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Browsing by Author "Aughterson, RD"

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Atomic origins of radiation-induced defects and interfacial strengthening in additively manufactured titanium aluminide alloy irradiated with Kr-ions at elevated temperature
(Elsevier, 2019-04-04) Zhu, HL; Qin, MJ; Aughterson, RD; Wei, T; Lumpkin, GR; Ma, Y; Li, HJ
The irradiation microstructure of the additively manufactured titanium aluminide (TiAl) alloy subjected to in situ transmission electron microscope (TEM) irradiation with 1 MeV Kr ions at the elevated temperature of 873K was investigated. Triangle and large hexagon shaped volume defects were observed within the γ-TiAl phase in the TEM images of the irradiated microstructure. High resolution TEM images and composition analyses revealed the volume defects were vacancy-type stacking fault tetrahedrals (SFTs). Molecular dynamic simulations showed that the increased diffusion coefficient at the elevated temperature promoted the movement and aggregation of vacancies, leading to the formation and growth of SFTs in the irradiated FCC γ phase. The lamellar interfaces in the irradiation microstructure were more effective for acting as strong sinks to absorb the primary point defects and defect clusters at the elevated temperature. The initial defects at the interfaces of the additively manufactured TiAl alloy enhanced the sink strength of the material and greatly refined SFTs near the lamellar interfaces. © 2019, The Authors.
Corrigendum to ‘Atomic origins of radiation-induced defects and the role of lamellar Interfaces in radiation damage of titanium aluminide alloy irradiated with Kr-ions at elevated temperature’ [Acta Mater. 172 (2019) 72–83]
(Elsevier, 2020-09-15) Zhu, HL; Qin, MJ; Aughterson, RD; Wei, T; Lumpkin, GR; Ma, Y; Li, HJ
The authors regret that the scale bars in Figure 8(c) BF-STEM and 8(d) HAADF-STEM for volume defects near the γ/γ lamellar interfaces in the Kr-ion irradiated microstructure of the TiAl alloy irradiated at 873 K are mislabelled. The authors would like to apologise for any inconvenience caused. © 2020 Acta Materialia Inc. Published by Elsevier Ltd.
Crystal chemistry and ion-irradiation resistance of Ln2ZrO5 compounds with Ln = Sm, Eu, Gd, and Tb
(John Wiley & Sons, Inc, 2021-12-22) Aughterson, RD; Lumpkin, GR; Zhang, ZM; Avdeev, M; Kong, L
The previously unattained fabrication of single phase Ln2ZrO5 (Ln = Sm, Eu, Gd, and Tb) compounds via relatively low sintering temperature (1400°C) is achieved in this study using a coprecipitation method. The crystal structures have been investigated by neutron, synchrotron X-ray powder diffraction, and electron diffraction techniques. While the general long-range structure may be well described by the defect-fluorite type structure with Fm3m symmetry, electron diffraction has highlighted a complex underlying modulated structure that varies between each compound. These compounds have been tested for ion-irradiation response using in situ 1 MeV krypton ions and transmission electron microscopy characterization. None of the compounds undergo a crystalline to amorphous transition, even holding at 50 K. Both the underlying fluorite and modulated superstructures are little affected by the irradiation. However, some atomic rearrangements are observed in the postirradiated electron diffraction patterns for the Sm2ZrO5 specimen. © 2021 Commonwealth of Australia.
Crystal chemistry of the orthorhombic Ln2TiO5 compounds with Ln=La, Pr, Nd, Sm, Gd, Tb and Dy
(Elsevier, 2015-07-01) Aughterson, RD; Lumpkin, GR; Thorogood, GJ; Zhang, ZM; Gault, B; Cairney, JM
The crystal structures of seven samples of orthorhombic (Pnma) Ln2TiO5 compounds with Ln=La, Pr, Nd, Sm, Gd, Tb and Dy were refined by Rietveld analysis of synchrotron X-ray powder diffraction (S-XRD) data. With increasing size of the lanthanide cation, the lattice parameters increase systematically: c by only ~1.5% whereas both a and b by ~6% from Dy2TiO5 to La2TiO5. The mean Ti–O bond length only increases by ~1% with increasing radius of the Ln cation from Gd to La, primarily due to expansion of the pair of Ti–O3 bonds to opposite corners of the Ti–O5 square based pyramid polyhedra. For Dy2TiO5 and Tb2TiO5, a significant variation in Ti–O1 and Ti–O4 bond lengths results in an increased deformation of the Ti–O5 base. The particular configuration consists of large rhombic shaped tunnels and smaller triangular tunnels along the b axis, which have implications for defect formation and migration caused by radiation damage or the ionic conductivity. © 2017 Elsevier B.V.
