Space Group Pm3m Research Articles

Complex dielectric function and opto-electronic characterization using VEELS for the lead-free BCZT electro-ceramic perovskite

The current work presents the complex dielectric function and the opto-electronic properties of lead-free Ba0.8Ca0.2Ti0.9Zr0.1O3 (BCZT) electro-ceramic, derived from valence electron energy loss spectroscopy, in transmission electron microscopy (VEELS–TEM).A single tetragonal perovskite phase, with P4mm space group, was determined by Rietveld refinement of the x-ray diffraction pattern. The VEELS–TEM experiment scanned the energy interval from 0–50 eV. The spectroscopic analysis started with the chemical identification of the atoms that conforms the BCZT solid-solution. Bulk and surface plasmons were located at 27.2 eV and 12.9 eV, respectively in the energy loss function. Complex dielectric function was obtained using Kramers–Kronig analysis from the Gatan Microscopy Suite software. Dielectric constant was calculated from the real part of the complex dielectric function, while the inter-band transitions were identified in the joint density of states function. The refraction index n and the extinction coefficient k, as a function of energy, were obtained from the complex dielectric function. The bandgap energy was determined using a polynomial fit in the optical absorption coefficient plot with an Eg = 3.2 eV.

Investigation of multifunctional characteristics in SmFeO3-BaTiO3 perovskite system for devices

The polycrystalline ceramic (SmFeO3)0.5 (BaTiO3)0.5 (SF-BT) is synthesized by high temperature solid state reaction method. The sample is investigated for its multifunctionality by analyzing its structural, dielectric, electrical and multiferroic properties. The XRD patterns and the rietveld refinement confirm the single phase forming of the compound in the tetragonal symmetry with P4mm space group. The dielectric properties of the material analyzed on the basis of Maxwell-Wagner phonological model. The room temperature dielectric constant reveals material can be useful for multilayer capacitor. Complex impedance and modulus studies confirm non-Debye type, negative temperature coefficient of resistance (NTCR) behavior and the electrical resistance in the material is only due to contribution grains. The short-range mobility of charge carriers is responsible for different types relaxation mechanism in the material. The Multiferroic studies show the existence of room temperature ferroelectric (ferroelectric (2P = 1.17 μC/cm2, EC = 0.65 kV/cm) and ferromagnetism (Mr = 0.77emu/g at HC = 1.1 kOe) properties in the material. The study reveals the leakage behavior of the material is reduced significantly and enhanced Multiferroic character for microelectric and memory devices.

Effect of calcium doping on Sm1–xCaxBaCo2O5+δ cathode materials for intermediate-temperature solid oxide fuel cells

Here, Sm1–xCaxBaCo2O5+δ (x = 0–0.4; SCBC) oxygen-deficient perovskites were synthesized by a sol–gel method and studied as potential novel cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). As an effective doping strategy, partial substitution of Ca for Sm in SmBaCo2O5+δ could reduce the thermal expansion coefficient (TEC) and improve the conductivity and catalytic activity of the oxygen reduction reaction (ORR). The x = 0–0.2 samples obtained after sintering at 1100 °C crystallized in an orthorhombic structure with the space group Pmmm and had good chemical compatibility with CeO2-based electrolytes at 1000 °C for 10 h. The TECs of the SCBC samples decreased from 20.2 × 10−6 K−1 (x = 0) to 17.7 × 10−6 K−1 (x = 0.2). The area-specific resistances (ASRs) of the x = 0–0.4 cathodes were 0.163, 0.114, 0.075, and 0.090 Ω cm2 at 700 °C. Additionally, the x = 0.2 cathode showed good electrochemical stability in a CO2-containing atmosphere. All results clearly indicated that double perovskite SCBC (x = 0–0.3) are promising cathode materials for IT-SOFCs.

