Study of the Influence of Doping Efficiency of CeO₂ Ceramics with a Stabilizing Additive Y₂O₃ on Changes in the Strength and Thermophysical Parameters of Ceramics under High-Temperature Irradiation with Heavy Ions

Review Report Form 1

The radiation damage is performed using Xe22+ ions.  Give much more information on this.  What energy?  How do you know they're 22+?  What accelerator?  What separator?  Using these ions at those energies, what penetration depths do you expect in the materials, meaning how thick is the skin of material that experiences damage?  (Note that SRIM from srim.org is a great simulation tool for ion range.)

The authors thank the reviewer for this comment, since in fact this information was not included in the text of the article.

Irradiation of the samples was carried out at the heavy ion accelerator DC-60, located in the Astana branch of the Institute of Nuclear Physics of the Ministry of Energy of the Republic of Kazakhstan. Irradiation was carried out with Xe²²⁺ ions with an energy of about 230 MeV (1.75 MeV/nucleon), the charge of the ions was controlled by selecting optimal acceleration parameters (magnetic field strength), based on determining the type of accelerated ions using mass spectroscopy. Radiation dose monitoring was carried out using a recording system based on the use of Faraday cups. Using the SRIM Pro software code, it was found that the maximum ion path length in the selected types of ceramics was about 13 – 15 μm, and the values of ionization losses during the interaction of ions with electron shells (dE/dx_electron) were about 23 – 23.5 keV/nm and nuclei (dE/dx_nuclear) were about 1.1 – 1.2 keV/nm. An analysis of the obtained values of ionization losses indicates that the main contribution to changes in the properties of ceramics is made by the interactions of ions with electron shells.

You should also discuss the average and maximum energy transfer possible for the different elements Ce, O, Y under irradiation from that energy Xe.  How do these energies compare with the lattice binding energies.  I know this is a macroscopic effects paper, but you do need this.  I want to recommend molecular dynamics calculations as well, but let's not go too deep into microscopic effects.

When calculating the simulation of the values of ionization losses of binding energy, about 25 eV were chosen for the Ce and Y elements and about 28 eV for the O element. These values were selected based on tabular data in the SRIM Pro program.

Unfortunately, at the moment we cannot carry out detailed molecular dynamics calculations, but in the future we will try to take this into account in similar works.

If there is only a very thin skin of damage, how do you expect this to affect bulk properties like swelling?

In the case of using heavy Xe²²⁺ ions with an energy of about 230 MeV, the maximum depth of damage is about 13 – 15 μm, which in the case of inert matrices of dispersed nuclear fuel is a near-surface layer that is in maximum close contact with the fissile material. In this regard, deformation embrittlement of this layer can lead to the formation of so-called structurally changed areas that are most susceptible to embrittlement, and in the case of a large number of such areas around particles of fissile nuclear material located randomly in inert matrices, destabilization of the entire volume may occur under high-dose irradiation. As a result, in order to prevent such effects, it is necessary to conduct studies of this kind, which make it possible to obtain data on changes in the properties of the material in contact with fissile materials by simulating the direct impact of heavy ions that are as close as possible to the type of fission fragments. 

Which leads to another question, how thick are your samples?  Did the ions pass through, giving a more uniform damage distribution?  How was swelling measured?  Any other properties you should describe measurements of?  You mentioned how hardness was determined.

The authors thank the reviewer for this comment, corrections have been made to the text of the article, a detailed explanation of the observed effects has been given.

The ceramic samples used for irradiation were prepared in the form of tablets with diameters of 10 mm and a thickness of about 15 μm in order to conduct irradiation experiments in such a way as to achieve the maximum effect of structural changes in the damaged layer comparable to the thickness of the samples, as well as to avoid the contribution of a large proportion of the non-irradiated sample to the determined values of swelling and changes in strength and thermophysical parameters. The assessment of changes in the swelling value of ceramics was determined by comparative analysis of the change in the crystal lattice volume before and after irradiation, which made it possible to determine not only the swelling value, but also the type of deformation distortion of the crystal structure.

