Standard Solid-state Reaction Research Articles

Effect of Ce4+→Ce3+ conversion on the structural and luminescence properties of Ce4+ doped Gd2Ti2O7 pyrochlore oxide

Ternary oxides with cerium oxide as dopant are now useful as blue chip for the production of WLED's. In this present work, pyrochlore oxides Gd2Ti2-xCexO7 with doping concentration x = 0, 0.04, 0.08, 0.12, and 0.16, were prepared through standard solid-state reaction route. A pyrochlore structured phase is formed in the synthesized series as confirmed by conventional techniques; i.e., X-ray diffraction and Raman spectroscopy. Both techniques were revealed a systematic unit cell expansion as a function of doping concentration. The SEM micrograph confirms the formation of spherically agglomerated micron sized grains. In the later section of the manuscript, Ce4+→Ce3+ conversion effect on structural and luminescent properties were investigated. A relatively larger amount of cell expansion and accumulation of the strain is observed in the pyrochlore structured reduced samples. X-ray photoelectron spectroscopic (XPS) was used to investigate the oxidation state of the Gd, and Ti cations and oxygen anion. PL excitation spectra showed two broad bands centered around 255 nm and 360 nm due to the 4f→5d transition of Ce3+ ions at λem = 425 nm. Moreover, PL emission spectrum shows a broad peak around 425 nm at λex = 360 nm due to the 5d to 2F7/2 and 2F5/2 transitions. We observed that for the Ce4+→Ce3+ conversion both the PL emission and excitation spectra give far better results as compared to unreduced samples. Concentration quenching effect was observed for the doping concentration of 4% of cerium dopant. For 4% doping of cerium ion, CIE chromaticity results showed that the reduced as well as unreduced samples produce a bright blue colored emission line. The present study provides an insight about the potential use of Ce4+→Ce3+: Gd2Ti2O7 to synthesize blue LED chips for the fabrication of WLED's.

Study of LaCoO3 Across Insulator–Metallic Phase Transition

The standard solid-state reaction method was used to prepare perovskite LaCoO3 crystal successfully. The crystal structure was confirmed by means of powder X-ray diffraction. An investigation of the electrical properties shows an interesting temperature dependence. The real and imaginary parts of the dielectric constant show maximum at 533 K and minimum at 548 K. This indicates an Insulating-Metallic phase transition. It was found that the activation energy \(\Delta E_{a}\) in the semiconducting region was about 0.80 eV. The grain resistance shows an inverse dependence on temperature justify negative temperature coefficient of resistance exhibit. The crystal exhibits non-Debye type dielectric relaxation.

Dielectric and ferroelectric characteristics of Ba(Ti0.25Zr0.25Hf0.25Sn0.25)O3 high-entropy ceramics

Ba(Ti0.25Zr0.25Hf0.25Sn0.25)O3 high-entropy ceramics were prepared by a standard solid state reaction process, and the dielectric and ferroelectric characteristics were investigated together with the structures. Both X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analysis demonstrated a single-phase perovskite structure in the present ceramics. A broad dielectric peak with strong frequency dispersion feature was determined, which indicated the typical relaxor nature originating from the nanoscale ferroelectric domain structures. These resulted from the structural distortion and chemical disorder due to high-entropy, where the long-range order of ferroelectric domains was destroyed. The homogeneous microstructure led to the reduced leakage current density and significantly improved dielectric strength, which was desired for the practical applications. Compared with the similar systems of Ba(Ti1-xZrx)O3 & Ba(Ti1-xSnx)O3, the present high-entropy ceramics indicated better relaxor ferroelectric characteristics.

