Space Group Pbnm Research Articles

Structural characterization and electrical/electrochemical studies of Nd1-xBaxCo1-y(Fe, Ti)y O3-δ (0 ≤ x ≤ 0.3, y = 0, 0.2) materials as cathode for SOFCs application

Perovskite oxide powders of Nd1-xBaxCo1-y (Fe, Ti)y O3-δ (0 ≤ x ​≤ ​0.3, y ​= ​0, 0.2) were synthesized by combustion technique and investigated as cathode materials for SOFCs application. The Rietveld refinement of the XRD data confirms the formation of single phase orthorhombic perovskite structure of Pbnm space group within the compositions (0 ​≤ ​x ​≤ ​0.1, y ​= ​0, 0.2). The microstructural studies revealed the grains generated are irregular in shape and non uniform in size in the micrometer range. The X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of mixed valence states of Co3+/Co4+, Fe3+/Fe4+, Ti4+/Ti3+ and O-Lattice/O-Chemisorbed/O-physisorbed species. The measured average CTE values are varies from 18–25 ​× ​10−6 ​K−1 in the temperature range 200–900 ​°C for all the synthesized samples. The electrical conductivity values are found to be 252 Scm−1, 308 Scm−1, 157 Scm−1 at 700 ​°C for the compositions Nd0.9Ba0·1CoO3-δ (NBC 0.1), Nd0.9Ba0·1Co0·8Fe0·2O3-δ (NBCFO), Nd0.9Ba0·1Co0·8Ti0·2O3-δ (NBCTO), respectively. XRD analysis reveals no chemical reactivity for the compositions NBCFO, NBCTO with 20 ​mol% gadolinium doped ceria oxide (Ce0.8Gd0.2O2−δ) electrolyte material after firing at 1200 ​°C for 8 ​h. The area specific resistances (ASR) were calculated for the symmetrical cells and are found to be 0.67 ​Ω ​cm2, 1.07 ​Ω ​cm2 at 850 ​°C for the NBCFO, NBCTO compositions, respectively. Among the compositions evaluated Nd0.9Ba0·1Co0·8Fe0·2O3-δ showed highest total electrical conductivity ~308 Scm−1 and lowest ASR value ~0.67 Ωcm2 compared to all other compositions. Hence the result suggests the synthesized Nd0.9Ba0·1Co0·8Fe0·2O3-δ composition could be a promising cathode material for SOFCs application.

Resurgence of ferromagnetic behavior coupled with Griffiths singularity in the electron doped La0.3Ca0.7MnO3 compound following the creation of oxygen deficiency

We report the effect of the oxygen deficiency on the structural and magnetic properties of La0.3Ca0.7MnO3-δ (0 ≤ δ ≤ 0.2) perovskites. The parent compound (δ = 0) was prepared by the solid- state reaction. This sample was used to prepare the oxygen deficiency compounds using iron as oxygen absorber. The X-ray diffraction (XRD) data have been analyzed by the Rietveld method using the FullProf program. We have noticed that all samples crystallized in the orthorhombic structure with Pbnm space group. Magnetic measurements show that the parent compound La0.3Ca0.7MnO3 exhibits a paramagnetic behavior at high temperature and an antiferromagnetic state (AFM) coupled with charge ordering (CO) at low temperature. With oxygen deficiency a magnetic transition from paramagnetic (PM) to ferromagnetic (FM) state is fixed at decreasing temperature. The compound with δ = 0.15 exhibit a PM-FM transition when decreasing the temperature at TC = 191 K with persistence of the charge ordering state at low temperatures below 81 K. The compound with δ = 0.2 exhibit a PM-FM transition when the temperature decreases at TC = 134 K with vanishing of the CO state at low temperature. Further investigations of the magnetization measurements reveal features consistent with the appearance of Griffiths phase (GP) in the sample with δ = 0.15 and δ = 0.2 which proves the existence of ferromagnetic clusters in the paramagnetic domain below TG = 250 K and 234 K for δ = 0.15 and δ = 0.2 respectively.