Improved room temperature dielectric properties of Gd3+ and Nb5+ co-doped Barium Titanate ceramics

In this paper, we report the synthesis of gadolinium (Gd) and niobium (Nb) co-doped barium titanate (BT) ceramic oxides prepared using a conventional solid-state reaction method. The X-ray diffraction pattern confirmed the formation of tetragonal phase – with the space group P4mm – in all samples. X-ray photoelectron spectroscopy shows the formation of oxygen vacancies with a variable concentration that depends on the site preference of Gd ions. Fourier – Transform infrared analysis shows the presence of the most prominent peak between 544 cm−1 and 588 cm−1. Raman spectroscopy shows the tetragonal phase, with a most prominent peak around 514 cm−1 due to A1(TO3)E(TO4) mode. Shifting of this peak suggests the formation of GdBa defects. UV measurement suggests an increase in bandgap from 2.928 eV to 3.047 eV with Gd doping. Photoluminescence shows the presence of multiple level emission mechanisms for all samples. The dielectric constant increases while dielectric loss decreased with increasing dopant concentration, which is attributed to the self-compensation mechanism and defect dipole formation. Impedance spectra, Z′and Z′′vs frequency, suggest the presence of space charge polarization. Modulus spectra, M′and M′′vs frequency indicates the presence of short-range mobility at low frequency and long-range mobility at high frequency. AC conductivity shows almost negligible change with variable dopants concentration. Thus, electrical properties were observed to improve with Gd and Nb co-doping on BT ceramic oxides.

Sol-gel synthesis and structural study of a lithium titanate phase Li 3xLa 2/3.x □1/3-2x TiO3 as solid electrolyte

Perovskite lithium lanthanum titanate (LLTO) was prepared as an inorganic solid electrolyte material for lithium ion batteries applications using sol-gel method. Three different compositions of : (a) 3x=0.3 (Li 0.3La 0.57TiO3), (b) 3x=0.5 (Li 0.5La 0.5TiO3) were prepared and calcined at 1000°C for 6h, and (c) 3x=0.1 (Li 0.1La 0.63TiO3) prepared and calcined at 1100°C for 6h. The effects of lithium content and calcination temperature on the structure of the perovskite powders were studied. The synthesized powders were characterized by X-ray diffraction analysis. Results indicate that the Li 0.3La 0.57TiO3 was crystallized in tetragonal structure of space group P4/mmm. On the other hand, Rietveld refinement analysis for the LLTO samples confirmed the formation of the Li 0.3La 0.57TiO3 crystalline phase in the tetragonal P4/mmm space group, the Li 0.5La 0.5TiO3 phase in the tetragonal P4/mmm space group, and Li 0.1La 0.63TiO3 phase in orthorhombic Pmmm space group.

Rietveld refinement analysis and influence of individual phases on the magnetoelectrically coupled (1-x)BSZT+ xNCZGF multiferroic composites

The magnetoelectric voltage coefficient at room-temperature is realized in various (1-x)BSZT+ xNCZGF composites by studying refined crystal structures, surface morphology, magnetic, electric and ferroeletric properties. The ferroelectric (BSZT) and ferrite (NCZGF) phases of the composites are prepared using standard solid-state reaction technique. Rietveld refinement confirmed that the BSZT phase forms perovskite structure with P4mm space group and NCZGF phase forms spinel structure with Fd3¯m space group. From FESEM surface morphology it was observed that the average grain diameter ranges 0.5–2.21 µm. EDX analysis confirms the formation of respective phases and composites. Initial permeability increases from 55 to 130 with increasing NCZGF content which is consistent with the value calculated theoretically using different models. The saturation magnetization also increases from 12 to 37 emu/g with increasing NCZGF content, consistent with the calculated value using law of approach to saturation technique. The dielectric constant of the composites is found to decrease with increasing NCZGF content which is in line with the Maxwell-Garnett, Bruggeman, Looyenga and Lichteneker theoretical approximations. Frequency dependence of the dielectric constant exhibits dispersion, which can be modeled using a modified Debye function that considers the probability of several ions contributing to the relaxation. The ac conductivity follows the Jonscher’s power law, and the conduction mechanism is attributed to the small polaron hopping. Complex impedance is evaluated using the Cole-Cole plot ensures the dominance of both grain and grain boundary resistances. The P-E hysteresis loops ensure the typical ferroelectric nature at room-temperature for x ≤ 0.2. The simultaneous M-H and P-E hysteresis loops confirm the magnetoelectric coupling between ferrite and ferroelectric phases. Furthermore, the maximum magnetoelectric voltage coefficient for 0.9BSZT+ 0.1NCZGF composite is found to be ~194 mV cm−1 Oe−1 that can be used in multifunctional devices.

