High Dielectric Constant Study of TiO 2

TiO2/polypyrrole composites with high dielectric constant have been synthesized by in situ polymerization of pyrrole in an aqueous dispersion of low concentration of TiO2, in the presence of small amount of HCl. Structural, optical, surface morphological, and thermal properties of the composites were investigated by X-ray diffractometer, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, and thermogravimetric analysis, respectively. The data obtained from diffractometer and thermal gravimetric analysis confirmed the crystalline nature and thermal stability of the prepared composites. The dielectric constant of 5 wt% TiO2 increased with filler content up to 4.3 × 103 at 1 kHz and then decreased to 1.25 × 103 at 10 kHz

Phase Pure Synthesis and Morphology Dependent Magnetization in Mn Doped ZnO Nanostructures

Zn 0.95 Mn 0.05 O nanostructures were synthesized using sol gel derived autocombustion technique. As-burnt samples were thermally annealed at different temperatures (400, 600, and 800 ∘ C) for 8 hours to investigate their effect on structural morphology and magnetic behavior. X-ray diffraction and scanning electron microscopic studies demonstrated the improvement in crystallinity of phase pure wurtzite structure of Mn doped ZnO with variation of annealing temperature. Energy dispersive X-ray elemental compositional analysis confirmed the exact nominal compositions of the reactants. Electrical resistivity measurements were performed with variation in temperature, which depicted the semiconducting nature similar to parent ZnO after 5 at% Mn doping. Magnetic measurements by superconducting quantum interference device detected an enhanced trend of ferromagnetic interactions in thermally annealed compositions attributed to the improved structural morphology and crystalline refinement process

Influence of Gd content on structural, electronic, thermoelectric, and optical properties of WO3

WO _3 -based semiconductor materials are optimistic competitors for modern electronic devices because of their outstanding electronic and optical properties. Simulations on pure and Gd-doped WO _3 compositions were executed using Tran and Blaha modified Becke–Johnson approximation. Experimentally, thin films of these compositions were prepared using the chemically derived technique. X-ray diffraction spectra of thin films exhibited cubic structure having space group 221-Pm-3m in all compositions. Field emission scanning electron micrographs reveal the uniform growth of thin films with rod-like compact morphology. The density of states spectra for electronic properties demonstrate the main contribution of W- d and O- p for pure WO _3 with p-d hybridization while Gd containing composition provides an additional prominent contribution from f -orbital. Band structure shows an indirect transition for WO _3 and band gap values were observed as 1.73 eV which decreased with increment of Gd content. A significant change in thermoelectric parameters was observed with an increment of temperature and Gd doping. The maximum value of the refractive index was observed as 3.02 in the visible energy regime and tends to decrease in Gd containing compositions. The experimentally obtained maximum dielectric constant was observed as 7.89 for pure WO _3 and decreased to 4.58 for maximum Gd containing composition. Optical parameters like extinction, absorption coefficient, and optical conductivity show a sharp increment in visible energy region which make these compositions favorable for photovoltaic and optoelectronic applications. The experimentally obtained optical parameters are found in good agreement with simulated results obtained through TB-mBJ approximation

Co-existence of magnetic and electric ferroic orders in La-substituted BiFeO3

The idea of combining ferroelectricity and ferromagnetism in a single material i.e. multiferroicity, have gained much importance in the development of the technological devices. In this context, the present work explores the effect of La substitution on the structural, ferromagnetic and ferroelectric characteristics of BiFeO3. Various compositions of general formula Bi1−xLaxFeO3 with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared by sol–gel auto-combustion method. Powder samples were subsequently calcined at 600 °C for 2 h, which manifested rhombohedral phase for 0.0 ≤ x ≤ 0.8 and orthorhombic for x = 1.0, as confirmed by X-ray diffraction. Field emission scanning electron microscopy revealed the uniform grain formation with decreasing grain size by increasing La contents. Electron dispersive X-ray spectroscopy revealed the true wt% of the elements in the prepared samples, corresponding to empirical formulae of the composition. The magnetic analysis was performed using a vibrating sample magnetometer and the hysteresis loops of magnetization vs applied magnetic field showed an enhancement in magnetic properties at higher substitution of La at Bi-site. Moreover, remanence, saturation polarization and electric coercive field were also found to be increased with higher La substitution due to decreasing particle size. Hence, modification in multiferroicity by La substitution can be utilized in novel spintronic based device applications. Keywords: Multiferroics, Doped-BiFeO3, Magneto-electric couplin

