STRUCTURAL-PROPERTIES OF THE SYSTEM M-ZRO2-ALPHA-FE2O3

The existence of solid solutions in the system m-ZrO2-alpha-Fe2O3 was studied by X-ray powder diffraction, A series of samples were prepared from aqueous solutions of corresponding nitrates and subsequent heati ng of the obtained precipitate up to 1100 degrees C. Diffraction patte rns were taken by step-scanning and determination of unit-cell paramet ers was performed by means of the powder-pattern-fitting methods. In t he whole concentration range there exist two types of solid solution, Z and F, of the form Zr1-xFe2xO2+x, very closely structurally related to m-ZrO2 and alpha-Fe2O3 respectively. Exclusively the Z phase exists for 0 less than or equal to x less than or similar to 002. Its unit-c ell parameters are different and its crystal lattice is asymmetrically distorted in relation to those of m-ZrO2. Exclusively the F phase exi sts for 0.99 less than or similar to x less than or equal to 1, having unit-cell parameters very similar to those of alpha-Fe2O3. In:the two -phase region, 0.02 less than or similar to x less than or similar to 0.99, the unit-cell parameters of both the Z and F phases did not chan ge, while the fraction of the F phase increased and the fraction of th e Z phase decreased as x increased. The terminal solid solubility limi ts at room temperature, (2.0+/-0.3) mol% of alpha-Fe2O3 in m-ZrO2 and (1.0+/-0.3) mol% of m-ZrO2 in alpha-Fe2O3 were found from the dependen ce of diffraction line intensities of both Z and F phases on x by extr apolation to zero intensity. The existence of solid solutions in the l imiting concentration ranges were confirmed by Mossbauer spectroscopy.