Crystallographic and magnetic structure of UNi4B11

We present an extensive powder and single-crystal neutron scattering investigation of the crystallographic structure and magnetic order of the frustrated metallic $f$-electron magnet UNi$_4$B. We carry out a full refinement of the crystallographic structure and conclude that the low-temperature lattice symmetry is orthorhombic (space group Pmm2; cell parameters: $a = 6.963(4)~\r{A}$ , $b = 14.793(9)~\r{A}$ , $c = 17.126(8)~\r{A}$). We determine the magnetically ordered structure, concluding that below $T_\mathrm{N} = 19.5~\mathrm{K}$ the material undergoes a transition into a partially ordered antiferromagnetic state. The magnetic structure is consistent with the existence of toroidal order in this material. We further test the proposal of a second magnetic transition occurring at $330~\mathrm{mK}$, concluding that the thermodynamic anomalies observed at these temperatures do not reflect modifications of the magnetic structure. Our study provides a consistent picture of the interrelationship of structural and magnetic properties in the frustrated magnet UNi$_4$B previously unresolved.

Structural and Conductivity of NiO-BCZY Anode Functional Layer for Proton Conducting Fuel Cell

The main objective of this study is to perform a structural analysis of NiO-BCZY anode functional layer (AFL) with different weight ratio (NiO:BCZY = 20:80 and 40:60). NiO commercial powder and in-house developed BCZY synthesized by a sol-gel method are mixed and ground and then sintered at 1450° C for 5 hours to produce AFL powder. The single-cell (anode | CG-AFL| electrolyte | cathode) is fabricated with the anode substrates firstly die-pressed, then compositionally gradient anode functional layer (CG-AFL) and spin-coated with electrolyte thin film, accordingly. Structural characterization of AFL powder and conductivity of the single cell is performed using room temperature X-ray diffraction (XRD) and in-house developed electrochemical impedance spectroscopy (EIS) test station, respectively. Rietveld refinement analysis of the XRD data confirms the high purity single phase of NiO and BCZY. Both NiO and BCZY show a cubic crystal structure and each belongs to space group Fm-3m and Pm-3m, respectively. The lattice parameter (a = b = c) of NiO and BCZY are about 4.1818 Å3 and 4.3433 Å3 for 20NiO-80BCZY and 4.1825 Å3 and 4.3439 Å3 for 40NiO-60BCZY. EIS results show ohmic resistance (RS) and polarization resistance (RP) of the single cell are 14.8 and 16.23 Ωcm2 at 800 °C, respectively.

Investigation on structure and stability of cerium doped (Ba0.5Sr0.5)(Fe1-xCex)O3-δ (x = 0–1.0) oxides by Rietveld refinement

Perovskite-type materials have been attracted due to their relevant applications in memory devices, tunable microwave displays, oxygen-permeable membranes, sensors, and capacitors. An attempt has been made here to analyze the structure of (Ba0.5Sr0.5)(Fe1-xCex)O3-ẟ (x = 0–1.0) oxides by Rietveld refinement under different space groups. It possesses cubic (space group Pm3m, Z = 1), cubic with orthorhombic, and orthorhombic (space group Pnma, Z = 4) structures for the composition x = 0, 0.10–0.60, and 0.80–1.0, respectively. The amount of cubic phase decreases from 100% to 24% with cerium content (x) = 0–0.60 and complete transformation to the orthorhombic phase occurred at x = 0.80. Moreover, single – dual - single structural phase transitions have been observed. The average bond length decreases with cerium content. The bond angles along O–B–O and B–O–B are deviated significantly due to the tilting and rotation of (Ce,Fe)O6 octahedra. The presence of distortion/oxygen vacancies makes the compound useful in industrial applications.

