Perovskite-related oxynitrides – Recent developments in synthesis, characterisation and investigations of physical properties

Abstract

Since the first investigations of perovskite type oxynitrides with the generalised composition ABO 3Àx N x about twenty years ago, these compounds have become of growing interest. The incorporation of nitride ions in the perovskite lattice results in distinct changes in the electronic structure leading to unusual physical properties. In this article we report on new synthesis techniques, different analytical methods, progress in the structural characterisation by comprehensive diffraction techniques and local spectroscopic methods like XAS and NMR as well as state of the art theoretical investigations. Various physical characteristics like electrical and thermal transport parameters and dielectric properties are described. The thermal and chemical stability of oxynitride perovskites are investigated and their applications in different photocatalytic reactions are discussed.

Crystal structure of Eu-doped magnetoplumbite-type lanthanum aluminum oxynitride with emission site splitting

“…The Eu 2+ was supported by a single absorption peak at 6972 eV in the XANES spectra for the Eu L III -edge. The former wavelength is comparable to that reported for MP-type LaMgAl 11 O 19 :Eu 2+ [11]; however, there is a characteristic shoulder peak at 464 nm in Eu-doped LaAl 12 (O,N) 19 . The products exhibited broad excitation spectra between 250 and 360 nm for the emission at 440 nm, as depicted in Fig.…”

“…The emission wavelength was shorter than that for Eu-doped LaAl 12 (O,N) 19 . It is believed that the long wavelength emission is attributed to covalent bond character and a large crystal field splitting effect on Eu 2+ 5d band [28] with Ca 2+ (r Ca2+ = 0.120 nm, for C.N.…”

“…2(b). XRD patterns indicated no impurities were present in the products, however trace amount of LaAlO 3 (1 wt%) was observed in neutron diffraction pattern of La 0.97 Eu 0.03 Al 12 (O,N) 19 due to the higher detectability as shown in Fig. 4.…”

“…Eu-doped lanthanum aluminum oxynitride (LaAl 12 (O,N) 19 ) with magnetoplumbite structure was prepared by nitridation of the oxide precursor obtained from aluminum glycine gel and subsequent post-annealing. Eu-doped lanthanum aluminum oxynitride exhibited blue light emission at 440 nm with a shoulder at 464 nm under excitation at 254 nm.…”

“…cis-TaO 4 N 2 octahedra have been assumed in the structure of perovskite-type SrTaO 2 N and BaTaO 2 N tantalum oxynitrides [19][20][21][22]. The large dielectric constant of these perovskites was considered to be related to the polarity induced in the distorted octahedra.…”