Abstract: | Contributions on the Thermal Behaviour of Oxoniobates of the Transition Metals. V. Chemical Vapour Transport of NiNb2O6 with Cl2 or NH4Cl. Experiments and Calculations Well shaped crystals of NiNb2O6 were obtained by CVT using Cl2 (added as PtCl2) or NH4Cl as transport agents (1020°C → 960°C). As a result of thermodynamic calculations the migration of NiNb2O6 in the temperature gradient in the presence of Cl2 can be expressed by the heterogenous endothermic equilibrium (1). Assuming ΔBH(NiNb2O6, s) = ?524.4 kcal/mol a satisfying agreement between thermodynamical calculation and experimental results can be reached. NH4Cl is less suitable as transport agent, because Ni2+ is partly reduced to the metal by NH3. The additionally H2O produced by this reduction leads to a less favourable equilibrium position of (2) and to low deposition rates. . |