Study of Carrier Transfer Mechanism When Substituting Strontium at Barium Sites in CuTl-1223 Superconducting Phase

Strontium-doped CuTl-1223 phase has been obtained by employing a nonstoichiometric composition of the form Tl1/2Cu1/2(Ba1−xSrx)Ca1Cu4Oy (x = 0, 0.1, 0.2, 0.3). The superconducting properties of the samples were investigated by x-ray diffraction analysis and four-probe resistivity, alternating-current (AC) susceptibility, and Fourier-transform infrared (FTIR) absorption measurements. The effect of doping strontium atoms on the intrinsic superconductor parameters of these samples was studied by excess conductivity analysis. All the samples showed orthorhombic crystal structure in space group Pmmm, and the cell parameters were determined by using all the planar reflections. The c-axis length and the unit cell volume decreased with Sr doping in the final compound. Suppression of the room-temperature resistivity followed by metallic variations in resistivity versus temperature measurements are typical features for these samples. The zero-resistivity critical temperature and the onset of diamagnetism were suppressed with increasing Sr doping in the final compound. The apical oxygen phonon mode of type Cu(1)–OA–Cu(2) observed at around 548 cm−1 hardened with increasing Sr doping. The excess conductivity analysis revealed that the coherence length along the c-axis, the interlayer coupling, and the Fermi velocity of the carriers increased for the Sr doping levels of x = 0.1 and 0.2 but decreased for the sample with x = 0.3. The values of Bc0(T), Bc1(T), and Jc0(0) increased with increasing Sr doping in the final compound. It is proposed that this effect arises due to an increase in the superconducting volume fraction. A decrease in the value of the London penetration depth λp.d. and the Ginzburg–Landau (GL) parameter shows that the flux-pinning characteristics of the samples were improved by Sr doping. An increase in the mean free time of the carriers and a decrease in the energy required to break apart Cooper pairs result from a decrease in the remanent field scattering induced by the increased population of pinning centers in Sr-doped samples.

Crystal structure and improved dielectric, magnetic, ferroelectric and magneto-electric properties of xCoFe2O4−(1−x)BaTiO3 multiferroic composites

Multiferroic composites having composition xCoFe2O4−(1−x)BaTiO3 (x = 0.10, 0.30, 0.50) were synthesized. XRD patterns of samples confirmed that the peaks of both ferroelectric (tetragonal symmetry) and ferrite (cubic symmetry) phases existed simultaneously. Rietveld refinement confirmed the existence of both phases with tetragonal symmetry having P4mm space group and cubic symmetry with Fd3m space group. Grain sizes of the composites have been calculated using FESEM. The frequency and temperature dependence of dielectric constant (ɛ′) and dissipation factor (tanδ) have been studied. In the lower frequencies, ɛ′ and tanδ show dispersion behaviour, and in higher frequencies, it becomes constant for all composites. M–H loops depict soft magnetic behaviour with a maximum value of magnetic moment 1.618 μB for 0.50BaTiO3–0.50CoFe2O4sample. P–E loops show that remanent polarization and coercive field decrease with increase in ferrite content. The maximum value of ME coefficient (α ~ 165.32 μV/cmOe) is obtained for 0.10CFO–0.90BT composite.

Rhodizonate complexes with transition metal ions: A new vision from an old building block

In this work a series of metal complexes containing the rhodizonate ion have been synthesized and characterized by means of structural and spectroscopic measurements. Compounds of general formula MC6O6.nH2O, where M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) were carefully obtained in an inert atmosphere, and the resulting complexes have been analyzed by powder X-ray technique, showing that manganese, cobalt, nickel and zinc compounds all present the same similar arrangement; the qualitative phase analysis indicate the Pmmm space group for manganese, cobalt, nickel and zinc salts, and P2/m for the copper salt. The unit cell volumes were determined, and they grow approximately with the number of water molecules in the structure measured by elemental and thermogravimetric analysis. The vibrational spectra are in concordance with the X-ray diffraction results since the salts of manganese, cobalt, nickel and zinc show a remarkably similar spectral profile, whereas the copper salt, shows a different spectral profile. It was observed that the number of bands in the Raman spectra of the compounds is greatly increased compared to the free rhodizonate ion. This fact is justified by the lower symmetry due to the complexation of the metal site. The vibrational modes related with the C=O stretching in the 1700–1500 cm−1 region are the most influenced with the metal coordination showing large displacements and band splitting. This last fact strongly supports the loss of symmetry experienced by the oxocarbon ion when coordinated to the metal centers in the complexes.