Crystal structure influence on ion-irradiation tolerance of Ln2TiO5 compounds
(Engineers Australia, 2014-11-26) Aughterson, RD; Lumpkin, GR; Gault, B; Whittle, KR; de los Reyes, M; Smith, KL; Cairney, JM
As a controllable and reproducible technique ion beam irradiation is routinely used as a method for simulating recoil damage caused by alpha-decay in actinide containing materials and neutron damage within fission and fusion reactor systems [1]. The transition from a crystalline to amorphous structure may lead to larger scale effects in the material properties such as an increase in volume (swelling) linked to the generation and agglomeration of defects and decreased thermodynamic and structural stability. Compounds in this study consist of the nominal stoichiometry Ln2TiO5 (where Ln represents the lanthanide series plus yttrium). There are 4 crystal structure symmetries in this series; orthorhombic Pnma, hexagonal P63/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. The final structure is dependent upon the lanthanide size and processing conditions used (pressure and temperature regime) [2]. Ln2TiO5 compounds have been proposed for potential nuclear based applications [3]. For example, Dy2TiO5 has been incorporated into inert matrix fuel as a neutron absorber [4] and Gd2TiO5 has also been proposed for similar use [5] and it’s radiation tolerance has been tested for this purpose [6]. In this study a systematic series of samples of the nominal stoichiometry Sm(x)Yb(2-x)TiO5 (where x = 2, 1.4, 1, 0.6, and 0) are used to test and compare the ion-irradiation tolerance of the major structures within the Ln2TiO5 system of compounds. An improved radiation tolerance with the higher symmetry cubic structures was found, which is consistent with previous studies of similar compounds.
Crystal structures of orthorhombic, hexagonal, and cubic compounds of the Sm(x)Yb(2−x)TiO5 series
(Elsevier, 2014-05) Aughterson, RD; Lumpkin, GR; Reyes, MDL; Sharma, N; Ling, CD; Gault, B; Smith, KL; Avdeev, M; Cairney, JM
A series of single phase compounds with nominal stoichiometry Sm(x)Yb(2−x)TiO5 (x=2, 1.4, 1, 0.6, and 0) have been successfully fabricated to generate a range of crystal structures covering the most common polymorphs previously discovered in the Ln2TiO5 series (Ln=lanthanides and yttrium). Four of the five samples have not been previously fabricated in bulk, single phase form so their crystal structures are refined and detailed using powder synchrotron and single crystal x-ray diffraction, neutron diffraction and transmission electron microscopy. Based on the phase information from diffraction data, there are four crystal structure types in this series; orthorhombic Pnma, hexagonal P63/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. The cubic materials show modulated structures with variation between long and short range ordering and the variety of diffraction techniques were used to describe these complex crystal structure types. © 2014, Elsevier Inc.
In-situ TEM studies of the radiation tolerance of ceramics
(Australian Microscopy and Microanalysis Society, 2016-02-04) Aughterson, RD; Cairney, JM; Zaluzec, NJ; Lumpkin, GR
For the nuclear industry ion-irradiation has been used to simulate recoil damage from alpha decay, and exposure to neutrons in fission and fusion reactors [1]. The particular focus of this research is on the crystalline to amorphous transition facilitated by exposure to accelerated ions. The complex ceramic oxides chosen for this study, Ln2TiO5 (Ln = lanthanides and yttrium), have several uses within the nuclear industry. The compound Dy2TiO5 has been used within WWER type reactors due to its good resistance to irradiation induced swelling and structural failure [2]. Of particular interest are the cubic symmetry compounds with defect fluorite structure, which gives good radiation response. Previous studies show the series of Ln2TiO5 compounds may take on a variety of crystal symmetries depending on the lanthanide size and fabrication conditions used [3, 4]. The study of ion-irradiation response was carried out using the in-situ approach where the test materials were exposed to 1 MeV Kr2+ ions and monitored for their transition from crystalline to amorphous state. This was carried out using the intermediate voltage electron microscope (IVEM)-Tandem