Response of ZrC to rapid heavy ion radiation Journal of Applied Physics

Response of ZrC to rapid heavy ion radiation  Journal of Applied Physics

The present study shows that ZrC, like many simple oxide compounds (e.g., CeO2), highly tolerant to SHI rays. There is no obvious change even after exposure to very high stimuli (6 x 1013Poison ions-2 ), and the only detectable physical modification of microcrystalline ZrC is expansion of the unit cell with microstrain buildup. Unlike the CEO2, unit cell expansion with ion flux proceeds in a complex manner and is characterized by two distinct processes (Figure 4). The initial damage accumulation process of micro-ZrC appears to be similar to that of CeO2 With direct impact defect creation mechanism. The diameter of the cylindrical damage zone, or “track,” for ZrC is about 10 nm, which agrees well with track sizes reported for many other ceramics irradiated under similar conditions.40 Defects within individual ion tracks are produced in a similar manner as in CeO2The relative expansion of the unit cell reaches a steady state of 0.03% for ZrC and 0.3% for CeO.2when paths overlap.41 Coupled X-ray diffraction and X-ray absorption measurements have previously shown that redox effects are an important component of radiation-induced swelling in CeO.2. A decrease in cerium cation corresponds to an increase in ionic radius, resulting in a relatively large expansion of the unit cell.12 Due to the covalent bonding of ZrC, along with the zirconium monomer, similar radiation-induced redox changes would not be expected. Synchrotron2 It shows that their effect on the unit cell parameter is small (low saturation swelling). The same Poisson-type trend in unit cell expansion was also reported for both materials in low-energy ion irradiation under the nuclear energy loss regime, where ZrC had a relative unit cell expansion of 0.14% with 4 MeV Au ions,27,28 With ZrC retaining its starting structure after exposure to low-energy ions. This was partly explained by the mixed covalent and metal-bonding nature of ZrC, which resulted in generally lower displaced atom mobility, resulting in increased local recombination. The increased recombination rate allows the production of steady-state defects and softening, leading to saturation.28,42 Neutron irradiation was also performed on zirconium at varying temperatures (between 600 and 1600 °C) inside a nuclear reactor.43 Under these conditions, the unit cell expansion is much higher, reaching ∼1.2% at 9 dpa.43 This swelling was associated with the formation of “black spot” defects that were identified as dislocation rings using transmission electron microscopy (TEM).43,44 Temperature effects were also linked in this study and, as expected from other materials,45,46 The average ring size grew with increasing neutron irradiation temperature as a result of increased vacancy mobility, with a concomitant decrease in ring density. Compared with all these previous irradiation studies, we show here that fast heavy ions cause damage to ZrC, leading only to isolated defect formation and changes in unit cell parameters.

A distinctive feature of ZrC is the presence of a second damage mechanism at high fluences that succeeds in direct impact behavior. This defect accumulation process is characterized by a linear swelling regime with increasing flux with no obvious saturation up to the maximum flux, where the relative swelling value reaches ∼0.11% at 6 × 1013 Poison ions-2 (Figure 4). The origin of this behavior is still unclear, and additional characterization is required to gain further insight (e.g., total neutron scattering or TEM). The second defect accumulation process is absent in CeO2 It must be related to the material properties of ZrC. The main differences between the two materials include (1) the presence of intrinsic carbon vacancies in ZrC with a maximum carbon site occupancy of ∼96 at; %28 (Unlike CeO2 with pure anionic stoichiometry), (ii) the apparent covalent bonding character in ZrC against Ionic bonding is present in CeO2,29,30 and (3) characteristic rock salt and fluorite structures of ZrC and CeO2respectively.

