Neptunium arsenide

Neptunium arsenide is a binary inorganic compound of neptunium and arsenic with the chemical formula. The compound forms crystals.

Synthesis
Heating stoichiometric amounts of pure substances:
 * $$\mathsf{ Np + As \ \xrightarrow{T, I_2}\ NpAs }$$

Physical properties
Neptunium arsenide forms crystals of several modifications:


 * Cubic system, space group Fm3m, cell parameters a = 0.5835 nm, exists at temperatures below –131 °С.
 * Tetragonal system, cell parameters a = 0.58312 nm, c = 0.58281 nm, exists in the temperature range –131 to –98 °С.
 * Cubic system, space group Fm3m, cell parameters a = 0.58318 nm, exists at temperatures above –98 °C.

Neptunium arsenide becomes antiferromagnetic at 175 K.