Structural phase transitions and crystal chemistry of the series Ba{sub 2} LnB'O{sub 6} (Ln=lanthanide and B'=Nb{sup 5+} or Sb{sup 5+})

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

DOI:https://doi.org/10.1016/j.jssc.2006.10.017· OSTI ID:21015664

Saines, Paul J ^[1]; Elcombe, Margaret M ^[2]

---

1. School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia)
2. Bragg Institute, ANSTO, Private Mail Bag 1, Menai, NSW 2234 (Australia)

The structures of 28 compounds in the two series Ba{sub 2} LnSbO{sub 6} and Ba{sub 2} LnNbO{sub 6} have been examined using synchrotron X-ray and in selected cases neutron powder diffraction at, below and above ambient temperature. The antimonate series is found to undergo a sequence of phase transitions from monoclinic to rhombohedral to cubic symmetry with both decreasing ionic radii of the lanthanides and increasing temperature. Compounds in the series Ba{sub 2} LnNbO{sub 6}, on the other hand, feature an intermediate tetragonal structure instead of the rhombohedral structure exhibited by the antimonates. This difference in symmetry is thought to be caused by {pi}-bonding in the niobates that is absent in the antimonates. The bonding environments of the cations in these compounds have also been examined with overbonding of the lanthanide and niobium cations being caused by the unusually large B-site cations. - Graphical abstract: Lattice parameters versus temperature for Ba{sub 2}NdNbO{sub 6}. The formation of the I4/m tetragonal phase contrasts with the antimonate series where a rhombohedral structure occurs instead. This difference is believed to be caused by the presence of {pi}-bonding present in the niobates but absent in the antimonates.

• OSTI ID: 21015664
• 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
AMBIENT TEMPERATURE
ANTIMONATES
ANTIMONY IONS
CUBIC LATTICES
LATTICE PARAMETERS
MONOCLINIC LATTICES
NEUTRON DIFFRACTION
NIOBATES
NIOBIUM IONS
OXIDES
PHASE TRANSFORMATIONS
RARE EARTH COMPOUNDS
SYNCHROTRON RADIATION
TETRAGONAL LATTICES