Ultra-low permittivity MgF2 ceramics with high Qf values and their role as microstrip patch antenna substrates

MgF 2 ceramics have been prepared via the standard solid-state reaction method, and their microwave dielectric properties are reported for the first time. The permittivity ( ε r ) and quality factor ( Qf ) of MgF 2 ceramics are closely related to porosity and lattice energy, respectively. The optimum microwave dielectric properties ( ε r = 4.67, Qf = 92,233 GHz, and τ f = −67.1 ppm/°C) are obtained when sintered at 1100 °C. The ultra-low permittivity and high Qf value distinguish MgF 2 ceramic as a perfect substitute for the commonly used polymer-based FR4 epoxy in the coming 5G/6G era. The feasibility of using MgF 2 ceramics as antenna substrates is demonstrated by fabricating an X-band microstrip patch antenna. The MgF 2 -based antenna resonating at 8.25 GHz exhibits excellent antenna performance with a return loss (S 11 ) of −23.39 dB and impedance bandwidth of 318 MHz.

Influence of scandium codoping on the stability of barium cerate electrolyte

Proton (H+) conducting electrolytes significantly outperform oxide ion (O2–) conducting electrolytes in terms of performance while also costing less to operate the cell. This makes them popular and potential electrolytes in future electrochemical devices such as intermediate temperature solid oxide fuel cells (IT-SOFCs). The standard solid-state reaction method has been utilized in the synthesis of scandium (Sc) co-doped barium zirconium cerate ceramics, BaCe0.8-xZr0.2ScxO3-δ. The powder X-ray diffraction spectra confirmed that the prepared samples are of single phase and have orthorhombic symmetry. The samples were analyzed for thermal stability by employing thermogravimetric analysis (TGA). All samples are stable up to 800 °C, according to TGA performed on dried and pre-hydrated samples—however, the samples under higher partial pressure of water exhibit lower degree of stability. Raman analysis was used to determine the stability of perovskite phase of the studied compositions both before and after TGA. This study showed that most initial phases either persisted or remained stable when the samples were treated at high vapor pressure. The thermal stability increased as the amount of Sc-substitution increased. Also, to investigate how the presence of grains and grain boundaries influenced the total resistance of samples with different Sc concentrations, complex impedance spectroscopy (CIS) was performed.

Enhanced superconducting transition temperature for Cr-substituted Tl2Ba2CaCu2O8-δ

Cr-substituted Tl2Ba2CaCu2O8-δ (Tl-2212) high temperature superconductor for x = 0–0.5 has been prepared using the standard solid-state reaction method. The precursor powders consisting of Ba2CaCu2Od were sintered at 900 °C for 24 h. The powders were then added with Tl and Cr, ground and pressed into pellets. The pellets were heated at 910 °C in oxygen flow for 4 min followed by furnace cooling. The d.c. electrical resistance (R) versus temperature (T) measurements were carried out using the four-point probe method with silver paste contacts. The transition temperature was determined from the slope of the resistance versus temperature graph. The superconducting critical region was divided into three: onset transition temperature (Tc-onset), middle transition temperature (Tc-mid) and zero-resistance temperature (Tc-zero). The non-substituted sample showed onset transition temperature, Tc-onset of 97 K. The x = 0.2 sample (Tl1.8Cr0.2Ba2CaCu2O8-δ) showed the highest Tc-onset (102 K). Further substitutions of Cr (x ≥ 0.3) decreased the transition temperature. All samples except the non-substituted samples showed at least two peaks in the dR/dT curves. This indicated that superconductivity within grains and intergrain occurred at different temperatures for all Cr-substituted samples. This work showed that Cr (x = 0.2) slightly enhanced the transition temperature of Tl-2212.

Low-temperature dielectric and impedance properties of Ba1-xSrxTiO3 and BaTi1-xTaxO3 ceramics

In this work, two series of BaTiO3-based ceramics, Ba1-xSrxTiO3 (x = 0, 0.2, 0.4, 0.6, 0.8) and BaTi1-xTaxO3 (x = 0.03, 0.06, 0.075, 0.09, 0.1), were synthesized by using standard solid-state reaction method at 1350 ?C, and then sintered at 1400 ?C for 10 h in air. Frequency-dependent dielectric and impedance properties were investigated at low temperature range of 100-300K. The changes in dielectric properties of the Ba1-xSrxTiO3 ceramics are believed to originate from the phase transition due to the different A-site Sr2+ doping concentration. The local electron-pinned defect-dipole effect is responsible for the enhancement of dielectric constant observed in the B-site Ta5+ doped BaTi1-xTaxO3 ceramics. The complex impedance analysis was used to discern the temperature and frequency dependence of grains and grain boundaries responses. The results suggest that A- and B-site doped BaTiO3 ceramics can be applied for different dielectric devices at low temperatures.