facility at Argonne National Laboratory. The critical dose of irradiating ions, Dc, required to render the Ln2TiO5 completely amorphous was determined by monitoring selected area electron diffraction patterns for loss of diffraction spots (Bragg maxima) and replacement with diffuse rings. Within the Ln2TiO5 series of compounds studied a linear relationship appears between the radii of the lanthanide and the radiation response. This follows a similar trend found in related pyrochlore compounds. Possible explanations for this trend are investigated. For the nuclear industry ion-irradiation has been used to simulate recoil damage from alpha decay, and exposure to neutrons in fission and fusion reactors [1]. The particular focus of this research is on the crystalline to amorphous transition facilitated by exposure to accelerated ions. The complex ceramic oxides chosen for this study, Ln2TiO5 (Ln = lanthanides and yttrium), have several uses within the nuclear industry. The compound Dy2TiO5 has been used within WWER type reactors due to its good resistance to irradiation induced swelling and structural failure [2]. Of particular interest are the cubic symmetry compounds with defect fluorite structure, which gives good radiation response. Previous studies show the series of Ln2TiO5 compounds may take on a variety of crystal symmetries depending on the lanthanide size and fabrication conditions used [3, 4]. The study of ion-irradiation response was carried out using the in-situ approach where the test materials were exposed to 1 MeV Kr2+ ions and monitored for their transition from crystalline to amorphous state. This was carried out using the intermediate voltage electron microscope (IVEM)-Tandem facility at Argonne National Laboratory. The critical dose of irradiating ions, Dc, required to render the Ln2TiO5 completely amorphous was determined by monitoring selected area electron diffraction patterns for loss of diffraction spots (Bragg maxima) and replacement with diffuse rings. Within the Ln2TiO5 series of compounds studied a linear relationship appears between the radii of the lanthanide and the radiation response. This follows a similar trend found in related pyrochlore compounds. Possible explanations for this trend are investigated.
The influence of crystal structure on ion-irradiation tolerance in the Sm(x)Yb(2-x)TiO5 series
(Elsevier B.V., 2016-04-01) Aughterson, RD; Lumpkin, GR; de los Reyes, M; Gault, B; Baldo, P; Ryan, EA; Whittle, KR; Smith, KL; Cairney, JM
This ion-irradiation study covers the four major crystal structure types in the Ln2TiO5 series (Ln = lanthanide), namely orthorhombic Pnma, hexagonal P63/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. This is the first systematic examination of the complete Ln2TiO5 crystal system and the first reported examination of the hexagonal structure. A series of samples, based on the stoichiometry Sm(x)Yb(2-x)TiO5 (where x = 2, 1.4, 1, 0.6, and 0) have been irradiated using 1 MeV Kr2+ ions and characterised in-situ using a transmission electron microscope. Two quantities are used to define ion-irradiation tolerance: critical dose of amorphisation (Dc), which is the irradiating ion dose required for a crystalline to amorphous transition, and the critical temperature (Tc), above which the sample cannot be rendered amorphous by ion irradiation. The structure type plus elements of bonding are correlated to ion-irradiation tolerance. The cubic phases, Yb2TiO5 and Sm0.6Yb1.4TiO5, were found to be the most radiation tolerant, with Tc values of 479 and 697 K respectively. The improved radiation tolerance with a change in symmetry to cubic is consistent with previous studies of similar compounds. © 2016 Elsevier B.V.
Investigating the foliar uptake of zinc from conventional and nano-formulations: a methodological study
(CSIRO Publishing, 2019-06-06) Read, TL; Doolette, CL; Cresswell, T; Howell, NR; Aughterson, RD; Karatchevtseva, I; Donner, E; Kopittke, PM; Schjoerring, JK; Lombi, E
