Oxygen-induced structural change of the tetragonal phase around the tetragonal–cubic phase boundary in ZrO₂–YO_1.5 solid solutions

Abstract

In the ZrO2-YO~.5 solid solutions, the phase changes among the cubic phase (Fm3m, Z = 4), the t" form and the t' form were investigated by neutron and X-ray powder diffraction, where the t" and t' forms are defined as tetragonal phases (P42/nmc, Z = 2) with axial ratios of c/ay = 1 and c/a s > 1, respectively, which were prepared by a diffusionless transition from the high-temperature cubic phase during quenching, ay is the lattice parameter of the pseudofluorite cell. The crystal structure of the tetragonal phase of Zrl _ xYxO2-xn [ = (ZrO2)l--x(YOl.5)x; X = 0.10, 0.12, 0.14 and 0.16] has been refined both by the direct estimation of the integrated intensity ratio I(102)/I(101) and by the Rietveld analysis of neutron powder diffraction data collected at 293 K [A = 1.5301 (3) or 1.5314 (2)/k]. The crystal structure of Zrl-xYxO2-x/2 (X = 0.18 and 0.20) has also been refined assuming either tetragonal (P4Jnmc, Z--2) or cubic symmetry [Fm3m, Z--4] by the Rietveld analysis of neutron powder diffraction data collected at 293 K [A--1.5301 (3)A]. The lattice parameters were determined by profile-fittings of Cu Ka X-ray powder diffraction data. The oxygen displacement from the ideal anion coordinate of the cubic fluorite-type structure, 0.25-z, decreased with an increase of YO~.5 content, where z is the atomic coordinate of oxygen. The axial ratio c/a I also decreased with an increase of YO~.5 content. The Zro.84Yo.16Oi.92 sample, whose axial ratio c/afis equal to unity within experimental error, has clearly exhibited oxygen displacement along the c axis from the ideal site (8c) of the fluorite-type structure (t" form). The space group of the t" form was finally assigned to be P42/nmc after the examination of various space groups which are subgroups of Fm3m and supergroups of P42/nmc. The coexistence of the t' and t" forms in the Zro.86Yo.~40~.93 sample suggests the existence of an energy barrier between them and that the high-temperature cubic phase transforms into the t" form and then a part of the t'" form transforms into the t' form.

Influence of Isothermal Heat Treatment on Porosity and Crystallite Size in Axial Suspension Plasma Sprayed Thermal Barrier Coatings for Gas Turbine Applications

“…Refined values of average crystallite sizes were obtained by exploiting the Rietveld method [35] and including a Lorentzian function for profile fitting. For the Rietveld refinement, CIF (Crystallography Information File) with the collection code 75309 in ICSD (Inorganic Crystal Structure Database) was used [36], i.e., phase with P42/nmcS space group. Rietveld refinement of the obtained diffraction pattern was done with TOPAS 4.2 software to (1) quantify the identified phases and the mean crystallite sizes and (2) refine lattice parameters.…”

New high-pressure phase and equation of state of Ce2Zr2O8

“…Recently, Surble et al 20 [24][25][26][27][28][29] In particular, Ce 2 Zr 2 O 8 exists as a cubic fluorite structure 29,30 or metastable tetragonal structures. 31,32 It also is well known that the fluorite structure transforms to different crystalline modifications with pressure. 33 HP studies on CeO 2 suggest a fluorite to orthorhombic a-PbCl 2 -type structure transition.…”

Chemical Interaction between Perovskite La0.6Sr0.4FeO3and Super-Ionic Zr0.84Y0.16Ox

“…The unit cell of the YSZ electrolyte does not change significantly despite the possible presence of point defects. It has been shown before that this unit cell is relatively not sensitive to such changes [18].…”