Structural and electrical characteristics of double perovskite: Nd2CoMnO6

Recent progress on optical properties of double perovskite phosphors

Dielectric, electrochemical and magnetic properties of the hydrothermally synthesized double perovskite La2NiMnO6 for energy storage applications

The double perovskite gadolinium cobalt manganate (Gd2CoMnO6) ceramic material was prepared via mixed oxide route. The preliminary X-ray structural study reveals that the material was found in monoclinic structure. We have found the small voids with almost uniform distribution of grains from the microstructural analysis. Analysis of the dielectric and electrical data, collected in a wide range of frequency range (1 kHz–1 MHz) and temperature (25–500 °C), has provided many interesting results. We have discussed frequency dependence dielectric parameter by Maxwell–Wagner model. We found that the room temperature dielectric constant at 1 kHz frequency is 300 and tangent loss is nearly equal to 2. A dielectric anomaly (ferroelectric–paraelectric phase transition) was found in the temperature dependence of dielectric study. The study of diffuse phase transition exhibits the existence of relaxation process in the compound. In the Nyquist plots, both grain and grain boundary effects are observed which is characterized by (RQC) and (RQC)(RC) circuits. As the resistance decreases with increase of temperature, the material shows the semiconductor behavior. The existence of non-Debye type of relaxation mechanism in the material is confirmed by the depression angle. The frequency dependence of electric conductivity has been studied using the Jonscher’s power law, in which the frequency exponent n (< 1) signifies the translational motion with involvement of an intuitive hopping of charge carriers. The leakage current and conduction mechanism follow the space charge-limited conduction phenomenon. The low leakage current density may be suitable for high-temperature applications.

BaBi2Sb2Ti4O15, a four-fold layered structured ceramic compound is synthesized by the mixed oxide process at sintering temperature 875 °C. The structural and electrical properties of the material measured in a broad temperature (25–500 °C) and frequency (103–106 Hz) range are presented here. From the preliminary X-ray structural analysis, it is confirmed that this compound has an orthorhombic structure. The temperature and frequency-dependent dielectric constant of the material is observed. Modified Curie Weiss’s law explains the extent of diffusivity observed in a phase transition. The presence of grain and grain boundary effects is confirmed from the Nyquist plots. Non-Debye-like relaxation is noticed from complex impedance and modulus analyses. Reduction in grain resistance is noticed with the enhancement of temperature indicating the existence of negative temperature coefficient of resistance (NTCR) properties in the compound. It is concluded from the above results that this compound may have wide applications in electronics as well as high-temperature devices.

The toxicity of lead ions in halide perovskite absorbing materials is the main bottleneck for practical application. To replace the traditional lead halide perovskites by environmental friendly double perovskite, computational tools based on density functional theory were employed to predict the intrinsic properties of potential double perovskites to efficiently and rapidly find more double perovskites with properties suitable for optoelectronic applications. Screening homovalent alternatives for B and X‐site ions in vacancy‐ordered double perovskite Cs2BX6 for solar cell applications and photocatalyst was done using Perdew–Burke–Ernzerhof and Heyd–Scuseria–Ernzerhof functional with spin‐orbit coupling. Three empirical factors and formation enthalpy were used to evaluate the stability of 30 materials at different temperatures. Finally, the Cs‐based vacancy‐ordered double perovskites with suitable bandgap for optoelectronic applications can thus be obtained. Using computational techniques, this study can also provide theoretical guidance for the rational design of possible double perovskite materials with improved photocatalytic characteristics.image

Preparation and characterization of LiFe 1/2Ni 1/2VO 4

Impedance and electric modulus analysis of Sm-modified Pb(Zr 0.55Ti 0.45) 1− x/4 O 3 ceramics

