers, correlating with increased Yb3+ doping concentrations. Additionally, a discernible reduction in bandgap energy, from 2.15 to 1.98 eV, was observed with increasing doping levels. An improved dielectric response was observed with Yb3+ doping. Electrochemical assessments, employing cyclic voltammetry and galvanostatic charge–discharge techniques, revealed the superior electrochemical performance of the 30 % Yb-doped bismuth ferrite-modified electrode, demonstrating a specific capacitance of 575 Fg−1 at a scan rate of 10 mVs−1. These findings underscore the tailored engineering of Yb-doped bismuth ferrite nanoparticles, positioning them as promising candidates for the next generation of supercapacitor devices.

Enhanced magnetic behavior of LaFeO3 by co-doping with Nd3+ and V5+ substitution (La0.8Nd0.2Fe0.95V0.05O3)

To enhance the quality of applications of LaFeO3 (LFO) as a magnetoelectric multiferroic through the improvement of magnetic behaviour, co-doping of Nd3+ (20 %) and V5+ (5 %) was considered for partial substitution in place of La3+ and Fe3+, respectively. Co-doped sample of La0.8Nd0.2Fe0.95V0.05O3 (LNFVO) was prepared by solid state reaction method. Rietveld analysis of X-ray diffractograms confirmed the formation as well as successful incorporation of dopants (Nd3+ and V5+) in La3+ and Fe3+ sites of the distorted perovskite structure with Pbnm space group. Morphological features including information related to crystallographic phase were examined by TEM. Distortion due to co-doping helped to achieve the stated objectives. Valence states of dopants and host cations were explored by analyzing XPS observations. Detailed magnetic measurements in the temperature range starting from 300 K down to 2 K suggested that magnetic property was drastically enhanced compared to that of the undoped, which was attributed to mismatch of valence states, ionic diameters etc. between dopants with host cations. The doped sample showed antiferromagnetic to ferromagnetic transition at and below 19 K. All such findings related to magnetic property would be quite attractive for the improvement of multiferroic applications as the low value of magnetization of pristine sample of LFO restrict it to become a good magnetoelectric multiferroic.

Structural, optical, and magnetic properties of Bi0.93Gd0.07FeO3 multiferroic nanoparticles

Gadolinium (Gd) doped bismuth ferrite Bi1-xGdxFeO3 (x = 0.07) nanoparticles (NPs) were synthesized by a sol–gel technique. Crystalline nature was analyzed by X-ray diffraction (XRD) which showed a rhombohedral distorted perovskite structure with space group R3c. By using the Debye-Scherrer formula, the crystallite size was found to be 32.5 nm. Field Emission Scanning Electron Microscope (FESEM) image verified that at higher concentrations of Gd, particle size decreases. Raman spectroscopy confirmed the Bi-O and Fe-O vibrational modes in the NPs. In the UV–visible absorption spectra, a peak was obtained at 455 nm and the band gap of the Bi0.93Gd0.07FeO3 NPs was determined to be 2.30 eV. The non-linear M−H loop of 7 % Gd-doped BiFeO3 NPs is attributed to a weakly ferromagnetic nature.

Non-volatile voltage-controlled magnetization in single-phase multiferroic ceramics at room temperature

Single-phase multiferroics (MFs) exhibiting ferroelectricity and ferromagnetism and the strong magnetoelectric (ME) coupling effect at room temperature are seen as key to the development of the next-generation of spintronic devices, multi-state memories, logic devices and sensors. Herein, the single-tetragonal phase (1–x) (Sr0·3Bi0·35Na0·329Li0.021)TiO3-xBiFeO3 (x = 0.2 or 0.4) system was designed to study the intrinsic ME coupling effect at room temperature and high frequencies. The polarization arises from the cooperative displacement of both Fe3+ and Ti4+ relative to the oxygen sublattice in the tetragonally distorted perovskite structure, and the magnetization stems from indirect exchange magnetic interaction between adjacent iron ions. A switchable voltage-controlled magnetization was confirmed by a change of the coercive magnetic field, Hc, and remnant magnetization, Mr, in the x = 0.4 component subjected to an external electric field at room temperature and was possibly attributed to a strain-mediated ME coupling effect. In addition, resonance behaviours of the complex magnetic permeability and complex dielectric permittivity in the GHz band indicate that this ME effect is intrinsic in nature and could broaden the applications of multiferroics to devices operating at microwave frequencies.

