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Title: Modification of the physical properties of semiconducting MgAl{sub 2}O{sub 4} by doping with a binary mixture of Co and Zn ions

Journal Article · · Materials Research Bulletin
 [1];  [2];  [3]
  1. Surface and Solid State Chemistry Laboratory, Department of Chemistry, Quaid-i-Azam University, Islamabad 45320 (Pakistan)
  2. Physics of Nanostructured Materials, University of Vienna, Boltzmanngasse 5, A-1090 Vienna (Austria)
  3. Department of Inorganic Chemistry/Materials Chemistry, University of Vienna, Waehringerstrasse 42, A-1090 Vienna (Austria)

Graphical abstract: Plot of (Co,Zn) content against normalized values of crystallite size, X-ray density and the dielectric constant. Highlights: Black-Right-Pointing-Pointer Co and Zn ions doped MgAl{sub 2}O{sub 4} nanomaterials. Black-Right-Pointing-Pointer Materials show better thermal stability in the temperature range of 298-1773 K. Black-Right-Pointing-Pointer High resistivity, high dielectric constant and loss observed in the doped materials. Black-Right-Pointing-Pointer Thermal conductivity and diffusivity are lowered and heat capacity is increased. Black-Right-Pointing-Pointer Three spin allowed electronic transitions of Co{sup 2+} at tetrahedral lattice sites. -- Abstract: The effects of doping of MgAl{sub 2}O{sub 4} by a binary mixture of Co and Zn ions on the absorbance, electrical resistivity, capacitance, thermal conductivity, heat capacity and thermal diffusivity are reported in this paper. The materials with the nominal composition Mg{sub 1-2x}(Co,Zn){sub x}Al{sub 2}O{sub 4} (x = 0.0-0.5) are synthesized by solution combustion synthesis assisted by microwave irradiation. The substituted spinels are produced with a Scherrer crystallite size of 18-23 nm, as opposed to 45 nm for undoped samples, indicated by X-ray diffraction and confirmed by transmission electron microscopy. These materials also show better thermal stability in the temperature range of 298-1773 K. Three strong absorption bands at 536, 577 and 630 nm are observed for the doped samples which are attributed to the three spin allowed ({sup 4}A{sub 2} (F) {yields} {sup 4}T{sub 1} (P)) electronic transitions of Co{sup 2+} at tetrahedral lattice sites while pure magnesium aluminate remains transparent in the whole spectral range. The semiconducting behavior of the materials is evident from the temperature dependence of the electrical resistivity. Resistivity and activation energy are higher for the substituted samples. Fitting of the resistivity data is achieved according to the hopping polaron model of solids. Both dielectric constant and loss increase on account of doping. The dielectric data are explained on the basis of space charge polarization. The thermal conductivity and diffusivity are lowered and the heat capacity is increased in the doped materials. Wiedemann-Franz's law is used to compute the electronic and lattice contributions towards the total thermal conductivity.

OSTI ID:
22212341
Journal Information:
Materials Research Bulletin, Vol. 46, Issue 12; Other Information: Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0025-5408
Country of Publication:
United States
Language:
English