Crystal structure of lanthanum bismuth silicate Bi2-xLaxSiO5 (x∼0.1)

A melting and glass recrystallization route was carried out to stabilize a new tetragonal form of Bi2SiO5 with bismuth partially substituted by lanthanum. The crystal structure of Bi2-xLaxSiO5 (x similar to 0.1) was determined from powder X-ray and neutron diffraction data (space group I4/mmm, a = b = 3.8307(3) angstrom, c = 15.227(1) angstrom. V = 224.18 angstrom(3), Z = 2, reliability factors: R-Bragg = 5.65%, R-p = 14.6%, R-wp = 16.8%, R-exp = 8.3%, chi(2) = 8.3 (X-ray) and R-Bragg = 2.40%, RP = 8.1%, R-wp = 7.5%, R-exp = 4.2%, chi(2) = 3.3 (neutrons); 11 structural parameters refined). The main effect of lanthanum substitution is to introduce, by removing randomly some bismuth 6s(2) 1one pairs, a structural disorder in the surroundings of (Bi2O2)(2+) layers, that is in the (SiO3)(2-) pyroxene files arrangement. It results in a symmetry increase relatively to the parent compound Bi2SiO5, which is orthorhombic. The two structures are compared. (c) 2006 Elsevier Inc. All rights reserved.