Enhancing the relaxor character in K0.5Bi0.5TiO3 based ternary system for energy storage applications

Lead-based ferroelectric materials dominate the electronic industry due to their possible applications in sensors, actuators, advanced storage materials, microwave devices, and MEMS. Due to the toxicity of lead, there is a need for the development of environmentally compatible alternatives. Lead-free ternary solid solutions of (1−2x)K0.5Bi0.5TiO3-xBaTiO3-xLiNbO3 (KBLN100x) with x = 0.03, 0.05, 0.07, and 0.09 are synthesized using a standard solid-state reaction method. X-ray diffraction studies confirm the pseudocubic structure of the samples. Structural, Raman, dielectric and piezoelctric studies indicate that a normal to relaxor ferroelectric transition occurs as dopant concentration increases, and it is attributed to the increase in charge fluctuation and site disorder that resulted in the reduction in correlation lengths of the inbuilt dipole moments. A recoverable energy density of 1.3 J/cm3 was achieved for the KBLN7 sample, making it an attractive candidate in the energy storage realm. A strain value of 0.17% with Smax/Emax of 218 pm/V is observed for KBLN3 sample, indicating that K0.5Bi0.5TiO3 (KBT)-based systems can be used for actuator applications on further improvement. The normal-relaxor crossover of KBT with appropriate dopants indicates that KBT-based systems are efficient for both actuator and energy storage applications on improvising and tuning as required.

Study on Factors Hindering the Single-phase Formation of Divalent-ion-stabilized W-type Ferrites

Me-substituted W-type ferrites (AMe2Fe16O27 with A = Sr, Ba, …, and Me = Co, Ni, Zn, Mg, …) can be obtained by standard solid state reaction but always contain secondary phases. Phase stability of SrMe2Fe16O27 with Me = Co, Ni, Zn, and Mg sintered in various oxygen pressures of pO2 = 0.2, 1, 10 and 387 atm were investigated using X-ray diffraction analysis, wavelength-dispersive X-ray (WDX) analysis, and transmission electron microscopy (TEM). WDX analysis revealed that the W-type ferrites are described as SrMe2-δFe16+δO27 because Fe3+ is partially reduced to Fe2+ even when synthesis is initiated from SrMe2Fe16O27. Increasing the oxygen pressure suppresses the reduction of Fe3+ and the formation of the secondary phases. In addition, TEM analysis shows that the SrCo2Fe16O27 single crystal is free of stacking faults. We conclude that the single-phase formation of the Me-substituted W-type ferrites is hampered by the discrepancy between initial and actual chemical composition caused by the appearance of Fe2+.

Investigation of transport mechanism through charge-active regions in Sm0.5Ca0.5MnO3

Polycrystalline system of Sm0.5Ca0.5MnO3 has been synthesized through standard solid state reactions method. Phase purity and structural analysis have been investigated by refinement of XRD pattern using FullProf code that displayed perovskite orthorhombic structure of space group Pbnm. A low fields magnetic study reveals two prominent peaks, one at TCO ∼ 270 K and other at TC ∼ 110 K. A broad investigation on conduction phenomena has been made by employing impedance spectroscopy in frequency range 1–10 MHz and temperature ranging 78 K − 300 K. A careful study has been carried out of the system for hopping process of charge carriers through charge active regions of grain and grains boundaries with temperature and frequency degree of freedom. Contrary to the typical investigation of Arrhenius behavior, the conduction of the system has been analyzed using Small Polaron Hopping (SPH) and Variable Range Hopping (VRH) models. This effort may present a detail and systematic addition to understanding the charge transport in divalent doped rare earth manganites.

