Decrease Of Ionic Radius Research Articles

Polar phonons features and intrinsic dielectric properties of RE2CoMnO6 (RE = Tb, Dy, Ho, Tm and Yb) double perovskites

RE-based double perovskite (DP) oxides of the RE₂TMTM'O₆ family exhibit intriguing magnetodielectric (MD) properties and magnetocaloric effects (MCEs), making them promising candidates for applications in high-performance supercapacitors, memories, spintronic devices, and cryogenic magnetic refrigeration. This paper addresses the vibrational properties of RE2CoMnO6 (RE = Tb, Dy, Ho, Tm, and Yb) ceramics for the first time using infrared reflectance spectroscopy. The dielectric merit factors in the microwave (MW) range, including the quality factor (Qu) and the static dielectric constant (ɛ0), were estimated. It was observed that the intrinsic dielectric constants decrease from approximately 26.2 to 14.4 as the rare earth ionic radius decreases. The mean values of these compounds suggest their suitability for applications in MW circuitry devices.

The B-site ordering in RFe0.5Cr0.5O3 ceramics and its effect on magnetic properties

Abstract To insight into the B-site ordering in RFe0.5Cr0.5O3 ceramics, a series of RFe0.5Cr0.5O3 ceramics (R = La, Y, Lu) were synthesized by the sol–gel method, and the structural and magnetic properties were systemically investigated. By using the Rietveld refinement of all samples, it is found that the structural distortion is increased as the R ionic radius decreases, leading to the weakened interactions between Fe/Cr ions. Moreover, the Fe and Cr are arranged in disorder in LaFe0.5Cr0.5O3, but partially ordered in YFe0.5Cr0.5O3 and LuFe0.5Cr0.5O3, showing an increasing trend of the proportion of ordered domains with the decrease of R ionic radius. Through fitting the temperature-dependent magnetizations, it is identified that the magnetization reversal (MR) in disorder LaFe0.5Cr0.5O3 is resulted from the competition between the moments of Cr and Fe sublattices. In the partially ordered YFe0.5Cr0.5O3 and LuFe0.5Cr0.5O3 ceramics, because of the presence of Fe–O–Cr networks in the ordered domains whose moment is antiparallel to that of Fe–O–Fe and Cr–O–Cr in the disordered domains, the compensation temperature T comp of MR is increased by nearly 50 K. These results suggest that the changing of R-site ions could be used very effectively to modify the Fe–O–Cr ordering, apart from the structural distortion, which has a direct effect on the magnetic exchange interactions in RFe0.5Cr0.5O3 ceramics. Then at values of composition where ordered domains are expected to be larger in number as compared to disordered domains and with a weaker structural distortion, one can expect a higher transition temperature T comp, providing a different view for adjustment of the magnetic properties of RFe0.5Cr0.5O3 ceramics for practical applications.

Beyond static: Tracking the dynamic nature of water absorption and Young's modulus in IPMC devices

AbstractIonomeric polymer‐metal composites (IPMC) are advanced materials designed to mimic biological systems. Their performance depends on various factors, including electrical stimulus intensity, membrane hydration, ionic migration, and Young's modulus. However, there is a lack of studies in the literature investigating how the water absorption capacity and elastic modulus change over time in IPMCs. Understanding the hydration level variation as a function of time is essential because as this parameter deviates, the ionic migration capacity and Young's modulus also change, altering the device's electromechanical efficiency over time. To address this research gap, Nafion/Pt‐based IPMC devices exchanged with four monovalent cations (H+, Li+, Na+, and K+) and one ionic liquid (1‐butyl‐3‐methylimidazolium—BMIM+) were prepared, and a comprehensive investigation on how the water absorption capacity and Young's modulus vary as a function of time, relative humidity (RH), and counterion size was performed. The results revealed that the water uptake capacity is significantly higher and occurs more rapidly at higher RH levels and when the counterion's ionic radius decreases. Consequently, the time required for the device to reach osmotic equilibrium can range from 40 to 270 min, depending on the RH and counterion used. Furthermore, it was observed that the first natural frequency and Young's modulus also exhibit time‐dependent behavior. Under constant RH conditions, the mechanical properties of the IPMC can vary by up to 50% in less than 60 min. Notably, the combined results from water uptake capacity, Young's modulus, electrochemical impedance spectroscopy, and electromechanical response analyses (including blocking force, displacement, displacement rate, current, coulombic efficiency, and voltage) suggest that a morphological transformation within the polymer is likely to occur once RH exceeds 60%. This finding strengthens the hypothesis that ion migration is mainly influenced by their movement through Nafion's ionomeric channels rather than the filling of ionic agglomerates.

