Neutron Diffraction Study of the Size-Induced Tetragonal to Monoclinic Phase Transition in Zirconia Nanocrystals (original) (raw)

Size-Induced Tetragonal to Monoclinic Phase Transition in Zirconia Nanocrystals

MRS Proceedings, 2003

Accurate neutron powder diffraction experiments at D20, ILL Grenoble, allowed to monitor the reconstructive tetragonal to monoclinic phase transition as a function of the size of zirconia nanoparticles. In the nanocrystals, both phases are identical to the ones generally observed in micrometric zirconia. Rietveld refinements on these samples point out an increase of the tetragonal fraction and a decrease of the lattice parameters when the size of the particle decreases. An uniaxial strain depending on the grain size is also observed. The phase transition definitely occurs above a threshold crystal size. These results are analysed within the Landau theory and they can be understood as a mechanism of size-dependent phase transition where the primary order parameter is altered by the nanoparticle size.

Monoclinic to tetragonal semireconstructive phase transition of zirconia

Physical Review B, 2003

Accurate data, obtained by neutron diffraction, have been used to monitor the first-order reconstructive monoclinic↔tetragonal phase transition as a function of the temperature both during heating and cooling. Data analysis supports an orientational relationship ͓010͔ m ʈ ͓001͔ t and (100) m ʈ (110) t between the tetragonal and the monoclinic phases. The analysis of the oxygen atoms evolution in the tetragonal phase supports a displacive mechanism for the monoclinic↔tetragonal phase transition. Based on these data, a microscopic model is proposed explaining the unusual behavior of zirconia.

Phase stability in nanostructured and coarse grained zirconia at high pressures

Nanostructured Materials, 1995

Zirconia powders with grain sizes from the nanometer (5-30 nm) to the micrometer (-1 pm) regime were investigated by in-situ high-pressure X-ray dieaction at pressures up to 14 GPa. In micrometer sized ZrOz, a broad transition is observed at increasing pressurefrom the monoclinic to the orthorhombic polymorph. Thisfirst-order phase transition is, therefore, concluded to be martensitic in character. In the nanosized material, a metastable tetragonal polymorph exists ana' the stabilization is interpreted as a result of the surface stress of the nanocrystalline grains. An effective internal pressure in the particles above 2.5 GPa is estimated. The critical particle radius for the stabilization of the metastable phase in nanosized ZrO2 is calculated to be 4-6 nm.

Mechanisms of room temperature metastable tetragonal phase stabilisation in zirconia

International Materials Reviews, 2005

Mechanisms of tetragonal phase stabilisation, at room temperature, in nanocrystalline (,100 nm), submicrometre-sized (100 nm-1 mm), and bulk zirconia (ZrO 2) (.1 mm) are reviewed in detail. The merits, demerits and scope of each individual model are outlined. The analysis of the literature shows that, although the mechanism of tetragonal phase stabilisation in bulk ZrO 2 is well understood, the room temperature tetragonal phase stabilisation mechanism in undoped, nanocrystalline ZrO 2 is controversial. Various proposed models, based on surface energy (nanocrystallite size), strain energy, internal and external hydrostatic pressure, structural similarities, foreign surface oxides, anionic impurities, water vapour and lattice defects (oxygen ion vacancies), are discussed in detail. It is proposed that generation of excess oxygen ion vacancies within the nanocrystalline ZrO 2 is primarily responsible for the room temperature tetragonal phase stabilisation, below a critical size. Hence, the mechanism of tetragonal phase stabilisation in nanocrystalline ZrO 2 appears to be the same as that in doped ZrO 2 (at room temperature) and undoped ZrO 2 (at higher temperature).

Phase transition of pure zirconia under irradiation: A textbook example

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006

One of the most important goals in ceramic and materials science is to be able to design materials with specific properties. Irradiation seems to be a powerful tool for the design of advanced ceramics because of its ability to modify over different scales the microstructure of solids. Nowadays, it is clearly proved that irradiation induces order-disorder phase transitions in metallic alloys and in some ceramics. In this paper, we show that a displacive phase transition can also be induced by irradiation. Based on many experimental facts, a microscopic model is proposed to explain the displacive phase transition observed in this material after irradiation. Defects, produced in the oxygen sublattice, induce important strain fields on a nanometric scale. This strain field can be handled as a secondary order parameter within the Landau theory approach, leading to a decrease of the phase transition temperature and thus quenching the high temperature tetragonal phase.

Phase field modeling of the tetragonal-to-monoclinic phase transformation in zirconia

Acta Materialia, 2013

The allotropic phase transformation in zirconia from the tetragonal to monoclinic double lattices is known to occur by a martensitic twinning mechanism which shows a complex dependence on temperature, stress and environment. This paper is concerned with the development of a phase field model which accounts for the main metallurgical mechanisms governing this martensitic transition. The symmetry reduction and orientation relationship between the parent and product phases were simulated using several non-conserved order parameters representing different transformation paths. Inhomogeneous and anisotropic elastic properties were considered to determine the resultant elastic stresses. Governing equations of the tetragonal-to-monoclinic transformation were solved in a finite element framework under a variety of initial and boundary conditions. It was shown that applying different initial conditions, such as seed embryo or random, did not change the twinning patterns or the final volume fractions of the parent and product phases after the relaxation period. On the other hand, enforcing different boundary conditions resulted in completely different twinning patterns and phase volume fractions. The model was able to predict both the "V" shape morphology of twinning and the surface stress relief with "gable roof" patterns, which were observed by transmission electron microscopy and atomic force microscopy to be characteristic of the tetragonal-to-monoclinic transition.

Phases and phase transformations in nanocrystalline ZrO2

Journal of Nanoparticle Research, 2006

Starting from results from He-pycnometry, electron diffraction, Extended X-ray Absorption Fine Structure Spectroscopy and Perturbed Angular Correlation Spectroscopy the phase transformations and structures of zirconia are described. From a comparison of these results with those obtained on other oxide nanoparticles it is concluded that the phases and structure of nanoparticles are different compared to those of coarse-grained material. The difference of the transformation temperature of bare and coated nanoparticles was used to estimate enthalpy and entropy of the tetragonal fi monoclinic transformation for nanoparticulate zirconia. By comparison with results obtained from other nanocrystalline oxides, the following rules were derived: Provided the particles are sufficiently small, particles made of materials showing phase transitions crystallize in the high temperature structure. However, compared to coarse-grained materials of the same structure, the density of nanoparticles is reduced. A first estimation limits this phenomenon to particle sizes well below 10 nm. Those nanoparticles follow the generalized phase diagram postulated by Tammann.

Unified Landau description of the tetragonal, orthorhombic, and monoclinic phases of zirconia

Physical Review B, 2002

We compute an explicit lowest-order polynomial form of the strain-dependent Gibbs potential which provides a unified description of the tetragonal, orthorhombic, and monoclinic phases of zirconia (ZrO 2). The resulting energy function interpolates well the available experimental data for this material, reproducing its known elastic moduli, equilibrium strains, and phase diagram to about 1700 K and 8 GPa.