Sort:
Open Access Research Article Issue
Mechanically induced stiffening, thermally driven softening, and brittle nature of SiC
Journal of Advanced Ceramics 2016, 5 (1): 13-34
Published: 31 March 2016
Abstract PDF (806.4 KB) Collect
Downloads:18

An effective interionic potential calculation with long range Coulomb, charge transfer interaction, covalency effect, short range overlap repulsion extended, van der Waals interaction, and zero point energy effect is implemented to investigate the pressure dependent structural phase transition (ZnS-type (B3) to NaCl-type (B1) structure), and mechanical, elastic, and thermodynamic properties of silicon carbide (SiC). Both charge transfer interaction and covalency effect are important in revealing the pressure induced structural stability, Cauchy discrepancy, anisotropy factor, melting temperature, shear modulus, Young’s modulus, and Grüneisen parameter. We also present the results for the temperature dependent behaviors of normalized volume, hardness, heat capacity, and thermal expansion coefficient. SiC is mechanically stiffened and thermally softened as inferred from pressure (temperature) dependent elastic constant’s behavior. The Pugh’s ratio ϕ=BT/GH, the Poisson’s ratio ν, and the Cauchy’s pressure C12C44 for SiC ceramic confirm its brittle nature.

Open Access Research Article Issue
Rare earth (La) and metal ion (Pb) substitution induced structural and multiferroic properties of bismuth ferrite
Journal of Advanced Ceramics 2015, 4 (4): 292-299
Published: 24 November 2015
Abstract PDF (1.4 MB) Collect
Downloads:23

In this study, bulk samples of multiferroic with compositional formula, BiFeO3 and Bi0.825A0.175FeO3 (A=La, Pb), were synthesized by solid state reaction route. X-ray diffraction (XRD) along with the Rietveld refinement revealed the distorted rhombohedral (R3c) structure for pristine BiFeO3 and Bi0.825La0.175FeO3 and tetragonal (P4/mmm) for Bi0.825Pb0.175FeO3 ceramic. To support the structural results, bond length between atoms for both of the compounds was calculated. A change in Raman mode position in BiFeO3 (BFO) has been observed with La and Pb substitution from Raman scattering measurements and also recommended a structural change with rare earth and metal ion substitution at Bi site. From the frequency dependent dielectric constant and dielectric loss plots, a decrease in dielectric values with increase in frequency was observed for both of the samples. For microelectronic devices, porous ceramics with lower value of dielectric constant are most useful. Thus, further studies are also needed to carefully tune the magnetoelectric properties and structural distortion after La/Pb substitution in BFO.

Open Access Research Article Issue
Structural, vibrational and magnetic properties of Ti substituted bulk hematite: α-Fe2-xTixO3
Journal of Advanced Ceramics 2014, 3 (4): 269-277
Published: 30 November 2014
Abstract PDF (638.6 KB) Collect
Downloads:19

Ti doped hematite α-Fe2-xTixO3 (x = 0.0, 0.0206 and 0.0344) samples are synthesized using solid-state ceramic route technique. Single phase and corundum (Al2O3) type structure is revealed from the X-ray diffraction (XRD) pattern. On substitution of Ti at Fe site, all Raman active modes are shifted to higher wave numbers. An additional feature of Eu (LO) mode at about 660 cm–1 is observed. The Eu mode frequency is decreased and pronounced systematically as a function of Ti doping, and it reaches a value of 658 cm-1 for x = 0.0344. The coercivity Hc (remanence Mr) for x = 0.0, 0.0206 and 0.0344 are determined to be 995 Oe (0.44 emu/mg), 1404 Oe (0.00019 emu/mg) and 2023 Oe (0.00016 emu/mg), respectively. The larger coercivity for Ti doped samples can be attributed to their enhanced shape and magneto-crystalline anisotropy. The observed isomer shift (δ) from room temperature Mössbauer data clearly shows the presence of ferric (Fe3+) and Ti4+ ions illustrating strong ferromagnetic ordering up to x = 0.0206 in α-Fe2-xTixO3 hematite and weak ferromagnetic ordering of α-Fe2-xTixO3 for x = 0.0344.

Open Access Research Article Issue
Role of phonon drag and carrier diffusion in thermoelectric power of polycrystalline La0.97Na0.03MnO3 manganites
Journal of Advanced Ceramics 2014, 3 (3): 224-229
Published: 02 September 2014
Abstract PDF (265.4 KB) Collect
Downloads:15

We develop a theoretical model for quantitative analysis of temperature-dependent thermoelectric power of monovalent (Na) doped La0.97Na0.03MnO3 manganites. In the ferromagnetic regime, we have evaluated the phonon thermoelectric power by incorporating the scattering of phonons with impurities, grain boundaries, charge carriers and phonons. In doing so, we use the Mott expression to compute the carrier (hole) diffusion thermoelectric power ( Scdiff) using Fermi energy as carrier (hole)-free parameter, and Scdiff shows linear temperature dependence and phonon drag Sphdrag increases exponentially with temperature which is an artifact of various operating scattering mechanisms. It is also shown that for phonons the scattering and transport cross-sections are proportional to ω4 in the Rayleigh regime where ω is the frequency of the phonons. Numerical analysis of thermoelectric power from the present model shows similar results as those revealed from experiments.

Open Access Research Article Issue
Magnetic and structural properties of pure and Cr-doped haematite: α-Fe2-xCrxO3 (0 ≤ x ≤ 1)
Journal of Advanced Ceramics 2013, 2 (4): 360-369
Published: 04 December 2013
Abstract PDF (441.9 KB) Collect
Downloads:26

Solid-state ceramic technique route is used for synthesizing Cr-doped haematite α-Fe2-xCrxO3 (x = 0, 0.125, 0.50 and 1) samples. Single phase and corundum (Al2O3) type structure is revealed from the X-ray diffraction (XRD) patterns. The Raman spectra of α-Fe2-xCrxO3 illustrate seven phonon modes. On substitution of Cr (x = 0, 0.125, 0.50 and 1) at Fe site, all Raman active modes are shifted to higher wave numbers. The coercivity and remanence of Cr-doped haematites increase as x increases. The increased coercivity and remanence for Cr-doped samples can be attributed to their enhanced shape and magneto-crystalline anisotropy. The observed isomer shift δ values from room-temperature Mössbauer data clearly show the presence of ferric (Fe3+) and Cr3+ ions illustrating strong ferromagnetic ordering up to x = 0.125 in α-Fe2-xCrxO3 haematite and weak ferromagnetic ordering for α-Fe2-xCrxO3 (x > 0.125) haematites.

Total 5