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

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

First principles study of magnetic and electronic properties of A2BB'O6 (A = Ba, Sr) (BB0 = FeRe, MnMo, and MnRe) double perovskites

Pro výpočet strukturálních, elektronických a magnetických vlastností A2BB0O6 (A = Ba, Sr) a (BB0 = FeRe, MnMo a MnRe) se uplatňuje metoda Full-potential linearized augmented plane wave (FP-LAPW). Strukturní vlastnosti v kubické fázi se zkoumají s optimalizovaným objemem. Elektronické pásmové struktury se vypočítají použitím nejúčinnější modifikované aproximace gradientu pro oba spin-kanály. Přiblížení gradientů plus parametr Hubbard (GGA + U). Spirálové (SO) vazebné efekty přidané k GGA + U ukazují, že všechny sloučeniny mají polovodičovou povahu v obou spinových kanálech. Hustota stavů ukazuje, že valenční pásmo má většinou charakter O-2p, zatímco vodivý pás dominuje stav Fe / Re, Mn / Mo a Mn / re-d. Vyhodnocený magnetický moment ukazuje užitečnost těchto sloučenin pro spintronické aplikace těchto sloučenin.Full-potential linearized augmented plane wave (FP-LAPW) method is applied to calculate the structural, electronic and magnetic properties of A2BB0O6 (A = Ba, Sr) and (BB0 = FeRe, MnMo, and MnRe). The structural properties in cubic phase are studied at optimized volume. Electronic band structures are calculated by using the most efficient modified generalized gradient approximation for both spin-channels. This revealed that these materials have metallic behavior while some revealed half metallic behavior in generalized gradient approximation plus Hubbard parameter (GGA+U). Spin orbit (SO) coupling effects added to GGA+U reveal that all the compounds have semiconducting nature in both spin channels. Density of states shows that valence band has the majority O-2p state character while conduction band is dominated by the Fe/Re, Mn/Mo, and Mn/re-d state. The evaluated magnetic moment shows the utility of these compounds for the spintronics application

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

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

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

Investigation of Structural, Magnetic, and Optical Properties of ZnO Codoped with Co and Cd

Co and Cd have been codoped in ZnO using a simple solid state reaction technique to synthesize dilute magnetic oxide semiconductors of composition Zn0.9Co0.1−xCdxO (x = 0.0-0.1 with an increment of 0.02). Hexagonal wurtzite structure has been obtained for samples up to x = 0.06, using X-ray diffractometry. However, at x = 0.08 and 0.1, secondary peak of CdO is observed. Raman spectra of the samples have been obtained in 200–800 cm−1 range. UV-VIS spectrophotometer is used to study the optical properties, which shows that band gap energy decreases with the increase in Cd concentration. A weak ferromagnetic behavior was evident which decreased further by adding Cd in the series. Room temperature resistivity measurements performed using four-point probe technique showed that their values lie in the semiconductor range. Structural morphology of the samples has been investigated by a scanning electron microscope and grain size has been determined. Raman spectra and Fourier transform infrared spectroscopy revealed the successful incorporation of Co and Cd ions into the host ZnO lattice

Enhanced Magnetization of Sol-Gel Synthesized Pb-Doped Strontium Hexaferrites Nanocrystallites at Low Temperature

Effect of Pb doping on the structural and low temperature magnetic properties of SrPbxFe12-xO19 (x=0,0.1,0.2,0.3,and  0.4), synthesized by sol-gel autocombustion technique, has been investigated. The powder samples were sintered at 800°C for 2 h in order to develop the stable hexagonal phase, characteristic of the SrFe12O19 structure. The consequences of Pb substitution (at iron sites) on various structural parameters like lattice constants, unit cell volume, crystallite size, and porosity have been discussed. Fourier transform infrared frequency bands were utilized to determine the formation of tetrahedral and octahedral clusters of M-type ferrites. Hexagonal texture of the grains, a characteristic of the hexagonal crystal structure of SrFe12O19, was refined by Pb substitution. The magnetic properties, determined using a vibrating sample magnetometer, revealed that saturation magnetization decreased, while coercivity was increased with the increase of Pb contents. However, the increased squareness ratio and hence the energy product motivate the utilization of these ferrite compositions where hard magnetic characteristics are required. The increased values of saturation magnetization were observed at reduced temperature of 200 K, attributable to the better spin alignments of individual magnetic moments at low temperature