Effect of Pr3+ Substitution at the A-Site on the Structural and Electrical Properties of Hole-Doped La-Based Manganites

In this study, the effect of praseodymium substitution at La-site on structural and electrical transport properties of La0.5Ba0.5MnO3 was investigated. Polycrystalline La0.5-xPr0.5x Ba0.5MnO3 (x = 0, 0.50, 1.00) were synthesized using a conventional solid-state method. The powder X-ray diffraction patterns show a single-phase orthorhombic distorted perovskite structure with space group Pnma. The Rietveld refinement analysis showed that the unit cell volume decreased as Pr3+ substitution increased which may be attributed to the different ionic radii of ions. Electrical resistivity measurements by using standard four-point probe resistivity measurement in a temperature range of 30 K to 300 K. As the Pr3+ concentration increases, metal-insulator transition, TMI decreases from 264K (x=0) to 157K (x=1.00) while resistivity increases from 1.16 Ω.cm (x = 0) to 20.3 Ω.cm (x =1.00). The decreased TMI are attributed to the decrease in tolerance factor which indicates enhancement in MnO6 octahedral distortion consequently reduce double exchange interaction. The electrical resistivity in the metallic region for all samples was fitted with the combination of domain/ grain boundary, electron-electron, electron-magnon and electron-phonon scattering processes. The resistivity behaviour in the insulating region for all samples was attributed to small polaron hopping model which revealed that the activation energies increased as Pr3+ content increased due to the enhancement in the distortion of MnO6 octahedral.

Probing the effect of LaFeO3 on the structural, electrical, and dielectric properties of Sr0.8Sn0.2Bi2Nb2O9 processed through solid state route method

SrBi2Nb2O9 belongs to the class of Aurivillius layered ferroelectric oxide materials and this article offers a suitable method for understanding the structural and electrical properties of this class material for industrial application. With this aim we have synthesized LaFeO3 (LFO) doped Sr0.8Sn0.2Bi2Nb2O9 (SBN) novel ceramic by solid state route using ball milling in an ethanol medium for 20 h with 200 rpm, followed by single-step microwave sintering. For better phase formation, the obtained powders are compressed into cylindrical pellets and fired at 1000 °C for 5 h. The sample was critically analyzed using powder X-ray diffraction data confirming the distorted perovskite structure. The dielectric properties were studied in a frequency range of 10 Hz to 2 MHz at different temperatures revealing many exciting results. Further analyzing the impedance spectroscopy gives an idea about the contribution of different electrically dynamic regions in different conduction processes.

Phase formation, microstructural and dielectric properties of bismuth ferrite nanoceramics synthesized by low-temperature molten salt flux route

BiFeO3 nano-ceramics were synthesized using the low-temperature molten salt synthesis route to study the influence of calcination temperature and salt ratios. The Rietveld refinement revealed the distorted perovskite structure of BFO. These granular-shaped BFO samples’ grains morphology was studied using the FESEM. The FTIR revealed the presence of Metal-Oxygen bonds in the BFO ceramics. The XPS studies exhibited the respective constituent elements’ oxidation states and validated the presence of oxygen ion vacancies. The frequency-dependent dielectric properties were measured at various temperatures. The electrical conductivity measurement showed a linear variation as a function of frequency which validated Jonscher’s power law.