A lead free polycrystalline material Ba(Bi0.5Nb0.5)O3 was prepared using a high-temperature mixed oxide technique using high purity ingredients. The formation of the material in monoclinic crystal structure was confirmed by an X-ray structural analysis at room temperature. The nature and texture of microstructure by scanning electron microscopy show that the compound has well defined grains uniformly distributed throughout the surface of the sample. Detailed studies of dielectric and impedance properties of the material, carried out in the frequency range of (1 kHz–1 MHz) at different temperatures (30 °C to 475 °C), have shown many interesting properties. Dielectric study showed an existence of diffuse phase transition around 317 °C. The temperature dependence of impedance parameters (impedance, modulus etc.) of the material exhibits a strong correlation of its micro-structure (i.e., bulk, grain boundary, etc.) with the electrical parameters. An existence of negative temperature coefficient of resistance (NTCR) type behavior in the material similar to that of semiconductors was also observed. The complex electric modulus analysis indicates the existence of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The ac conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law. The temperature dependent pre-exponential factor (A) shows peak and frequency exponent (n) possesses a minimum at transition temperature.

Double perovskite materials have been studied in detail by many researchers, as their magnetic and electronic properties can be controlled by the substitution of alkaline earth metals or lanthanides in the A site and transition metals in the B site. Here we report the temperature-driven, p–n-type conduction switching assisted, large change in thermopower in La3+-doped Sr2TiFeO6-based double perovskites. Stoichiometric compositions of LaxSr2−xTiFeO6 (LSTF) with 0 ⩽ x ⩽ 0.25 were synthesized by the solid-state reaction method. Rietveld refinement of room-temperature XRD data confirmed a single-phase solid solution with cubic crystal structure and space group. From temperature-dependent electrical conductivity and Seebeck coefficient (S) studies it is evident that all the compositions underwent an intermediate semiconductor-to-metal transition before the semiconductor phase reappeared at higher temperature. In the process of semiconductor–metal–semiconductor transition, LSTF compositions demonstrated temperature-driven p–n-type conduction switching behavior. The electronic restructuring which occurs due to the intermediate metallic phase between semiconductor phases leads to the colossal change in S for LSTF oxides. The maximum drop in thermopower (ΔS ~ 2516 µV K−1) was observed for LSTF with x = 0.1 composition. Owing to their enormous change in thermopower of the order of millivolts per kelvin, integrated with p–n-type resistance switching, these double perovskites can be used for various high-temperature multifunctional device applications such as diodes, sensors, switches, thermistors, thyristors, thermal runaway monitors etc. Furthermore, the conduction mechanisms of these oxides were explained by the small polaron hopping model.

Theoretical pressure-tuning bandgaps of double perovskites A2(BB’) X6 for photo-voltaics

Role of structural, morphological, and electronic characteristics in investigating the low temperature transport and magnetic behavior of Sr doped Sm2NiMnO6

First principle insights on mechanical, electronic and optical properties of direct bandgap material Cs2KScX6 (X=Cl, Br and I) for optoelectronic applications

Double perovskite materials have emerged as key players in the realm of advanced materials due to their unique structural and functional properties. This research mainly focuses on the synthesis and comprehensive characterization of Ba2CoWO6 double perovskite nanopowders utilizing a high-temperature conventional solid-state reaction technique. The successful formation of Ba2CoWO6 powders was confirmed through detailed analysis employing advanced characterization techniques. Rietveld refinement of X-ray diffraction (XRD) and Raman data established that Ba2CoWO6 crystallizes in a cubic crystal structure with the space group Fm-3m, indicative of a highly ordered perovskite lattice. The typical crystallite size, approximately 65 nm, highlights the nanocrystalline nature of the material. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) discovered a distinctive morphology characterized by spherical shaped particles, suggesting a complex particle formation process influenced by synthesis conditions. To probe the electronic structure, X-ray Photoelectron Spectroscopy (XPS) identified cobalt and tungsten valence states, critical for understanding dielectric properties associated with localized charge carriers. The semiconducting character of the synthesized Ba2CoWO6 nanocrystalline material was confirmed through UV-Visible analysis, which revealed an energy bandgap value of 3.3 eV, which aligns well with the theoretical predictions, indicating the accuracy and reliability of the experimental results. The photoluminescence spectrum exhibited two distinct emissions in the blue-green region. These emissions were attributed to the transitions 3P0→3H4, 3P0→3H5, and 3P0→3H6, primarily resulting from the contributions of Ba2+ ions. The dielectric characteristics of the compound were analyzed across a different range of frequencies, spanning from 1 kHz to 1 MHz. Magnetic characterization using Vibrating Sample Magnetometry (VSM) revealed antiferromagnetic behavior of Ba2CoWO6 ceramics at room temperature, attributed to super-exchange interactions between Co3+ and W5+ ions mediated by oxygen ions in the perovskite lattice. Additionally, first-principles calculations based on the Generalized Gradient Approximation (GGA+U) with a modified Becke–Johnson (mBJ) potential were employed to gain a deeper understanding of the structural and electronic properties of the materials. This approach involved systematically varying the Hubbard U parameter to optimize the description of electron correlation effects. These results deliver an extensive understanding of the structural, optical, morphological, electronic, and magnetic properties of Ba2CoWO6 ceramics, underscoring their potential for electronic and magnetic device applications.

