Towards MXPn‐Type Compounds in the Systems Ge‐I‐Pn (Pn = P, As) – New Insights in the Structures and Properties of Inverse Type I Clathrates

Two ternary systems, Ge-I-P and Ge-I-As were investigated for the existence of double helical GeIPn phases (Pn = P, As). However, experiments in the temperature range of 673-1073 K always led to the formation of inverse type I clathrates. Optimization of the synthesis parameters resulted in phase pure samples for both clathrates on a gram scale. We found slightly varying compositions than for clathrates reported before in the two systems. Structural characterization by means of single crystal analysis and Rietveld refinement showed a defect model for the guest structures in combination with a mixed site occupancy for the host lattice sites. Both compounds reveal promising thermal conductivities and Seebeck coefficients but only small overall electrical conductivities.