It has been previously reported that ZrC cannot be completely synthesized, with a calculated limit of ZrC0.96±0.01;47,48 However, ZrC, as well as many covalently bonded transition metals, retains phase homogeneity despite this asymmetric nature down to ZrC0.62±0.02.48 It is shown that carbon vacancies occur in chemically deficient ZrCs Samples (0.5 ≥ × ≥ 1.0) create a short-run order (SRO) associated with Zr8C7 Phase determined by TEM and neutron scattering.49,50 ZrC is synthesized by carbothermic reduction of ZrO2 It may result in residual oxygen being retained within the sample.51 This remaining oxygen remains dissolved within the rock salt structure and contributes to filling the intrinsic carbon vacancies.51,52 The additional vacant carbon sites are likely the result of oxygen-filled SHI irradiation, which leads to the observed lattice shrinkage in the nanosized ZrC;52 Oxygen entry appears to be much less in ZrC microcrystals as evidenced by consistent unit cell expansion and lack of ZrO2 Formation across all three sample series. A recent study of total neutron and0.98±0.02.32 Therefore, a similar SRO can be expected in the feedstock, which cannot be detected by long-term XRD analysis. This SRO is likely modified under irradiation through (a) the accumulation of point defects resulting from the initial direct impact regime and local stoichiometric fluctuations, as well as (B) Migration of vacancies at carbon sites thanks to intense ionizing radiation, which promotes the formation of more complex vacancy groups. Complex vacancy clusters are unfavorable in non-irradiated ZrC partly due to the coordination of the second closest vacancy site being restricted,49 But the highly nonequilibrium conditions generated by SHI irradiation may alleviate this limitation. Such vacancy groups may explain the unsaturated swelling at higher fluences because they create hypothetically larger local domainspure“ZrC stoichiometry with increasing unit cell size.”48 They form additional free volume into which the network can expand as shown for other materials.51 Additional studies are needed to evaluate the effect of SRO and carbon stoichiometry on the swelling behavior of ZrC and to determine whether or not stoichiometry can explain unsaturated unit cell swelling at higher fluences.

Covalent bonding in ceramic materials (ZrC) is less restrictive than that of ionic systems (CeO2), allowing for a wide range of defect configurations. Covalent forces tend to dominate short-range interactions, unlike ionic forces, which dominate long-range interactions.52,53 Covalent bonding allows more numerous paths of atomic mobility in irradiated materials via energetic pairs of atoms that work cooperatively to break the existing bond.52,54 In many systems (eg, ABO3) This can lead to out of shape.54,55 Although no transformation is observed here, a similar pattern of covalently bonded individual atomic pairs (i.e., Zr–C and C–C) may act together to break bonds in the ZrC crystal during the thermal rise phase and before recrystallization during the quench phase. SHI irradiation.40 This may explain how larger and more complex defects can form and contribute to the second swelling mechanism. both elements (a) And (B) may depend on pre-irradiation of the structure (i.e., a first-swelling mechanism), where minor defects weaken the bonds and create initial lattice swelling.

Additional structural considerations may also contribute to the different radiative responses of CeO2 And your visit. Both materials are cubic, but the anionic sublattices of the systems in question are simple cubic (CeO2) and face-centered cube (ZrC). This results in different sliding regimes, which changes how intermolecular bonds within the crystalline material break under pressure.56 This may contribute to the formation of more complex defects such as rings and clusters at higher fluences. It has previously been shown that track sizes are similar in a wide range of amorphous ceramics with different chemical compositions and structures.40 However, the final damage profile within the ionic pathways depends on the recrystallization processes that follow thermal elevation and the structure of the target material.57 The arrangement of the different anions and related diffusion properties may contribute to the observed effects.57

Within the irradiated nanocrystalline ZrC, the fluctuation in the oxide phase fractions indicates a heterogeneous oxidation process. It remains unclear at what point oxidation occurred and whether it occurred during or after ion beam exposure. Oxygen has been consistently reported as complex ZrC, dissolved within the vacant carbon sublattice sites of the rock salt structure with no obvious signature in the XRD patterns.51,52 Under the rapid and intense heavy ion irradiation, additional oxygen may be pushed into ZrC, exceeding the dissolution limit, and forming ZrO2 In Florence higher. This effect was not observed in microcrystalline ZrC, which can likely be attributed to a significant reduction in dissolved oxygen in the original sample due to the lower proportion of vacant carbon sublattice sites and the lower relative surface area to volume ratio.39 Compressive strain induced by ZrO2 The phase can lead to shrinkage of the unit cell within the ZrC, which explains the observed radiative response of the nanosized ZrC.58,59 The opposite is observed in nanocrystalline CeO2which experiences ∼30% greater swelling compared to microcrystalline CeO2.12This effect has been shown to be a result of the reduction of cations (Ce4+ to what3+), which is further improved for nanocrystalline samples.12As mentioned above, redox effects are inactive in ZrC due to the monovalent character of the zirconium cation. Despite the unclear trend in unit cell volume change, it is still clear that nanocrystalline ZrC retains a high degree of flexibility in the face of SHI irradiation.

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