Study of Polymorphic Transformation Processes and Their Influence in Polycrystalline ZrO2 Ceramics upon Irradiation with Heavy Ions

Abstract

The aim of this work was to study the mechanisms of polymorphic transformations in ZrO2 ceramics under irradiation with heavy ions, as well as to determine the nature of structural distortions in the case of t-ZrO2 → c-ZrO2 type transformations and associated anisotropic deformations. The samples of ZrO2 ceramics were irradiated with Kr15+ heavy ions with an energy of 150 MeV and fluences of 1011–1016 ion/cm2. During evaluation of the structural changes depending on the irradiation fluence, it was found that at low irradiation fluences (1011–1012 ion/cm2), the main role is played by deformation distortions of the crystal lattice, which have a pronounced anisotropic character. Meanwhile, at fluences above 1013 ion/cm2, the main role is played by polymorphic transformations of the t-ZrO2 → c-ZrO2 type, followed by amorphization of the damaged layer at fluences above 1015 ion/cm2. It was established that the anisotropic distortion of the crystal lattice is more pronounced along the crystallographic a axis, as well as the (011) texture orientation, which is characteristic of t-ZrO2. The polymorphic transformation processes of the t-ZrO2 → c-ZrO2 type occur at irradiation fluences of 1013–1014 ions/cm2, which are characterized by the formation of an overlap of local areas of defects that appear along the trajectory of ions in the material. The dependences of changes in the strength and thermophysical properties of ZrO2 ceramics on the irradiation fluence were obtained. The mechanisms of influence of the structural disorder and polymorphic transformations on the decrease in strength and crack resistance were established.

Study of the Effect of Variation in the Phase Composition of ZrO2/MgO Ceramics on the Resistance to Radiation Damage during Irradiation with Kr15+ Ions

“…However, it is important to highlight that in the case of the initial undoped samples with irradiation fluences of 10 13 -10 14 ion/cm 2 , a sharp change in the volume of the crystal lattice (values ∆V) is due to the effect of radiation-induced polymorphic transformation of the type m-ZrO 2 → t-ZrO 2 . This behavior of ceramics aligns well with the findings from experimental studies [21][22][23], in which it was shown that irradiation with ions with fluences above 10 12 ion/cm 2 leads to polymorphic transformations in the damaged layer. Moreover, these polymorphic transformations are due to the accumulation of radiation-induced damage and structural distortions in the damaged layer, the accumulation of which leads to the destabilization of the monoclinic structure and its subsequent transformation into a tetragonal or cubic one, followed by an increase in volume due to deformation distortions.…”

“…However, one of the limiting factors of the use of ZrO 2 ceramics as inert matrix materials is the polymorphism of the phase composition, which arises under external influences (mechanical and deformation). In addition, as was shown in a number of works, radiation damage accumulation occurs upon exposure to heavy ion irradiation, comparable in energy to uranium fission fragments [21][22][23]. In this case, one of the ways to enhance the radiation damage resistance and the resistance to the initiation of polymorphic transformation processes-which, as a rule, are accompanied by a destructive change in volume and a subsequent sharp deterioration in the thermophysical or strength properties of ceramics-is the use of stabilizing dopants, such as Y 2 O 3 , CaO, CeO 2 , and MgO.…”

Influence of the Change of Phase Composition of (1 − x)ZrO2–xAl2O3 Ceramics on the Resistance to Hydrogen Embrittlement

“…As a rule, these effects for high-energy ions are observed at fluences above 10 12 -10 13 ions/cm 2 . Here, when irradiated with heavy ions (even in the case of energies above 200 MeV), the maximum thickness of the affected layer is no more than 20-25 µm [31,32].…”

Study of Radiation Damage Kinetics in Dispersed Nuclear Fuel on Zirconium Dioxide Doped with Cerium Dioxide

“…This difference can be explained by the fact that in the case of a monoclinic structure, which is characteristic of the ZrO 2 and Zr 0.98 Ce 0.02 O 2 phases, deformation distortions occur more intensely. Since it is known that during irradiation of ceramics with a ZrO 2 monoclinic phase at high irradiation fluences, polymorphic transformation processes occur, arising from the deformation distortion accumulation [55][56][57]. However, when it comes to proton irradiation, the values of ionization losses are much smaller than in the case of irradiation of heavy ions [55][56][57], which in turn results in the formation of a large number of deformation distortions, but is not sufficient to initiate the processes of polymorphic transformations of the m-ZrO 2 → t-ZrO 2 type [55][56][57], which are characteristic of irradiation with heavy ions.…”

“…Since it is known that during irradiation of ceramics with a ZrO 2 monoclinic phase at high irradiation fluences, polymorphic transformation processes occur, arising from the deformation distortion accumulation [55][56][57]. However, when it comes to proton irradiation, the values of ionization losses are much smaller than in the case of irradiation of heavy ions [55][56][57], which in turn results in the formation of a large number of deformation distortions, but is not sufficient to initiate the processes of polymorphic transformations of the m-ZrO 2 → t-ZrO 2 type [55][56][57], which are characteristic of irradiation with heavy ions. In this case, it can be concluded that ceramics with a monoclinic type of crystal lattice are less resistant to deformation distortions arising from ionization processes, since the structure of ceramics itself is a metastable state, which changes under any external influences, including ionization effects and a change in the electron density.…”