Structural, optical and electrical studies of non-toxic oxide- RMnO3 [R=Y, Er, Yb] hexagonal manganite thin-films

Recently, ferroelectric-photovoltaics have come under the spotlight as a potential class of materials for application in photovoltaic devices. However, the broad bandgap of these ferroelectric-photovoltaic materials causes them to have modest photocurrents[1]. To overcome this challenge hexamanganites can be used to achieve high photovoltaic efficiency as it has a small band gap. Here we present a stable, non-toxic, and cost-efficient hexamanganite RMnO3 [R=Y, Er, Yb] thin films prepared by spray pyrolysis method. The formation of the single phase is confirmed by X-ray diffraction analysis. Morphological studies show grains are uniform and closely packed and the grain size increases with the decrease in ionic radii of rare earth ions. A narrow optical band gap of nearly 1.5 eV is observed for the films. The results of this investigation show that Ultraviolet ray irradiation can be used to tune the bandgap. With a carrier concentration of around 10+14 cm−3, Hall measurements proved that the films are p-type semiconductors. This research illuminates the exploration of stable oxide semiconductors with a small band gap for applications in futuristic solar cells.

Electrical Resistivity Behavior and Small Polaron Conduction Transport Mechanism in Semiconducting <I>R</I>MnO<sub>3</sub> Manganites

Rare earth manganites, denoted by the chemical formula <I>R</I>MnO<sub>3</sub>, where <I>R</I> signifies a rare earth element, have garnered significant interest in recent years. These perovskite oxides exhibit intriguing phenomena such as multiferroicity, ferroelectricity, and colossal magnetoresistance, primarily attributed to the role of polarons in conduction. The incorporation of rare earth ions imparts flexibility, making these compounds promising for applications in spintronics, sensors, and information storage devices. This study delves into the electrical resistivity behavior and Small Polaron Conduction (SPC) mechanisms of rare earth manganites, particularly <I>R</I>MnO<sub>3</sub>. In this manuscript, electrical resistivity of the pristine <I>R</I>MnO<sub>3</sub> (<I>R</I> = Sm, Eu, Gd) manganites are analyzed within the framework of adiabatic nearest-neighbor hopping of SPC. The high temperature state of <I>R</I>MnO<sub>3</sub> within the SPC mechanism is influenced by polaron concentration, hopping distance, and resistivity coefficient. The localized charge carriers in undoped manganites enable one to estimate the activation energy for the electrical conduction. The activation energy decreases with the decrease in ionic radii from Sm to Gd. Deduced polaron activation energy is low for GdMnO<sub>3</sub> as compared to SmMnO<sub>3</sub> and is attributed to reducing disorder state in GdMnO<sub>3</sub> as compared to SmMnO<sub>3</sub>. This work contributes to the fundamental understanding of condensed matter physics and the potential applications of rare earth manganites in emerging technologies. The interplay between electrical resistivity and Small Polaron Conduction offers insights for customizing these materials for specific technological needs.

Raman spectroscopic study of anhydrous and hydrous REE phosphates, oxides, and hydroxides.

Rare earth elements (REE) include the lanthanides (La-Lu), Y, and Sc which are critical elements for the green energy transition. The REE show a decrease in ionic radii with increased atomic numbers, which results in a so-called lanthanide contraction systematically affecting crystal structures and mineral properties. Here we present a compilation of reference Raman spectra of ten REE sesquioxides (A-, B- and C-type), five REE hydroxides, eight xenotime-structured REE phosphate endmembers and two solid solutions, seven monazite-structured REE phosphate endmembers and two solid solutions and seven rhabdophane endmembers with up to five Ce1-xLREEx rhabdophane solid solutions (LREE = La-Gd). Raman mode assignment is based on a detailed literature review summarizing existing analytical work and theoretical calculations and systematic trends observed in this study by analyzing different REE-bearing solids. The wavenumbers of the main REE-O Raman band systematically increase with decreasing ionic radii forming discrete linear trends within isostructural mineral groups, that can be used to estimate the REE-O mode in other solids with known REE-O coordination numbers. Photoluminescence using 266 nm, 532 nm and 633 nm excitation laser wavelengths for REE-bearing oxides, hydroxides, anhydrous and hydrous phosphates is also presented providing a new framework for identifying REE-phases in phosphate-bearing natural mineral deposits.