Zinc (Zn) deficiency affects half of the world’s arable soil and one-third of the world’s human population. Application of Zn foliar fertilisers to cereal crops can be an effective way to increase grain Zn content; however, commonly used formulations can scorch the leaf (e.g. soluble Zn salts) or are prohibitively expensive (e.g. chelated Zn, ZnEDTA). Zinc oxide nanoparticles (ZnO-NPs) may offer an efficient and cost-effective alternative, but little is known regarding the mechanisms of Zn uptake and translocation within the plant. Foliar-applied Zn is analytically challenging to detect, locate and quantify, as it is omnipresent. Furthermore, any single analytical technique does not have the detection limit or spatial resolution required. In this study, the uptake and mobility of foliar-applied ZnEDTA, ZnO-NPs and ZnO microparticles (ZnO-MPs) to wheat (Triticum aestivum L.) were investigated using inductively coupled plasma mass spectroscopy (ICP-MS), synchrotron-based X-ray fluorescence microscopy (XFM) and radiotracing techniques using 65Zn-labelled formulations. The three techniques were compared to highlight limitations and advantages of each. We also report, for the first time, a novel time-resolved in vivo autoradiography imaging technique that can be used to visualise 65Zn in live plants treated with foliar applications of 65ZnO-NPs and MPs. The images were supplemented by gamma spectroscopy analysis for quantification. The results of this study provide important insights into the analytical challenges faced when investigating foliar-applied Zn nanofertilisers in plants. Potential solutions using nuclear techniques are also discussed, which in turn may ultimately lead to the development of more efficient foliar fertilisers. © CSIRO 2019
Ion beam irradiation of ABO4 compounds with the fergusonite, monazite, scheelite, and zircon structures
(https://doi.org/10.1111/jace.17288, 2020-06-04) de los Reyes, M; Aughterson, RD; Gregg, DJ; Middleburgh, SC; Zaluzec, NJ; Huai, P; Ren, CL; Lumpkin, GR
The effects of irradiation on CaWO4, SrWO4, BaWO4, YVO4, LaVO4, YNbO4, and LaNbO4 were investigated on thin crystals using 1.0 MeV Kr ions at 50‐1000 K. All of the ABO4 compounds can be amorphized with calculated damage cross sections (σa = 1/Fc0) in the range of ~0.30‐1.09 × 10‐14 cm2 ion−1 at zero Kelvin. The analysis of fluence‐temperature data returned critical temperatures for amorphization (Tc) of 311 ± 1, 358 ± 90, 325 ± 19, 415 ± 17, 541 ± 6, 636 ± 26, and 1012 ± 1 K, respectively, for the compounds listed above. Compared with previous in situ irradiation of ABO4 orthophosphate samples using 0.8 MeV Kr ions, the Tc values of LaVO4 and YVO4 are higher than those of LaPO4 and YPO4 by 82 K and 124 K, respectively. The Tc values of the three scheelite structures, CaWO4, SrWO4, and BaWO4, indicate that they are the most radiation tolerant compounds under these conditions. The A‐B cation anti‐site energies, EfAB, determined by DFT range from 2.48 to 10.58 eV and are highly correlated with the A‐B cation ionic radius ratio, rA/rB, but are not correlated with Tc across the different structure types, suggesting that the formation and migration energies of Frenkel defects play a more important role in damage recovery in these compounds. We also discuss the role of cation and anion charge/iconicity as determined by DFT. ABO4 compounds with the zircon structure and B = P or V have a distinct advantage over those with B = Si as the damaged regions do not appear to be significantly affected by polymerization of (PO4)3− or (VO4)3− groups which might stabilize the amorphous fraction and ultimately lead to phase separation as observed in zircon (ZrSiO4). © 1999-2020 John Wiley & Sons, Inc.
Ion beam irradiation of lanthanum compounds in the series La2O3-TiO2
(Materials Research Society, 2010-04-08) Whittle, KR; Blackford, MG; Aughterson, RD; Smith, KL; Lumpkin, GR; Zaluzec, NK
Thin crystals of La2O3, La2/3TiO3, La2TiO5, and La2Ti2O7 have been irradiated in situ using 1 MeV Kr2+ ions in the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), at the Argonne National Laboratory (ANL). We observed that La2O3 remained crystalline to a fluence greater than 3.1 × 1016 ions cm-2 at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (Tc) of 840 K for La2Ti2O7, 865 K for La2/3TiO3, and 1027 K for La2TiO5. The Tc values observed in this study, together with previous data for TiO2, are discussed with reference to the phase diagrams for La2O3-TiO2 systems and the different local environments within the crystal structures. Results suggest an observable inverse correlation between Tc and melting temperature (Tm) in the two systems.
