Preparation of NbO2 single crystals by chemical transport reaction

The preparation of NbO2 single crystals was carried out by chemical transport using TeCl4 as a transport agent. Well formed octahedral crystals limited by faces of (101), (011) families were deposited on the cold zone. The crystal size was as large as 1 mm. Simultaneously, needle or platelet crystals were deposited on the colder zone. These crystals were identified to be an orthorhombic modification of Nb12O29. Their unit cell constants were determined to be a = 28.90 A, b = 3.80 A, c = 20.72 A and their growth direction to be in the b-crystal axis. The necessity of buffering the oxygen partial pressure for the selective growth of either one of the crystals was described. The chemical transport of NbO was also tentatively made.