Crystal structure and compressibility of a high-pressure Ti-rich oxide, (Ti0.50Zr0.26Mg0.14Cr0.10)O1.81, isomorphous with cubic zirconia

A Ti-rich oxide, (Ti0.50Zr0.26Mg0.14Cr0.10) 1⁄4 1.0O1.81, was synthesized at 8.8GPa and 1600 1C using a multi-anvil apparatus. Its crystal structure at ambient conditions and compressibility up to 10.58GPa were determined with single-crystal X-ray diffraction. This high-pressure phase is isomorphous with cubic zirconia (fluorite-type) with space group Fm3̄m and unit-cell parameters a 1⁄4 4.8830(5) Å and V 1⁄4 116.43(4) Å. Like stabilized cubic zirconia, the structure of (Ti0.50Zr0.26Mg0.14Cr0.10)O1.81 is also relaxed, with all O atoms displaced from the (4, 1 4, 1 4) position along /10 0S by 0.319 Å and all cations from the (0, 0, 0) position along /111S by 0.203 Å. No phase transformation was detected within the experimental pressure range. Fitting the high-pressure data (V vs. P) to a third-order Birch–Murnaghan EOS yields K0 1⁄4 164(4)GPa, K0 1⁄4 4.3(7), and V0 1⁄4 116.38(3) Å. The bulk modulus of (Ti0.50Zr0.26Mg0.14Cr0.10)O1.81 is significantly lower than that (202GPa) determined experimentally for cubic TiO2 or that ( 210GPa) estimated for cubic ZrO2. This study demonstrates that cubic TiO2 may also be obtained by introducing various dopants, similar to the way cubic zirconia is stabilized below 2370 1C. Furthermore, (Ti0.50Zr0.26Mg0.14Cr0.10)O1.81 has the greatest ratio of Ti 4+ content vs. vacant O sites of all doped cubic zirconia samples reported thus far, making it a more promising candidate for the development of electrolytes in solid oxide fuel cells. & 2009 Elsevier Ltd. All rights reserved.