Chemical order and local structure of the lead-free relaxor ferroelectric Na{sub 1/2}Bi{sub 1/2}TiO{sub 3}

Journal Article · Mon Aug 15 00:00:00 EDT 2011 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2011.05.044· OSTI ID:21580209

Groeting, Melanie ^[1]; Hayn, Silke ^[1]; Albe, Karsten ^[1]

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1. Fachgebiet Materialmodellierung, Institut fuer Materialwissenschaft, TU Darmstadt, Petersenstr. 32, 64287 Darmstadt (Germany)

The A-site mixed perovskite sodium bismuth titanate (Na{sub 1/2}Bi{sub 1/2})TiO{sub 3} (NBT) is investigated by means of first-principles calculations based on density functional theory. By studying different geometries with varying occupations of the A-site, the influence of chemical order on the thermodynamic stability and local structure is explored. We find that the hybridization of Bi 6sp with O 2p-states leads to stereochemically active Bi{sup 3+} lone pairs and increases the stability of structures with high Bi concentrations in {l_brace}001{r_brace}-planes. This goes along with displacive disorder on the oxygen sublattice, which up to now has been neglected in experimental studies. The calculated ordering energies are, however, small as compared to the thermal energy and therefore only short-range chemical order can be expected in experiments. Thus, it is conceivable that chemically ordered local areas can act as nucleation sites for polar nano-regions, which would explain the experimentally observed relaxor behavior of NBT. - Graphical abstract: First-principles calculations give relative stabilities of different chemically ordered structures. The results suggest a new model for the local structure of Na{sub 1/2}Bi{sub 1/2}TiO{sub 3} with 001-ordered nano-regions embedded in a chemically disordered matrix. Chemical order/disorder additionally induces displacive disorder within the oxygen sublattice. Highlights: > Lead-free relaxor ferroelectric Na{sub 1/2}Bi{sub 1/2}TiO{sub 3} is studied by ab initio-calculations. > Structural relaxations in the oxygen sublattice are decisive for relative stabilities. > Chemical environment of oxygen determines relaxation ability. > Bi 6s{sup 2} lone pair formation is the driving force for relaxation. > New structure model: Chemically 001-ordered nano-regions embedded in disordered matrix.

• OSTI ID: 21580209
• Journal Information: Journal of Solid State Chemistry, Vol. 184, Issue 8; Other Information: DOI: 10.1016/j.jssc.2011.05.044; PII: S0022-4596(11)00293-3; Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BISMUTH
BISMUTH IONS
DENSITY FUNCTIONAL METHOD
FERROELECTRIC MATERIALS
OXYGEN
PEROVSKITE
RELAXATION
STABILITY
TITANATES
TITANIUM OXIDES
CALCULATION METHODS
CHALCOGENIDES
CHARGED PARTICLES
DIELECTRIC MATERIALS
ELEMENTS
IONS
MATERIALS
METALS
MINERALS
NONMETALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PEROVSKITES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
VARIATIONAL METHODS