LANTHANIDE CONTRACTION IN CHELATES OF ETHYLENEDIAMINETETRAACETIC ACID BASED ON CRYSTALLOGRAPHIC DATA: A SHORT REVIEW

The lanthanide (Ln) series has been attracted so much attention not only for its physical properties but also for its applications in organic synthesis and biomedical engineering. In the lanthanide chemistry, lanthanide contraction is a crucial concept meaning the gradual decrease in ionic radii as the atomic number of the Ln series increases. As a prominent chelator, ethylenediaminetetraacetic acid (EDTA) has been well-known to give stable complexes with various metals including Ln ions, resulted in forming (EDTA−4H)4− anion by deprotonation; over 100 kinds of Ln-EDTA complexes have hitherto been synthesized and structurally characterized using X-ray crystallography. While the lanthanide contraction phenomenon has been extensively studied in certain complexes of Ln, systematization on the Ln-EDTA remains inadequate though the chelates of EDTA are commonly used. Thus, this study presents a comprehensive analysis based on the data from the Cambridge Crystallographic Data Centre (CCDC). In mononuclear EDTA complexes X[Ln(EDTA−4H)(H2O)m]·nH2O (X+ = NH4+and its analogues) systematic lanthanide contraction depending on their coordination number are presented except for a few cases. However, in the case of non-mononuclear complexes or coordination polymers, the compositions become more complicated, and a greater variation in atomic bond length occurs, which is unusual for the lanthanide contraction studies in previous research. These varieties are considered to be influenced by different types of counter-cations, inorganic anions, solvent molecules and bridging O atoms from another EDTA anions. This suggests the flexibility and versatility of EDTA as a ligand. Such findings in the Ln-EDTA complexes could potentially provide us further development of a novel function in the future.

Complexation of a Nitrilotriacetate-Derived Triamide Ligand with Trivalent Lanthanides: A Thermodynamic and Crystallographic Study.

Non-heterocyclic N-donor nitrilotriacetate-derived triamide ligands are one of the most promising extractants for the selective extraction separation of trivalent actinides over lanthanides, but the thermodynamics and mechanism of the complexation of this kind of ligand with actinides and lanthanides are still not clear. In this work, the complexation behaviors of N,N,N',N',N″,N″-hexaethylnitrilotriacetamide (NTAamide(Et)) with four representative trivalent lanthanides (La3+, Nd3+, Eu3+, and Lu3+) were systematically investigated by using 1H nuclear magnetic resonance (1H NMR), ultraviolet-visible (UV-vis) and fluorescence spectrophotometry, microcalorimetry, and single-crystal X-ray diffractometry. 1H NMR spectroscopic titration of La3+ and Lu3+ indicates that two species of 1:2 and 1:1 metal-ligand complexes were formed in NO3- and ClO4- media. The stability constants of NTAamide(Et) with Nd3+ and Eu3+ obtained by UV-vis and fluorescence titration show that the complexing strength of NTAamide(Et) with Nd3+ is lower than that with Eu3+ in the same anionic medium, while that of the same lanthanide complex is higher in ClO4- medium than in NO3- medium. Meanwhile, the formation reactions for all metal-ligand complexes are driven by both enthalpy and entropy. The structures of lanthanide complexes in the single ClO4- and NO3- medium and the mixed one were determined to be [LnL2(MeOH)](ClO4)3 (Ln = La, Nd, Eu, and Lu), [LaL2(EtOH)2][La(NO3)6], and [LaL2(NO3)](ClO4)2, separately. The average bond lengths of lanthanide complexes decrease gradually with the decrease in ionic radii of Ln3+, indicating that heavier lanthanides form stronger complexes due to the lanthanide contraction effect, which coincides with the trend of the complexing strength obtained by spectroscopic titration. This work not only reveals the thermodynamics and mechanism of the complexation between NTAamide ligands and lanthanides but also obtains the periodic tendency of complexation between them, which may facilitate the separation of trivalent lanthanides from actinides.