SYNTHESIS AND PROPERTIES OF NdMe<sup>II</sup>TeO4.5 (MeII – Ca,Ba) TELLURITES

The aim of this work was to synthesize and investigate the roentgenographic and electro-physical properties of new phases, namely double tellurites of neodymium. Oxotellurites of the composition NdMeIITeO4.5(MeII - Ca, Ba) were synthesized by the method of ceramic technology with high-temperature interaction of Nd2O3, TeO2 oxides with carbonates of alkaline earth metals in the interval of 800°С - 1200°С. Roentgenograms of the synthesized compounds were obtained using an Empyrean powder diffractometer by PANalytical and indication was determined using the X’Pert HighScore Plus program. It was found that the synthesized tellurites were crystallized in tetragonal syngony. The unit cell parameters, roentgen and pycnometric densities of the compounds were determined. It was revealed that with increasing ionic radii from Ca to Ba, the lattice parameters and unit cell volumes of synthesized tellurites increase. The assumed structure of the synthesized double tellurites of neodymium is a distorted perovskite structure. A study of the temperature dependence of the dielectric permittivity and electrical resistance of tellurites of neodymium-alkaline earth metals established that they can possess semiconducting properties at 293 K - 483 K. Temperature coefficients of resistance and forbidden zone width of tellurites were calculated.

Solution-phase synthesis of alloyed Ba(Zr1-xTix)S3 perovskite and non-perovskite nanomaterials.

Chalcogenide perovskites, especially BaZrS3 and its related alloys, present a promising alternative to lead halide perovskites for optoelectronic applications due to their reduced toxicity and enhanced stability. However, the elevated temperature conditions necessary for preparing these materials create a barrier to their incorporation into thin-film devices. In this work, we report a solution-phase synthesis of colloidal nanoparticles of titanium-alloyed BaZrS3, Ba(Zr1-xTix)S3. The titanium alloying was achieved using reactive amide precursors in oleylamine solvent, and N,N'-diethylthiourea served as the sulfur source. Our methodology allowed for the synthesis of Ba(Zr1-xTix)S3 nanomaterials at temperatures at or below 300 °C. The resulting nanocrystals exhibited a phase transition from an orthorhombic distorted perovskite structure to a hexagonal non-perovskite phase as the titanium content surpassed x = 0.11, accompanied by a morphological evolution from nanoplatelets to nanohexagons and ultimately nanobars. The UV-Vis-NIR absorption spectra of Ba(Zr1-xTix)S3 nanoparticles exhibit increasing low-energy absorption as the titanium content is increased. This work contributes to the development of low-temperature synthesis methods for Ba(Zr1-xTix)S3 nanomaterials, offering new potential pathways for materials design of chalcogenide perovskites for advanced optoelectronic applications.

An investigation of the dielectric behavior of Bi0.7La0.3FeO3 compound under the influence of different calcination temperatures

This paper presents the synthesis and characterization of bismuth nanoferrite and lanthanum-doped bismuth nanoferrite (Bi0.7La0.3FeO3). The compounds were synthesized, through the sol-gel method and the doped compound was calcinated at three different temperatures 400 °C, 600 °C, and 800 °C. Following that, the compounds are further analyzed using several characterization methods such as; X-ray diffraction (XRD) analysis confirmed the formation of bismuth ferrite with a distorted perovskite structure and the R3c space group. The crystallite sizes were determined using Sherrer's formula, with bismuth nanoferrite having a size of 14.9 nm and lanthanum-doped bismuth nanoferrite calcinated at different temperatures exhibiting sizes of 13 nm, 17.7 nm, and 20 nm. Fourier transform infrared spectroscopy (FTIR) analysis confirmed the presence of ferrite by observing metal-oxygen (M-O) stretching vibrations in the fingerprint region, with characteristic Fe-O bond peaks in the 430–480 cm−1 range. Ultraviolet-visible spectroscopy revealed promising energy band gaps for the synthesized compounds. Scanning electron microscopy (SEM) was utilized to examine the surface morphology of the compounds, revealing agglomerated structures. Dielectric properties of bismuth nanoferrite have been extensively studied, and lanthanum doping has been shown to improve them. The lanthanum-doped bismuth nanoferrite has a higher dielectric constant than bare bismuth nanoferrite. Additionally, there is less dielectric loss. Hence these results lead to significant potential for many applications, like gas sensors, memory devices, microwave devices, and biomedical applications.

How the Temperature and Composition Govern the Structure and Band Gap of Zr-Based Chalcogenide Perovskites: Insights from ML Accelerated AIMD.

