Microstructure and charge carrier dynamics in Dy substituted phase stabilized cubic Bi₂O₃

Abstract

Room temperature phase stabilization of cubic Bi 2 O 3 has been achieved by adding Dy 2 O 3 as dopant, using low temperature citrate-auto-ignition method. The samples were sintered at different temperatures retaining the cubic fluorite structure. Rietveld refinement of the X-ray diffraction profiles has given the detailed microstructural information of the prepared samples.The transmission electron micrographs confirmed the presence of atomic planes as obtained from X-ray diffraction. The Uv-Vis spectra show a red shift of the absorption peak with the increase in sintering temperature. Impedance spectroscopy studies of the samples exhibited thermally activated non-Debye type relaxation process. In addition, the studies of electrical conductivity have suggested the negative temperature coefficient of resistance (NTCR) behavior of the samples. The comparable values of activation energies, obtained from different parameters, indicated that the ions follow same type of mechanism for conduction as well as for relaxation.The temperature independence of the processes has been confirmed from scaling of different spectra. The correlation between structural and electrical properties of the samples has been discussed and interpreted accordingly. INDIA email: adutta@phys.buruniv.ac.in ; Telephone: +913422657800; Fax: +91342 2634015 1. Introduction: In the family of solid oxide full cells (SOFC), Bi 2 O 3 based materials have proven themselves as one of the most important members because of their superiority in oxide ion conductivity over conventional Ceria or Zirconia based ionic conductors 1-4 . Out of its different crystallographicpolymorphs, interest has been centered on cubic δ-Bi 2 O 3 because of its ability for highest oxygen ion conductivity among the family 5 . This cubic fluorite structure of bismuth oxide consists of a disordered oxygen sub-lattice with a short-range ordering of oxygen vacancies along the <111> direction 6 . The high ionic conductivity of δ-Bi 2 O 3 is ascribed both to the large number of oxygen vacancies and high anionic mobility. The high concentration of oxygen vacancies (25% of the lattice sites) is a result of obtaining the cubic fluorite structure with Bi 3+ cation. The high anionic mobility is related to the high polarizability of the Bi 3+ cation with its lone pair of electrons 7 . However, this cubic phase is only stable in a narrow temperature range (730°C to melting point), and transforms to monoclinic α-phase through a dramatic phase transition 8 . The cubic phase at high temperature can be stabilized down to room temperature by the additions of dopants of comparable cation radii such as isovalent rare earth cations (Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ , Yb 3+ ),Y 3+ , WO 3 etc 1, 9 . However, these doped bismuth oxides show lower ionic conductivity and

Mechanosynthesis of Nanocrystalline Fully Stabilized bcc γ-phase of Bi2O3 without Any Additive: Manifestation of Ferroelasticity in Microstructure, Optical, and Transport Properties

“…As far as applications in energy conversion are concerned, such as chemical processing, controlled combustion, and sensing, solid electrolytes are the most important part of electrochemical devices. Recent investigations − established that bismuth oxide-based compounds have emerged as one of the important materials in the family of solid electrolytes over conventional zirconia- or ceria-based electrolytes. According to literature review, − out of six polymorphs of Bi 2 O 3 , the body-centered cubic (bcc) γ-phase, face-centered cubic (fcc) δ-phase, tetragonal β-phase, and monoclinic α-phase are the very important materials.…”

“…Among different phases of bismuth oxide, 25% inherent vacancy of oxygen sublattice makes the δ-Bi 2 O 3 structure highly disordered and an excellent oxygen ion (O 2– ) conductor at elevated temperature [∼1 Ω –1 ·cm –1 at 750 °C] . This high temperature stable phase can be stabilized at room temperature on doping of the Bi 2 O 3 matrix with either isovalent (e.g., Dy 3+ , Ho 3+ , and Y 3+ ) , or aliovalent (e.g., Ba 2+ ) cations . However, such substitutions result in lowering of the ionic conductivity of doped Bi 2 O 3 systems due to ⟨111⟩ ordering of disordered oxygen sublattice .…”

Reinforced properties of ethylene–propylene–diene monomer composites by vinyltrimethoxysiloxane functionalised barium titanate

“…It is observed that EPDM with 40 and 50 vol.-% BaTiO 3 both have semicycles, which is called Cole–Cole semicycle. 32, 33 Each semicycle is ascribed to one Debye relaxation caused by the interfacial polarisation between BaTiO 3 and EPDM matrix. 34 It showed that at 40 vol.-% of BaTiO 3 , EPDM composite starts to show greater interfacial polarisation between BaTiO 3 and EPDM matrix.…”

Remarkable enhancement of mechanical and dielectric properties of flexible ethylene propylene diene monomer (EPDM)/ barium titanate (BaTiO3) dielectric elastomer by chemical modification of particles

“…In literatures, Cole-Cole model and Debye relaxation are oen used to evaluate the dielectric properties of compostes. [32][33][34][35][36] Cole-Cole semicycles are oen shown by the plot of dielectric constant versus dielectric loss. 29…”