Spatial Modulation and Thermal-Induced Spin Phase Transition on the Negative Thermal Expansion of ScF3 with Metal Dopants

Negative thermal expansion (NTE) is an intriguing physical property of solids, which is often related to the lattice, phonons, charges, and spin. However, most of the studies are mainly focused on the phonons, and the spin-related mechanism in open framework compounds remains unclear owing to the lack of more experimental pieces of evidence. Here, based on the first-principles calculations combined with the quasi-harmonic approximation, we carried out studies of the NTE properties of ScF3 with metal dopants to reveal the roles in NTE of both the spatial effects and spin states. For most of the dopants, the NTE coefficient decreases with the decrease of ionic radius, obeying a linear scaling relationship. Interestingly, for magnetic impurities with a spin phase transition from a high spin state to a low spin state, we show that they will exhibit a Jahn–Teller distortion behavior and enhance the longitudinal vibration mode. In turn, the longitudinal vibration mode has a large positive Grüneisen parameter, which can offset the NTE obviously. This work not only proposes a new insight into the NTE mechanism about impurities in ScF3 but also provides an approach to tailor the NTE properties for fluorides with magnetic impurities as well as oxides.

Ionic radius effect on the evolution of the griffiths phase and the magnetocaloric response at low temperature of A2Mn2O7 (A: Fe, Al and La)

In the present paper a comparative research study has been conducted on the magnetic and magnetocaloric response of the materials of A2Mn207 (A: Fe, Al and La) oxides. . The XRD refinement analysis suggests that the A2Mn207 oxides are crystallized in monoclinic structure with space group P2/m. The thermal evolution of the magnetization reveals a ferromagnetic transition and a presence of a Griffith's phase at low temperature. A2Mn207 oxides exhibit a clear correlation between the ionic radius rA3+, in the A-site, and the magnetic transition temperature and that of Griffiths. However, this correlation is not obvious for the value of the universal exponent λ. In addition, the current study reveals an increase in the Relative Cooling Power (RCP) value with a decrease in ionic radius. Furthermore, the magnetocaloric effect (MCE) value, has been found to be exploited over a wide temperature range by increasing the cationic radius rA3+.

Probing the effect of R-cation radii on structural, vibrational, optical, and dielectric properties of rare earth (R=La, Pr, Nd) aluminates

The present study correlates the effect of R-cation radii on structural, vibrational, optical, and dielectric properties of rhombohedral rare earth aluminates RAlO3 (R = La, Pr, Nd). The polycrystalline samples of RAlO3 have been synthesized using sol-gel synthesis technique. Pure rhombohedral phase of RAlO3 samples has been confirmed with X-ray diffraction. Systematic decrements in the lattice parameter, bond length, and bond angle have been observed, giving rise to structural distortion due to decrease in ionic radii of R-cation. The phononic properties of RAlO3 have been investigated through Raman spectroscopy, where the degree of distortion of AlO6 octahedra can be analyzed with the peak position of Eg and A1g modes. An increase in the energy bandgap with decreasing R-cation radii shows an interconnection with the decrease in Al–O bond length. Interestingly, the decreasing dielectric constant with decreasing ionic radii of R-cation has been correlated with the difference in electronegativity of cation(R3+)-anion(O2−) pair. Also, a positive linear relationship between dielectric constant and energy bandgap has been investigated using Penn model.

Stable Lanthanide Metal-Organic Frameworks with Ratiometric Fluorescence Sensing for Amino Acids and Tunable Proton Conduction and Magnetic Properties.

