Geoscience Reference
In-Depth Information
because of the covalent bonding. Alpha-berlinite is relatively stable compared to
β
-berlinite with reference to the action of
the dopants. The difference in
10
2
5
C
2
1
,
which shows that the c-axis is more susceptible to thermal expansion than the
10
2
5
C
2
1
and
α
a
(max)
2
α
a
(min)
0.39
α
c
(max)
2
α
c
(min)
1.572
5
3
5
3
α
-axis.
The coefficient of
thermal expansion is quite high when rare earths are used
as admixtures.
5.3.6 Piezoelectric Properties of Berlinite
The piezoelectric properties of berlinite have been studied in detail by several
authors. Chang and Barsch (1976)
[68]
, and Ballato and Iafrate (1976)
[102]
pointed out the attractive properties of Y rotated and doubly rotated cuts of berlinite
in terms of its large coupling coefficient (twice that of quartz), with a constraint of
zero first-order frequency temperature coefficient (FTC). Several groups appeared
throughout the world immediately to study the growth and characterization (with
reference to its first-, second-, and third-order FTCs) of berlinite.
Figure 5.27
shows
the comparison of Y quartz and Y berlinite resonators. It can be noted that the Q
factor is greater by an order of magnitude than for resonators. In
Figure 5.27
, also
given the frequency response of the Y quartz plate of a similar design whose Q fac-
tor is not so different and whose coupling coefficient is smaller. The higher order
TCs measured with different crystals, even with different plates of the same crystal,
show values much larger than for quartz resonators of the corresponding orienta-
tion.
Table 5.9
gives the comparison between quartz and berlinite. However, it has
been demonstrated that the water dissolved in berlinite crystal induces low values
A
(dB)
F
C
0
φ
= 3.5 mm
φ
e
= 2.77 mm
Quartz
AIPO
4
R
= 1.8‰
R
= 2.2‰
20
K
= 11.1%
K
= 13.1%
Quartz
Y
40
F
C
= 9927.320
60
AIPO
4
Y
F
C
= 8307.220
80
9927.320
8364.680
100
-100
-80
-60
-40
-20
0
+20
+40
+60
+80
Δ
F
(kHz)
-100
Figure 5.27 Frequency response of the Y quartz plate
[68]
.
