Barium Hexaaluminates Research Articles

Chemical Composition of and Eu2+ Luminescence in the Barium Hexaaluminates

This paper consists of two parts. In the first part the chemical composition of two kinds of barium hexaaluminate (one poor and one rich in barium) is explained using the local electroneutrality concept. In the second part a reinvestigation of the Eu2+ luminescence in these compounds is reported. The emission spectrum of each of the two compounds shows two emission bands: a blue and a green emission band, indicating the presence of two Eu2+ sites. The blue emission band is ascribed to Eu2+ ions at barium sites, whereas the green emission band is identified with Eu2+ ions incorporated at aluminum sites within spinel blocks of the structure.

High Temperature Catalytic Combustion over Cation-substituted Barium Hexaaluminates

Abstract The combustion activities of various oxide catalysts were investigated using BaO·6Al2O3 as support. Conventional impregnation of oxide catalysts only lead to a decrease in surface area of the support. Cation-substituted barium hexaaluminates generally retained the large surface area. In particular, BaMnAl11O19−α′, showed the excellent activity and the large surface area of 13.7 m2/g after calcination at 1300 °C.

The luminescence properties of Eu 2+- and Mn 2+-doped barium hexaaluminates

The existence of two different barium hexaaluminates is confirmed: one poor in barium 0.82Ba0.6Al 2O 3 and one rich in barium 1.29Ba0.6Al 2O 3. The compound, poor in Ba with β-alumina structure, yields a highly efficient blue-green emitting Eu 2+-phosphor as well as a highly efficient green emitting Eu 2+, Mn 2+-phosphor. This compound is closely related to BaMgAl 10O 17. Solid solutions between both compounds are found to be formed. The compound rich in Ba, tentatively described as having the β′-alumina structure, yields a highly efficient blue emitting Eu 2+-phosphor. In the presence of Mn 2+ or Mg 2+ this compound is not stable. Instead the compound poor in Ba will be formed along with secondary phases.

Electron microscopic study of barium hexaaluminates

The crystallographic relation between phase I and phase II of barium hexaaluminates, which were conventionally considered as the single compound “barium hexaaluminate (BaAl 12O 19),” was investigated using principally the electron diffraction method. Phase I (Ba 0.79Al 10.9O 17.14) was found to have β-alumina type structure with space group P6 3 mmc . On the other hand, phase II (Ba 2.34Al 21.0O 33.84) exhibited an a√3 × a√3 superstructure, which is probably due to the ordering of excess Ba ions within BaO layers. Possible structure models of both phases are presented.