V. Nassif et Re. Carbonio, Neutron diffraction study of the crystal structure of BaMoO4: A suitable precursor for metallic BaMoO3 perovskite, J SOL ST CH, 146(1), 1999, pp. 266-270
BaMoO3, metallic and Pauli paramagnetic, has been prepared by controlled re
duction of BaMoO4. This precursor, containing Mo(VI), is unusually stable a
gainst reduction, due to structural factors. The crystal structure of BaMoO
4 has been refined from neutron powder diffraction data: space group I4(1)/
a (no. 88), Z = 4, a = 5.5479(9), and c = 12.743(2) Angstrom. A bond-valenc
e study allowed us to detect the presence of slight tensile and compressive
stresses in the crystal structure of BaMoO4, in which Ba is overbonded and
Mo is underbonded. However, this effect is less pronounced than in other A
MO(4) oxides with a scheelite structure (A = Ca, Sr, Ba; M = Mo, W): BaMoO4
contains the M cation exhibiting the closest valence to the nominal value
of 6+, suggesting a large covalent contribution to the Mo-O bonds. This obs
ervation is coherent with the large thermal stability of this compound agai
nst reduction, taking place at temperatures above 920 degrees C in H-2 flow
. (C) 1999 Academic Press.