Gallium Orthophosphate - GaPO4 FAQs
Q: What is the crystal structure of GaPO4?
A: Gallium Orthophosphate is a quartz homeotypic piezoelectric crystal with a high sensitivity and a thermal stability up to 970 °C.
Q: What are the values of the piezoelectric constants?
A: As Gallium Orthophosphate has the same symmetry as quartz, this value is exactly zero. Both crystals belong to the point group "32" which only has two independent piezoelectric coefficients, d11 and d14. Take a look at the piezoelectric coefficient matrix of GaPO4:
[d11 |
-d11 |
0 |
d14 |
0 |
0] |
[0 |
0 |
0 |
0 |
-d14 |
-2d11] |
[0 |
0 |
0 |
0 |
0 |
0] |
For Gallium Orthophosphate shear cuts you can use the piezoelectric constant d26. It shows the same perfect thermal stability as d11 but twice the sensitivity (d26 = -2d11).
When you are used to manufacturing transducers with LiNbO3, LiTaO3 (both point group "3m") or ceramics ("6mm"), the values for d11 and d14 are zero, so you have to use the d15 for X-cut or Y-cut shear mode.
Q: Why has GaPO4 no Curie temperature ?
A: GaPO4 is not ferroelectric, so there is no Curie temperature. The limiting factor for the use of GaPO4 in applications is its phase transition at 970 °C. Up to that temperature many physical constants are really "constants".
Q: Is GaPO4 pyroelectric ?
No.
Q: How high is the electric resistivity of GaPO4 ?
A: Extremely high.
We measured values of >10^17 Ohm*cm at room temperature (limited by the experimental setup) and values >10^11 Ohm*cm at 500 °C.
Q: What about outgassing ?
A: There is none.
Due to the high homogeneity of hydrothermally grown crystals compared to crystals grown from the melt and the strong chemical bond of the oxygen atoms to the phosphorus atoms in the PO4 tetrahedron, which is much stronger than the bond between e.g. the relatively large Nb atoms and O in lithiumniobate, no outgassing has been observed in GaPO4.
Q: Is there an AT-cut in GaPO4 ?
A: The quartz AT-cut is used for frequency stability over temperature. In GaPO4 there are many crystal orientations meeting these requirements (see the section "temperature compensated orientations"). The best suited cut angle is depending on the application and on the operating temperature. Are you working on Bulk Acoustic Wave (BAW) applications or Surface Acoustic Wave (SAW) applications? Do you need a high coupling or a high Q-factor? In any case GaPO4 offers temperature compensated orientations with a better frequency stability over temperature than other crystals.
Our service: you choose the temperature range - we determine the best suited cut angle for your application to guarantee best performance.
Q: What are the values of the temperature coefficients of the resonant frequency?
A: Up to 80 °C they can be compared to the values of quartz, above 80 °C the resonant frequency of GaPO4 resonators exhibits an even lower temperature dependence up to at least 700 °C.
Q: Where are the turnover points of the frequency vs. temperature characteristics?
A: You choose them!GaPO4 offers temperature compensation up to at least 700 °C. Depending on the operating temperature of your application we determine the best suited cut angle to guarantee the lowest temperature dependence of the resonator crystals. See the section "temperature compensated orientations".
Q: What is a GaPO4-HiQ resonator?
A: GaPO4-HiQ resonator is a resonator with a higher quality factor Q than comparable quartz resonators. The temperature dependence of the resonant frequency between 60 °C and 100 °C is very low so a GaPO4-HiQ resonator is a preferable choice for high end OCXOs.
Q: Can I use the calculation programs that I am using for quartz?
A: Yes.
GaPO4 belongs to the same point group, so it has these the same symmetry. All you have to do is to use the material constants of GaPO4 given in the section "material properties".