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Encyclopedia > Gallium orthophosphate
GaPO4
GaPO4 crystal
General
Category crystal
Chemical formula (or Composition) GaPO4
Identification
Color Clear
Crystal system Trigonal
Crystal class 32 or D3 (Schönflies)
Cleavage None
Fracture Conchoidal
Mohs Scale hardness 5.5
Refractive index no=1.605, ne=1.623
Pleochroism None
Streak White
Density 3570 kg/m3
Solubility insoluble in pH = 5 - 8
other properties
Pyroelectricity None
Particular characteristics quartz isotype, piezoelectric effect up to 950°C (1742°F)

Gallium phosphate (GaPO4 or gallium orthophosphate) is a colorless trigonal crystal with a hardness of 5.5 on the Mohs scale. GaPO4 is isotypic with quartz, possessing very similar properties, but the silicon atoms are alternately substituted with gallium and phosphorus, thereby doubling the piezo electric effect. GaPO4 has many advantages over quartz for technical applications, like a higher electromechanical coupling coefficient in resonators, due to this doubling. Contrary to quartz, GaPO4 is not found in nature. Therefore, a hydrothermal process must be used to synthesize the crystal. Quartz crystal In chemistry and mineralogy, a crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... The chemical composition of a substance refers to the elements of which the substance is composed. ... In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... In crystallography, the hexagonal crystal system is one of the 7 lattice point groups. ... In crystallography, a crystallographic point group or crystal class is a set of symmetry operations that leave a point fixed, like rotations or reflections, which leave the crystal unchanged. ... In crystallography, a crystallographic point group is a set of symmetry operations, like rotations or reflections, that leave a point fixed while moving each atom of the crystal to the position of an atom of the same kind. ... Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... A fracture is the separation of a body into two, or more, pieces under the action of stress. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... The refractive index (or index of refraction) of a material is the factor by which the phase velocity of electromagnetic radiation is slowed in that material, relative to its velocity in a vacuum. ... Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other. ... Minerals are natural compounds formed through geological processes. ... Density (symbol: ρ - Greek: rho) is a measure of mass per volume. ... It has been suggested that Solid solubility be merged into this article or section. ... pH is a measure of the acidity of a solution in terms of activity of hydrogen ions (H+). For dilute solutions, however, it is convenient to substitute the activity of the hydrogen ions with the molarity (mol/L) of the hydrogen ions (however, this is not necessarily accurate at higher... CRYSTAL SYMMETRY: Crystal structures can be divided into 32 classes, or point groups, according to the number of rotational axes and reflection planes they exhibit that leave the crystal structure unchanged. ... Quartz is amongst one of the most common minerals in the Earths continental crust. ... Isotype - the International System of Typographic Picture Education - was developed by the Austrian educator and philosopher Otto Neurath, along with the illustrator Gerd Arntz. ... Piezoelectricity is the ability of crystals to generate a voltage in response to applied mechanical stress. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... Quartz is amongst one of the most common minerals in the Earths continental crust. ... General Name, Symbol, Number silicon, Si, 14 Chemical series metalloids Group, Period, Block 14, 3, p Appearance dark gray, bluish tinge Atomic mass 28. ... General Name, Symbol, Number gallium, Ga, 31 Chemical series poor metals Group, Period, Block 13, 4, p Appearance silvery white   Atomic mass 69. ... General Name, Symbol, Number phosphorus, P, 15 Chemical series nonmetals Group, Period, Block 15, 3, p Appearance waxy white/ red/ black/ colorless Atomic mass 30. ... Piezoelectricity is the ability of crystals to generate a voltage in response to applied mechanical stress. ... A crystal oscillator (sometimes abbreviated to XTAL on schematic diagrams) is an electronic circuit that uses the mechanical resonance of a physical crystal of piezoelectric material along with an amplifier and feedback to create an electrical signal with a very precise frequency. ... Hydrothermal circulation in the oceans is the passage of the water through mid-ocean Ridge (MOR) systems. ...

Contents

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Modifications

GaPO4 possesses, in contrast to quartz, no α-β phase transition, thus the low temperature structure (structure like α-quartz) of GaPO4 is stable up to 970°C, as are most of its other physical properties. Around 970°C another phase transition occurs which changes the low quartz structure into another structure similar with cristobalite. In physics, a phase transition, (or phase change) is the transformation of a thermodynamic system from one phase to another. ... Common in volcanic rocks, cristobalite is a high-temperature polymorph of quartz and tridymite. ...

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Structure

The specific structure of GaPO4 shows the arrangement of tetrahedrons consisting of GaO4 and PO4 that are slightly tilted. Because of the helical arrangement of these tetrahedrons, two modifications of GaPO4 exist with different optical rotation (left and right). When polarized light is passed through a substance containing chiral molecules (or nonchiral molecules arranged asymmetrically), the direction of polarization can be changed. ...

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Sources

GaPO4 does not occur in nature; thus it must be grown synthetically. Presently, only one company in Austria produces these crystals commercially.

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History and technical importance

Pressure sensors based on quartz have to be cooled with water for applications at higher temperatures (above 300°C). Starting in 1994 it was possible to substitute these big sensors with miniaturized, non cooled ones, based on GaPO4. Further exceptional properties of GaPO4 for applications at high temperatures include its nearly temperature independent piezo effect and excellent electrical insulation up to 900°C. For bulk resonator applications, this crystal exhibits temperature compensated cuts of up to 500°C while having Q factors comparable with quartz. Due to these material properties, GaPO4 is very suitable for piezoelectric pressure sensors at high temperatures and for high temperature microbalance. Quartz: When a force is applied to the tetrahedon a displacement of the cation charge towards the center of the anion charges occurs Over the past 50 years piezoelectric sensors have proven to be a versatile tool for the measurement of various processes. ... The term electrical insulator has the same meaning as the term dielectric, but the two terms are often used in different contexts. ... A crystal oscillator (sometimes abbreviated to XTAL on schematic diagrams) is an electronic circuit that uses the mechanical resonance of a physical crystal of piezoelectric material along with an amplifier and feedback to create an electrical signal with a very precise frequency. ... A crystal oscillator (sometimes abbreviated to XTAL on schematic diagrams) is an electronic circuit that uses the mechanical resonance of a physical crystal of piezoelectric material along with an amplifier and feedback to create an electrical signal with a very precise frequency. ... Quartz: When a force is applied to the tetrahedon a displacement of the cation charge towards the center of the anion charges occurs Over the past 50 years piezoelectric sensors have proven to be a versatile tool for the measurement of various processes. ... Microbalance is an instrument capable of measuring amount of weight to at least 1 million parts of a gram ( g - the unit symbol for gram). ...

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Literature

G. Gautschi: „Piezoelectric Sensorics“, published by Springer

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External links

  • data sheet

 
 

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