Synthesis, characterization, ferroelectric, and piezoelectric properties of (1 − x)BaTiO3−x(BaNi0.5Nb0.5O3) perovskite ceramics

Single-phase ceramic samples of (1 − x)BaTiO3−x(BaNi0.5Nb0.5O3), where 0 ≤ x ≤ 0.05, were prepared. The Rietveld analyses of the X-ray diffractions indicated that the crystal structure of the samples of x = 0, 0.01, 0.02, and 0.04 are tetragonal with p4mm space symmetry group, while those of x = 0.03 and 0.05 are cubic with pm-3m space group of symmetry. The average grain size of all investigated samples was calculated based on field-emission scan electron microscopy (FE-SEM). Both Raman and photoluminescence spectra were recorded at room temperature. The polarization–electric field (P–E), hysteresis loops indicated that the coercive field, remanent polarization, and energy losses are dependent on x value. The bipolar and unipolar strain–electric field (S–E) were studied for all synthesized ceramics. The piezoelectric properties of the parent sample (x = 0) are enhanced with increasing x. The outcome results of this work are promising for applications.

Structural, optical, and electrical properties of vanadium-doped, lead-free BCZT ceramics

In this paper, we report the synthesis of vanadium (V)-doped Ba0.9Ca0.1Ti0.9−xVxZr0.1O3 (BCZT) ceramic oxides prepared using conventional solid-state reaction methods. The X-ray diffraction (XRD) pattern confirmed the formation of the tetragonal phase—with the space group P4mm—in all samples. A barium vanadate (Ba3V2O8) impurity phase was observed in the doped samples, which suggests that the solubility limit of V was reached in the BCZT ceramics. X-ray photoelectron spectroscopy shows the formation of oxygen vacancies, which attain a maximum value at a concentration x = 0.02, i.e., 38.65%. Fourier-transform infrared analysis shows prominent peaks between 560 cm−1 to 558.1 cm−1, with a secondary-phase peak around 1017 ± 2 cm−1, as suggested by XRD. Photoluminescence (PL) spectra suggest that oxygen vacancies play important roles in promoting luminescence by trapping the excited photoelectrons. Oxygen vacancies also reduce the recombination rate of photo-generated electrons and holes. Ultraviolet–visible analysis agreed with PL studies, with comparable bandgap energy. Raman spectroscopy also shows the tetragonal phase, with the most-prominent peak around 520 cm−1 due to the A1(TO3)/E(TO) mode. We attribute two peaks observed around 330 cm−1 and 780 cm−1 to the Eg and A1g modes, respectively, of the secondary phase. Electrical studies performed for all samples reveal that variable oxidation states of Vin the presence of oxygen vacancies readily influence the resistivity—and thus the activation energy—of each sample. We obtained a maximum DC resistivity ρDC (max.) = 1.653 × 10−11(Ω cm) and a corresponding minimum DC conductivity σDC (min.) = 8.581 × 10−12 for x = 0.02, which is due to the presence of only an acceptor (V3+) concentration for this sample. The Curie temperature (Tc) also decreased from 71.8 °C to 31 °C with increasing V-ion concentration. The drift mobilities observed for all samples are in accordance with the Verwey–de Boer mechanism. Thus, the substitution of V ions at Ti sites can significantly influence the optical and electrical properties of BCZT ceramics.

Synthesis and characterization of temperature stable low-loss (1−x)Mg(Ti0.95Sn0.05)O3–(x)BaTiO3 (0 ≤ x ≤ 0.1) ceramics for microwave applications

