The disordered structures and low temperature dielectric relaxation properties of two misplaced-displacive cubic pyrochlores found in the Bi{sub 2}O{sub 3}-M{sup II}O-Nb{sub 2}O{sub 5} (M=Mg, Ni) systems

Journal Article · Sat Sep 15 04:00:00 EDT 2007 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2007.07.003· OSTI ID:21043841

Nguyen, Hai Binh; Noren, Lasse; Yun, Liu ^[1]; Xiaoyong, Wei ^[2]; Elcombe, Margaret M ^[3]

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1. Research School of Chemistry, Australian National University, Canberra, ACT 0200 (Australia)
2. Electronic Materials Research Laboartory (EMRL), Xian Jiaotong University, Xian, Shaanxi 710049 (China)
3. Bragg Institute, Building 87, Australian Nuclear Science and Technology Organisation PMB, Menai, NSW 2234 (Australia)

The disordered structures and low temperature dielectric relaxation properties of Bi{sub 1.667}Mg{sub 0.70}Nb{sub 1.52}O{sub 7} (BMN) and Bi{sub 1.67}Ni{sub 0.75}Nb{sub 1.50}O{sub 7} (BNN) misplaced-displacive cubic pyrochlores found in the Bi{sub 2}O{sub 3}-M{sup II}O-Nb{sub 2}O{sub 5} (M=Mg, Ni) systems are reported. As for other recently reported Bi-pyrochlores, the metal ion vacancies are found to be confined to the pyrochlore A site. The B{sub 2}O{sub 6} octahedral sub-structure is found to be fully occupied and well-ordered. Considerable displacive disorder, however, is found associated with the O'A{sub 2} tetrahedral sub-structure in both cases. The A-site ions were displaced from Wyckoff position 16d (1/2 , 1/2 , 1/2 ) to 96 h (1/2 , 1/2 -{epsilon}{sub A}, 1/2 +{epsilon}{sub A}) while the O' oxygen was shifted from position 8b (3/8 , 3/8 , 3/8 ) to Wyckoff position 32e (3/8 +{epsilon}{sub o}{sup '}, 3/8 +{epsilon}{sub o}{sup '}, 3/8 +{epsilon}{sub o}{sup '}). The refined displacement magnitudes off the 16d and 8b sites for the A and O' sites were 0.408 A/0.423 A and 0.350 A/0.369 A for BMN/BNN, respectively. - Graphical abstract: The final displacively disordered average structure of Bi{sub 1.667}Mg{sub 0.70}Nb{sub 1.52}O{sub 7} (BMN) projected along a close to <110> direction.

• OSTI ID: 21043841
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 9 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
DIELECTRIC MATERIALS
NEUTRON DIFFRACTION
NIOBIUM OXIDES
PYROCHLORE
RELAXATION
VACANCIES