You mention fluence in the text but I'm not sure how to relate things.  What fluence rate was used?  Or did it vary?  You have dpa in the figures but how do you relate fluence to dpa?  Did you simulate?  Calculate?  Make TEM images?  Describe and quantify the fluence to dpa process.

The authors thank the reviewer for this comment, the text of the article contains a description of the calculations of dpa values.

For the purpose of possible comparison of the observed changes caused by irradiation with heavy ions with other types of irradiation (for example, neutron irradiation), all changes are presented as dependences on the magnitude of atomic displacements (dpa). The value was calculated according to the method proposed in [22], in which the authors, using calculated data from the SRIM Pro program code, calculated the dependence of the change in the magnitude of atomic displacements along the trajectory of ion motion, as well as depending on the irradiation fluence. The assessment results are presented in Figure 1. To analyze changes in structural, strength and thermophysical parameters, the maximum dpa value was used.

Figure 1. Dependence of changes in the magnitude of atomic displacements upon irradiation with heavy Xe²²⁺ ions along the trajectory of ion motion

You have plots with dpa on the horizontal axis.  Are these all performed over different lengths of time?  If so, let's discuss the effects of temperature over time.

 You have a short discussion of temperature near the end, but all your measurements of irradiation have both temperature and irradiation as variables.  Can you measure hardness differences for materials that have been heated to those temperatures over those times?  If you measured and there's no difference, say so.  If you measured and there is a difference, then you need to include that in your analysis of irradiation tests at different temperatures over different times to isolate the radiation effect.  If you did not measure the hardness etc change due to temperature cycling alone then please do.  If the samples are thick and there is no Xe penetration to the back side you can even check those same samples on the back side.

The authors thank the reviewer for this comment and a fairly large and detailed explanation of the possible effects. These factors were taken into account during the study, and the text describing these effects is given in the article. 

The choice of sample heating time is determined by the irradiation time with the maximum irradiation fluence, during which the samples are exposed to both temperature and irradiation. At the same time, test experiments, determining the change in the  value depending on time, comparable to the irradiation times, showed the absence of any significant changes in the value when changing the annealing time. The main changes in the  value are comparable both after 1 hour of annealing and after 200 hours.

Explain the temperature raising and lower process and times.  Are the samples irradiated the entire time they're held at high temperature? Are all samples tested and heated at the same time but only some are irradiated for longer times?  You want to know how much annealing there might be so give details on irradiation and on heating.

High-temperature irradiation of samples was carried out by placing the samples on a special holder equipped with a thermocouple to control the temperature of the sample, as well as heating elements, with the help of which the samples are heated before irradiation and subsequently maintaining the selected temperature regime during the entire irradiation. The process of high-temperature irradiation itself consists of placing the sample on a holder, evacuating the irradiation chamber, heating the sample to a given temperature, stabilizing the sample in order to establish a constant temperature, irradiating the sample under constant heating at a given temperature, cooling the sample for 15 – 20 hours after irradiation together with the chamber under vacuum, in order to avoid sudden oxidation processes when removing heated samples to air.

For the paragraph starting on line 322 you explain the effects.  I trust you, but since this is a research paper please cite other studies with similar explanations.  Same for paragraph starting on line 344.  Again with comments starting on line 455.

The authors thank the reviewer for this comment, links to articles with similar effects have been added.

When introducing softening as the difference in hardness over the initial hardness, it can (your choice) help if you have a quick in line equation like s = delta h/ h0  or something.

The authors thank the reviewer for this comment, in fact, the softening value was calculated using this formula by comparing the hardness values after irradiation with the initial hardness value.

Lines 190-191 increase in decrease in hardness... please rephrase

The authors thank the reviewer for this comment, a correction has been made to the text of the article, the expression has been paraphrased.

It should also be noted that the most pronounced changes in hardness associated with the processes of softening and destabilization of strength properties are observed with irradiation temperature growth. It follows from this that the main effect on the deterioration of strength properties is exerted by the temperature effect during irradiation.

Line 315 an growth... do you mean to say an increase?

