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Phase evolution and microwave dielectric properties of A5M5O17-type ceramics

Ali M., Iqbal Y., Muhammad R.

Materials Science Poland

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2017

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Vol. 35, No. 2

362--367

EN

A number of A5M5O17 (A = Na, Ca, Sr, La, Nd, Sm, Gd, Dy, Yb; B = Ti, Nb, Ta) type compounds were prepared by a solid-state sintering route and characterized in terms of structure, microstructure and microwave dielectric properties. The compatibility of rare earths with mixed niobate/tantalate and titanate phases was investigated. The larger ionic radii mismatch resulted in the formation of pyrochlore and/or mixed phases while in other cases, pure A5M5O17 phase was formed. The samples exhibited relative permittivity in the range of 35 to 82, quality factor (Q × fo) = 897 GHz to 11946 GHz and temperature coefficient of resonance frequency (τf) = -120 ppm/°C to 318 ppm/°C.

2

Influence of preparation method on structural, optical and magnetic properties of nickel ferrite nanoparticles

Khan A. A., Javed M., Khan R. A., Iqbal Y., Majeed A., Hussain S. Z., Durrani S. K.

Materials Science Poland

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2017

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Vol. 35, No. 1

58--65

EN

Nanocrystalline NiFe2O4 particles were prepared by conventional sol-gel, citrate-nitrate sol-gel combustion and co-precipitation methods. The synthesized samples were annealed at 1000 ºC for two hours and structural, chemical, morphological, optical and magnetic properties of nickel ferrite were investigated. The structural properties were investigated by X-ray diffraction (XRD) technique which confirmed the formation of single phase NiFe2O4 particles derived by the three methods. The chemical properties were analyzed by Fourier transform infrared (FT-IR) spectroscopy which confirmed the corresponding vibration modes in the samples. The optical properties were studied by UV-Vis spectroscopy. The morphological study of the as-synthesized samples was carried out by scanning electron microscopy (SEM). SEM images showed the agglomerated nanoparticles of NiFe2O4. The magnetic properties were investigated by vibrating sample magnetometer (VSM), which showed that the calcined samples exhibited typical magnetic behavior.

3

Leaching of manganese ores using corncob as reductant in H2SO4 solution

Ali S., Iqbal Y., Farooq U., Ahmad S.

Physicochemical Problems of Mineral Processing

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2016

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Vol. 52, iss. 1

56--65

EN

In this study, corncob was used as reductant for sulfuric acid leaching of manganese ore from Daweezi, Upper Mohmand Agency, Pakistan. X-ray diffraction of representative powdered samples revealed the presence of manganese silicate MnSiO(SiO4), calcite (CaCO3), and -quartz (SiO2). X-ray diffraction and energy dispersive spectroscopy analyses indicated that the examined manganese ore was siliceous in nature. Three process parameters were investigated in the present study including the particle size of the ore, leaching temperature, and amount of corncob. Manganese extraction of 92.48 wt% was achieved for a leaching time of 60 min at 90 oC using 1.9 mol/dm3 H2SO4 concentration and 4 g of corncob. The present results demonstrated that corncob is a low cost, renewable, and non-hazardous reducing agent for manganese leaching under mild acid conditions in comparison to the other available reagents.

4

Synthesis and electrical characterization of Ca2Nd4Ti6O20 ceramics

Muhammad R., Uzair M., Iqbal M. J., Khan M. J., Iqbal Y., Rambo C. R.

Materials Science Poland

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2016

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Vol. 34, No. 1

164--168

EN

Ca2Nd4Ti6O20, a layered perovskite structured material was synthesized via a chemical (citrate sol-gel) route for the first time using nitrates and alkoxide precursors. Phase analysis of a sample sintered at 1625 degrees C revealed the formation of an orthorhombic (Pbn21) symmetry. The microstructure of the sample after sintering comprised rod-shaped grains of a size of 1.5 to 6.5 μm. The room temperature dielectric constant of the sintered sample was 38 at 100 kHz. The remnant polarization (Pr) and the coercive field (Ec) were about 400 μC/cm2 and 8.4 kV/cm, respectively. Impedance spectroscopy revealed that the capacitance (13.7 pF) and activation energy (1.39 eV) of the grain boundary was greater than the capacitance (5.7 pF) and activation energy (1.13 eV) of the grain.

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Phase, microstructure and microwave dielectric properties of A-site deficient (La, Nd) 2/3TiO3 perovskite ceramics

Saleem M., Iqbal Y., Qin S., Wu X., Zhu F.

Materials Science Poland

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2015

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Vol. 33, No. 1

126--130

EN

(La, Nd)2/3TiO3 ceramics were prepared through a conventional solid state mixed oxide route. For phase and microstructure analysis, XRD and SEM were used, respectively. Microwave dielectric properties were measured using a network analyzer. XRD patterns revealed the formation of the parent (La, Nd)2/3TiO3 phase along with (La, Nd)4Ti9O24 as a secondary phase. The microstructure consisted of rectangular and needle shaped grains, which decreased in size from 4 μ m to 2 μm with an increase in sintering temperature from 1300 °C to 1350 °C. Decrease in grain size caused an increase in density of the samples from 4.81 g/cm3 to 5.17 g/cm3. Microwave dielectric properties of the samples calcined and sintered in air atmosphere were εr = 40.35, Q × f = 3499 GHz and τ f = 0 ppm/°C, whereas for a sample calcined in nitrogen and sintered in air they were εr = 40.18, Q × f = 4077 GHz and τ f = +4.9 ppm/°C, respectively.

6

Phase, microstructure and dielectric properties of 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics prepared by sol-gel technique

Uddin S., Iqbal Y., Ullah A.

Materials Science Poland

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2013

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Vol. 31, No. 3

410--414

EN

0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics were fabricated by sol-gel technique. The XRD results revealed the formation of a single phase perovskite structured Bi0.5Na0.5TiO3-BaTiO3 at 600 °C. The SEM images showed dense microstructure and the optimum density of the ceramics sintered at 1100 °C was 5.2 g/cm3. The saturation polarization (P s ) was found to be increased with increasing temperature while the remnant polarization (P r ) was found to be increased gradually and then decreased abruptly near 85 °C, which could be attributed to the phase transformation. The coercive electric field (E c ) was found to be decreased gradually with increasing temperature. The maximum value of dielectric constant (ɛ r ) at room temperature was 800 and dielectric loss at 1 MHz was 0.07.