Semiconductors are key materials in modern electronics and are widely used to build, for instance, transistors in integrated circuits as well as thermoelectric materials for energy conversion, and there is a tremendous interest in the development and improvement of novel materials and technologies to increase the performance of electronic devices and thermoelectrics. Tetramorphic Ag(10)Te(4)Br(3) is a semiconductor capable of switching its electrical properties by a simple change of temperature. The combination of high silver mobility, a small non-stoichiometry range and an internal redox process in the tellurium substructure causes a thermopower drop of 1,400 microV K(-1), in addition to a thermal diffusivity in the range of organic polymers. The capability to reversibly switch semiconducting properties from ionic to electronic conduction in one single compound simply by virtue of temperature enables novel electronic devices such as semiconductor switches.

Ag10Te4Br3 is polymorphic with four polymorphs in the temperature range from 3 to 450 K. It represents the first member of a formerly unseen class of materials featuring covalently and ionically bonded tellurium substructures. Thermal analyses (DSC and C p) prove the reversibility of the α−β, β−γ, and γ−δ phase transitions at 355, 317, and 290 K, respectively. The existence of the low-temperature δ-phase is substantiated by C p measurements down to 3 K. Temperature-dependent single-crystal structure analysis and nonharmonic refinements of the silver distribution for all polymorphs reveal a high silver mobility over the whole temperature range. A significant change in the dimensionality of the silver distribution, from an exclusively 2D (δ, γ) to a 3D (β, α) arrangement, can be observed for Ag10Te4Br3 with the increase in temperature. The enhanced silver mobility causes a structural frustration and disorder phenomena of the predominantly covalently bonded tellurium substructure for the high-temperature α- and β-polymorphs. The increase in disorder comes along with the occurrence of diffuse scattering in form of Kagomé nets, indicating a structural frustration in a rod packing arrangement. An ionic conductivity, approaching the values of most of the known silver super ion conductors and only 1 order of magnitude lower than that in RbAg4I5, are a remarkable feature of air-, photo-, and moisture-stable Ag10Te4Br3.

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Polyphosphides composed by late transition metal ions with closed d10 shells are subject of this review. Recent progress has been made during the past years in this field and many new compounds have been discovered. The spectrum of compounds extends from classical binary and ternary compounds, adduct phases of metal halides and molecular species to composites of intermetalloid clusters and molecular anion substructures. Phosphorus is highly reactive to late transition metals forming d10 ions and they entirely react to a plenthora of materials. Only a handful of elements do not form binary compounds with phosphorus and the number is decreasing. This review is focussed on synthetic procedures and the structure property relations of d10 ion polyphosphides. A brief overview is also given to the progress in phosphorus allotrope chemistry and their perspectives and applications. Especially black phosphorus as active material for batteries and its de‐laminated form “phosphorene” is added.

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