In the present work, we prepared (1−x)Mg(Ti0.95Sn0.05)O3–(x)BaTiO3 (0 ≤ x ≤ 0.1) solid-solutions via traditional solid-state reaction process and investigated their structural, optical, electrical, dielectric, and shielding properties. We report that these (1−x)Mg(Ti0.95Sn0.05)O3–(x)BaTiO3 compounds experienced structural phase transitions, wherein the tetragonal-structured BaTiO3 (space group P4mm) got transformed to monoclinic-structured Ba4Ti11O26 (space group C12/m1), and triclinic-structured Ba2Ti9O20 (space group P1). Interestingly, the Mg(Ti0.95Sn0.05)O3 showed no structural phase transition and was crystallized in its purest form without secondary phase formation. Additionally, the prepared compositions showed ten Raman active modes, and the relative density of all the samples exceeded 93.5%. The optical bandgap (Egap) values and DC conductivities of the samples were in the range of 3.82 eV–3.92 eV and 9.03 × 10−10 Sm−1–2.55 × 10−9 Sm−1, respectively. The composition 0.925 Mg(Ti0.95Sn0.05)O3–0.075BaTiO3 exhibited the best dielectric properties having relative permittivity (ɛr) of 19.69, loss tangent (tan δ) of 5.1 × 10−3, and temperature coefficient of resonant frequency (τf) of -8.5 ppm/°C at 1 MHz. In the Ku-band (12.4–18 GHz), this composition showed ɛr in the range of 14.62–15.49 and tan δ in the range of 2.85 × 10−2–5.89 × 10−2. An investigation of shielding properties in the Ku-band revealed that the prepared samples delivered average shielding effectiveness in the range of 5.98–6.65 dB. The prepared materials are proposed for microwave applications.

Synthesis of mesoporous silica with ionic liquid surfactant as template

Ionic liquid surfactants (ILSs), N-hexadecyl-N-methylpiperidinium bromide ([C16MPip][Br]), N-hexadecyl-N-methylmorpholinium bromide ([C16MMor][Br]) and N-hexadecyl-N- methylpyrrolidinium bromide ([C16MPyr][Br]), were respectively synthesized and were used to prepare mesoporous silica with controllable morphology in alkaline medium via hydrothermal method. The silica prepared with [C16MPip][Br] or [C16MMor][Br] is mesoporous MCM-41 with hexagonal structure of space group p6mm and regular pores ordered, and the pore diameter and specific surface area are about 2 nm and 850 m2∙g−1, respectively. The mesoporous silica prepared with [C16MPyr][Br] has the larger pore size (2.53 nm) and the smaller specific surface area (650 m2∙g−1) , the channel structure is not more regular and orderly than the other two mesoporous silica.

Rietveld refined structure, ferroelectric, magnetic and magnetoelectric response of Gd- substituted Ni-Cu-Zn ferrite and Ca, Zr co-doped BaTiO3 multiferroic composites

The room temperature magnetoeletric coupling was investigated thoroughly in various xNi0.48Cu0.12Zn0.40Gd0.04Fe1.96O4 + (1-x)Ba0.985Ca0.015Zr0.10Ti0.90O3 multiferroic composites. Ferrite and ferroelectric phase of the composites have been prepared by the standard solid state reaction technique. Structural study was conducted by the X-ray diffraction (XRD) and the Rietveld refinement was adopted for further analysis of the structure. The refined XRD patterns confirmed all composites having a biphasic spinel-perovskite structure with Fd3¯m, and P4mm space group, respectively. Microstructural characteristics of all samples have been analyzed using Field Emission Scanning Electron Microscopy images. The magnetoeletricaly coupled composites is illustrated by an obvious modification in lattice, dielectric, ferroelectric and magnetic properties as a function of ferrite content. The dielectric constant of the composites was found to decrease with the addition of ferrite content in line with the theoretical estimations of the Bruggeman, Maxwell-Garnett, Lichtencker and Looyenga models, respectively. The dielectric constant and initial permeability were calculated theoretically using the different models and compared with the experimental values. The discrepancy between the calculated and experimental values of dielectric constant and initial permeability might be attributed to the diffusion of ions and interaction between two phases of the composites. The ac conductivity analysis revealed that the conduction mechanism is attributed to the small polaron hopping and also obeyed the Jonscher’s power law. Complex impedance was evaluated using the Nyquist plot which ensured the dominance of both grain and grain boundary resistance. The hysteresis loops (M-H and P-E) ensured the typical ferromagnetic and ferroelectric nature for all composites at room-temperature. Magnetic studies show an improvement of initial permeability, relative quality factor and magnetization, whereas magnetic loss gradually reduces with the increment of ferrite content. The maximum magnetoelectric response (~173 mVcm−1Oe−1) was found for x = 0.10 composite that could be utilized in the future multifunctional devices.