Solution Combustion Synthesis of Rare Earth Orthoferrite Nanoparticles: a Comparative Study on Multiferroic Properties of Er–FeO3 vs (La,Yb)FeO3

Rare earth (RE = La, Er, and YbFeO3) ferrites are prepared from their nitrate precursors using the solution combustion method. Structural analysis using powder X-ray diffraction (XRD) technique indicates that the synthesized La-, Er-, and Yb–FeO3 perovskite nanoparticles have pure phase orthorhombic super unit cells. The XRD patterns of Er–FeO3 and Yb–FeO3 are found to be indexed in Pbnm (62) space group with cell dimensions in the range of ao = 5.2611–5.2784 A, bo = 5.5729–5.5898 A, and co = 7.596–7.6002 A, while the space group of Pnma (62) with ao = 5.5688 A, bo = 7.8523 A, and co = 5.5542 A are obtained for LaFeO3. Surface morphological studies show aggregated spherical-shaped nanoparticles having an orthorhombic crystal structure with an average particle size of ~ 50 nm. Magnetic properties of all the three RE ferrite synthesized in this work exhibit antiferromagnetic behavior. The study of dielectric properties of all the three RE ferrites shows dispersive behavior at low frequencies with low loss. Temperature-dependent dielectric studies confirm that the antiferromagnetic-paramagnetic transition temperature appears at 445 K. A larger P-E loop with a squareness ratio of 1.583 for ErFeO3 orthoferrites suggests that it is more advantageous than LaFeO3 and YbFeO3 for making modern electronic devices.

Temperature-Dependent Dielectric and Magnetic Properties of Scandium-Substituted HoFeO3 Nanoparticles

In the present work, the HoFeO3 and HoFe0.8Sc0.2O3 nanoparticles prepared by the solution combustion method have been studied to understand their structural, dielectric, and magnetic properties. The refined X-ray diffraction pattern (XRD) confirms the single-phase formation with orthorhombic structure having space group Pbnm (D2h16). The average crystallite size observed in nanometer for both samples and field emission-scanning electron microscopy (FE-SEM) confirms that the grain sizes were about in the region of micrometer. The temperature-dependent dielectric parameters were obtained such as the real part of the dielectric constant, dielectric loss tangent, and AC conductivity studied with frequency. The real part of the dielectric constant is high at lower frequencies and it is constant at higher frequency region. This sort of dielectric behavior can additionally be clarified based on various polarization mechanisms happening in various frequency ranges. The dielectric loss tangent increases with temperature. For both samples, the AC conductivity increases with temperature and frequency. The magnetic transitions and magnetic parameters were studied through the temperature-dependent susceptibility and field-dependent magnetization. For HoFeO3 and HoFe0.8Sc0.2O3, the Neel temperature transition at 5 and 8 K was observed which is characterized to the antiferromagnetic nature. The M-H loop confirms the antiferromagnetic nature at 5 K for HoFeO3 and the ferromagnetic nature at 5 K for HoFe0.8Sc0.2O3. Overall, it confirms the changes of nature from antiferromagnetic nature to ferromagnetic nature after substitution of Sc3+ on HoFeO3.

Magnetic properties of EuFe0.5Mn0.5O3 complex perovskite

In this study, we determined the crystallographic, magnetization and electrical resistivity properties of a EuFe0.5Mn0.5O3 complex perovskite produced using a combustion synthesis method. The sample crystallized as an orthorhombic perovskite belonging to the Pbnm space group. Magnetization measurements indicated spin reorientation at 206 K and weak ferromagnetic-like ordering at low temperatures. Determining the magnetization as a function of the magnetic field demonstrated the presence of magnetic order, even at room temperature. Resistivity measurements indicated the existence of a small polaron conduction mechanism at high temperature.

