[Cd3Cu]CuP10 is the first representative of a class of compounds featuring polyphosphidic adamantine-analogous [P10] units, which tend to be fragmented and polymerized to [P6] rings and tubular [P26] units in the solid state. A new polyphosphide with nominal composition Cd15Cu10P46 results, featuring isolated and polymerized polyanions. Thermoanalytic experiments and phase analytic measurements substantiated the consecutive loss of P4 and Cd of the starting material via different intermediate steps. After P4 loss, the new polyphosphide occurred followed by various binary copper phosphides to the final product Cu3P.
Several methods are established in thermal analysis to investigate phase formation, phase transition, and decomposition reactions. The analysis of phase equilibria with volatile components is particularly feasible by using standard method of thermogravimetry. Hardly any investigations of phase formation reactions are possible to realize if one of the components is lost by vaporization. By using the “High-Temperature Gas-Balance” (HTGB), the vapor phase is enclosed in a silica ampoule and thus forms an equilibrium gas phase in permanent contact with the solid phase. The measurement signal Δmmeas is caused by change of the leverage of the horizontal balance support during evaporation and condensation. The application of the HTGB allows the analysis of solid–gas equilibria in the working range from 0.01 till 15 bar at temperatures up to 1,100 °C. The first comparison of evaporation reactions determined by standard thermogravimetric analyses and by measurements using the HTGB is given for the inorganic systems: P, As, SeO2, PtI2, and Hg/I.