Magnetic and spectroscopic studies on cupric azide

Abstract

Optical and magnetic properties of cupric azide have been examined in relation to its explosive properties. Raman lines and absorption peaks in the infrared spectrum are explained in terms of vibrations of a distorted octahedron [Cu(N₃)₄(N^′₃)₂]. The high stretching frequency of the Cu—N bond is indicative of its high strength. Doublets in the infrared spectrum suggest the existence of two types of azide groups in the crystal. The visible spectrum of cupric azide in pyridine solution suggests that the cupric ion environment is a distorted octahedron such that the distance between cupric ion and the end atom of the azide ion is smaller than that between ions in cupric chloride, implying fractional double bonding between cupric and azide ions.

Three magnetic transitions occur between 270 K and 95 K. The Néel temperature occurs at 259 K; a superparamagnetic phase exists between 230 K and 95 K, and there is a flattening of the (magnetic susceptibility-temperature) curve at 95 K. Since the Néel temperature is proportional to exchange integral, a large superexchange interaction which facilitates energy transfer is proposed.