Effect of La3+ substitution on the physical properties of CaTiO3–0.15KNbO3-based lead-free ceramics

Polycrystalline samples $$ {\text{Ca}}_{0.85 - x} {\text{La}}_{x} {\text{K}}_{0.15 - x} {\text{Ti}}_{0.85} {\text{Nb}}_{0.15} {\text{O}}_{3} $$ (x = 0 and 0.05) were synthesized by the conventional solid-state reaction method. The X-ray diffraction showed that these compounds crystallized, at room temperature, in the orthorhombic structure with Pbnm space group. The scanning electron microscopy analysis showed a decrease in grain size with the La3+ substitution rate. Through the diffuse reflectance spectroscopy, we extracted the band gap energy, which decreases with the addition of La3+, which implies the improvement of the semiconductor behavior. Filament, a study on the dielectric properties, in the frequency range from 1 kHz to 1 MHz, of our samples, shows that the substitution of calcium and potassium by lanthanum in A site introduced an improvement to these properties and the appearance of a new transition.

Enhanced properties of the chemically prepared Gd-doped SrSnO3 thin films: Experimental and DFT study

Abstract In the present paper, we investigate in detail the Gd doping effect on the properties of the chemically prepared SrSnO3 thin films. Unlike previous preparation attempts that utilized a very sophisticated vacuum methods and high annealing temperature, a very simple path was followed by employing the simple ultrasonic spray method with an annealing process at only 800 °C, resulting a high quality films. The crystallographic identification using XRD analysis confirmed the formation of SrSnO3 phase crystallizing in the orthorhombic structure with Pbnm space group. The percentage of the gadolinium doping affected the obtained structure majorly after passing the 5%. Structural properties were further investigated with Raman and FT-IR analysis confirming the results obtained by the XRD. Morphology and chemical composition of Gd-doped SrSnO3 thin films were evaluated using a field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectrometer (EDX). The surface scanning shows an amelioration in the morphology of the films as dopant ratio increased, while EDX and mapping analysis confirmed the purity of the resulted films with the presence of the dopant element. The Gd-doping effect on the optical properties was noticed through the decrement of the transparency of the films and the dropping of the band gap from 3.88 to 2.85 eV for the 7% of dopant content. The first principles calculations revealed a major modifications on the electronic and optical properties of SrSnO3 generated by the 4f state of Gd. A remarkable variation of the band gap was measured decreasing from 4.08 eV to 2.17 eV, which emphasizes our experimental findings.

Study of La(Fe, Zn)O3 on the structural properties prepared by sol-gel method

Partial substitution of other metallic ions at La and/or Fe sites of LaFeO3 had been applied to modify the structural properties and for enhancing the properties of its material. In this present work, we prepared LaFeO3 by replacing a portion of Fe3+ with Zn2+ with x = 0.03; 0.05; and 0.07 to study the effect on the structural which prepared by sol-gel method. The samples were identified by X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF), Fourier Transform Infrared (FTIR) spectra, Raman spectroscopy, and Ultraviolet-Visible Diffuse Reflectance spectroscopy (UV-Vis DRS). XRD pattern showed all of the samples formed in single crystal and are having an orthorhombic structure with space group Pbnm. The lattice parameters were found to be slightly increased with the increase of Zn concentration. The result of FTIR spectra and Raman spectra also show further information about the formation of LaFeO3 with the distortion due to the replacement of Zn2+ into Fe3+. The absorbance and reflectance of samples are measured using UV-Vis DRS and the energy band gap of LaFe1-x Zn x O3 ( x = 0.03; 0.05; and 0.07) are determined by Tauc plot using Kubelka-Munk function and was found the energy band gap slightly decreased as the concentration of Zn2+ increased.

