Synthesis and Structural Evolution of the Solid Solution Bi(Bi12−xTexO14)Mo4−xV1+xO20(0≤x<2.5)

✍ Scribed by A. Castro; R. Enjalbert; P. Baules; J. Galy

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 531 KB
• Volume: 139
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1998.7831

✦ Synopsis

A new solid solution of general formula Bi(Bi 12؊x Te x O 14 ) Mo 4؊x V 1؉x O 20 with x up to 2.5 has been prepared by simultaneous substitution of the couple Te 4؉ -V 5؉ for Bi 3؉ -Mo 6؉ in Bi 13 Mo 4 VO 34 . These materials have been studied by X-ray powder diffraction and thermal analysis, showing a structural evolution with changing x values. Crystal growth of these phases has been carried out; the single crystals have been studied by transmission electron microscopy and their structure determined by X-ray single crystal diffraction techniques performed for the x ‫؍‬ 1 and x ‫؍‬ 2 samples. Both materials crystallize in a monoclinic unit cell, space groups P2 for Bi(Bi 11 TeO 14 )Mo 3 V 2 O 20 (x ‫؍‬ 1) and P2/c for Bi(Bi 10 Te 2 O 14 )Mo 2 V 3 O 20 (x ‫؍‬ 2), with respective unit-cell parameters a ‫؍‬ 11.704(9), b ‫؍‬ 5.820(1), c ‫؍‬ 12.16(1) A s , ‫؍‬ 100.90(2)°(Z ‫؍‬ 1) and a ‫؍‬ 11.642(2), b ‫؍‬ 5.771(1), c ‫؍‬ 24.22(1) A s , ‫؍‬ 101.16(4)°(Z ‫؍‬ 2). The structures keep the basic framework of ''columns'' present in the parent oxide Bi(Bi 12 O 14 )Mo 4 VO 20 ; they are built up by infinite (Bi 12؊x Te x O 14 ) columns along the [010] direction and surrounded by independent (Mo, V)O 4 tetrahedra organized in layers parallel to (100) and ( 001) planes. The extra Bi cations are located at the intersection of these layers. The x ‫؍‬ 1 compound exhibits original structural features due to its acentric structure. The observed structural evolution can be correlated to the different charge balance between columns (Bi 12؊x Te x O 14 ) (8؉x)؉ and tetrahedral environment, as well as to the lower stereochemical activity of the 6s 2 lone pair of electrons of Bi 3؉ relative to the 5s 2 electrons of Te 4؉ cation.