Four new isostructural lanthanide metal-organic frameworks (MOFs), namely {[Ln(DMTP-DC)1.5(H2O)3]·DMF}n [H2DMTP-DC = 2',5'-dimethoxytriphenyl-4,4″-dicarboxylic acid; LnIII = EuIII (1), GdIII (2), TbIII (3), and DyIII (4)], have been synthesized and characterized. Single-crystal structure analysis reveals that 1-4 are three-dimensional Ln-MOFs with rich H-bonding of coordinated H2O molecules in the network channels. The X-ray diffraction patterns indicate that Ln-MOF 1 displays good stabilities in organic solvents and aqueous solutions with distinct pH values. Both 1 and 3 show characteristic emission of LnIII ions. Ln-MOF 1 can be used as a ratiometric fluorescence sensor for arginine and lysine in aqueous solution, and the detection limits are 24.38 μM for arginine and 9.31 μM for lysine. All 1-4 show proton conductivity related to relative humidity (RH) and temperature, and the maximum conductivity values of 1-4 at 55 °C and 100% RH are 9.94 × 10-5, 1.62 × 10-4, 1.71 × 10-4, and 2.67 × 10-4 S·cm-1, respectively. The value of σ increases with the decrease in ionic radius, indicating that the radius of the LnIII ions can regulate the proton conductivity of these MOFs. Additionally, 2 exhibits a significant magnetocaloric effect (MCE) with a magnetic entropy change (-ΔSm) of 18.86 J kg-1 K-1 for ΔH = 7 T at 2 K, and 4 shows weak field-induced slow relaxation of magnetization. The coexistence of good fluorescence sensing capability, attractive proton conductivity, and relatively large MCE in Ln-MOFs is rare, and thus, 1-4 are potentially multifunctional MOF materials.

Evidence for Participation of 4f and 5d Orbitals in Lanthanide Metal–Ligand Bonding and That Y(III) Has Less of This Complex-Stabilizing Ability. A Thermodynamic, Spectroscopic, and DFT Study of Their Complexation by the Nitrogen Donor Ligand TPEN

The formation constants (log K1) of lanthanide(III) (Ln) ions [except for Pm(III)] and the Y(III) cation have been measured with the ligand TPEN (N,N,N',N'-tetra-2-picolylethylenediamine). These log K1 values show a typical variation with ionic radius, with a local maximum at Sm(III) and a local minimum at Gd(III), with an overall increase in log K1 from La(III) to Lu(III) as the ionic radius decreases. The log K1 for the Y(III)/TPEN complex is much lower than expected from its ionic radius, while the literature log K1 for Am(III) is much higher. The latter effect is thought to be due to greater covalence in the M-L (metal-ligand) bond than for Ln(III) ions: the low log K1 for Y(III) is interpreted as being due to lower covalence. The f → f transitions in the Nd(III) and Pr(III) complexes were examined for effects that might indicate the participation of f orbitals in M-L bonding. The intensity of the f → f transitions in the Nd(III)/TPEN complex was greatly increased compared to that of the Nd3+ aqua ion, which appeared to be due to additional sharp peaks, possibly parity forbidden transitions where parity rules were broken by covalence in the M-L bond. The Pr(III)/TPEN complex showed that all of the f → f transitions shifted to longer wavelengths by some 5 nm, with modest increases in intensity. The effects seen in the f → f transitions of Nd(III) and Pr(III) with TPEN with its six nitrogen donors were present to a much smaller extent in the EDTA and other complexes with fewer nitrogen donors. The changes in the f → f transitions of the TPEN complexes of Er(III) and Ho(III) were small, suggesting a smaller contribution of f orbitals to M-L bonding in these heavier Ln(III) ions. The intense Laporte allowed f → d transitions in Ce(III) complexes show large shifts to longer wavelengths as complexes of, for example, EDTA with increasing numbers of nitrogen donors, suggesting the participation of both f and d orbitals, or either, in M-L bonding. The nature of M-L bonding in M(III)/TPEN complexes was further investigated via density functional theory calculations.