The authors thank the reviewer for this comment, the correction has been made to the text of the article.

Fig 4 caption, please describe the numbers above the dashed lines (the text following the figure says, but put it in the caption too)

The authors thank the reviewer for this comment, a correction has been made to the text of the article, a caption with an explanation has been added.

Dotted lines and lines with arrows indicate the difference in changes in the magnitude of the deformation distortion of the crystal lattice of the samples (numbers above the dotted lines) in comparison between CeO₂ and 0.85 M CeO₂ – 0.15 Y₂O₃ ceramics.

Review Report Form 1

The paper provides the results of a comparative analysis of doping CeO2 ceramics with a stabilizing additive Y2O3. The analysis focuses on the effectiveness of these changes on the strength and thermo-physical parameters of ceramics during high-temperature irradiation with heavy ions. This irradiation is comparable in energy to fission fragments of nuclear fuel, allowing for the simulation of radiation damage that is as similar as possible to the fission processes of nuclear fuel.

The research aims to investigate how the doping efficiency of CeO2 ceramics with a stabilizing additive Y2O3 can affect the strength and thermo-physical parameters of ceramics when exposed to high-temperature irradiation with heavy ions. The main question addressed by the study is how the addition of Y2O3 affects the behavior of CeO2 ceramics under such conditions. The topic is original and relevant to the field. The methodology is well established.

The conclusions presented are consistent with the evidence and arguments and successfully address the main question. The references are appropriate.

Additional comments: 1. Line 367, formula 1: reference is needed.

The authors thank the reviewer for such a high assessment of our article, as well as the comments provided, corrections were made to the text of the article in accordance with the indicated shortcomings in the first version.

Review Report Form 1

"the main contribution to changes in the properties of ceramics is made by the interactions of ions with electron shells."

If you keep this sentence (you may delete it) then please explain why you think the ionizations and excitations change the structure.  You certainly can have the ionization and excitation initiate chemistry, and we see this in liquids and gasses, but if you think that's changing the structure of the solid then please find the probable reactions and mechanisms for structural change.  Typically you would see displacements caused by nuclear interactions causing the swelling.  It may be better if you just delete that part of the sentence if you don't want to spend several paragraphs and chemical reaction equations explaining it.

You might mention that the energy loss of the heavy ion beam can certainly displace the atoms given those ...eV lattice binding energies.

The authors of the work thank the reviewer for this comment; the sentence was deleted according to the reviewer’s suggestion, so as not to provide an additional description of chemical processes.

Taking into account the fact that the values of ionization losses are quite large, and the binding energies in the structure are of the order of 25 – 28 eV, during the interaction of incident ions, effects associated with the displacement of atoms from their positions are possible.

" High-temperature irradiation..." Does this mean that the more irradiated samples were hot for longer than the less irradiated samples?  Or the irradiation was only a short period in the whole heating-cooling cycle and they all have approximately the same heating-cooling time?  Please say which.  If different heating times, then try the heat cycle and tests without any irradiation.

The authors of the work thank the reviewer for this comment; below is the information added to the article.

The heating time of the samples depended on the final temperature to which it was necessary to heat the samples (500, 700 and 1000 K) and was controlled by the heating rate, which was 20 K/min. The temperature of 500, 700 or 1000 K was maintained using a heater during the entire irradiation time, which made it possible to combine the influence of temperature exposure and radiation damage caused by irradiation on changes in the properties of the samples. Cooling of the samples after irradiation was carried out identically for all samples together with the irradiation chamber, without access to the atmosphere, until the temperature in the chamber reached room temperature. This procedure was performed to exclude the effects of possible oxidation processes during the interaction of heated samples with the atmosphere.

SO THE BIG QUESTION IS, DOES DPA ALSO SCALE WITH TIME AT HIGH TEMPERATURE, AND THEREFORE WE MAY JUST BE LOOKING AT HEAT EFFECTS?

