Gallium phosphate - AbsoluteAstronomy.com

GaPO₄

General
Category	crystal Crystal A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
Chemical formula Chemical formula A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound.... (or Composition)	GaPO₄
Identification
Color	Clear
Crystal system Crystal system In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals...	Trigonal
Crystal class	32 or D₃ (Schönflies)
Cleavage Cleavage (crystal) Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the...	None
Fracture Fracture A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...	Conchoidal
Mohs Scale hardness	5.5
Refractive index Refractive index In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....	n_o=1.605, n_e=1.623
Pleochroism Pleochroism Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles with polarized light.- Background :Anisotropic crystals will have optical properties that vary with the direction of light...	None
Streak Streak (mineralogy) The streak of a mineral is the color of the powder produced when it is dragged across an unweathered surface. Unlike the apparent color of a mineral, which for most minerals can vary considerably, the trail of finely ground powder generally has a more consistent characteristic color, and is thus...	White
Density Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...	3570 kg/m³
Solubility Solubility Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...	insoluble in pH PH In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline... = 5 - 8
other properties
Pyroelectricity Pyroelectric crystal Pyroelectric crystals are crystals that generate electricity when heated. It is similar to piezoelectricity.-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...	None
Particular characteristics	quartz Quartz Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,... isotype Isotype Isotype can refer to:* In crystallography, an "isotype" is a synonym for isomorph* In biology, per the International Code of Botanical Nomenclature, the "isotype" is a duplicate of the holotype.... , piezoelectric effect Piezoelectricity Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure... 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

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

, possessing very similar properties, but the silicon

Silicon

Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

atoms are alternately substituted with gallium

Gallium

Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...

and phosphorus

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

, thereby doubling the piezoelectric effect

Piezoelectricity

Piezoelectricity is the charge which accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure...

. GaPO₄ has many advantages over quartz for technical applications, like a higher electromechanical coupling coefficient

Electromechanical coupling coefficient

Electromechanical coupling coefficient is a numerical measure of the conversion efficiency between electrical and acoustic energy in piezoelectric materials.Qualitatively the electromechanical coupling coefficient, k, can be determined as:...

in resonators

Crystal oscillator

A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency...

, due to this doubling.
Contrary to quartz, GaPO₄ is not found in nature. Therefore, a hydrothermal process must be used to synthesize the crystal.

Modifications

GaPO₄ possesses, in contrast to quartz, no α-β phase transition

Phase transition

A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....

, 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

Cristobalite

The mineral cristobalite is a high-temperature polymorph of silica, meaning that it has the same chemical formula, SiO2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the quartz group which also include coesite, tridymite and stishovite...

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

Optical rotation

Optical rotation is the turning of the plane of linearly polarized light about the direction of motion as the light travels through certain materials. It occurs in solutions of chiral molecules such as sucrose , solids with rotated crystal planes such as quartz, and spin-polarized gases of atoms...

(left and right

Chirality (chemistry)

A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....

Sources

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

History and technical importance

Pressure sensors

Piezoelectric sensor

A piezoelectric sensor is a device that uses the piezoelectric effect to measure pressure, acceleration, strain or force by converting them to an electrical charge.-Applications:...

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

Electrical insulation

thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...

up to 900°C. For bulk resonator applications, this crystal exhibits temperature compensated cuts

Crystal oscillator

of up to 500°C while having Q factors

Crystal oscillator

comparable with quartz. Due to these material properties, GaPO₄ is very suitable for piezoelectric pressure sensors

Piezoelectric sensor

A piezoelectric sensor is a device that uses the piezoelectric effect to measure pressure, acceleration, strain or force by converting them to an electrical charge.-Applications:...

at high temperatures and for high temperature microbalance

Microbalance

A microbalance is an instrument capable of making precise measurements of weight of objects of relatively small mass: of the order of a million parts of a gram. In comparison, a standard analytical balance is 100 times less sensitive; i.e. it is limited in precision to 0.1 milligrams...

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