| Abstract: | SrNi10P6, EuNi10P6, and BaCo10As6: Phase Transitions and Crystal Structures SrNi10P6, EuNi10P6 and BaCo10As6 were prepared by heating mixtures of the elements in the range of 800°–1000 °C and were investigated by means of single‐crystal X‐ray methods. At higher temperatures the isotypic Ni phosphides (HT‐SrNi10P6: a = 6.481(2), b = 16.080(4), c = 8.763(2) Å (350 °C); HT‐EuNi10P6: a = 6.509(2), b = 16.063(4), c = 8.766(4) Å (500 °C)) crystallize in the BaNi10P6 type structure (Cmca; Z = 4), which can be described as an arrangement of Ni14P12 cages with Sr or Eu atoms in the centres. The cages are linked to layers separated by additional Ni atoms, which are coordinated tetrahedrally by P atoms of different cages. Cooling down both compounds undergo from about 270 °C (SrNi10P6) and 410 °C (EuNi10P6) respectively a second‐order phase transition involved with a change to an orthorhombic P lattice. In the structure of the NT phases (Pnma; Z = 4; NT‐SrNi10P6: a = 15.993(1), b = 6.473(1), c = 8.735(1) Å; NT‐EuNi10P6: a = 15.925(1), b = 6.478(1), c = 8.720(1) Å (25 °C)) the Ni14P12 cages are slightly distorted in comparison with the high temperature modifications. BaCo12As6 (a = 16.405(9), b = 6.858(4), c = 8.955(7) Å) crystallizes in the same structure (Pnma), but doesn't exhibit a comparable phase transition up to 600 °C. Measurements of the suszeptibiliy of EuNi10P6 between 4 K and 850 K showed divalent Europium and no magnetic order down to 4 K. |
