Dielectric behavior of β-SiC nanopowders in air between 30 and 400 °C

Silicon carbide (SiC) is regarded as a semiconductor and thus characterized mainly for its electrical conductivity. However, SiC does exhibit significant electrical resistance at low ambient temperatures and represents a possible dielectric insulator. In this paper, the dielectric properties of the β-SiC nanopowders were examined by X-ray diffraction and dielectric spectroscopy within the humid Malaysian environment. Research emphasis is placed on the stable dielectric behavior of the nanopowder itself as the nanopowder phase is susceptible to hydroxyl oxidization as mentioned by the nanopowder manufacturer. The XRD results identified the presence of β-SiC peaks whereas EDX detected minor oxygen presence in the nanopowder. Dielectric permittivity response of the nanopowder pellet indicated stable Quasi-DC dielectric behavior from 30 to 400 °C with minor increments of the initial relative dielectric permittivity at the lower temperatures. The relative dielectric permittivity of the SiC nanoparticles was determined to be 44 (30 °C) to 31 (400 °C) at 1 MHz. Arrhenius plot of the dielectric data resulted in a two linear energy activation plots due to possible hopping mechanisms within the SiC nanoparticles covalent structure. Overall, the β-SiC nanopowder exhibited a stable Quasi-DC behavior at the measured temperatures

Dielectric behavior of b-SiC nanopowders in air between 30 and 400˚C

Silicon carbide (SiC) is regarded as a semi-conductor and thus characterized mainly for its electrical conductivity. However, SiC does exhibit significant electrical resistance at low ambient temperatures and represents a possible dielectric insulator. In this paper, the dielectric properties of the b-SiC nanopowders were examined by X-ray diffraction and dielectric spectroscopy within the humid Malaysian environment. Research emphasis is placed on the stable dielectric behavior of the nanopowder itself as the nanopowder phase is susceptible to hydroxyloxidization as mentioned by the nanopowder manufacturer. The XRD results identified the presence of b-SiC peaks whereas EDX detected minor oxygen presence in the nanopowder. Dielectric permittivity response of the nanopowder pellet indicated stable Quasi-DC dielectric behavior from 30 to 400° C with minor increments of the initial relative dielectric permittivity at the lower temperatures. The relative dielectric permittivity of the SiC nanoparticles was determined to be 44 (30° C) to 31 (400° C) at 1MHz. Arrhenius plot of the dielectric data resulted in a two linear energy activation plots due to possible hopping mechanisms within the SiC nanoparticles covalent structure. Overall, the b-SiC nanopowder exhibited a stable Quasi-DC behavior at the measured temperatures

The sol-gel synthesis and characterization of strontium titanate doped with Pr and Al ions

Strontium Titanate (SrTiO3) doped with Praseodymium (Pr) as an oxide compound phosphor show a potential application for a field emission display (FED). Addition of Aluminum ions (Al3+) has been attracting interest as a sensitizer to improve the luminescent efficiency of phosphors. In this study, the influence of Al3+ as a dopant on the crystallization, surface morphology and luminescent properties of SrTiO3:Pr,Al nanophosphors were investigated. Nanophosphor with the nominal composition of SrTiO3 undoped and doped with Pr3+ and Al3+ were synthesized at relatively low temperature by the sol-gel method. The crystal structures and average grain sizes were examined using x-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns indicated that crystalline SrTiO3 which has been synthesized at calcining temperature of 800°C for 2 h present a cubic structure. Moreover, the improvement of single crystalline phase is confirmed by increasing the temperature. SEM micrographs indicate that the addition of Pr3+ and Al3+ influence the texture and morphology of the samples. Nanoparticles samples with various sizes of 25-55 nm were obtained as a function of Pr and Al concentration using Scherrer?s equation. Fourier Transform Infrared (FTIR) spectra from SrTiO3 doped and undoped are also reported. The effect of doping on the infrared spectral of SrTiO3 structure is clearly shown in the low-frequency regions but overlapped with O-Ti-O bending mode. Raman spectroscopy was employed to investigate the evolution of the cubic phase in the nanocrystals during annealing and doping concentration. By addition of dopants, Raman spectra show formation of second-order Raman Scattering of SrTiO3. The luminescent properties of SrTiO3:Pr,Al phosphor were investigated by Photoluminescence (PL) spectroscopy. Under 325 nm excitation, SrTiO3:Pr,Al phosphor exhibited a strong red emission, peaking at about 615 nm. The intensity of emission spectra was enhanced by the addition of Al3+ ions

Effects of sintering temperature on morphology and dielectric properties of SrTio₃-doped CaCu₃Ti₄O₁₂ prepared via mechanical alloying

