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Content available remote Processing and microwave dielectric properties of Sr5Ta4TiO17 ceramics
Manan A., Ahmad A. S., Ullah A., Shah A. A.
Materials Science Poland
|
2017
|
Vol. 35, No. 4
767--772
EN
Sr5Ta4TiO17 ceramics was processed via solid state mixed oxide sintering route. X-ray diffraction revealed single phase formation of Sr5Ta4TiO17 ceramics that crystallized into an orthorhombic crystal structure with a space group Pnnm with lattice parameters of a = 5.681 Å, b = 32.542 Å and c = 3.968 Å, refined by the least squares method. The unit cell density (ρth) was 6.71 g/cm3. The microstructure consisted of plate-like grains and the average size was increased from 2 µm to 5 µm with an increase in sintering temperature from 1450 °C to 1575 °C. Optimum microwave dielectric properties, i.e. єr ~ 66, Qufo ~ 8500 GHz and τf ~ 180 ppm/°C, were achieved for Sr5TaTiO17 ceramics sintered at 1550 °C for 4 h.
2
Content available remote Raman spectroscopy and microwave dielectric properties of Sn substituted SrLa4Ti5O17 ceramics
Manan A., Ullah A., Ahmad A. S.
Materials Science Poland
|
2016
|
Vol. 34, No. 1
1--5
EN
SrLa4Ti5-xSnxO17 (0 ≤ x ≤ 2) ceramics were fabricated through solid state ceramic route and their microwave dielectric properties were investigated in an attempt to tune their temperature coefficient of resonant frequency to zero. The compositions were sintered to single phase SrLa4Ti5 O17 and SrLaa4Ti4,5Sn0,5O17 ceramics at x = 0 and x = 0.5, and SrLa4Ti4-xSnxO17 along with a small amount of La2Ti2O7 at x = 1. The major phase observed at x = 2 was La2Ti2O7 but along with SrLa4Ti4SnO17 and SrLa4Ti4O15 as the secondary phases. Τf decreased from 117 to 23.0 ppm/°C but at the cost of dielectric constant ("r) and quality factor multiplied by resonant frequency (Qufo) which decreased from 65 to 33.6 and 11150 to 4191 GHz, respectively. The optimum microwave dielectric properties, i.e. τf = 38.6 ppm/°C, εr = 45.5 and = 7919 GHz, correspond to the SrLa4Ti5-xSnxO17 composition with x = 1.
3
Content available remote Transformation mechanism of magnetite nanoparticles
Khan U. S., Amanullah, Manan A., Khan N., Mahmood A., Rahim A.
Materials Science Poland
|
2015
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Vol. 33, No. 2
278--285
EN
A simple oxidation synthesis route was developed for producing magnetite nanoparticles with controlled size and morphology. Investigation of oxidation process of the produced magnetite nanoparticles (NP) was performed after synthesis under different temperatures. The phase transformation of synthetic magnetite nanoparticles into maghemite and, henceforth, to hematite nanoparticles at different temperatures under dry oxidation has been studied. The natural magnetite particles were directly transformed to hematite particles at comparatively lower temperature, thus, maghemite phase was bypassed. The phase structures, morphologies and particle sizes of the produced magnetic nanoparticles have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX) and BET surface area analysis.
4
Content available remote Phase, microstructure and microwave dielectric properties of Mg0:95Ni0:05 Ti0:98Zr0:02O3 ceramics
Manan A., Khan D. N., Ullah A., Ahmad A. S.
Materials Science Poland
|
2015
|
Vol. 33, No. 1
95--99
EN
Mg0.95Ni0.05 Ti0.98Zr0.02O3 ceramics was prepared via conventional solid-state mixed-oxide route. The phase, microstructure and microwave dielectric properties of the sintered samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and a vector network analyzer. The microstructure comprised of circular and elongated plate-like grains. The semi quantitative analysis (EDS) of the circular and elongated grains revealed the existence of Mg0.95Ni0.05 T2O5 as a secondary phase along with the parent Mg0.95Ni0.05 Ti0.98Zr0.02O3r~17.1, Qufo~195855 ± 2550 GHz and tf ~ -46 ppm/K was achieved for the synthesized Mg0.95Ni0.05 Ti0.98Zr0.02O3 ceramics sintered at 1325 °C for 4 h.
