Defect structure and optical phonon confinement in ultrananocrystalline BixSn1−xO2 (x = 0, 0.03, 0.05, and 0.08) synthesized by a sonochemical method. Issue 8 (3rd February 2016)

• Record Type: Journal Article
• Authors: Aswaghosh, L.; Manoharan, Divinah; Jaya, N. Victor
• Is Part Of: Physical chemistry chemical physics. Volume 18:Issue 8(2016)
• Page Start: 5995
• Page End: 6004
• Publication Date: 2016-02-03
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c5cp06214d
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Relaxation of the zone-centre optical phonon selection rule due to size effect causes interesting changes in vibrational spectra. Abstract : We report the structure of defect and the oxygen vacancy-induced optical phonon confinement in phase pure tetragonal rutile crystal structured ultrananocrystalline Bi x Sn1− x O2 ( x = 0, 0.03, 0.05, 0.08) with high surface area synthesized by sonochemical method. As the Bi ion incorporates into the SnO2 host lattice, it replaces the Sn ions marked by the lattice expansion, which leads to the formation of oxygen vacancies so as to maintain charge neutrality. The grain size reduces from 6 nm to 3 nm with increase in Bi content from 0% to 8%. The size effect and the increased oxygen vacancy concentration were found to induce phonon confinement within the grain. This has led to interesting changes in the vibrational spectra of the ultrananocrystalline Bi x Sn1− x O2 as the size reduces below 9 nm. Absence of periodicity beyond this critical particle size relaxes the zone-centre optical phonon selection rule, causing the Raman spectrum to have contributions also from phonons away from the Brillouin-zone centre. The structure of defects, such as the in-plane, bridging and sub-bridging oxygen vacancies present, was confirmed using Raman spectroscopic analysis. The reason for enhancement in photoluminescence behaviour with increased Bi content is discussed. The energy band gap was found to be wider (∼4 eV) compared to the bulk and reveals an increasing trend as a function of Bi%. The increase in band gap with decrease in particle size marks the quantum confinement effect. The variation of band gap upon doping is due to the BM shift effect, which arises as a result of the increase in carrier concentration.