Effect of La/Cr co-doping on dielectric dispersion of phase pure BiFeO3 nanoparticles for high frequency applications

Energy storage materials play a vital role in modern technology. A single device can perform multifunctions if fabricated using a multifunctional material like BiFeO3. For this purpose, a series of La and Cr doped BiFeO3 was synthesized using sol‒gel auto-combustion technique. A single phase rhombohedral distorted perovskite crystal structure related to bismuth ferrite with space group R3c (161) was confirmed from the X-ray diffraction patterns. Doping of La/Cr at Bi/Fe lattice sites in BiFeO3 did not affect the crystal symmetry of the parent compound. Morphological analysis exhibited homogeneous micro structures showing uniform distribution of multi-shaped grains with decreasing porosity and grain sizes with increasing Cr contents. These materials exhibited the conventional ferrite-like dielectric response, which gradually decreased with increasing frequency and lastly became constant in the high frequency regime. Impedance spectroscopy revealed the contribution of grains, grain boundaries and interfaces in electrical response of the samples. Frequency dependent electric modulus analysis confirmed the non-Debye type relaxation

Dielectric and magnetic investigations of mixed cubic spinel Co-ferrites with controlled Mg content

High temperature frequency dependent dielectric properties, and room temperature magnetic behavior of mixed ferrites with controlled content of Mg in Co₁₋ₓMgₓFe₂O₄ (x=0.0,0.1,0.3,0.5,0.7,0.9 and 1.0) compositions are studied. Single phase spinel structure with cubic symmetry, lattice parameters, crystallite size, magnetic and dielectric properties were substantiated with x-ray diffractometer, transmission electron microscope, vibrating sample magnetometer and impedance analysis, respectively. Due to interfacial polarization, dielectric behavior of all the compositions shows dispersion with increase in frequency. The dielectric data was investigated by comparing the tangent loss and electric modulus for assigning the type and mechanism of dielectric relaxation. Temperature dependent dielectric constant, tangent loss and AC conductivity increase due to thermal activation of charge carriers and drift mobility. Furthermore, room temperature weak ferromagnetic behavior is observed due to the incorporation of non-magnetic Mg ions.8 page(s

Rapid switching capability and efficient magnetoelectric coupling mediated by effective interfacial interactions in Bi0·9La0·1FeO3/SrCoO3 bi-phase composites for ultra-sensitive pulsating devices

Magnetoelectric coupling and switching charge density in multiferroics have gained the attention of researchers around the world for energy storage, energy harvesting, and their potential applications for pulsating devices. In multiferroics, the absence of inversion symmetry and the presence of antiferromagnetic symmetry give rise to intriguing magnetoelectric coupling. In this paper, bi-phase composites, (1–x)Bi0·9La0·1FeO3 + xSrCoO3 for x = 0.1, 0.2, 0.3 are made by a facile and time-saving sol–gel auto-combustion technique. For this, we employed lanthanum-doped BiFeO3 to avoid the volatilization of bismuth ions. The composition 0.8Bi0·9La0·1FeO3 + 0.2SrCoO3 (x = 0.2) showed the maximum polarization (Pmax = 2.45 × 10−3 μC/cm2) and effective interfacial interactions depicting symmetrical magnetoelectric coupling response with least distortion along with significant switching charge density (i.e., Qsw = – 2.124 × 10−5 μC/cm2). Whereas reduction in leakage current density is observed with the inclusion of SrCoO3 contents into pure BLFO during polarization phenomena, confirming its insulating properties. Switching charge density from the positive-up- negative-down sequence not only ensured the suitability of switching applications in pulsating devices but also displayed its reliability and long-term stability. The symmetric magnetoelectric coupling showed its potential use in piezoelectric actuators and energy harvester applications. Magnetic attributes and multidomain structures were confirmed by the vibrating sample magnetometer. The maximum value of the squareness ratio appears to be 0.1035 confirming the existence of a multidomain structure for all samples. These outcomes suggest that this particular composition seems extremely viable in developing ultra-sensitive pulsating devices attributed with significant switching charge density

