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Crystal Structure of Bi2.5Me0.5Nb2O9(Me=Na, K): A Powder Neutron Diffraction Study

Authors
Journal
Journal of Solid State Chemistry
0022-4596
Publisher
Elsevier
Publication Date
Volume
157
Issue
1
Identifiers
DOI: 10.1006/jssc.2000.9069
Keywords
  • Aurivillius Phase
  • Bi2.5Na0.5Nb2O9
  • Bi2.5K0.5Nb2O9
  • Powder Neutron Diffraction.

Abstract

Abstract The room temperature structures of the two-layer Aurivillius phases Bi 2.5 Me 0.5Nb 2O 9 ( Me=Na, K) have been refined with the Rietveld method from powder neutron diffraction data ( λ=1.470 Å). They consist of (Bi 2O 2) 2+ layers interleaved with perovskite (Bi 0.5 Me 0.5Nb 2O 7) 2− ( Me=Na, K) slabs. The structures were refined in the orthorhombic space group A2 1 am, Z=4, and the unit cell parameters of the two oxides are a= 5.4937(3), b=5.4571(4), c=24.9169(14) Å and a=5.5005(8), b=5.4958(8), c=25.2524(16) Å, respectively. The orthorhombic distortion increases with decreasing Me + cation size in the perovskite layer (Bi/ Me) 2+ site and the lone pair electrons from the Bi 3+ cation are influencing the site distortion. This is in agreement with other two-layer Aurivillius phases and originates from bonding requirements depending on size and electronic environment.

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