Formation and Transformation of Solid Solutions in the System Nb 2 O 5 –Ta 2 O 5

In the system Nb 2 O 5 –Ta 2 O 5 , a continuous series of δ‐Nb 2 O 5 (δ‐Ta 2 O 5 ) solid solutions with a hexagonal cell is formed while heating amorphous materials prepared by the simultaneous hydrolysis of niobium and tantalum alkoxides. The lattice parameters a and c change linearly with increasing Ta 2 O 5 content; the former value increases from 0.3604 to 0.3620 nm, and the latter value decreases from 0.3923 to 0.3883 nm. They transform to γ‐Nb 2 O 5 (β‐Ta 2 O 5 ) solid solutions with an orthorhombic cell at higher temperatures. The changes in lattice parameters a and c as functions of composition are the same as those of hexagonal solid solutions, whereas parameter b is relatively constant.