Preparation and Characterization of Nanosized Substituted Perovskite Compounds with Orthorhombic Structure

In this work, five substituted perovskite such as (Gd0.9Sr0.1) Mn0.8Co0.2O3, Tb0.8Sr0.2FeO3, Gd0.6Sr0.4RuO3, SrCe0.95Y0.05O3, and Mn0.6Co0.4SnO3 were synthesized by tartrate and hydroxide precursor method. The resulting samples were characterized by inductively coupled plasma spectroscopy, energy dispersive X-ray analysis, infrared spectroscopy, thermal analysis, X-ray powder diffraction, transmission electron microscope (TEM), selected field of electron diffraction (SAED), d.c. electrical conductivity, Hall effect, dielectric measurements, and low-temperature magnetization measurements. The X-ray diffraction pattern for all compounds was indicated the formation of single-phase perovskite with orthorhombic structure except Tb0.8Sr0.2FeO3 and Mn0.6Co0.4SnO3 perovskite. These compounds showed a cubic and rhombohedral structure, respectively. The lattice parameter and the unit cell volume slightly decreased as ionic radii decrease in agreement with the lanthanide contraction. The average size of cation ˂ RA ˃, mismatch factor (σ2), and tolerance factor (t) gives the combined effects of disorder and inhomogeneity in these compounds. The average particle size determined from TEM was in the range of 22 to 77 nm for all compounds. The temperature dependence of electrical conductivity for all compounds showed a definite break in 500 K to 610 K. except the Gd0.6Sr0.4RuO3 compound, which corresponds to semiconducting behavior. While the Gd0.6Sr0.4RuO3 sample shows a metallic-like semiconductor. The thermoelectric power and Hall effect measurements for all compounds were n-type semiconductivity except the SrCe0.95Y0.05O3 compound. It showed p-type semiconductivity. The frequency dependence of the dielectric constant and dielectric loss in these substituted perovskites were discussed using the Maxwell-Wagner model. Magnetic studies showed that the thermo-magnetic irreversibility for all compounds.

Thermochemistry of stoichiometric rare earth oxyfluorides REOF

AbstractRare earth oxyfluorides (REOF) have potential applications in luminescent devices and energy storage and are important for synthesis and properties of RE‐doped oxyfluoride glasses. This study evaluates the thermodynamic properties of stoichiometric REOF with varying RE (RE = La, Nd, Gd, Ho, Y, and Yb) elements using high temperature oxide melt solution calorimetry and investigates the phase transitions of YbOF by differential scanning calorimetry. The formation enthalpies from binary oxides and fluorides are exothermic and become less exothermic with the decrease of ionic radius of RE3+, showing that REOF compounds are energetically stable relative to equal molar mixtures of RE2O3 and REF3 and the RE–O interactions contribute to most of their thermodynamic stabilities. Different from REOF with large RE ions (La–Er and Y) having the rhombohedral phase, REOF with small cations (e.g., Yb) possesses the monoclinic structure as the more energetically stable phase at room temperature. However, the slow transition between the monoclinic and cubic phases easily generates the rhombohedral phase, which is favored by kinetics.

Influence from the electronic shell structure on the range distribution during channeling of 40–300 keV ions in 4H-SiC

Ion implantation is performed in 4H-SiC with 11B, 27Al, 31P, 51V, 71Ga, and 75As ions using energies between 40 and 300 keV at various fluences along the [000-1] or the ⟨11-2-3⟩ axes. Secondary ion mass spectrometry is utilized to determine the depth distribution of the implanted elements. A Monte Carlo binary collision approximation (MC-BCA) code for crystalline targets is then applied to explain the influence of the electronic shell structure on electronic stopping and the obtained channeled ion depth distributions. The results show that, as the atomic number increases in a row of the periodic table, i.e., as the ionic radius decreases and the electron clouds densify, the interaction with the target electrons increases and the range is reduced. The decreased range is particularly pronounced going from 27Al to 31P. The reduction in channeling depth is discussed in terms of electronic shells and can be related to the ionic radii, as defined by Kohn–Sham. It is shown that these shell effects in channeled implantations can easily be included in MC-BCA simulations simply by modifying the screening length used in the local treatment of electronic stopping in channels. However, it is also shown that, for vanadium ions with an unfilled d-shell, this simple model is insufficient to predict the electronic stopping in the channels.