The effects of temperature and composition on the structural and electronic properties of chalcogenide perovskite (CP) materials AZrX3 (A = Ba, Sr, Ca; X = S, Se) in the distorted perovskite (DP) phase are investigated using ab initio molecular dynamics (AIMD) accelerated by machine-learned force fields. Long-range van der Waals (vdW) interactions, incorporated into the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional using the DFT-D3 scheme, are found to be crucial for achieving correct predictions of structural parameters. Our calculations show that the distortion of the DP structure with respect to the parent cubic (C) phase, realized in the form of interoctahedral tilting, decreases with the increasing size of the A cations. The tendency for a gradual transformation of the DP-to-C phase with increasing temperature is shown to be strongly composition-dependent. The transformation temperature decreases with the size of cation A and increases with the size of anion X. Thus, within the range of the temperatures considered here (300-1200 K), a complete transformation is observed only for BaZrS3 (∼600 K) and BaZrSe3 (∼900 K). The computed band gap of CPs is shown to monotonically decrease with increasing temperature, and the magnitude of this decrease is found to be proportional to the extent of the thermally induced changes in the internal structure. Diverse factors affecting the magnitude of band gaps of CP materials are analyzed.

Structure, ferroelectric and magnetic behavior in Mn doped 0.75 BiFeO3-0.25BaTiO3 ceramics

Lead-free polycrystalline 0.75 BiFe 1-xMn xO3-0.25BaTiO3 (x = 0.00, 0.01, 0.02 and 0.03 hereby designated as BF-BT) ceramics were synthesized by high temperature solid state reaction technique. This study dwells on the role of Mn doping on the structure, ferroelectric and magnetic behavior of BF-BT ceramics. Structural phase analysis of the samples carried out by X-ray diffraction and Raman scattering measurements revealed single phase distorted perovskite structure with rhombohedral symmetry. No alteration in crystal structure was observed with increasing Mn concentration. The average crystallite size of the compounds increases (12.9–27.8 nm) with increasing Mn concentration. The saturated value of ferroelectric polarization (Pr) was found to decrease with increasing Mn-concentration and a maximum remnant polarization (Pr) of 0.6 μC/cm2 was recorded at an applied field of 25 kV/cm for x = 0.00 sample. Leakage current density was found to increase with increase in Mn concentration. Oxidation states of the cations probed by X-ray photoelectron spectroscopy (XPS) suggested that Fe/Mn were in mixed state (+3/+2), while Ti-ion demonstrated (+3/+4) state. Presence of multivalence states of Fe/Mn/Ti causing distortion in the lattice (attributed to Jahn Teller) with increasing Mn concentration significantly affects the magnetic behavior of the ceramics. A maximum value of saturation magnetization of Ms∼0.80emu/gm was recorded for x = 0.03 composition.

Bandgap tuning of Mn-doped BiFeO3 thin films for photovoltaic application

The Mn doped BFO thin films were made on the glass substrates by simple spin coating method and its structural and optical properties were examined. The results obtained from X-ray diffraction pattern of Mn doped BFO confirmed the rhombohedral distorted perovskite structure with stress relaxation. The Bi–O and Fe–O bonds were detected in the perovskite structure, the shifting of all the stretching and bending vibrations of pristine BFO was observed from FTIR analysis. The XPS spectra of Mn-doped BFO thin film declared that the valence states of Bi, Fe and Mn from their respective binding energies. A narrow optical band gap energy of 1.65 eV was observed for Mn doped BFO as against the pristine BFO (2.17 eV) that indicated a reduction in the band gap energy between O 2p valence and Fe 3d conduction band upon Mn doping.

High-Pressure Synthesized Perovskite CdMnO3 with C-Type Antiferromagnetic Spin Configuration

CdMnO3 had not been previously reported and was a missing piece in the A2+Mn4+O3 series. We succeeded in synthesizing this compound by a high-pressure method and confirmed that it is crystallized in a distorted perovskite structure with a Cd2+Mn4+O3 charge configuration. The obtained insulating CdMnO3 exhibits an antiferromagnetic transition at about 86 K. First-principles calculations revealed that the Mn4+ (t2g3) spins form a C-type antiferromagnetic structure, which is in sharp contrast to the G-type antiferromagnetism in the isostructural and isoelectronic CaMnO3. Significant overlap of the Mn-3d and O(2)-2p orbitals produces distorted octahedra with a large Mn-O(1)-Mn tilt and induces antiferromagnetic couplings in the ac plane and the ferromagnetic couplings along the b axis.