Effect of Bi Substitution on Structural and AC Magnetic Susceptibility Properties of Nd1−xBixMnO3

This study synthesizes the neodymium-based manganites with Bi doping, Nd1−xBixMnO3 (x = 0, 0.25 and 0.50) using the solid-state reaction route. The crystal structural, morphological and magnetic properties were determined using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and AC magnetic susceptibility. The Rietveld refinement confirmed that the compounds were in the single-phase orthorhombic structure of the NdMnO3 with Pbnm space group and lattice parameter b increased with doping from 5.5571 (x = 0) to 5.6787 (x = 0.5). FTIR spectra showed that absorption bands were located within the range of 550–600 cm−1, which corresponded to the Mn–O stretching vibration. FESEM exhibited homogenous compound. The AC magnetic susceptibility measurement studies showed a strong antiferromagnetic (AFM) to paramagnetic (PM) transition existed at 76 K, 77 K and 67 K for samples (x = 0, 0.25 and 0.50), respectively.

Charge transport mechanism and percolation model in La0.75Ca0.25−xNaxMnO3 (0 ≤ x ≤ 0.10) manganites

In this communication, La0.75Ca0.25−xNaxMnO3 (0 ≤ x ≤ 0.10) samples were synthesized by the Flux method and their structural and electrical properties were systematically undertaken. X-ray diffraction of the samples showed an orthorhombic structure with a Pbnm space group. Furthermore, to get a better understanding of the electrical properties, the resistivity ρ(T) as a function of temperature was measured by a standard four-probe method. The maximum resistivity values decreased and the insulator–metal transition temperature (TM–SC) increased with increasing magnetic field. At low-temperature region (T TM–SC) region, the transport mechanism was explained using the adiabatic small polaron hopping and the variable-range hopping models. Then, to get insights into the change in the resistivity plots, in entire temperature, ρ(T) was fitted by the percolation model. Interestingly, it is important to note that the activation energy (Ea) decreased with increasing Na+ content, which indicates the enhancement of the double-exchange (DE) interaction. Moreover the magnetoresistance (MR %) effect was studied.

Investigation of alteration in physical properties of dysprosium orthochromite instigated through cobalt doping

Abstract We report the systematic investigations on DyCr1–xCoxO3 (0 ≤ x ≤ 0.3) samples prepared through sol-gel auto combustion process. Rietveld refinement of the powder x-ray diffraction patterns assures the formation of mono-phase orthorhombic structure with space group Pbnm. In order to get an obvious view about the effect of substitution of Cr3+ with Co3+ ions on crystallographic parameters of these samples, the tilt angles, cell and orthorhombic distortions were calculated. The average crystallite sizes and lattice strain as computed from the Williamson-Hall analysis are found to rise with the increase in Co content. The porosity of the synthesized samples lies in between ∼30 and 38%. The Fourier transform infrared (FTIR) spectra of these samples affirm the formation of desired crystal structure. Field emission scanning electron microscopy (FESEM) images exhibit the existence of polycrystalline microstructure. The energy dispersive x-ray (EDX) analysis assures the elemental compositions of the prepared samples. UV/Visible spectroscopy is utilized to estimate the energy band gap, Urbach energy and threshold wavelength. The energy band gap reduces whereas Urbach energy and threshold wavelength enhance on increasing the cobalt content. Dielectric responses of these samples have been analysed in view of “universal dielectric response” model. AC conductivity increases with the increase in frequency and that affirm the small polaron hopping type of conduction mechanism in the investigated frequency range. The relaxation peaks appear in imaginary part of impedance spectra shift toward lower frequencies with the increase in Co concentration which indicates the higher values of relaxation time in the doped samples. Differential thermal analysis reveals the structural transitions and improved thermal stability of the Co doped samples.

Structural distortions in rare-earth transition-metal oxide perovskites under high pressure

