Gallium orthophosphate

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Structural formula
No drawing available
General
Surname Gallium orthophosphate
other names

Gallium phosphate

Molecular formula GaPO 4
Brief description

colorless solid

External identifiers / databases
CAS number
  • 14014-97-2
  • 23653-37-4 (dihydrate)
PubChem 9815301
Wikidata Q906969
properties
Molar mass 164.69 g mol −1
Physical state

firmly

density

3.57 g cm −3

Melting point

1670 ° C

Refractive index

1.623 (ne), 1.605 (no)

safety instructions
GHS hazard labeling
no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Gallium orthophosphate (gallium phosphate) is a chemical compound of gallium from the group of phosphates .

Occurrence

Since gallium orthophosphate, unlike quartz, does not occur naturally, the crystal can only be produced synthetically. At the moment gallium orthophosphate is only produced commercially by the Piezocryst company in Austria. As with synthetic quartz, the cultivation is hydrothermal.

Extraction and presentation

Gallium orthophosphate (like other gallium phosphates) can be obtained by reacting gallium hydroxide with phosphorus oxy acids. The anhydrate can be prepared by heating the dihydrate or by reacting gallium with phosphoric acid . The crystal growth is similar to that of berlinite hydrothermally at temperatures below 250 ° C.

properties

Gallium orthophosphate is a colorless gallium salt that crystallizes in the trigonal crystal system and has a hardness of 5.5 according to the Mohs hardness scale .

The crystal structure of gallium orthophosphate is isotypic to α- quartz in that silicon is alternately replaced by gallium and phosphorus.

That is why this compound has almost the same properties as quartz, but like the also intensively investigated aluminum orthophosphate, it has a piezo effect that is twice as large . This doubling results in advantages over quartz for many technical applications, such as a higher coupling constant in resonators .

Analogous to quartz, gallium orthophosphate is made up of GaO 4 and PO 4 tetrahedra, which are slightly tilted against each other. The spiral arrangement along the c-axis leads to optically right- and left-rotating crystals ( enantiomorphism ).

In contrast to quartz, gallium orthophosphate does not have an α-β phase transition up to 933 ° C (other source 976 ° C) , so that the low-temperature phase of the gallium orthophosphate (structure like α-quartz) is stable up to this temperature and thus also the physical properties of the crystal. Above this, however, there is a phase transformation into a cristobalite- like structure. A UV luminescence could be detected for the connection . Its solubility in phosphoric acid decreases with increasing temperature.

The dihydrate has a monoclinic crystal structure with the space group P 2 1 / n (space group no. 14, position 2) (a = 9.77, b = 9.64, c = 9.68 Å , β = 102.7 ° ). Template: room group / 14.2

use

For pressure measurement in internal combustion engines, gallium orthophosphate was developed as a piezo material especially for high temperature applications, which is characterized in particular by a high piezoelectric sensitivity that is largely independent of temperature. What is remarkable about gallium orthophosphate is its temperature resistance up to over 900 ° C, a sensitivity that is about twice as high as that of quartz, which remains almost unchanged up to well over 500 ° C, a high electrical insulation resistance up to high temperatures, the stability stable against voltage-induced twinning and the lack of a pyroelectric effect.

Quartz-based pressure sensors must be cooled with water for applications at higher temperatures (from 300 ° C). The desire to replace these comparably large sensors with miniaturized, uncooled ones was first met in 1994 when it was possible to replace quartz in piezoelectric pressure sensors with gallium orthophosphate.

In addition to the almost temperature-independent piezo effect, gallium orthophosphate also has excellent electrical insulation values ​​at high temperatures. There are also temperature-compensated crystal cuts up to over 500 ° C and resonator qualities comparable to quartz. Due to these material properties, GaPO 4 is used in particular for piezoelectric high-temperature pressure sensors and in high-temperature microbalances .

