Pb5.0(1)In8.4(1)Bi1.6(1)S20, a new quaternary lead indium bismuth sulfide

The title phase, first detected in the early 1980s but hitherto unpublished, has been resynthesized and structurally characterized. Unambiguous determination of the chemical composition was not possible by structure analysis alone, but required additional analytical methods. The complex structure shows a close similarity to the structures of two related compounds, one known by the formula Pb_1.6In₈Bi₄S₁₉ and the other being the ternary compound Pb₆In₁₀S₂₁. This is despite the fact that the three phases correspond to very different Pb:Bi ratios. A geometric mechanism is described by which the three structures can be transformed into each other, provided that the heavy atoms Pb and Bi are treated as equivalent.