Ca_xWO₃ BRONZE SYNTHESIZED UNDER HIGH PRESSURE. Zibrov I.P.¹, Filonenko V.P.².¹Institute of Crystallography, Russian Academy of Sciences, 117333 Moscow, Leninsky pr.59, Russia. ²Institute for High Pressure Physics, Russian Academy of Sciences, 142092 Troitsk, Moscow Region, Russia.

A new intergrowth tungsten bronze (ITB), Ca_xWO₃ x=0.04-0.06 has been prepared by solid state reaction (CaO+WO₃+W) at P=50-80 kbar and T>1300 C. The compounds were studied by X-ray powder diffraction and high resolution transmission electron microscopy. The samples with starting composition x=0.05-0.5 were investigated. Ca_xWO₃(ITB)+ CaWO₄ were revealed in the samples with x<0.15, the mixture of CaWO₄+ Ca_xWO₃(HTB[1]+PTB[2])- in the samples with x>0.15. The calculated unit cell parameters of the ITB phase are: a=10.152, b=7.423 and c=3.790Å.

According to the nomenclature of the ITB families of related phases introduced in [3], the structure of this compound is denoted (2)-ITB and belongs to the (n)-ITB family of related phases. The number n corresponds to the number of WO₆-octahedra across the WO₃-type slabs in the structure. The theoretical upper limit of [[chi]] is 0.20. However, in the Ca_xWO₃(ITB) phase the sixsided tunnels seems to be filled to about 25%. The (2)-ITB structure can be considered to consist of hexagonal tungsten bronze (HTB) slabs, one single hexagonal tunnel row wide, which are mutually linked by corner-sharing.

[1]. P.E.Bierstedt et. al., Solid State Commun. 4, 25, 1966.

[2]. D.Vandeven et. al., Mater. Res. Bull., 2, 809,1967.

[3]. A.Hussain and L.Kihlborg, Acta Cryst. A32, 551 (1976).

This research was made possible in part by Grant N 95-03-08146a from Russian Foundation of Fundamental Investigations.