Structural and optical studies on Dy3+ doped Gd2Ti2O7 pyrochlore as white light emission

A series of Dy3+ trivalent ion embedded into the GTO pyrochlore (Gd2-xDyxTi2O7 (x = 0.5, 1.0, 1.5, 2.0, and 2.5 mol%)) have been synthesized through standard solid state reaction technique. The single phasic nature with Fd3m space group was determined through XRD, Raman spectroscopy, and photoluminescence spectroscopy. Rietveld refinement analysis results confirm that the substitution is not going to disturb the crystallographic structure as well unit cell dimensions. From Raman deconvoluted spectrums, it was found that all the vibrational bands show a very small blue shifting on Dy3+ substitution. The photoluminescent EM-spectra for all the samples were examined under the excitation wavelength 347 nm gives two high intense emission bands centered around 484 nm (blue) and 581 nm (yellow) due to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions respectively, and less intense band appeared at wavelength of 456 nm arising due to the 4I13/2 → 6H13/2 transition of Dy3+ ions. For the optimum Dy3+ concentration (2.0 mol%), the Y/B ratio is found to be 0.8753 which is close to unity hence combination of both yellow and blue emission bands emits white light as validated by CIE chromaticity coordinates calculated values are (x = 0.34959, y = 0.35381). Therefore, the results reveal that Dy3+ substituted GTO pyrochlore samples could be used as luminescent material for wLEDs application.

Structural, complex dielectric, Ac conductivity and impedance properties of Mn3-xCrxTeO6 (x = 0.02, 0.04, 0.06 and 0.08) compounds

In this communication, the synthesis of polycrystalline Mn3-xCrxTeO6 (MCTO) (x = 0.02, 0.04, 0.06 and 0.08) compounds is carried out using the standard high-temperature solid-state reaction (SSR) method. The X-ray Diffraction (XRD) technique revealed the trigonal (hexagonal axes) crystal structure of MCTO compounds. The doping of Chromium (Cr) on the Mn site does not affect the structure of the compound. The compositional purity and morphological observations are also investigated. Dielectric parameters are examined throughout a wide frequency range. Detailed investigation obtained by theoretical fitting of the cole-cole model revealing a non-Debye type relaxation mechanism which is also evident from the complex modulus studies. An investigation on electrical conductivity is carried out by conceptually fitting experimental data using a power law and indicates a Correlated Barrier Hopping mechanism in MCTO compounds as the cause of conduction. The resistance and capacitance were validated by impedance analysis, and the effect of grains and grain boundaries was also studied accordingly. In-depth, this study demonstrates an effective synthesis approach and a thorough examination of Cr-doped Mn3TeO6 multiferroic compounds, potentially providing fundamental attributes to investigate their applications in various fields of multiferroics.

Structural, Gas Sensing and Dielectric Properties of HoXFe1-X FeO3 Perovskite Compound

Environmental pollutions and resources depletion motivates scientific research to innovate technologies for sustainable productive systems. To develop gas sensing substance with optimized performance a perovskite compound of HoxFe1-x FeO3 (where x= 0, 0.01, 0.03 and 0.05) were prepared by standard solid state reaction technique. The crystal structure was studied by XRD, which confirmed the formation of polycrystalline orthorhombic structure with space group Pbnm type perovskite. The preferred crystal growth of the main peak was (211). The structural parameters were also calculated and it was found that the lattice constants and particle size increased with the Ho doping ratio. The electrical properties were studied using the Hall effect, studied using the Hall effect, where the Hall coefficient, D.C conductivity (from 2.24E-06 (Ω-1.cm-1) at x=0) to 2.67E. -06 (Ω-1.cm-1) at x=0.05), mobility) 7.26 (cm2 / V.sec) at x=0 and decreased to 5.97 (cm2 / V .sec) at x=0.05 (and the concentration of charge carriers (2.14 E13 cm-3 at x=0 ) to 2.79E. 13 cm-3 at x=0.05 ) were calculated. The charge carrier concentration increased and charge mobility decreased with Ho addition. The Hall coefficient results revealed an n-type conduction mechanism. The dielectric constant ε r (in its real and imaginary parts) decreased with the increase in frequency of the applied electric field. tan δ and the AC conductivity were also calculated, and It was found that with the raise in the doping rate, the values of AC conductivity increase while tan δ decreases.

