Geoscience Reference
In-Depth Information
Figure 7.84 Photographs of Li
2
B
4
O
7
crystals
[363]
.
Figure 7.85 Photograph of tetragonal crystal of
Li
2
B
4
O
7
[363]
.
show cracking due to the thermal stress during the sudden quenching of the auto-
claves after the experiments. Striations and thermal cracking are commonly noticed
in Li
2
B
4
O
7
crystals obtained by Czochralski and Bridgman techniques. However,
the greatest advantage in the hydrothermal growth is that the thermal stress either
during the growth or during the quenching can be easily overcome. Further, the
hydrothermal method helps in growing the pure and large single crystals. This
work has clearly demonstrated the advantages of growing Li
2
B
4
O
7
crystals devoid
of all the macrodefects. Even the separately crystallized Li
2
B
4
O
7
crystals with the
experimental duration of 8
10 mm
3
size which shows fairly higher growth rates. Therefore, a careful study of the
growth parameters and an introduction of seed will make this technique a more
attractive one for Li
2
B
4
O
7
. It is well known that both Li
2
B
4
O
7
and berlinite are the
most suitable piezoelectric materials having high SAW coupling coefficients for
high-frequency and -temperature compensation. Here, it is appropriate to mention
that the growth of berlinite has been proved it to be extremely difficult to obtain
large single crystals of high quality, owing to the difficulties associated with the
highly corrosive nature of P
2
O
5
, its high reaction susceptibility, and the negative
temperature coefficient of solubility. Therefore, the successful growth of high-
quality Li
2
B
4
O
7
by the hydrothermal technique would solve the existing problems
with respect to the other techniques adopted so far. Also, the use of Teflon liners
10 days have yielded crystals of 12
12
3
3
