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

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

Structural and luminescene properties of magnesium strontium metaphosphat e doped with europium and dysprosium ions

A series of samples based on xMgO-(50-x)SrO-50P2Os (with 0 < x <50 mol %) were prepared using solid state reaction method and sintered at 900°C. The crystalline phase of powder samples were characterized using X-ray diffraction (XRD) while the assignments of the vibration modes were determined using Fourier Transform Infrared (IR) and Raman spectroscopies. The XRD analysis indicated that the prepared samples were polycrystalline phase of Sr(PO3)2, SrMgP2O7, Mg2P4O12 and Mg2P2O7. The optimum sintering temperature of the prepared samples is 900oC. The Infrared and Raman studies showed that the magnesium strontium metaphosphate system consists of a main network of Q2, Q1 and Q° tetrahedral units. There were four peaks observed in the both spectra which are P=O group (1320 cm-1), PO2 group (1200 - 1170 cm-1), PO3 and PO4 groups (1160 - 950 cm-1) and P-O-P group (950 - 704 cm-1). This study illustrated that SrO and MgO act as modifiers and also improved chemical and physical stability of the phosphate material. The dopant ions (Eu3+ and Dy3+) as studied using XRD, IR and Raman spectra showed that small quantities of europium and dysprosium ions does not affect the local structure of magnesium strontium metaphosphate network. The luminescence property of the Eu3+ and Dy3+ as dopants in magnesium strontium metaphosphate was studied using photoluminescence spectroscopy. The emission peaks for Eu3+ doped sample were located at 568 nm, 582 nm, 605 nm, 642 nm and 689 nm, due to the 5D0 —^ 7Fj (j = 0, 1, 2, 3, 4) transition. Meanwhile for Dy3+ doped sample, two intense peaks appear at 477 nm and 564 nm are due to the 4F9/2 — 6H15/2 and 4F9/2 — 6H13/2 transitions. For sample doped with Eu3+ and Dy3+, the intensity of the main peak increases. This study also showed that magnesium strontium metaphosphate doped with Eu3+ and Dy3+ has better luminescence characteristic as compared to strontium metaphosphate or magnesium metaphosphate. The results of the study suggested that magnesium strontium metaphosphate is a potential candidate for plasma display applications

Effects of sintering temperature on microstructure and complex permittivity of magnesium titanate-doped barium strontium titanate prepared via mechanical alloying

Uncovering the relationship between microstructure and dielectric properties is beneficial knowledge for finding high dielectric constant materials with low loss for technological purposes. Thus this research work attempts to understand the evolving relationship over sintering temperature between permittivity and microstructure properties in barium strontium titanate (BST), magnesium titanate (MT) and magnesium titanate doped barium strontium titanate (BST-MT). BST, MT and BST-MT samples were mechanically crush activated using a high energy ball mill for 10, 12 and 2 hours respectively. Pellets were formed followed by a sintering process from 500 oC up to 1300 oC with 100 oC increment. The phase analysis carried out using X-ray diffraction (XRD) showed a highly crystalline BST, MT or BST-MT ceramic could not be formed during milling alone. At 500 oC, the major reflection (Ba0.5Sr0.5TiO3, MgTiO3 or Ba0.5Sr0.5TiO3/MgTiO3) grew from a broad peak into a sharp peak as it reached 1300 oC. In BST-MT system, there was no trace of dopant, MgTiO3 observed in XRD for all sintering temperatures. However, the energy dispersive X-ray (EDX) images confirmed the presence of Mg ion in BST-MT system. Sintering activity showed an improvement in the density where it increased from 3.67 g/cm3 to 4.88 g/cm3 for BST samples, 3.08 g/cm3 to 3.56 g/cm3 for MT samples and from 3.914 g/cm3 to 5.318 g/cm3 BST-MT sample. Field emission scanning electron microscope (FESEM) presented the average starting particle sizes were 39 nm, 89 nm and 78 nm for BST, MT and BST-MT respectively. There were an improvement in the grain growth where the grain size increased from 32.9 nm to 174.8 nm for BST, 87.5 nm to 1575.0 nm for MT and 80.8 nm to 267.5 nm for BST-MT. The dielectric properties investigated using the Agilent 4294A Impedance analyzer revealed the dielectric constant, ԑr’ showed a decreasing trend below 104 HZ with increasing frequency for all samples due to the interfacial polarization. At 1 MHz, εr’ increased from 49.28 to 143.68 (BST), from 28.15 to 47.39 (MT) and from 46.52 to 120.81 (BST-MT) with the rise of sintering temperatures. Therefore it revealed the dependency of dipolar polarization on the grain size and the crystalline structure resulting in a remarkable increase in polarizability. The tangent loss was found to decrease with frequency where a high tan δ at low frequency due to the decrement of hopping process of ions. The Nyquist plot in all sample revealed the attribution to the grain property of the material with the rise of sintering temperature. Complex modulus revealed one semicircle observed for higher sintered BST and MT. However, the introduction of dopant caused two semicircle observed for BST-MT sintered at 1200 oC and 1300 oC at all measuring temperatures suggesting the presence of both the grain and grain boundary contribution in the sample. BST-MT samples sintered at 1200 oC showed a prominent candidate for energy storage application as it experience a good physical properties with dielectric constant of 97.9 and 65% lesser dielectric loss compared to pure BST

