Impedance Spectroscopy and Structural Studies on Silver Doped Hydroxyapatite
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1239-VV07-18
Impedance spectroscopy and structural studies on silver doped hydroxyapatite Brajendra Singh1,4, Samayendra Kumar2, Bikramjit Basu3, Rajeev Gupta1,2 1
Department of Physics, Indian Institute of Technology Kanpur, Kanpur – 208016, Uttar Pradesh, INDIA 2 Materials Science programme, Indian Institute of Technology Kanpur Kanpur – 208016, Uttar Pradesh, INDIA 3 Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kanpur, Kanpur – 208016, Uttar Pradesh, INDIA 4 Centre of Material Sciences, University of Allahabad, Allahabad -211002 Uttar Pradesh, INDIA
ABSTRACT We report the structural transformation and the transport studies of Silver doped hydroxyapatites Ca10-xAgx(PO4)6(OH)2 (0.0 ≤ x ≤ 1.5). A dramatic increase in the conductivity by two orders of magnitude for hydroxyapatite in presence of silver ions is recorded using impedance spectroscopy measurements in the temperature range of 450oC to 650oC. The characteristic surface plasmon resonance effect is used to explore the presence of silver nanoparticles, and Ag+ ions in hydroxyapatite using optical absorption measurements. The activation energy has been found to be 0.07 eV in silver doped composition in comparison to 0.39 eV for the parent hydroxyapatite. The sintering temperature dependence and compositional variation on the structural transformations from hydroxyapatite into tricalcium phosphate phases have been explored using Raman Spectroscopy and X-ray diffraction techniques.
INTRODUCTION Hydroxyapatite (HAp, Ca10(PO4)6(OH)2) crystallizes in hexagonal crystal structure (space group P63/m), which is similar to known ionic conductor apatites [1]. The presence of hydroxyl ions along the c-axis oriented channels facilitate the electrical conductivity in Hap [24]. On the other hand, silicate apatites known for its oxide conduction and oxide ions, follow direct linear conduction path (Ea=1.26 eV, vacancy mechanism) along c-axis or non-linear sinusoidal path (Ea=0.56eV, interstitial mechanism)[5.] The substitution of lower valence cations or cation deficiency increases the ionic conduction in silicate apatites [6.] The ionic conductivity of hydroxyapatite has been increased by substituting Ca+2 with larger ions (Pb+2), monovalent ion (Na+) or trivalent ion (La+3, Y+3), however the conductivity of HAp is lower than other known ionic conductors i.e. silicate apatites and silver based superionic solids [2-4,7]. In this manuscript, we report the results of the structural transformations of silver substituted Ca10-xAgx(PO4)6(OH)2 (0.0 ≤ x ≤ 1.5) compositions using X-ray diffraction, room temperature Raman spectroscopic studies and ionic conductivity studies. A critical analysis of the obtained results enable us to document the following aspects (i) the systematic transformation of hydroxyapatite phase into tricalcium phosphate with the increase in Ag content in 1200oC sintered samples, (ii) synthesis of Silver ions embedded sintered hydroxyapatite (iii) enhanced ionic conductivity of silver doped hydroxyapatite.
EXPERIMENT
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