Effect of the Composition of the Ceramics (MCeMgSr)O2-δ (M = Y, Sm) on the Microstructure, Mechanical and Electrical Properties for Solid Electrolyte

The samples of ceramics (Y,Ce,Mg,Sr)O2-δ; 10YCe3Mg5Sr; 10SmCe3Mg5Sr were obtained by the method of standard solid-state reaction. According to X-ray analysis, all systems have the fluorite cubic structure, but in the (Y,Ce,Mg,Sr)O2-δ system, the presence of the second orthorhombic phase was observed. The microstructure of powders and synthesized tablets were characterized by electron-microscopy. The average particle size of the powder was shown to be 23.88 nm; 22.32 nm; and 13.4 nm for the compositions (Y,Ce,Mg,Sr)O2-δ; 10YCe3Mg5Sr; and 10SmCe3Mg5Sr, respectively. After the sintering at temperature 1450 °C; the grain size increased to 5.1 μm; 3.95 μm; 5.07 μm for (Y,Ce,Mg,Sr)O2-δ; 10YCe5Mg5Sr; and 10SmCe5Mg5Sr, respectively. The ionic conduction of the obtained samples was defined by ac impedance spectroscopy. The activation energy was then calculated. The 10SmCe5Mg5Sr system was found to have the highest electrical conductivity, reaching 20.5 mS/cm at a temperature of 700 °C. The activation energy was 0.62 eV in the temperature range of 600–800 °C. The results of the density, microhardness, and crack resistance measurements of the solid solutions under investigation were obtained.

Structure-based magnetic, electrical and transport properties of Ni–Zn–Co ferrite by V5+ substitution

This article presents the modification of structure-based magnetic, electronic and transport properties along with the conduction mechanism and its relaxation process in a Ni–Zn–Co ferrite tailored by V5+ substitution at B-site replacing Fe3+ ions. The composition Ni0.7Zn0.2Co0.1Fe2-xVxO4(0≤x≤0.12) was synthesized by standard solid-state reaction method and all samples were crystallized with a single-phase cubic spinel structure belonging to the Fd3‾m space group. The lattice constants decreased gradually from 8.3673Å to 8.3602Å and the average grain sizes (DSEM) are also decreased from 6.92μm to 1.99μm due to V5+ ions substitution at Fe3+ of B-site. However, more than 25% of Fe3+ ions migrate to A-site from B-site due to V5+ substitution at Fe3+ of B-site. In all samples θD does not strictly follow the Anderson's prediction, rather it monotonically decreases to a low value until x=0.12. Magnetic phase transition temperature shifted to the lower temperature and the net magnetization (ηBe) decreases due to V5+ substitution in Ni–Zn–Co ferrite. Apart this, during conduction charge carriers should require more energy to jump from one cationic site to other for V5+ substitution in the Ni–Zn–Co ferrite and the activation energy (Ea) is much more higher in V5+ substituted sample. Moreover, long-range interaction with localized relaxation mechanism is observed in V5+ doped samples. The resistance at the grain (Rg) is maximum (243.09 Ω) for the sample x=0.10 while grain boundary resistance (Rgb) is maximum (5.98×105Ω) for the sample x=0.07. However, the higher value of ρdC for x=0.12 sample ensures to be suitable for electromagnets, transformers, electronic inductors, and at high-frequency applications. Moreover, x=0.07 sample displays high value of TCR (−8.6%/K at 418K) which may be utilized as an infrared detector for night vision bolometer material.

