Zinc phosphide ( Zn₃ P₂) is an

inorganic An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemistry''. Inor ...

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

. It is a grey solid, although commercial samples are often dark or even black. It is used as a

rodenticide Rodenticides are chemicals made and sold for the purpose of killing rodents. While commonly referred to as "rat poison", rodenticides are also used to kill mice, woodchucks, chipmunks, porcupines, nutria, beavers, and voles. Some rodenticides ...

. Zn₃P₂ is a II-V

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

with a direct band gap of 1.5 eV and may have applications in photovoltaic cells. A second compound exists in the zinc-phosphorus system, zinc diphosphide (ZnP₂).

Synthesis and reactions

Zinc phosphide can be prepared by the reaction of

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...

with

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

; however, for critical applications, additional processing to remove

arsenic Arsenic is a chemical element; it has Symbol (chemistry), symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is not ...

compounds may be needed. :6 Zn + P₄ → 2 Zn₃P₂ Another method of preparation include reacting tri-n-octylphosphine with dimethylzinc. Zinc phosphide reacts with water to produce highly toxic

phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...

(PH₃) and zinc hydroxide (Zn(OH)₂): :Zn₃P₂ + 6 H₂O → 2 PH₃ + 3 Zn(OH)₂

Structure

Zn₃P₂ has a room-temperature

tetragonal In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the Cube (geometry), cube becomes a rectangular Pri ...

form that converts to a

cubic Cubic may refer to: Science and mathematics * Cube (algebra), "cubic" measurement * Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex ** Cubic crystal system, a crystal system w ...

form at around 845 °C.Evgeniĭ I︠U︡rʹevich Tonkov, 1992, High Pressure Phase Transformations: A Handbook, Vol 2, Gordon and Breach Science Publishers, In the room-temperature form there are discrete P atoms, zinc atoms are tetrahedrally coordinated and phosphorus six coordinate, with zinc atoms at 6 of the vertices of a distorted cube. The crystalline structure of zinc phosphide is very similar to that of cadmium arsenide (Cd₃As₂), zinc arsenide (Zn₃As₂) and cadmium phosphide (Cd₃P₂). These compounds of the Zn-Cd-P-As quaternary system exhibit full continuous solid-solution.

Applications

Photovoltaics

Zinc phosphide is an ideal candidate for thin film photovoltaic applications, for it has strong optical absorption and an almost ideal band gap (1.5eV). In addition to this, both zinc and phosphorus are found abundantly in the Earth's crust, meaning that material extraction cost is low compared with that of other thin film

photovoltaics Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commerciall ...

. Both zinc and phosphorus are also nontoxic, which is not the case for other common commercial thin film photovoltaics, like cadmium telluride. Researchers at the

University of Alberta The University of Alberta (also known as U of A or UAlberta, ) is a public research university located in Edmonton, Alberta, Canada. It was founded in 1908 by Alexander Cameron Rutherford, the first premier of Alberta, and Henry Marshall Tory, t ...

were the first to successfully synthesize colloidal zinc phosphide. Before this, researchers were able to create efficient

solar cell A solar cell, also known as a photovoltaic cell (PV cell), is an electronic device that converts the energy of light directly into electricity by means of the photovoltaic effect.

s from bulk zinc phosphide, but their fabrication required temperatures greater than 850 °C or complicated vacuum deposition methods. By contrast, colloidal zinc phosphide

nanoparticle A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At ...

s, contained in a zinc phosphide “ink”, allows for inexpensive, easy large-scale production, by means of slot-die coating or spray coating. The testing and development of these zinc phosphide thin films is still in its early stages, but early results have been positive. Prototype heterojunction devices fabricated from zinc phosphide nanoparticle ink exhibited a rectification ratio of 600 and

photosensitivity Photosensitivity is the amount to which an object reacts upon receiving photons, especially visible light. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished, photoallergy and phototoxicit ...

with an on/off ratio near 100. These are both acceptable suitability benchmarks for solar cells. Development still needs to be made on optimizing the nanoparticle ink formation and device architecture before commercialization is possible, but commercial spray-on zinc phosphide solar cells may be possible within ten years.

Pest control

Rodenticide

Metal phosphides have been used as

s. A mixture of food and zinc phosphide is left where the rodents can eat it. The acid in the digestive system of the rodent reacts with the phosphide to generate toxic

gas. This method of vermin control has possible use in places where rodents are immune to other common poisons. Other pesticides similar to zinc phosphide are aluminium phosphide and calcium phosphide. : Zn₃P₂ + 6H⁺ → 3Zn⁺⁺ + PH₃ ↑ Zinc phosphide is typically added to rodent baits in amount of around 0.75-2%. Such baits have a strong, pungent

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plants in the genus '' Allium''. Its close relatives include the onion, shallot, leek, chives, Welsh onion, and Chinese onion. Garlic is native to central and south Asia, str ...

-like odor characteristic of phosphine liberated by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

. The odor attracts rodents, but has a repulsive effect on other animals; However, birds, notably

wild turkey The wild turkey (''Meleagris gallopavo'') is an upland game bird native to North America, one of two extant species of Turkey (bird), turkey and the heaviest member of the order Galliformes. It is the ancestor to the domestic turkey (''M. g. dom ...

s, are not sensitive to the smell. The baits have to contain sufficient amount of zinc phosphide in sufficiently attractive food in order to kill rodents in a single serving; a sublethal dose may cause aversion towards zinc phosphide baits encountered by surviving rodents in the future. Rodenticide-grade zinc phosphide usually comes as a black powder containing 75% of zinc phosphide and 25% of

antimony potassium tartrate Antimony potassium tartrate, also known as potassium antimonyl tartrate, potassium antimontarterate, or tartar emetic, has the formula K2Sb2(C4H2O6)2. The compound has long been known as a powerful emetic, and was used in the treatment of schistoso ...

, an

emetic Vomiting (also known as emesis, puking and throwing up) is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenteritis, preg ...

to cause vomiting if the material is accidentally ingested by humans or domestic animals. However, it is still effective against rats, mice, guinea pigs and rabbits, none of which have a vomiting reflex.

Pest control in New Zealand

The New Zealand Environmental Protection Authority has approved the import and manufacture of Microencapsulated Zinc Phosphide (MZP Paste) for the ground control of

possums Possum may refer to: Animals * Didelphimorphia, or (o)possums, an order of marsupials native to the Americas ** Didelphis, a genus of marsupials within Didelphimorphia *** Common opossum, native to Central and South America *** Virginia opossum, ...

. The application was made by Pest Tech Limited, with support from Connovation Ltd, Lincoln University and the Animal Health Board. It will be used as an additional vertebrate poison in certain situations. Unlike 1080 poison, it cannot be used for aerial application.

Safety

Zinc phosphide is highly toxic, especially when ingested or inhaled. The reason for its toxicity is the release of phosphorus compounds, usually

, when it reacts with water and acids. Phosphine is very toxic and, with trace amounts of P₂H₄,

pyrophoric A substance is pyrophoric (from , , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolithium compounds and triethylb ...

. Phosphine is also denser than air and may remain close to the ground without sufficient

ventilation Ventilation may refer to: * Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation ** Mechanical ventilation, in medicine, using artificial methods to assist breathing *** Respirator, a ma ...

References

External links

Zinc Phosphide Pesticide Information Profile - Extension Toxicology Network

*

MD0173
- Pesticides in the military {{rodenticides Phosphides phosphide Rodenticides II-V semiconductors II-V compounds Foul-smelling chemicals