literature

Individual evidence

  1. ↑ Physical characterizations of # x003B1; -GaPO4 single crystals grown by the flux method . May 1, 2007, p. 1077-1081 , doi : 10.1109 / FREQ.2007.4319245 .
  2. ↑ Ion Tiginyanu, Pavel Topala, Veaceslav Ursaki: Nanostructures and Thin Films for Multifunctional Applications Technology, Properties and Devices . Springer, 2016, ISBN 978-3-319-30198-3 , pp. 195 ( limited preview in Google Book search).
  3. ↑ a b Guogang Xu, Jing Li, Jiyang Wang, Hongyang Zhao, Hong Liu: Flux Growth and Characterizations of Ga 3 PO 7 Single Crystals. In: Crystal Growth & Design. 8, 2008, p. 3577, doi: 10.1021 / cg7012649 .
  4. ↑ P. Armand, M. Beaurain, B. Ruffle, B. Menaert, D. Balitsky, S. Clement, P. Papet: Characterizations of piezoelectric GaPO4 single crystals grown by the flux method. In: Journal of Crystal Growth. 310, 2008, p. 1455, doi: 10.1016 / j.jcrysgro.2007.11.049 .
  5. ↑ This substance has either not yet been classified with regard to its hazardousness or a reliable and citable source has not yet been found.
  6. ↑ europa.eu: European Commission: CORDIS: Projects and Results Service: New Piezoelectric Crystals for Sensory Applications , accessed March 12, 2017.
  7. ↑ a b c d e K. Byrappa, Masahiro Yoshimura: Handbook of Hydrothermal Technology . Cambridge University Press, 2008, ISBN 978-0-08-094681-8 , pp. 248 ( limited preview in Google Book search).
  8. ↑ Jacqueline I. Kroschwitz: Kirk-Othmer Encyclopedia of Chemical Technology, Fuel Resources to Heat ... Wiley, 1994, ISBN 0-471-52681-9 , S. 311 ( limited preview in Google Book search).
  9. ↑ a b c Günter P. Merker, Rüdiger Teichmann: Fundamentals of internal combustion engines, functionality, simulation, measurement technology . Springer-Verlag, 2014, ISBN 978-3-658-03195-4 , pp. 558 ( limited preview in Google Book search).
  10. ↑ archives-ouvertes.fr: Study on the origin of 1 / f in bulk acoustic wave resonators , accessed on March 12, 2017.
  11. ↑ ELENA C. SHAFER, RUSTUM ROY: Studies of Silica-Structure Phases: I, GaPO 4 , GaAsO 4 , and GaSbO 4 . In: Journal of the American Ceramic Society. 39, 1956, p. 330, doi: 10.1111 / j.1151-2916.1956.tb15598.x .
  12. ↑ Anatoly N Trukhin, Krishjanis Shmits, Janis L Jansons, Lynn A Boatner: Ultraviolet luminescence of ScPO4, AlPO4 and GaPO4 crystals. In: Journal of Physics: Condensed Matter. 25, 2013, p. 385502, doi: 10.1088 / 0953-8984 / 25/38/385502 .
  13. ↑ Govindhan Dhanaraj, Kullaiah Byrappa, Vishwanath Prasad, Michael Dudley: Springer Handbook of Crystal Growth . Springer Science & Business Media, 2010, ISBN 978-3-540-74761-1 , p. 614 ( limited preview in Google Book search).
  14. ^ RCL Mooney-Slater: The crystal structure of hydrated gallium phosphate of composition GaPO 4 .2H 2 O. In: Acta Crystallographica. 20, 1966, p. 526, doi: 10.1107 / S0365110X6600118X .
  15. ↑ P. Krempl, G. Schleinzer, W. Wallno¨fer: Gallium phosphate, GaPO 4 : a new piezoelectric crystal material for high-temperature sensorics. In: Sensors and Actuators A: Physical. 61, 1997, p. 361, doi: 10.1016 / S0924-4247 (97) 80289-0 .
  16. ↑ Jason Millichamp, Ebrahim Ali, Nigel P. Brandon, Richard JC Brown, David Hodgson, Christos Kalyvas, George Manos, Daniel JL Brett: Application of a GaPO 4 Crystal Microbalance for the Detection of Coke Formation in High-Temperature Reactors and Solid Oxide Fuel cells. In: Industrial & Engineering Chemistry Research. 50, 2011, p. 8371, doi: 10.1021 / ie200188z .