Effect of Crystal Structure and Phase on the Dielectric, Ferroelectric, and Piezoelectric Properties of Ca2+- and Zr4+-Substituted Barium Titanate

Barium titanate (BaTiO3) and its associate ternary metal oxide systems constitute versatile materials with immense potential for various technological applications in electronics and optoelectronics. Herein, we report on the synthesis and property optimization of lead-free ceramic samples, namely BaTiO3 (BT), BaZr0.2Ti0.8O3 (BZT), Ba0.7Ca0.3TiO3 (BCT), and BaZr0.2Ti0.8O3–0.5 Ba0.7Ca0.3TiO3 (BZT–BCT) composites. All of these materials were synthesized by the standard solid-state chemical reaction method, where tuning the composition and the crystal structure yields materials suitable for multifaceted applications related to capacitors, memory storage, and high-energy switching and transducers. Structural studies carried out using X-ray diffraction and Raman spectroscopy confirm the tetragonal phase for BT, BZT, and BZT–BCT samples, whereas BCT is a biphasic crystal system, which contains a small amount of the CaTiO3 phase. Scanning electron microscopy characterization of the surface morphology indicates the granular-dense microstructures of all of the samples. Energy dispersive spectroscopy confirms the high degree of purity and chemical homogeneity of the synthesized samples in addition to a well-maintained composition. Density measurements using Archimedes principles show that all of the samples have densities above 4.96 g/cm3. All of these materials exhibit typical polarization–electric field (P–E) hysteresis and field-induced strain butterfly (S–E) loops, which confirm their ferroelectric and piezoelectric nature. The frequency response of the dielectric constant shows a maximum dielectric constant of 2441 for pure BT and it decreases for higher frequencies, above 0.1 MHz. The dielectric properties of BT imply significant prospects for its future capacitor applications. Ferroelectric measurements, which are established by measuring the P–E hysteresis loop at 300 K, show that the BCT samples exhibit a 0.50 squareness ratio. The detailed analyses indicate that BCT is a candidate material for permanent memory storage device (FeRAM) applications, whereas BZT is good for switching applications. Furthermore, a moderately higher remnant polarization (Pr = 10.81 μC/cm2) is obtained for BT and a lower coercive field (Ec = 0.78 kV/cm) is obtained for the BZT sample. Also, piezoelectric coefficient and strain measurements show that BT has a piezoelectric coefficient of 183 ± 1 pC/N and a converse piezoelectric coefficient of 365.7 ± 2 pm/V, which are the highest values. The Q-factor for the BZT–BCT composite was observed to be 4.16 × 10–4 (cm2/μC)2, which is maximum, implying that BZT–BCT is suitable for energy conversion transducer applications. In this work, we comprehensively elucidate and discuss the properties and potential applications of BT and its associated ternary metal oxide systems.

Using liquid phase precursor method to create a high-efficiency Ca<sub>2</sub>SiO<sub>4</sub>:Eu<sup>2+</sup> green-emitting phosphor

A standard solid-state reaction (SSR), a new fluid phase preparatory method utilizing LPP-SiO2(sol), and a water-based soluble silicone compound were employed to manufacture green Eu2+-based Ca2SiO4 phosphors liquid phase precursor (LPP-WSS). The generated phosphors feature large excitation spectra in the range of 225–450 nm and a strong green emission reaches the peak value at 502 nm owing to a 4f65d1→4f7(8S7/2) transition of Eu2+. These samples burned at 1100 1C produce the highest luminous intensity. The luminous properties of phosphors, which are manufactured by the liquid phase precursor LPP-WSS technique, were investigated at the range of 0.1-5.0 mol percent of Eu2+, with the maximum emission density observed at the value of 3.0 mol percent of Eu2+. The phosphors produced by the LPP-WSS technique exhibited a more uniform phase dispersion and higher luminous strength than those produced using the other procedures, according to a detailed report based on numerous characterizations. As a result, Ca2SiO4:Eu2+ has an indisputable possibility in white light-emitting diodes WLEDs and fluorescent lighting.

