Thermal stability, morphology and electronic band gap of Zn(NCN)

The thermal behavior of zinc carbodiimide Zn(NCN) was examined in the temperature range between 200 and 1100 degrees C in Ar atmosphere. The material starts to partially decompose at about 800 degrees C. Heat treatment at temperatures beyond 800 degrees C results in the formation of the byproducts nitrogen-containing bamboo-like multiwall carbon-nanotubes of 20-50 nm in diameter due to a partial decomposition of Zn(NCN) into dicyan (CN)(2), zinc and nitrogen gas followed by the polymerization of the former product to paracyanogen (CN)(n). At 1100 degrees C, the yield of the residual carbodiimide depends on the dwelling time and the initial amount of powder used for pyrolysis. One hour dwelling at 1100 degrees C yields similar to 50% of the Zn(NCN) separated as pure material. Temperature-induced change in the band structure, namely indirect-to-direct band gap transition, is registered when compared the Zn(NCN) at room temperature with the residual material annealed at 1100 degrees C. The transition from indirect (E-g = 4.32 eV) to direct band gap (E-g = 4.93 eV) is due to the thermal annealing process which results in healing of crystal defects. (C) 2013 Elsevier Masson SAS. All rights reserved.