Photodegradation of methyl orange based on manganese-substituted bismuth ferrite nanoparticles

Herein, a microwave-assisted approach for the synthesis of manganese (II) (Mn2+)-doped bismuth ferrite (BMFO) nanoparticles is presented. Various techniques were used to examine the structure, morphology and electrical characteristics of the as-synthesized BMFO nanoparticles. X-ray diffraction and Raman analysis revealed a rhombohedral distorted perovskite structure with space group R3c. The crystallite size of BMFO was found to be 18.77 nm. Scanning electron microscopy studies of the BMFO nanoparticles showed the highly agglomerated nature of the particles. The ultraviolet diffuse reflectance spectrum of BMFO revealed a bandgap of 1.56 eV, which was smaller than the bandgap of pure bismuth ferrite (2.41 eV). The methyl orange (MO) dye degradation behavior of the synthesized BMFO was examined for a dye sample solution in the presence of solar radiation. After 120 min, irradiation resulted in 81.08% photodegradation of the MO dye. Kinetic studies demonstrated a pseudo-first-order rate mechanism for the photodegradation of the MO dye. The corresponding coefficient of determination R 2 and t 1/2 were 0.92864 and 63.0 min, respectively. Finally, a methodology for the degradation of MO dye using BMFO is proposed.

Investigation of multiferroic properties of dysprosium substituted bismuth ferrite (Bi1-xDyxFeO3) prepared by auto combustion technique

A simple and inexpensive auto combustion procedure was used to create the Bi1-xDyxFeO3 (x=0.0, 0.015, 0.03, 0.045, 0.060) multiferroics samples. In bismuth ferrite, the average crystallite size increased with growing Dy3+ concentration in BFO, revealing a rhombohedral distorted perovskite structure of space group R3c. During morphological analyses of the produced samples, a spherical structure with little aggregation was found. When Dy3+ is substituted at the B-site, the Raman modes widen and the cation site occupancy changes even more. The frequency-dependent dielectric properties (εr, tanδ), electric conductivity (ac), impedance (Z), and electric modulus (M' and M′′) of the samples were assessed using an impedance analyzer at frequencies between 20 Hz and 20 MHz. All samples had the maximum dielectric constant, which was discovered at a relatively low frequency. The highest value of impedance was found at low frequency and it lowers with increasing frequency as a result of the contributions from the grain and grain boundary. It is discovered that the samples' ac conductivity is frequency-dependent and changes depending on how much Dy3+ is doped into the BFO.

Structural, Electrical and Optical Properties of TM (Mn and Cr) Doped BiFeO3 Nanoparticles

In this paper, the sol-gel technique has been employed to prepare the pure and TM (Mn, Cr) doped BiFeO3 nanoparticles. The synthesized nanoparticles were characterized using X-ray diffraction, UV-vis spectroscopy, photoluminescence, and dielectric measurements. Crystal structural analysis infers that pure and TM-doped BiFeO3 nanoparticles displayed a rhombohedral distorted perovskite structure with R3c space group, along with a minor phase of Bi2Fe4O9. Lattice parameters have been found to decrease with TM doping. The particle size, measured with the help of the XRD spectra, was found to decrease from 54.4 nm to 38.7 nm with TM doping. The bandgap, determined using the UV-vis spectra, was observed to be 1.92, 1.66, and 1.54 eV for undoped, 5% Mn, and 5% Cr-doped BiFeO3 nanoparticles, respectively. The dielectric constant shows a normal dispersion behavior at room temperature and its value increases with TM doping. The ac conductivity also increases with TM doping in BiFeO3 nanoparticles.