Structural modification and evaluation of dielectric, magnetic and ferroelectric properties of Nd- modified BiFeO3 – PbTiO3 multiferroic ceramics

0.9Bi1- x Nd x FeO3 − 0.1PbTiO3 solid solution with x = 0.05, 0.10, 0.15 and 0.20 were success fully synthesized by the standard solid-state reaction method. The effect of Nd3+ion substitution on structural, micro structural, ferroelectric, magnetic and dielectric properties of 0.9BiFeO3-0.1PbTiO3 have been investigated. The XRD analysis for the samples under study revealed distorted rhombohedral structure with R3C space group. 0.9Bi1- x Nd x FeO3 − 0.1PbTiO3 i.e. (BNFPT)x with x = 0.05, 0.10, 0.15 and 0.20 compounds crystallized as single-phase materials with the same structure as the parent BiFeO3 compound. The SEM study revealed the uniform grain scattering for all prepared samples. Raman spectroscopy showed disappearance of some Raman modes indicated a structural phase transition with substitution of Nd dopants at Bi site and also confirmed the distorted rhombohedral perovskite structure of (BNFPT)x compounds with R3c symmetry. Dielectric measurements reveals that, around Neel temperature, all the samples exhibit magneto-electric coupling and also improved dielectric properties with addition of dopants in BiFeO3(BFO) compound. All the prepared samples exhibit weak ferro-magnetic character at room temperature. However, the variation in linear behavior and enhancement in magnetization is found at 5 K which shows gradual increase in remnant magnetization from 0.00785 emu/g to 0.37513 emu/g with increase in Nd doping for all (BNFPT)x samples. Nd doping reduces leakage current by three orders of magnitude, from 10−4 to 10−7. Ferroelectric study revealed the pinning effect in hysteresis loops with low remnant polarization and coercive field which can be related to the energy storage performance of the samples.

Key role of Tb3+ doping on structural and photoluminescence properties of Gd2Ti2O7 pyrochlore oxide

Pyrochlore structured compounds form a special class of ceramics as host matrices in phosphors with better luminescent properties. In the present work, the optical properties of pyrochlore oxide Gd2-xTbxTi2O7 (0 ≤ x ≤ 0.16) were investigated and linked with structural properties via examination of structural distortion produced with the doping of rare-earth element. These oxide compositions were produced through standard solid-state reaction method. The investigations using advanced characterization techniques; X-ray diffraction and Raman spectroscopy give a signature of single phasic pyrochlore structure in the synthesized samples optimized through multiple heating protocol. The diffraction patterns and Raman spectra, both were continuously being shifted towards lower 2θ value and lower wave-number side, respectively with the doping concentration which can be interpreted by the production of defects in cationic lattice. A similar decreasing trend in particle size has been observed from W–H plot (728 Å to 616 Å) and Scanning electron micrographs (0.82 μm–0.78 μm) with the introduction of Tb3+ ion. The band-gap for the host matrix Gd2Ti2O7 through UV absorption pattern came out to be 2.26 eV. From photoluminescence excitation (λem = 545 nm), a broad excitation band was observed in the wavelength range 305 nm–380 nm due to the f→d transition of 4f shell of Tb ion. Furthermore, emission spectra (λex = 375 nm) consist of bands at 489 nm, 545 nm, 585 nm and 623 nm due to the transitions at 5D4 → 7F6,5,4, and 3, respectively with doping. For an optimum doping concentration with x = 0.12, a high intensity green emission line at 545 nm came out as 5D4 → 7F5 dominating transition of terbium ion. Hence, the results explore the application of Gd2Ti2O7 composition as Tb-fluorescence with the optimum doping concentration of 6%.

Structural, electrical and ferroelectric characteristics of lead-free ceramic: Bi(Fe0.85Gd0.15)O3

Structural and electrical properties of Bi(Fe0.85Gd0.15)O3 ceramics, synthesized via standard solid state reaction technique is reported in this communication. Powder X-ray diffraction analysis reveals the phase transition from rhombohedral to orthorhombic symmetry. The structural study shows the formation of a dense compact high quality sample. The average crystallite size was found to be 38 nm. High dielectric permittivity value is observed with an increasing temperature. Impedance spectroscopy analysis suggests a semiconductor nature and conductivity study confirms the presence of correlated barrier hopping mechanism. The P-E loop study shows an enhancement in remnant polarization. Furthermore, several other interesting features are also reported in this work.