Regarding the issue regarding scaling the dpa value for irradiated samples. This value is a calculated value depending on the irradiation fluence and is used to compare the effects of irradiation with other experiments, if necessary, in view of the fact that the dpa value has a generally accepted value that allows one to compare observed effects, and also to use it to be able to compare observed changes with neutron effects (under certain conditions that take into account the penetration depth of heavy ions). In this case, the use of the dpa value was chosen to reflect the observed changes caused by irradiation under different irradiation conditions, i.e. in the case of variations in irradiation temperature.

" It should also be noted that the most pronounced changes in hardness associated 234 with the processes of softening and destabilization of strength properties are observed 235 with irradiation temperature growth. It follows from this that the main effect on the deterioration of strength properties is exerted by the temperature effect during irradiation."

Not sure what this is saying.  Are you saying high temperature is responsible for deterioration of strength?  Or localized heating from irradiation?  Or a combination?  What are the effects with just heating, without irradiation?  Please redo measurements if you have none with only heating and no irradiation.

The authors thank the reviewer for this remark; the results of the effect of thermal annealing on the samples are presented in the text of the article. Below is a description of the observed changes in sample hardness.

At the same time, the data presented in Figure 2c, reflecting the change in hardness of samples of non-irradiated ceramics subjected to thermal annealing at temperatures of 500 – 1000 K for a time comparable to the irradiation time, showed that the change in hardness is of the order of 0.1 - 0.2 % for CeO₂ ceramics and 0.06 - 0.17 for 0.85 M CeO₂ – 0.15 Y₂O₃ ceramics after 200 hours of thermal annealing (the time corresponding to the maximum irradiation time). The obtained values of changes in hardness for non-irradiated samples indicate that the thermal effect on samples without radiation exposure (irradiation with heavy ions) does not have a significant effect on the softening of ceramics, and also indicates a fairly high resistance of the selected oxide ceramics to thermal annealing. From which we can conclude that irradiation with heavy ions, and as a consequence, the accumulation of deformation damage and distortions associated with the interaction of ions with the crystal lattice, is the main factor influencing the deterioration of the strength properties of ceramics. At the same time, a more pronounced manifestation of the softening effects (decrease in hardness) of samples during irradiation at high temperatures can be explained by the influence of a combination of factors of thermal broadening of the crystal structure, leading to more intense damage.

Figure 2. c) Results of changes in the hardness of samples of CeO₂ and 0.85 М CeO₂ – 0.15 М Y₂O₃ ceramics, obtained during thermal annealing for a time characteristic of the irradiation time with different fluences

" The choice of sample heating time is determined by the irradiation time with the maximum irradiation fluence, during which the samples are exposed to both temperature and irradiation."  Does this mean some samples, in a set that are heated, are irradiated more than others?  This is also important to put much earlier, when discussing the irradiation and heating.

The authors thank the reviewer for this comment; a description of the heating technique, as well as control of the heating and subsequent cooling processes, is presented in the Materials and Methods section.

I'm still concerned that you don't have isolated, heating only measurements.  You have hardness/softness, deformation distortion, swelling.  Maybe look at the back of samples for hardness/softness, where they weren't irradiated.  Can you do the same for distortion and swelling? If not, REMEASURE with new samples cycled through high temperatures without irradiation.  You only really need to do this baseline case for room temp vs cycling at the highest temperature to prove there's no change, if there is no change.

The authors thank the reviewer for this comment. The text of the article contains the results of measurements of hardness, strain distortion, and volumetric swelling of ceramic samples without irradiation depending on the temperature and annealing time comparable to the irradiation time.

"The main changes in the ?(?) value are comparable both after 1 hour of annealing and after 200 hours."  This is great for the final swelling being heating independent.  You should mention that this suggests the effects are due to irradiation and not the heating.  Also, show both the 200 hr and 1 hr values. (You can Fig 7b for example, or have a table, or something).

Then you have coefficient of volume thermal expansion, which you say 1hr and 200 hrs at high temperature give the same result, which is good.  Just show numbers for that.

The authors thank the reviewer for this comment, corrections have been made to the text of the article, and data have been added.

Figure 7a shows the dependence of the change in the value of  as a function of the thermal annealing time, which reflects the absence of significant changes with a growth in annealing time.