and decreased beyond this limit while the area of the bands
of BO3 decreased slowly in the same range and increased beyond
this limit. The center of the band of the bending vibration of symmetric
BO3 triangles decreased in the range 0 ≤ x ≤ 10 mol% of
Bi2O3 content, increased at x = 15 mol% of Bi2O3 and retaining
its position beyond this limit.