5
Content available remote Influence of sintering temperature on secondary phases formation and microwave dielectric properties of Ca2Ce2Ti5O16 ceramics
Manan A., Khan S. U., Qazi I
Materials Science Poland
|
2014
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Vol. 32, No. 2
297--300
EN
Ca2Ce2Ti5O16 dielectric ceramics prepared by conventional solid-state ceramic route was investigated. Phase composition and microwave dielectric properties were measured using XRD and Vector network analyzer, respectively. XRD analysis of the calcined and sintered samples revealed the formation of CeO2 and another unidentified phase (that vanished at > 1400 °C) as secondary phases along with the parent Ca2Ce2Ti5O16 phase. The amount of the parent Ca2Ce2Ti5O16 phase increased with increasing sintering temperature from 1350 °C to 1450 °C accompanied by a decrease in the apparent density. The density decreased but er and Qu fo increased with sintering temperature. An er ~ 81.5, Qu fo ~ 5915 GHz and t f ~ 219 GHz were achieved for the sample sintered at 1450 °C.
6
Content available remote CuO as sintering additive to Sr0.4Ca0.6La4Ti5O17 ceramics
Manan A., Shah L. A., Attaullah
Materials Science Poland
|
2013
|
Vol. 31, No. 1
122-125
EN
The effects of CuO addition on the sintering behavior and microwave dielectric properties of Sr0:4Ca0:6La4Ti5O17 ceramics were investigated. CuO was selected as a liquid phase sintering aid to lower the sintering temperature of Sr0:4Ca0:6La4Ti5O17 ceramics. With CuO addition, the sintering temperature of Sr0:4Ca0:6La4Ti5O17 ceramics was effectively reduced from 1550 °C to 1475 °C. The crystalline phase exhibited no phase difference and no second phase was detected at all addition levels. The electric permittivity was not significantly affected by various amounts of CuO addition and ranged from 52 to 54. Small values (<+7 ppm/K) of the temperature coeficient of resonant frequency were obtained for Sr0:4Ca0:6La4Ti5O17 ceramics. However, the unloaded quality factor Qu was strongly dependent upon the CuO concentration. Qu fo - 10500 GHz was obtained for Sr0:4Ca0:6La4Ti5O17 ceramics with 0.5 wt.% of CuO addition, sintered at 1475 °C.
7
Content available remote The effect of processing conditions on the phase, microstructure and dielectric properties of SrCa4Nb4TiO17 and Ca5Nb4TiO17 microwave ceramics
Manan A., Reaney I. M.
Materials Science Poland
|
2012
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Vol. 30, No. 2
98--104
EN
The effect of processing conditions on the phase, microstructure and dielectric properties of SrCa4Nb4TiO17 and Ca5Nb4TiO17 microwave ceramics was investigated. The ceramics processed via solid state mixed-oxide route were characterized using XRD, Raman spectroscopy and SEM for phase, molecular vibrational modes and microstructural analysis respectively. Dielectric properties at low and microwave frequencies were measured using LCR meter and a vector network analyzer. The XRD results revealed the formation of a single phase for each ceramics. The microstructure was comprised of elongated and plate-like grains. The optimum microwave dielectric properties i.e. temperature coefficient of resonant frequency (t f ) --78 ppm/K, electric permittivity (er) -47:2 and quality factor multiplied by the resonant frequency (Qu fo) -11954 GHz, were achieved for SrCa4Nb4TiO17, sintered at 1475 °C for 4 h. For Ca5Nb4TiO17, sintered at 1450 °C for 4 h, the respective properties were: t f --137 ppm/K, er - 42 and Qu fo - 14800 GHz respectively.
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