Ceramic and Glass Materials

76 L.P. Davila et al.

Table 2Structure of low-quartza

Bravais lattice

Unit cell

dimensionsa

(a,b,c) in nm

Unit cell major

anglesa (a,b,g)

Space group

number

Symmetry

number

No. of ions per

unit cell

Hexagonal 0.49130,
0.49130,
0.54052

90.0, 90.0, 120.0P3 121 152 9

aFrom Accelrys software [11]; P = Primitive

Fig. 4 Atomic arrangement in low-quartz (looking down the c-axis). (Small dark and larger light
spheres represent oxygen and silicon ions respectively). The relative sizes of these ions correspond
to the significant degree of covalency in the Si−O bond [11]

Fig. 5 Illustration of the double helix formed by SiO 4 tetrahedra in low-quartz (viewed down an
a-axis) [11,13]