Structure-property correlations in solid solutions of (CuI)8P12-xAsx, 2.4< or = x < or =6.6

A series of P/As mixed pnicogen phases of composition (CuI)(8)P(12-x)As(x), in which x = 2.4, 4.2, 4.8, 5.4, and 6.6, have been synthesized and characterized by X-ray single crystal and powder diffraction, solid-state NMR spectroscopy, thermal gravimetric analysis, and impedance spectroscopy. These materials are isostructural to (CuI)(8)P(12) and consist of neutral, tubular P/As mixed pnicogen chains associated with Cu(I) and I(-) ions. The As is distributed throughout the pnicogen chains; however, the "roof" sites of the [P8] cage show preferred occupation by As relative to the other sites. Accordingly, the change in cell volume is not a linear function of the As incorporation. Solid-state (31)P NMR spectroscopy of the 40 % As incorporated sample are consistent with the X-ray structural model, with extensive broadening due to (31)P-(75)As coupling and site disorder, and a change in the chemical shifts of the resonances due to the As substitution into the lattice. The degree of copper ion site disorder, probed by single-crystal X-ray diffraction, increases with increasing As content. Although very little change is observed in the copper ionic conductivity of polycrystalline samples, which ranges from 1.8-5.1 x 10(-6) S cm(-1) for (CuI)(8)P(12-x)As(x), x = 0, 4.2, 5.4; a single crystal (x = 4.8) measured along the needle axis has a conductivity of 1.7 x 10(-3) S cm(-1) at 128 degrees C. This represents an order of magnitude improvement in conductivity over (CuI)(8)P(12) at the same temperature.