Rietveld Study of the Changes of Phase Composition, Crystal Structure, and Morphology of BiFeO3 by Partial Substitution of Bismuth with Rare-Earth Ions

BiFeO3 is an interesting material due to its multiferroic properties. It attracts attention due to its potential applications in spintronics and in microelectronics for data storage, among others. Single-phase bulk material from BiFeO3 is difficult to synthesize. The kinetics of perovskite phase formation most often leads to the presence of impurity phases. It has been shown that low levels of replacement of Bi with rare earth ions lead to stabilization of the perovskite phase. In the present work, Rietveld refinement of the crystal structure based on powder X-ray diffraction patterns was applied to study the influence of partial substitution of Bi by rare-earth (RE) elements with different ionic radii on structural and morphological properties of the ferrite phase. Substitution by large RE ions was found to preserve the rhombohedral symmetry of BiFeO3, whereas substitution by smaller RE ions led to the coexistence of two polymorphic perovskite phases with rhombohedral R3c and orthorhombic Pnma symmetries. The unit cell parameters as well as the interatomic distances and angles, not only around the A cation but also around the iron ions, were influenced by the substitution. The mean crystallite and particle size decreased with the decrease of ionic radius of substituting RE ion.

Structural and Magnetic Tuning of LaFeO3 Orthoferrite Substituted Different Rare Earth Elements to Optimize Their Technological Applications

Lanthanum partially substituted rare earth (RE) elements to form RE0.7La0.3FeO3; RE = Ce, Pr, Nd, Sm and Gd) nanoparticles. They were synthesized using the citrate–nitrate auto-combustion method. The crystal structure and microstructure were refined by applying Rietveld profile refinements using the Maud Program. The morphology, magnetic and optical properties of the inspected samples have been explored using HRTEM, VSM, and UV–Vis diffuse reflectance, respectively. The prepared-samples distortion increases as the substituted RE ionic radius decreases. Iron spins of RE orthoferrite samples are known to be ordered Anti-ferromagnetically (AFM). They also possess weak ferromagnetism due to the Dzyaloshinskii-Moriya interaction. This feeble ferromagnetism is reflected in their soft behavior, whereas Sm0.7La0.3FeO3 sample exhibits the butterfly shape hysteresis loop. The remnant magnetization, saturation magnetization, and coercivity are relatively small, but sometimes impressively, enhanced through Lanthanum-rare-earth substitution. Introducing rare earth ions into LaFeO3 decreases the Fe–O–Fe angle and the consequent reduction of the super exchange interaction. In particular, the coercivity of Sm0.7La0.3FeO3 is remarkably improved relative to the parent sample. It has the largest coercivity of all the prepared nanoparticles. Due to the aforementioned substitution, a slight reflectance edge red shift is observed in the spectra. The relation between the magnetic properties of the investigated samples and the ionic radii of RE was investigated and discussed. The experimental results of this work can provide fundamental support for the research and development of multiferroic materials.

Synthesis, structural and physical properties of some rare-earth doped nickel chromites

A systematic investigation of structural, magnetic and transport properties of NiCr1.9R0.1O4 (R = Eu, Dy and Ho) has been undertaken. Rietveld analysis of powder X-ray diffraction data revealed that all the compounds crystallize in the cubic symmetry with space group having small volume fraction of orthorhombic phase RCrO3. Both a and V decreases with the substitution of heavier rare earth ion which is consistent with the decrease in ionic radius of rare earth ion. Temperature dependent magnetization studies showed that all our investigated compounds have negative value of Weiss constant (Θ) indicating the dominance of anti-ferromagnetic interactions in the samples. The phases are semi-conductors and the conduction mechanism was dominated by Arrhenius model in the high temperature paramagnetic semiconducting region.

Correlation between experimental and theoretical study of scheelite and wolframite-type tungstates

Structural and optical properties of AWO4(A=Ba, Sr, Ca, Mg, and Zn) ceramics were investigated. The structural analysis confirmed the scheelite-type tetragonal structure for (A=Ba, Sr and Ca)WO4 and wolframite-type monoclinic structure for (A=Zn and Mg)WO4 compounds. The experimentally observed optical band gap (Eg) found to be in the range of 4.17–5.92 eV agree with those calculated with the help of density functional theory. A decrease in band gap value with the decrease in ionic radii of A2+ in the AWO4 compound was observed. An intense blue-green photoluminescence emission was observed for these materials and correlated with Eg. The environmental factor he calculated by complex chemical bond theory has been correlated with the broadening of PL excitation bands. The excitation spectra revealed that there subsists a negative relation between he and position of energy levels.