The origin of emission in strontium magnesium pyrophosphate doped with Dy2O3

This paper reports on the luminescence properties of Dy3+-doped 30SrO–30MgO–40P2O5, which had been prepared by solid state reaction. The crystalline phases were identified using X-ray diffraction (XRD) and their luminescence properties were studied using excitation and emission spectra obtained from photoluminescence spectroscopy. The results of XRD patterns indicate that the prepared sample contain crystalline phase of MgP2O6 and SrMgP2O7. The excitation spectrum of 30SrO–30MgO–40P2O5:Dy3+ consists of broad bands’ centre at ~280, 310 and 400–600 nm associated with defects and vacancies of host material. The other feature of sharp peaks is very similar and belongs to Dy3+ ions. The f–f transitions in the range of 417–475 nm correspond to the transitions from 6H15/2 to 4K17/2 + 4M19/2,21/2 + 4I13/2 + 4F7/2, 4G11/2, 4I15/2 and 4F9/2, in the range of 392 nm to 6P3/2 + 6P5/2, and in the range of 312–370 nm to 4K15/2, 6P7/2 + 4M15/2 and 4I11/2, respectively. The peaks at 482, 465, and 455 nm could be assigned to the transition of 4F9/2 → 6H15/2, 4I15/2 → 6H15/2 and 4G11/2 → 6H15/2 of Dy3+, respectively. Dy3+ has emissions due to the atomic energy levels of itself and emissions due to the acceptor levels of defect sites formed by Dy3+

Vibrational studies of crystalline phase strontium magnesium phosphates doped with Eu2O3

In order to verify the assignments of the vibration modes and to find correlations in the changes induced by Eu2O3 in strontium magnesium phosphate with the composition of 27.5SrO-27.5MgO-45P2O5 as phosphor host matrix was prepared and investigated using Raman and Infrared (IR) spectroscopy. The doping concentration of Eu2O3 ions were varies from 1-5 mol%. The results of this study shows that Raman spectroscopy was give better structure change comparable to IR spectroscopy. Raman spectra of the studied sample present the specific bands of the phosphate network when doping with Eu2O3 ions, but structural change in IR spectra is unnoticeable, due to a characteristic of symmetry materials. The position of most Raman and IR bands do not coincide indicating a higher symmetry. The characteristics features of 27.5SrO-27.5MgO-45P2O5 undoped spectrum are the PO2 asymmetric stretching vibration band at 1240 cm-1, ?as(PO2), the PO2 symmetric stretching vibration band at 1171 cm-1, ?s(PO2), the ?as(PO3) groups (chain-end groups) at 1136 cm-1, the ?s of PO3 groups near 1062 cm-1, the ?as of POP groups at 900 cm-1, the ?s of POP groups at 780 and 688 cm-1 and the deformation modes of P–O-(PO43-) groups at 562 and 477 cm-1. The crystallized phases obtained with high doping Eu2O3, exhibited the Raman bands related to the orthophosphate (Q0) structure along with the pyrophosphate (Q1), and traces of metaphosphate (Q2) units. Based on stoichiometric, only Q1 and Q2 units were expected to be present, but the Raman spectra indicated detectable concentration of Q0 units, which results from disproportion reactions that occur during the reorganization of the powder sample

Luminescence properties of 30SrO-30MgO-40P2O5DOPED WITH Dy2O3

This paper reports on the luminescence properties of Dy3+ (1.0 mol%) doped 30SrO-30MgO-40P2O5, which had been prepared by solid state reaction. The crystalline phaseswere identified using X-ray diffraction (XRD) and their luminescence properties werestudied using excitation and emission spectra obtained from photoluminescencespectroscopy. The results of XRD patterns indicate that the prepared sample containMg2P4O12 and SrMg P2O7 crystalline phase. The excitation spectrum of 30SrO-30MgO-40P2O5: Dy3+ consist many dominant broad bands’ center at ~280,310 and 400-600 nm.The broad band excitation spectrum associated with defects and vacancies of hostmaterial through two different crystalline phases present in host material. The otherfeature of sharp peaks is very similar and belongs to Dy3+ ions. The observed f-ftransitions in the range of 417-475nm correspond to the transitions from 6H15/2 to 4K17/2+ 4M19/2, 21/2 + 4I13/2 + 4F7/2, 4G11/2, 4I15/2 and 4F9/2, in the range of 392nm to 6P3/2 + 6P5/2,and in the range of 312-370nm to 4K15/2, 6P7/2 + 4M15/2 and 4I11/2 respectively. The sharpemission peaks like at 482,465, and 455 nm could be assigned to the transition of4F9/2→6H15/2, 4I15/2→ 6H15/2 and 4G11/2→ 6H15/2 of Dy3+.respectively. Dy3+ has emissionsdue to the atomic energy levels of itself and emissions due to the acceptor levels ofdefect sites formed by Dy3+. In addition, the SrO-MgO-P2O5 is found a new self-activeluminescent material