The syntheses, crystal structures, electrical properties, and optical absorbance spectra ofsix perovskite oxynitrides, AMO
2N (A = Ba, Sr, Ca; M = Ta, Nb) have been investigated.The average crystal structure of BaTaO
2N is a cubic perovskite,
with a Ta-O/N distance of2.056 Å. SrTaO
2N and CaTaO
2N are distorted by octahedral tilting, sho
wing noticeablysmaller Ta-O/N distances of approximately 2.02 Å. Electron diffraction studies of BaTaO
2Nare consistent
with the simple cubic perovskite crystal structure determined using X-raypo
wder diffraction methods. Each of the niobium oxynitrides is isostructural
with its tantalumanalogue, though the Nb-O/N distances are observed to be slightly longer. The optical bandgaps are estimated from diffuse reflectance spectra as follo
ws: BaTaO
2N, 1.8 eV; SrTaO
2N,2.1 eV; CaTaO
2N, 2.4 eV; BaNbO
2N, 1.8 eV; SrNbO
2N, 1.9 eV; CaNbO
2N, 2.1 eV. Impedancespectroscopy
was carried out on sintered pellets of the ATaO
2N and BaNbO
2N to investigatethe dielectric and electrical transport properties. The BaNbO
2N sample sho
ws metallic-typeconductivity apparently from a slight reduction that occurs during sintering. In contrast,the tantalum compounds are semiconductors/insulators
with conductivities of ~10
-5 S/cm(A = Ba, Sr) and ~10
-8 S/cm (A = Ca). Interpretation of the impedance data for BaTaO
2Nand SrTaO
2N reveals that these t
wo compounds have unexpectedly high bulk dielectricconstants,
![](/images/entities/ap.gif)
4900 and 2900, respectively, at room temperature. The dielectric constantsof both compounds are frequency dependent and sho
w a relatively
weak linear dependenceupon temperature
with no sign of a phase transition over the temperature range 300-180K.