Proof-of-concept thermoelectric oxygen sensor exploiting oxygen mobility of GdBaCo2O5+δ

In this paper, we demonstrate a proof-of-concept oxygen sensor based on the thermoelectric principle using polycrystalline GdBaCo2O5+δ, where 0.45 < δ < 0.55 (GBCO). The lattice oxygen in layered double perovskite oxides is highly susceptible to the ambient oxygen partial pressure. The as-synthesized GBCO sample processed in ambient conditions shows a pure orthorhombic phase (Pmmm space group) and a δ-value close to 0.5 as confirmed by x-ray diffraction Rietveld refinement. The x-ray photoelectron spectroscopy (XPS) shows a significant Co3+ oxidation state in non-octahedral sites in addition to Co3+ as well as Co4+ in octahedral sites. The insulator-to-metal transition (MIT) is observed at 340 K as seen from resistivity and Seebeck coefficient. The Seebeck coefficient shows a large change of 10–12 μV/K with a time constant of ∼20 s at 300 K, when the gas ambience is changed from 100% oxygen to nitrogen and vice versa. The diffusion of oxygen in the GdOδ planes leads to the hole doping, which is a dominant factor for a large change observed in the Seebeck coefficient. This is also evident from the higher fraction of oxidized Co4+ as seen from XPS measurements. The interfacial grain boundary in addition to the oxygen diffusion contributes to the change in Seebeck. The change in Seebeck coefficient is minimal in the metallic state due to an insignificant increase in the carrier concentration, but the response is fairly well and reproducible for stoichiometry δ = 0.5 ± 0.05 below MIT. This principle shall be of significant importance in designing oxygen sensors operational at room as well as cryogenic temperatures.

Observation of dielectric anomalies and enhanced multiferroic properties in (1-x) Ba0.80Sr0.20TiO3-(x) LaFeO3 ceramics near at MPB region

Polycrystalline solid solution of (1-x)Ba0.8Sr0.2TiO3 - xLaFeO3 (0 ≤ x ≤ 0.50) samples were prepared by a conventional solid state process. The crystal structure of the samples transformed from tetragonal structure with P4mm space group (for x < 0.15) to orthorhombic structure with Pbnm space group (x > 0.35) alongside Morphotropic phase boundary region of 0.2 ≤x ≤ 0.35 samples. The evolution in Raman modes also indicated structural phase transition of the samples and corroborated the XRD findings. An increase in grain size with increase of LaFeO3 concentration up to x = 0.30 was observed. The ferroelectric properties were strongly dependent on composition and were correlated to the crystal structure of the samples. An enhancement in magnetization along with weak ferromagnetic hysteresis loops could be the presence of long range superexchange interaction via Fe3+−O−Ti−O−Fe3+ along the pathway. Dielectric anomalies near magnetic transitions were observed for the samples with x = 0.25 and 0.35 at temperatures 293 °C and 318 °C respectively, were ascribed to presence of strong magnetoelectric coupling. The observed dielectric relaxation in loss data attributed to hopping of oxygen vacancies.

Rietveld refinement structure, electric, dielectric and ferroelectric properties of lead-free Ba0.985Sr0.015Zr0.10Ti0.90O3 ceramics

Ba0.985Sr0.015Zr0.10Ti0.90O3 (BSZT) compound is prepared using the standard solid-state reaction technique to explore for energy storage applications. Samples prepared from this compound are sintered at various sintering temperatures (Ts) of 1200, 1250 and 1300 °C, respectively. Influences of Ts on the structural, morphological, dielectric and ferroelectric properties are studied in detail. Rietveld refinement is used on the X-ray diffraction pattern to confirm the crystal structure of the BSZT samples and each sample indicates the tetragonal phase with the P4mm space group. Interestingly, with increasing Ts, the tetragonality increases up to 1250 °C, and then decreases for further increasing Ts, suggesting a transformation to the cubic structure. Morphological analysis of the BSZT samples show that a dense microstructure is attained for higher Ts. Temperature-dependent dielectric studies show that the degree of diffuseness increases up to 1250 °C, and then decreases for further increasing Ts, suggesting a weakening of the relaxor ferroelectric behavior. A non-Debye type relaxation process in the complex impedance and the modulus spectroscopy studies confirm the significant contribution of both the grain and grain boundary to the electrical response of the studied sample. The ferroelectric behaviors of the sample are explored from the polarization versus electric field hysteresis loops. Ferroelectric properties are significantly improved with the Ts.