High pressure dissociation of CaTiO3 perovskite into CaO and CaTi2O5

In this study, we investigated phase transformations of CaTiO3 perovskite using x-ray diffraction at high pressure and high temperature up to 170 GPa and 4500 K in a laser-heated diamond-anvil cell. We report a high-pressure dissociation of CaTiO3 into CaO-B2 and CaTi2O5 with a monoclinic P2/m structure, instead of the expected transformation of the orthorhombic distorted perovskite structure into a post-perovskite phase. We propose that this transition may be favored by the B1 to B2 phase change of CaO at around 60 GPa. In order to provide additional information on the high pressure properties of CaTiO3 perovskite, we measured its melting temperature using CO2 laser heated diamond anvil cell up to 55 GPa yielding a fit of the melting curve to a Kraut-Kennedy empirical law according to: Tm (K) = 2188 ∗ [1 + 4.23 ∗ (ΔV/V0)]. To provide some further insight into the thermodynamic properties of CaTiO3, we determined the P-V-T equation of state of the orthorhombic mineral perovskite, fitted by using a third order Birch-Murnaghan equation of state and a Berman thermal expansion model. The fit of the data yields to K0 = 180.6(4) GPa, K′0 = 4 (fixed), ∂K/∂T = −0.022(1) GPa K−1, α1 = 3.25(5) x 10−5 K−1, α2 = 1.3(1) x 10−8 K−2

Tunable physical properties of Ba doped BiFeO3 multiferroic nanoceramics for capacitor and memory storage devices

Recently, perovskite structured bismuth ferrite (BiFeO3) multiferroic material has been widely studied owing to its potential applications in various devices like spintronics, energy storage, sensors and photovoltaic devices. Interestingly, the presence of two or greater stable polarization states in this material and the ease of polarization switching by way of electric field exhibited high energy storage densities, making it appropriate for information storage devices. However, the large leakage current and weak magnetism associated with the material at 300 K hinders its usage in practical applications. It is noticed that the substitution of Bi by alkaline earth elements (Mg2+, Sr2+, Ca2+) could significantly enhance the physical properties of BiFeO3 ceramics. In this work, Bi1-xBaxFeO3 (x = 0.05–0.2 mol %) nanoceramics were prepared by adopting low temperature molten salt synthesis route using NaCl as flux. The X-ray diffraction studies revealed the formation of distorted perovskite structure of BiFeO3 phase in all the range of compositions studied. The FESEM analysis demonstrated the presence of nanosized grains of BiFeO3 and the average grain size decreases with an increase in Ba doping content. The X-ray photoelectron spectra revealed the existence of different valence states of the elements present in BiFeO3 nanoceramics. It is interesting to observe that the dielectric properties of Ba doped BiFeO3 ceramics are superior to the undoped samples, especially at the higher frequency range due to the ionic size difference of barium and bismuth ions in the crystal lattice of BiFeO3, which would significantly influence the energy storage capacity in the non-volatile random access memory storage devices.

Enhanced dielectric and magnetic properties of Cr / Co and Mn co-doped single phase multiferroic bismuth ferrite nanoparticles

Multiferroic nanoparticles of single-phase bismuth ferrite (BiFeO3 or BFO) by choosing transition metal ions of chromium (Cr)/cobalt (Co) in A-sites and manganese (Mn) in B-sites were synthesized by using sol-gel autocombustion method. X-ray diffraction (XRD) data reveal the existence of rhombohedrally distorted perovskite structure for all the samples. High resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX) studies were carried out to estimate the particle size, morphology along with the chemical purity of the samples. Dielectric studies as a function of frequency and temperature resemble typical space charge polarization with almost negligible dielectric losses in the doped samples. Magnetic measurements using vibrating sample magnetometer reveals the considerable enhancement in the magnetic order in Co/Cr and Mn co-doped samples. The obtained structural, microstructural, dielectric and magnetic results were well recommended that the influence of co-doping in BFO will certainly modify its spin cycloid structure and hence enhanced properties in these doped samples. Thus, these co-doped samples were suggested to be well suitable for the multifunctional based devices such as spintronic, multifunctional memories, and for sensors.