Lanthanum phosphide
Lanthanum phosphide is an inorganic compound of lanthanum and phosphorus with the chemical formula LaP. Synthesis
Lanthanum phosphide can be made by heating lanthanum metal with excess phosphorus in a vacuum:

 4 La + P4 → 4 LaP

Physical properties
Lanthanum phosphide forms black crystals of a cubic system, space group Fm3m, cell parameters a = 0.601 nm, with number of formulas per unit cell Z = 4. The crystals are very unstable and decompose in the open air. Chemical properties
Lanthanum phosphide reacts with water, releasing highly toxic phosphine gas:

 LaP + 3H2O → La(OH)3 + PH3

Uses
Lanthanum phosphide compound is a semiconductor used in high power, high frequency applications, and in laser diodes. Lanthanum polyphosphide
In addition to the simple phosphide, LaP, lanthanum and phosphorus can also form phosphorus-rich compounds such as LaP5 and LaP7. References

Phosphides
Lanthanum compounds
Semiconductors
Rock salt crystal structure