The local crystal chemistry and dielectric properties of the cubic pyrochlore phase in the Bi{sub 2}O{sub 3} - M {sup 2+}O-Nb{sub 2}O{sub 5} (M {sup 2+}=Ni{sup 2+} and Mg{sup 2+}) systems

Journal Article · Thu Feb 15 04:00:00 EST 2007 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2006.10.039· OSTI ID:21015682

Nguyen, Binh ^[1]; Yun, Liu ^[1]

---

1. Research School of Chemistry, Australian National University, Canberra, ACT 0200 (Australia)

The composition, dielectric properties and inherent displacive disorder of a Bi-based, misplaced-displacive cubic pyrochlore phase found in two ternary Bi{sub 2}O{sub 3} - M {sup 2+}O-Nb{sub 2}O{sub 5} (M=Ni and Mg) systems has been investigated. The dielectric permittivities (up to 1 MHz) of (Bi{sub 0.825}Ni{sub 0.125}{open_square}{sub 0.05}){sub 2}(Ni{sub 0.25}Nb{sub 0.75}){sub 2}O{sub 7} and (Bi{sub 0.835}Mg{sub 0.085}{open_square}{sub 0.08}){sub 2}(Mg{sub 0.235}Nb{sub 0.765}){sub 2}O{sub 7} at room temperature are found to be 116 and 151, respectively, while the dielectric loss tangents are 0.00065 and 0.00042, respectively, at 100 kHz. A highly structured characteristic diffuse intensity distribution apparent in electron diffraction is reported in both cases and partially interpreted in terms of large amplitude, {beta}-cristobalite-type tetrahedral rotations of the O'A {sub 2} tetrahedral framework sub-structure of the ideal pyrochlore structure type. Bond valence sum calculations are used to investigate the local crystal chemistry responsible for this displacive disorder. - Graphical abstract: The characteristic {beta}-cristobalite-type displacive disorder of the O'A {sub 2} sub-structure (of the ideal pyrochlore structure type) drawn relative to the surrounding B {sub 2}O{sub 6} octahedral framework sub-structure and responsible for the observed structured diffuse intensity distribution in the Bi{sub 1.65}Ni{sub 0.75}Nb{sub 1.50}O{sub 7} and Bi{sub 1.67}Mg{sub 0.64}Nb{sub 1.53}O{sub 7} misplaced-displacive cubic pyrochlores.

• OSTI ID: 21015682
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 2 Vol. 180; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
BISMUTH OXIDES
CRISTOBALITE
CUBIC LATTICES
DIELECTRIC MATERIALS
DISTRIBUTION
ELECTRON DIFFRACTION
KHZ RANGE 100-1000
MAGNESIUM IONS
MHZ RANGE
NICKEL IONS
NIOBIUM OXIDES
PERMITTIVITY
PYROCHLORE
TEMPERATURE RANGE 0273-0400 K