Synthesis and crystal chemical characterization of the pyrochlore type MgZrSi2O7

Highlights: → We synthesized new pyrochlore type MgZrSi2O7 at high pressure and temperature. → We characterized this MgZrSi2O7 by Rietveld method. → A-site of pyrochlore A2B2O7 is randomly occupied by two species in a 1:1 ratio. → The MgZrSi2O7 pyrochlore has higher RA/RB ratio than previous A2B2O7 pyrochlores. - Abstract: The pyrochlore type of MgZrSi2O7 was synthesized at 25 GPa and 1500 deg. C using a Kawai-type, multi-anvil apparatus. Powder X-ray diffraction and Rietveld analysis revealed that the phase assumed the pyrochlore structure (space group Fd3-bar m, cubic) with the lattice parameter a = 9.2883(1) A and the structural parameter x = 0.4295(4). Chemical analysis by the electron probe microanalysis (EPMA) confirmed the stoichiometry of MgZrSi2O7. It was demonstrated that the eight-fold coordinated 16c site is randomly occupied by both Mg2+ and Zr4+ ions in a 1:1 ratio. The high ionic radius ratio RA/RB (where A and B denote Mg + Zr and Si, respectively) of 2.22 necessitates a relatively high pressure to stabilize the pyrochlore structure.