Owing to their structural complexity and wide range of possible chemical combinations, perovskite oxides exhibit many technically important physical properties. Pressure is a thermodynamic parameter which is useful for tuning physical properties; however, the response of the complex crystal structure to high pressure has not been thoroughly studied and rationalized. This study focuses on in situ high-pressure x-ray diffraction of the orthorhombic perovskite oxides ${A}^{3+}{B}^{3+}{\mathrm{O}}_{3}$, commonly found for the rare-earth transition-metal oxides of the $RM{\mathrm{O}}_{3}$ formula. Each of the four families of $RM{\mathrm{O}}_{3}$ ($M=\mathrm{Ti}$, Cr, Mn, Fe) perovskites in this study all crystallize in the same orthorhombic perovskite structure with the Pbnm space group. The lanthanide contraction in these materials leads to varying degrees of orthorhombic distortions that are primarily associated with octahedral site rotations. The pressure-induced change of the lattice parameters demonstrates an evolution from a suppression to an enlargement of the orthorhombic distortion for substitution of the rare-earth element from $R=\mathrm{La}$ to Lu in $RM{\mathrm{O}}_{3}$ perovskites. This unusual crossover of the lattice parameters' dependence on pressure contradict the results from first-principles calculation but can be rationalized by the intrinsic distortion of the perovskite structure.

Self-Activated Green-Yellow Emitting Gd₂CaZnO5 Phosphor for Efficient Ultra-Violet Light-Emitting Diodes.

A new self-activated green-yellow emitting Gd₂CaZnO5 (GCZO) phosphor was synthesized using solid-state reaction method at high-temperature. XRD analysis confirmed the orthorhombic structure of the sample with the Pbnm space group. SEM micrographs reveal the irregular morphology with micron sized particles. Detailed photoluminescence (PL) analysis revealed that the excitation of the phosphor lies in the UV range (˜377 nm) with the related broad green-yellow emission centered at 530 nm. The broad band emission ranging from ˜450 nm to 650 nm can be attributed to the surface defects and oxygen vacancies. The calculated luminescence decay lifetime for the optimized phosphor was found to be 2.925 μs. Furthermore, the color-coordinate (x, y) were calculated and found to be (0.44, 0.45), which lies in the green-yellow (˜540 nm) region of the electromagnetic spectrum. The values of color coordinates and Color correlated temperature of 3289 K support the synthesized phosphor for the emission of warm white-light. These results perfectly established the suitability of this green-yellow emitting GCZO phosphor for Ultra-Violet Light-Emitting Diodes (LEDs) excited white-LED applications.

Room temperature dual ferroic behavior induced by (Bi, Ni) co-doping in nanocrystalline Nd0.7Bi0.3Fe1−xNixO3 (0 ≤ x ≤ 0.3)

Nanocrystalline samples of Nd0.7Bi0.3Fe1−xNixO3 (x = 0, 0.1, 0.2, and 0.3) are synthesized using sol-gel auto-combustion process to investigate their structural, electrical, magnetic, and thermal properties. Phase purity and crystallinity of the samples are determined through x-ray diffraction (XRD) data. XRD patterns along with Rietveld refinement reveal orthorhombic structure with Pbnm space group. Unit cell parameters, bond angles, and bond lengths for all the samples have been determined. Crystallite size calculated by Scherrer equation is found to be in the range of 15–21 nm. The characteristic bands in the FTIR spectra further confirm the formation of our samples. FE-SEM images indicate the homogeneous distribution of particles on large scale and Ni-doped samples show some wall-like nanostructure in the morphology. EDX spectra confirm the elemental composition without any impurity element. The polarization versus electric field (P-E) and magnetization versus magnetic field (M-H) loops exhibit the multiferroic nature of the material. The sample with concentration x = 0.2 shows the maximum value of polarization (Pm) while maximum magnetization is achieved for x = 0.1 concentration. The specific heat capacity (Cp), endothermic, and exothermic peaks of the materials have been determined in the broad temperature range with the help of DTA measurements in the controlled nitrogen atmosphere. The Neel temperature of the parent system is found to be 742 K and that decreases up to 573 K on Ni doping.