Phase Pure Synthesis and Morphology Dependent Magnetization in Mn Doped ZnO Nanostructures

Zn0.95Mn0.05O nanostructures were synthesized using sol gel derived autocombustion technique. As-burnt samples were thermally annealed at different temperatures (400, 600, and 800°C) for 8 hours to investigate their effect on structural morphology and magnetic behavior. X-ray diffraction and scanning electron microscopic studies demonstrated the improvement in crystallinity of phase pure wurtzite structure of Mn doped ZnO with variation of annealing temperature. Energy dispersive X-ray elemental compositional analysis confirmed the exact nominal compositions of the reactants. Electrical resistivity measurements were performed with variation in temperature, which depicted the semiconducting nature similar to parent ZnO after 5 at% Mn doping. Magnetic measurements by superconducting quantum interference device detected an enhanced trend of ferromagnetic interactions in thermally annealed compositions attributed to the improved structural morphology and crystalline refinement process

Synthesis and Characterization of BaTiO₃/Polypyrrole Composites with Exceptional Dielectric Behaviour

Higher concentrations of ceramic fillers induce brittleness in the ceramic/polymer hybrids which restrict their applications to limited fields especially when such hybrids are prepared for their use as dielectrics. We have synthesized and characterized different BaTiO3-polypyrrole (PPy) composites by changing the concentration of BaTiO3 from 1% by weight of PPy taken to 5 wt % to explore its effect on the dielectric parameters of the final product and found that the BaTiO3-polypyrrole composite with weight ratio of 0.05:1 exhibited highest dielectric constant, lowest dielectric loss and thermally most stable. All the composites were prepared using in-situ polymerization of pyrrole in an aqueous dispersion of low content of BaTiO3 in the presence of small amount of Hydrochloric acid. These composites were characterized for their microstructure and crystallinity by X-ray diffractometer (XRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) while thermal stability by thermo gravimetric (TGA) analysis. An impedance analyser (LCR meter) was utilized to investigate the dielectric parameters. FT-IR data confirmed the presence of the two phases and their interaction, inferred from the shifting of normal PPy peaks. The data obtained from XRD confirmed the presence of crystallites of 2.8 to 5 nm with dominant crystallinity of the filler, TGA analysis (25 to 600 °C) confirmed the higher thermal stability induced on successive addition of the filler into the prepared composites as compared to that of pure PPy in a wide temperature range which is unusual for such a low % age addition of the filler. The SEM analysis together with XRD results reveal that the successive introduction of BaTiO3 particles produced crystallites of 2 to 5 nm size which bonded together and changed the hemispherical shaped larger grains of the matrix to regular shaped smaller grains. The dielectric constant of the composites was enhanced with filler contents from 178 to 522 at 1 MHz for 1 wt % and 5 wt % BaTiO3 respectively. It was concluded that the introduction of BaTiO3 into the polymer matrix with this new procedure has greatly affected the polymerization process, thermal stability, morphology and dielectric properties of the host matrix and has resulted in a novel series of the composites which may have broad applications

Pressure induced mechanical, opto-electronics, and transport properties of ZnHfO3 oxide for solar cell and energy harvesting devices

Based on the density functional theory, we systematically investigate the effect of pressure on the mechanical, optoelectronic, and transport properties of ZnHfO _3 . The pressure has been employed up to 30 GPa in a step-size of 10 GPa. A slight variation in the lattice constant and Bulk modulus have been observed at the applied pressure steps. The electronic properties are significantly tuned by applying pressure. The calculated bandgap values slightly increase with increasing the pressure and its values start to decrease after the critical pressure of 20 GPa. More interestingly, a transition from indirect to direct band has been observed at the critical pressure. This transition of the bandgap is also justified by studying the optical properties like dielectric constant, refraction, and absorption at different pressure. Furthermore, we studied the electronic transport properties in terms of electrical conductivity, thermal conductivity, See-beck coefficient, and power factor at temperature (300–800 K). The calculated lattice thermal conductivities are low while the electrical conductivities and Seebeck coefficients are high at all pressure. Thus, the properties of the ZnHfO _3 show high potential for thermoelectric applications