Local anionic ordering and anisotropic displacement in dielectric perovskite SrTaO2N

Abstract

The perovskite oxynitride SrTaO 2 N as a promising candidate for lead-free dielectric materials has been studied with a special emphasis on the structural characterization using neutron powder diffraction. SrTaO 2 N powders were prepared by means of ammonia nitridation via precursors obtained from a soft chemistry method and a solid state reaction route. All the products crystallized in tetragonal I4/mcm space group with only slight variation in the lattice constant, e.g., a = 5.7023(1) ¡ and c = 8.0786(1) ¡ for the soft-chemistry derived sample. Neutron diffraction analysis suggested the short-range O/N ordering involving a cis configuration in TaO 4 N 2 octahedra together with large anionic displacement within the ab plane on their axial position in the average crystal lattice. These facts are associated with local tilting of the TaO 4 N 2 octahedra which is likely to play a key role in the unusual dielectric behavior of SrTaO 2 N.

High pressure densification and dielectric properties of perovskite-type oxynitride SrTaO2N

“…However there have been no other reports to support the interesting information. Two independent reports in 2011 indicate the presence of cis-type TaO 4 N 2 in SrTaO 2 N from neutron diffraction data [2,3]. The cis-configuration of TaO 4 N 2 was maintained up to 1100 °C from high temperature neutron diffraction measurements [4].…”

“…SrTaO 2 N has a theoretical density of 7.95 g/cm 3 [2], which is less dense than those of simple tantalum oxides and nitrides such as 9.93 g/cm 3 for Ta 3 N 5 [30] [31] and around 15 g/cm 3 for rock-salt type TaO and TaN [32,33]. Rock-salt type TaO 0.9 has been reported to appear as a high temperature impurity phase in …”

Synthesis, structure and properties of new functional oxynitride ceramics

“…Its structure refinement was performed based on the tetragonal I4/mcm model. 32) Figure 2(a) indicates the refined crystal structure of SrTaO 2 N. The site occupations of nitride ions is always higher at the axial 4a site than the equatorial 8h site with the occupancies of O/N µ 0.5/0.5 and 0.75/0.25 for the former and the latter, respectively. This result is in good agreement with that reported by Clark et al 22) It should be noted that such preferential site occupations are little dependent on the synthesis route, because the crystal structure of SrTaO 2 N obtained by nitridation of oxide precursors was well refined in similar anionic occupancies.…”

Ammonolysis of HTiNbO5–n-Propylamine Intercalation Compound

“…Oxynitrides have attracted interest for application as white light emitting diode (LED) phosphors, 1,2 possible leadfree dielectric materials, 3,4 new superconductors, 5,6 inorganic pigments, 7,8 and as photocatalyts. [9][10][11] Oxynitrides that contain more than two different cations are of significant interest for improvement of these properties.…”