High-pressure synthesis and characterization of the alkaline earth borate β-BaB4O7

Raman scattering study of crystalline and melting states of BaO·2B2O3

“…We think that the shift of the low-frequency peaks and wide bands in the region 300-500 cm À 1 and their further splitting into b-BaB 4 O 7 (D¼ 94.7 À68.2 ¼26.5 cm À 1 ) compared to a-BaB 4 O 7 (D¼61.5 À49.8 ¼11.7 cm À 1 ) suggests changes in the structure and symmetry of the coordination polyhedra (associative complexes [9]). This agrees well with the results of the structural analysis [8]. Similar changes in the Raman spectra in LiB 3 O 5 crystals [10] were attributed to the shift of the Li atom and changes in its coordination to triangular (the first coordination sphere) on heating [11].…”

“…Its structure Our X-ray (Cu anticathode) powder patterns (Fig. 6a) agree well with X-ray powder patterns calculated from the structural data [8] (Fig. 6b).…”

“…But recently the synthesis of b-BaB 4 O 7 at high pressure and temperature has been reported in Ref. [8]. Crystals measuring 40 mm  20 mm  20 mm were grown by decreasing the temperature from 1100 to 500 1C at a constant pressure of 7.5 GPa.…”

“…Crystals measuring 40 mm  20 mm  20 mm were grown by decreasing the temperature from 1100 to 500 1C at a constant pressure of 7.5 GPa. The authors [8] showed b-BaB 4 O 7 crystallizes in the space group Pmnb c Z¼2. The structure net was composed solely of BO 4 -tetrahedra connected by common angles.…”

“…With decrease in temperature, the amount of (N 4 ) increases and that of (N 3 ), decreases [14,15]. However, the fact that the network-structure of b-BaB 4 O 7 is built-up solely of BO 4 linked via common corners [8] suggests that the growth of the a-or b-phase depends not only on the relation (N 4 )/(N 3 ), but also from the energy of structureforming barium cations.…”