Preparation and crystal structures of bismuth technetates: a new metal oxide system.
Two new oxides have been unambiguously identified as Bi2Tc2O7-delta with delta = 0.14(1) and Bi3TcO8 through X-ray absorption near-edge structure spectroscopy and neutron powder diffraction. The compound Bi2Tc2O7-delta has a cubic pyrochlore-type structure with a = 10.4746(1) A, space group Fd3m (origin choice 2), and Z = 8. The compound Bi3TcO8 is also cubic, a = 11.5749(1) A, space group P2(1)3, Z = 8, and has a fluorite-related crystal structure. In Bi2Tc2O7-delta the Tc(IV) cations are octahedrally coordinated, whereas in Bi3TcO8 the Tc(VII) cations are tetrahedrally coordinated. A third new phase, probably Bi3Tc3O11, could not be obtained pure, but preliminary X-ray powder diffraction data affords a primitive cubic lattice with a = 9.3433(1) A. On the basis of structural similarities between Bi2Tc2O7-delta and closely related oxides, Bi2Tc2O7-delta is expected to be a metallic oxide with Pauli paramagnetism. Electronic structure calculations of both Bi2Tc2O7-delta and Bi3TcO8 further support metallic conductivity in the former and insulating behavior in the latter. The inert pair effect of the Bi cations on the crystal structures of Bi2Tc2O7-delta and Bi3TcO8 is also described. In addition, calculations of the valence electron localization function for Bi2Tc2O7-delta and Bi3TcO8 provide further visualization of the Bi 6s(2) lone pair electrons in the real space of the crystal structures.
Manuel Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Efrain E
EE
Rodriguez
Frédéric
F
Poineau
Anna
A
Llobet
Ken
K
Czerwinski
Ram
R
Seshadri
Anthony K
AK
Cheetham