Perovskite materials are well known for their ability to produce high dielectric constant which had led to many important industrial applications in microelectronics and memory devices. In this research, the relationship between morphology and dielectric properties of perovskite Strontium Titanate, ST and the perovskite-related material Calcium Copper Titanate, CCTO were studied. Most of the works done on CCTO-ST system basically cover the composition of CCTO-ST towards their electrical properties, effect of doping and their dielectric and microstructure relationship at higher sintering temperatures. However, not much work was done on tracking the evolution of CCTO-ST at low sintering temperature until they evolve to their final sintering temperature. Hence, in this thesis, research findings on the parallel evolution of such morphological properties and dielectric properties were reported and elucidate their relationship. CCTO, ST and CCTO doped with ST were prepared via mechanical alloying using High Energy Ball Milling in a hardened steel vial for 10, 12 and 2 hours respectively. The pellet samples were sintered from 500 °C to final temperature at 100 °C increment. The phase and crystal structure formation of the synthesized materials were confirmed by X-ray diffraction (XRD) while the evolution of microstructure properties was studied using Field Emission Scanning Electron Microscopy, FeSEM. The as-milled ceramic confirmed the existence of CCTO peak for the CCTO and CCTO-ST samples. After the sintering process, the highly crystalline phase of ST, CCTO and CCTO-ST was form at 1000 °C, 1000 °C and 800 °C respectively. FeSEM revealed an improvement in grain growth as the sintering increased where the grain size increased from 126.5 nm to 559.6 nm (ST), 82 nm to 18467 nm (CCTO) and from 114.54 nm to 1658.02 nm (CCTO-ST). The relative densities also show an increment where it reaches 73.59%, 98.92% and 22.26% for CCTO, ST and CCTO-ST respectively at their final sintering temperature. The dielectric studies were carried out by using Impedance Analyzer in the frequency range 40 Hz to 1 MHz and varies from 30 °C to 200 °C. For ST samples, the dielectric constant showed interfacial polarization at low frequency and ɛr’ value increases from 49.753 to 517.603 at 100 kHz as the sintering temperature arise. Meanwhile, tangent loss (tan δ) was found in the range of 0.069 to 0.02 at 100 kHz at room temperature. For CCTO, the permittivity studies showed two polarizations occur. The relaxation belonged to the interfacial polarization. At 100 kHz, the ɛr’ varies from 72 to 5573 for CCTO samples sintered at 500 oC to 1100 oC. The frequency dependence of loss tangent, tan δ decreased to almost zero at higher frequencies for all sintering temperatures. The influence of ST on CCTO system does improved the microstructure and reduced the dielectric properties. The dielectric constant for CCTO-ST nanocomposite is lower than in CCTO ceramics which in the range of 139.956 at 100 kHz. However ST as a dopant also reduced tan δ to 0.03. CCTO-ST sintered at 1000 °C showed a prominent candidate for energy storage devices as it has the lowest tangent loss and moderate ɛr’

Vibrational studies of calcium magnesium ultraphosphate glasses

Phosphate glasses in a system of magnesium calcium phosphate for host matrix luminescent materials were investigated. The glass samples in a series of xMgO–(40- x)CaO–60P2O5 in molar ratio (0 ? x ? 40 mol%) were prepared using melt-quenching technique. The effect of Mg and Ca content on the structure and glass stability against crystallization in the system of MgO–CaO–P2O5 ultraphosphate has been investigated using XRD, Infrared and Raman spectroscopy. The compositions containing up to 40 mol% of CaO and /or MgO formed glasses and no crystalline phases were detected by XRD. The results of IR and Raman spectroscopy suggest that the phosphate network of these glasses is composed of middle (Q2) and branching (Q3) phosphate tetrahedral and other calcium/magnesium anions. All the symmetric and asymmetric stretching vibrations of POP and PO2 observed in the spectra are characteristic of Q3 and Q2 groups. The glass network, especially the Q2 units can be modified by the presence of Ca and Mg ions. This modification is primarily associated with the phosphate and the Q2 and Q3 phosphate units randomly distributed in the network. Spectroscopic results shows that the modification of the phosphate network is higher for the Ca containing glasses with respect to the Mg ones, at the same alkali earth content, due to the well defined Ca properties as a modifying cation. Formation of P–O–H bond expresses the hygroscopic nature of the phosphate glasses. This study shows that the vibrational spectroscopy (Infrared and Raman) are provide useful, complementary information about the network structures of ultraphosphate glasse

Structural studies on magnesium calcium tellurite doped with Eu2+ and Dy3+

The samples of phosphor material based on alkali earth tellurite, doped with rare earth have been prepared using solid state reaction method. The samples are with the composition in mol %: xMgO-(30-x)CaO-70TeO2 with 0=x=30 mol%, and have been doped with Eu2O3(2mol%) and Dy2O3(1mol%). The structure of the samples have been investigated by means of X-Ray Diffraction, Raman and Infrared spectroscopy. The xray diffraction results show that two phase are observed in the samples, which is MgTe2O5 and CaTe2O5 phase. Raman spectroscopy studies show that the vibrations of the samples are identical with the a-TeO2 vibrations, with a shift about 40-50cm-1. Strong bands are observed located at around 435, 616, 689, 785, and 807cm-1. As the concentration of the modifier, MgO and CaO increased, the coordination of TeO4 are transform from the corner sharing, a-TeO2 structure to the edge sharing, ß-TeO2 structure. It is also indicated that the increasing of MgO contribute to the increasing of symmetry vibration of TeO4 molecule, s(TeO4), while the addition of CaO increased the asymmetry vibration of TeO4 molecule, as(TeO4). The comparison between Raman and IR spectra is also include to identify the mode vibration of the samples