Transport Properties of Transitional Metal (Ni2+) Doped La0.67Ca0.33MnO3 Rare-Earth Manganites

The crystalline samples of La0.67Ca0.33Mn1-xNixO3 (x = 0, 0.05, and 0.1) manganites were prepared by conventional solid-state reaction method. The analysis of X-ray diffraction spectra revealed that all the prepared samples are single phased in nature and have acquired orthorhombic structure with space group Pbnm. Temperature-dependent dc resistivity measurements infer metallic nature of the samples in the lower temperature region (T > 50 K) where metal to insulator transition (TMI) occurs at temperature 238 K, 204 K, and 187 K for x = 0, 0.05, and 0.1, respectively. For the temperature below 50 K, a kind of transition from paramagnetic insulator to the ferromagnetic metallic phase was observed in all the materials. The application of magnetic field of 8 T indicates the shift of TMI toward the higher temperature region with high reduction in resistivity due to suppression of any thermal agitations present. The resistivity data analysis for conduction mechanism above 50 K infers that the grain/domain boundary scattering processes play a dominant role in the the metallic region. However, the analysis of the region below 50 K infers that weak localization effect is the responsible factor in conduction phenomena. Isothermal at 300 K for magnetoresistance study conveys that the pristine La0.67Ca0.33MnO3 manganite exhibits larger MR effect with rise in magnetic field compared to doped ones.

Dielectric relaxation, magneto-dielectric coupling, and pyrocurrent anomaly in point defect controlled HoCrO3

HoCrO3, a member of the rare-earth chromate family, is known to exhibit an orthorhombic structure with Pbnm space group in bulk at room temperature. We have employed the pressure driven powder consolidation technique, spark plasma sintering, for synthesizing HoCrO3 powder-compact, which exhibits a superior quality with fewer defects over that synthesized by conventional solid-state sintering (resulting in a large reduction of charge carrier mediated extrinsic dielectric contribution). The powder compact shows magneto-dielectric coupling but does not exhibit a detectable ferroelectric phase in the range of 50 K to 300 K. Low temperature Raman spectra show structural distortions below 250 cm−1, indicating Ho ion displacements. Temperature evolution of the crystal structure using synchrotron x-ray diffraction reveals a probable structural phase transition below 240 K. Pyrocurrent measurement, together with synchrotron x-ray diffraction analysis, further points to a magneto-structural transition at 100 K.

Structure evolution and improved microwave dielectric characteristics in CaTi1-x(Al0.5Nb0.5)xO3 ceramics

Enhanced microwave dielectric characteristics in (Al0.5Nb0.5)-co-substituted CaTiO3 ceramics were examined by means of structure evolution. CaTi1-x(Al0.5Nb0.5)xO3 solid solutions with orthorhombic structure in space group Pbnm were attained throughout the entire composition range x ≤ 0.75. The near-zero temperature coefficient of resonant frequency τf and significantly improved quality factor Qf value were achieved, while a tunable medium dielectric constant ϵr was achieved in the present ceramics. τf was tuned from 750 ppm/°C to 5 ppm/°C and became −80 ppm/°C finally (at x = 0.75), the Qf was first increased from 11,500 GHz up to 49,700 GHz due to the stable perovskite structure with increased bond strength and degree of covalency (%) and then slightly decreased to 43,100 GHz at x = 0.75. The best combination of significantly improved microwave dielectric characteristics was achieved at x = 0.45 (ϵr = 55.1, Qf = 49,700 GHz, τf = 5 ppm/°C). The present ceramics showed the great application potential in future wireless communication systems.

Gd doping effect on structural, electrical and dielectric properties in HoCrO3 orthochromites for electric applications

Abstract In this work, we investigate the structural, electrical and dielectric properties of HoCrO3, Ho0.9Gd0.1CrO3 and HoCr0.9Gd0.1O3 orthochromites successfully synthesized by the sol-gel process. Our samples were characterized by scanning electron microscopy, energy dispersive and X-ray diffraction (XRD) at room temperature. The XRD analysis shows that the samples crystallize in the orthorhombic system with the Pbnm space group. Depending on frequency in the range [40–107Hz] and temperature in the range [160–440K], the electrical properties were explored by impedance spectroscopy measurements. The obtained results demonstrate that the DC electrical conductivity decreases by doping HoCrO3 with Gd in A-site and increases if Gd occupies the B-site of the perovskite. The parent sample shows a semiconductor behavior until 400K where a transition to a metallic one appears. For doped samples, the transition temperature is estimated at 420K. The AC conductivity measurements can be described by the Jonscher power law and the conduction mechanism can be related to the cationic disorder. Electrical results reveal that the contribution of grains and grain boundaries in the conduction process differs according to the site of the doping by gadolinium. Furthermore, the impedance plots were well described by an adequate equivalent circuit taking into account the contributions of grains and grain boundaries. Colossal dielectric permittivities of the order of 105 F/m are obtained and were attributed to the Maxwell-Wagner interfacial effect. The dielectric losses can be described by Giuntini law and the dielectric relaxation phenomenon is shown to be obscured by the DC-conductivity process. The capacitance values are in the order of 10−2 μF for all studied compounds. These results can conduct the use of our compounds towards the electronic devices industry.