In this communication, the effect of gadolinium (Gd) substitution on structural, microstructural, electrical and dielectric properties of bismuth ferrite BiFeO3 (i.e. Bi(Fe0.95Gd0.05)O3 abbreviated as BFGO5) has been reported. The development of an environment-friendly lead-free multiferroic material by substituting a rare earth element at the uncommon site of BiFeO3 (BFO) (i.e. Gd at the Fe site rather than commonly preferred Bi site) for the tailoring of its multiferroic properties has been attempted in this study. The present studied material has been fabricated through a conventional standard solid-state reaction (SSR) method using carbonates and high-quality oxides in a stoichiometric amount. The phase formation and basic crystal data were analysed by X-ray diffraction technique which shows a single-phase formation of BFGO5 material in orthorhombic symmetry. The average crystallite size was calculated using Scherrer’s formula and found to be 84 nm. The surface morphology and compositions examined by FE-SEM, EDX, FT-IR and TEM show the formation of highly compact sample with uniform distribution of grains. Detailed studies of dielectric parameters (dielectric constant and tangent loss) in a selected frequency range (1–1000 kHz) at different temperatures (273–773 K) clearly exhibit enhancement on dielectric properties of BFO. Studies of its impedance spectroscopy, electrical modulus and electrical conductivity confirm the semiconductor behaviour [negative temperature coefficient of resistance (NTCR)] and non-Debye type relaxation process of the material. The polarization versus electric field (P–E) analysis of BFGO5 shows an improvement in remnant polarization as compared to the parent compound BFO. Therefore, based on the several investigations of results, the BFGO5 material could be considered as a favourable candidate for electronic device applications.

In this communication, detailed studies of the structural, microstructural, dielectric, and electrical properties of polycrystalline materials, (Bi0.5Ba0.25Sr0.25) (Ti0.5Fe0.5)O3 and (Bi0.5Ba0.25Sr0.25) (Ti0.25Mn0.25Fe0.5)O3, synthesized by using a high–temperature solid-state-reaction method, have been reported. X-ray structural and scanning electron micrograph studies exhibit phase pure tetragonal system and surface morphology (size and distribution of grains and grain boundaries) of the samples respectively. Analysis of the temperature and frequency dependence of dielectric and electrical (impedance, modulus, and conductivity) data reveals the ferroelectric relaxor behavior, relaxation mechanism, and semiconductor (negative temperature coefficient of resistance) properties of the bulk BFBST and Mn modified BFBST electro-ceramics. The relaxation time and activation energy (Ea) were calculated from the above data. The characteristics of Mn modified BFBST have been compared to that of it’s parent (BFBST) compound. The different inherent conduction mechanisms, such as Ohmic, hopping, space charge limited (SCLC) have been analyzed. The bulk- and interface-limited conduction processes were evidently found in the materials by the Poole–Frenkel (PF) and Schottky (SEmen modified BFBST have been compared to that of its parent (BFBST) compound) emission fitting of the J ∼ E characteristic data. The leakage data of BFBST-Mn (Mn modified Mn) quantified the average energy gap (Eg) in the range of 0.83–0. 87 eV for different applied voltages and in a wide range of temperature (25 °C–300 °C). With the increase in voltage, Eg decreases. This work suggests that Mn-substitution (Mn4+) at B (Ti4+) site keeping the stoichiometry undisturbed enhances structural, dielectric response (higher dielectric constant) and reduce the leakage behavior especially at low temperature and high-frequency range.