Structural relaxation and electrical conductivity of molybdovanadate glass

• Published in: Journal of materials science. Materials in electronics Vol. 29; no. 4; pp. 2654 - 2659
• Main Authors: Nishida, Tetsuaki, Furumoto, Isao, Fujita, Yuki, Kubuki, Shiro, Oka, Nobuto
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.02.2018
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Materials Science; Optical and Electronic Materials
• ISSN: 0957-4522; 1573-482X
• DOI: 10.1007/s10854-017-8191-9

57 Fe Mössbauer spectrum of conductive barium iron vanadate glass with a composition of 20BaO·10Fe 2 O 3 ·70V 2 O 5 (in mol%) showed paramagnetic doublet peak due to distorted Fe III O 4 tetrahedra with isomer shift ( δ ) value of 0.37 (± 0.01) mm s −1 . Mössbauer spectra of 20BaO·10Fe 2 O 3 · x MoO 3 ·(70 −  x )V 2 O 5 glasses ( x  = 20–50) showed paramagnetic doublet peaks due to distorted Fe III O 6 octahedra with δ ’s of 0.40–0.41 (± 0.01) mm s −1 . These results evidently show a composition-dependent change of the 3D -skeleton structure from “vanadate glass” phase, composed of distorted VO 4 tetrahedra and VO 5 pyramids, to “molybdate glass” composed of distorted MoO 6 octahedra. After isothermal annealing at 500 °C for 60 min, Mössbauer spectra also showed a marked decrease in the quadrupole splitting ( Δ ) of Fe III from 0.70 to 0.77 to 0.58–0.62 (± 0.02) mm s −1 , which proved “ structural relaxation ” of distorted VO 4 tetrahedra which were randomly connected to FeO 4 , VO 5 , MoO 6 , FeO 6 and MoO 4 units by sharing corner oxygen atoms or edges. DC -conductivity ( σ ) of barium iron vanadate glass ( x  = 0) measured at room temperature was 3.2 × 10 −6  S cm −1 , which increased to 3.4 × 10 −1  S cm −1 after the annealing at 500 °C for 60 min. The σ ’s of as-cast molybdovanadate glasses with x ’s of 20–50 were ca . 1.1 × 10 −7 or 1.2 × 10 −7 S cm −1 , which increased to 2.1 × 10 −2 ( x  = 20), 6.7 × 10 −3 ( x  = 35) and 1.9 × 10 −4  S cm −1 ( x  = 50) after the annealing at 500 °C for 60 min. It was concluded that the structural relaxation of distorted VO 4 tetrahedra was directly related to the marked increase in the σ , as generally observed in several vanadate glasses.