Influence of Mn doping on dielectric properties, conduction mechanism and photocatalytic nature of gadolinium-based orthochromites

The samples of manganese (Mn)-doped gadolinium chromite [GdCr1−xMnxO3 (x = 0, 0.1, 0.2 and 0.3)] are prepared through sol–gel auto combustion route. The influence of Mn-doping in GdCrO3 is studied in respect of structural, dielectric, electrical and photocatalytic studies. Raman spectra assured the formation of single-phase orthorhombic structure with Pbnm space group and Raman vibration modes for GdCrO3 shift on Mn doping which may be attributed to the influence of the lattice strain, defects, and crystallite size. Dielectric constant (e′), dissipation factor (tanδ) and AC conductivity (σac) are investigated as a function of frequency as well as temperature. Dielectric constant, energy dissipation factor and AC conductivity of pristine sample GdCrO3 show relatively higher values but these values decrease with the increase in Mn doping. The dielectric constant as a function of temperature for all the investigated samples peaks around 250 °C which may be attributed to the high temperature phase transformation. These peaks are observed to shift toward lower temperature with the increase in Mn-doping. The enhancement in AC conductivity is noticed for all the samples with the rise in temperature for the probing frequencies. The non-overlapping small polaron tunneling (NSPT) and correlated barrier hopping (CBH) models dominate the conduction mechanism in these samples. An increase in the experimental values of the hopping energy is observed with the increase Mn concentration for CBH as well as NSPT models. A systematic reduction in activation energy with frequency is noticed for all the samples except for GdCr0.9Mn0.1O3 sample. Real (Z′) and imaginary (Z″) values of impedance are found to reduce with the increase in frequency up to a certain limiting range and then become almost frequency independent at higher frequencies. Nyquist plots of the samples show single semicircular behaviour that indicates the dominance of grain boundary resistance as compared to grain resistance in this system. The grain and grain boundary resistances are determined, with the help of equivalent circuit designed using Zview software, to study the contribution of the grains and grain boundaries to the conductivity. Photo-degradation of Congo red dye under visible light irradiation was used to investigate the photocatalytic activity of the GdCrO3 and GdCr0.9Mn0.1O3 samples. The results confirmed that the catalytic function of the GdCrO3 enhances on Mn doping.

Role of B-site cation on the structure, magnetic and dielectric properties of nanosized La0.7Sr0.3Fe1−xMxO3 (M = Mn; Co and x = 0, 0.5) perovskites

The easiness of preparation and tailored properties of perovskite nanoparticles rendered them an important class of materials in the last decade. In this work, La0.7Sr0.3Fe1-xMxO3 (M = Mn, Co and x = 0, 0.5) orthoferrites were synthesized using combustion method and examined using X-ray diffraction. The orthorhombic structure was clearly obvious with Pbnm space group without the need of any thermal treatment. Field emission scanning electron microscopy (FESEM) accompanied by Energy-dispersive spectroscopy studies were also performed, evidencing the similarity of both nominal and chemical compositions for the studied orthoferrites. The thermal dependence of the dielectric properties was investigated (from room temperature to 698 K) in the frequency range (70 Hz–5 MHz). Magnetic properties were investigated at room temperature and discussed.