Gallium Orthophosphate - GaPO₄

FAQ

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:

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 ?
A: 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".

_{Reproduced by kind permission of AVL List GmbH. © AVL List GmbHSpecifications subject to change without notice. All rights reserved}