Zum chemischen Transport von Chrom- und Manganmonophosphid mit Iod. Experimente und Modellrechnungen

On the Chemical Vapour Transport of Chromium and Manganese Monophosphide. Experimental Results and Thermochemical Calculations Using iodine as transport agent well shaped crystals of a volume up to V ≈︁ 50 mm³ (CrP) or an edgelength of approximately 1 ≈︁ 10 mm (MnP) can be grown. CrP has been deposited at the lower temperature of a temperature gradient (1050 → 950°C). At a density of the transport agent higher than D = 26 · 10⁻⁶ mol I₂/cm³] CrP and CrI_2,1 coexist in the deposition region at the lower temperature. The determined composition of the condensed phases under equilibrium conditions are in accordance with thermochemical calculations assuming the heat of formation of CrP to be Δ_FH= −25.5 ± 2 kcal/mol]. Furthermore these calculations show that the solution of CrP in the gas phase leads to CrI_2,g, Cr₂I_4,g, P_2,g and P_4,g, while I_2,g, HI_g, PI_3,g and P₂I_4,g have to be considered as transport agents. The migration of MnP (1000 → 1100°C) results from an exothermic reaction. MnP_s exists besides MnI_2,1 in the source region. Thermochemical calculations are in good agreement with the experimental results and suggest the following heterogenous equilibrium to be responsible for the observed behaviour: .