Key Role of Bismuth in the Magnetoelastic Transitions
of Ba<sub>3</sub>BiIr<sub>2</sub>O<sub>9</sub> and Ba<sub>3</sub>BiRu<sub>2</sub>O<sub>9</sub> As Revealed by Chemical Doping
- Publication date
- Publisher
Abstract
The key role played by bismuth in
an average intermediate oxidation state in the magnetoelastic spin-gap
compounds Ba<sub>3</sub>BiRu<sub>2</sub>O<sub>9</sub> and Ba<sub>3</sub>BiIr<sub>2</sub>O<sub>9</sub> has been confirmed by systematically
replacing bismuth with La<sup>3+</sup> and Ce<sup>4+</sup>. Through
a combination of powder diffraction (neutron and synchrotron), X-ray
absorption spectroscopy, and magnetic properties measurements, we
show that Ru/Ir cations in Ba<sub>3</sub>BiRu<sub>2</sub>O<sub>9</sub> and Ba<sub>3</sub>BiIr<sub>2</sub>O<sub>9</sub> have oxidation states
between +4 and +4.5, suggesting that Bi cations exist in an unusual
average oxidation state intermediate between the conventional +3 and
+5 states (which is confirmed by the Bi L<sub>3</sub>-edge spectrum
of Ba<sub>3</sub>BiRu<sub>2</sub>O<sub>9</sub>). Precise measurements
of lattice parameters from synchrotron diffraction are consistent
with the presence of intermediate oxidation state bismuth cations
throughout the doping ranges. We find that relatively small amounts
of doping (∼10 at%) on the bismuth site suppress and then completely
eliminate the sharp structural and magnetic transitions observed in
pure Ba<sub>3</sub>BiRu<sub>2</sub>O<sub>9</sub> and Ba<sub>3</sub>BiIr<sub>2</sub>O<sub>9</sub>, strongly suggesting that the unstable
electronic state of bismuth plays a critical role in the behavior
of these materials
