Hg 2 Ru 2 O 7 , a new pyrochlore showing a metal–insulator transition

Hg2Ru2O7 was prepared by reaction of HgO and RuO2 at 400 °C under elevated oxygen pressure. According to a single crystal structure determination, the compound adopts the pyrochlore structure with a cubic lattice parameter of 10.2011(1) Å. From heat capacity measurements, a second order phase transition at 108 K was detected, consistent with a change from metallic to semiconducting behaviour as well as from paramagnetic to antiferromagnetic at lower temperatures. The behaviour is qualitatively very similar to that of Cd2Os2O7 and Tl2Ru2O7.