The ion irradiation tolerance of the fluorite RE2MO5 (RE = Sm, and Yb, M = Ti, Zr, and Sn) system
(Springer Nature, 2021-12-06) Aughterson, RD; Newman, R; Ionescu, M; Lumpkin, GR
In the search for novel ceramics for use within nuclear fuel–related applications and nuclear waste-form matrices, a major focus has been on the development of radiation-tolerant materials. Of particular interest in this field have been numerous compounds with either pyrochlore or the related fluorite-type structures. In this study, we look to expand the family of compounds with defect fluorite–type structure. We have fabricated three new compounds; Yb2Sn1.125O5.25, Yb2Sn1.25O5.5, and Yb2Sn1.375O5.75. The compound Yb2Sn1.125O5.25 was determined, via x-ray diffraction, to have the long-range defect fluorite structure, Fm-3 m symmetry, with cell parameter a = 5.17233(1). Further to this, Sm2ZrO5 and Yb2TiO5 compounds were also fabricated and crystal structures characterised. The use of transmission electron microscopy has revealed a much more complex crystal structure than that of the relatively high symmetry fluorite, with the presence of structural modulations being detected. The ion-irradiation response of these compounds was tested via bulk specimen irradiation using 15-MeV gold ions with grazing incidence x-ray diffraction characterisation. The results show that both Sm2ZrO5 and Yb2Sn1.25O5.5 are highly tolerant to ion-irradiation exposure whilst Yb2TiO5 is susceptible to amorphisation. Crown Copyright © 2021
Ion-beam irradiation of lanthanum compounds in the systems La2O3–Al2O3 and La2O3–TiO2
(Elsevier, 2010-10) Whittle, KR; Lumpkin, GR; Blackford, MG; Aughterson, RD; Smith, KL; Zaluzec, NJ
Thin crystals of La2O3, LaAlO3, La2/3TiO3, La2TiO5, and La2Ti2O7 have been irradiated in situ using 1 MeV Kr2+ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La2O3 remained crystalline to a fluence greater than 3.1×1016 ions cm−2 at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline–amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (Tc) of 647 K for LaAlO3, 840 K for La2Ti2O7, 865 K for La2/3TiO3, and 1027 K for La2TiO5. The Tc values observed in this study, together with previous data for Al2O3 and TiO2, are discussed with reference to the melting points for the La2O3–Al2O3 and La2O3–TiO2 systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between Tc and melting temperature (Tm) in the two systems. More complex relationships exist between Tc and crystal structure, with the stoichiometric perovskite LaAlO3 being the most resistant to amorphisation. © 2010, Elsevier Ltd.
Ion-irradiation resistance of the orthorhombic Ln2TiO5 (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb and Dy) series
(Elsevier, 2015-12-01) Aughterson, RD; Lumpkin, GR; Ionescu, M; de los Reyes, M; Gault, B; Whittle, KR; Smith, KL; Cairney, JM
The response of Ln2TiO5 (where Ln is a lanthanide) compounds exposed to high-energy ions was used to test their suitability for nuclear-based applications, under two different but complementary conditions. Eight samples with nominal stoichiometry Ln2TiO5 (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb and Dy), of orthorhombic (Pnma) structure were irradiated, at various temperatures, with 1 MeV Kr2+ ions in-situ within a transmission electron microscope. In each case, the fluence was increased until a phase transition from crystalline to amorphous was observed, termed critical dose Dc. At certain elevated temperatures, the crystallinity was maintained irrespective of fluence. The critical temperature for maintaining crystallinity, Tc, varied non-uniformly across the series. The Tc was consistently high for La, Pr, Nd and Sm2TiO5 before sequential improvement from Eu to Dy2TiO5 with Tc's dropping from 974 K to 712 K. In addition, bulk Dy2TiO5 was irradiated with 12 MeV Au+ ions at 300 K, 723 K and 823 K and monitored via grazing-incidence X-ray diffraction (GIXRD). At 300 K, only amorphisation is observed, with no transition to other structures, whilst at higher temperatures, specimens retained their original structure. The improved radiation tolerance of compounds containing smaller lanthanides has previously been attributed to their ability to form radiation-induced phase transitions. No such transitions were observed here. © 2017 Elsevier B.V.
The ion-irradiation tolerance of the pyrochlore to fluorite Ho(x)Yb(2-x)TiO5 and Er2TiO5 compounds: a TEM comparative study using both in-situ and bulk ex-situ irradiation approaches
(Elsevier, 2018-08-15) Aughterson, RD; Lumpkin, GR; Smith, KL; de los Reyes, M; Davis, J; Avdeev, M; Ridgway, MC; Cairney, JM
We refine the crystal structures of a systematic series of compounds with the general composition Ho(x)Yb(2-x)TiO5 (x = 2, 1.6, 1.2, 1, 0.8, 0.4, 0) and Er2TiO5 and find a transition from defect-pyrochlore to defect-fluorite structure with increasing ytterbium content, decreasing lanthanide radius. Short-range structure modulations consisting of pyrochlore-like nano-domains are systematically characterised using transmission electron microscopy. We test the Kr2+ 1 MeV ion-irradiation response of Ho2TiO5, HoYbTiO5, Yb2TiO5, and Er2TiO5, via the crystalline to amorphous transition observed by using the in-situ TEM approach. The critical dose of amorphisation, Dc, was measured at various temperatures and used to calculate the critical temperature for maintaining crystallinity, Tc. A trend of lower Tc values with decreasing lanthanide radius is found. We describe a new approach for determining Tc values using cross-sectional TEM analysis of ex-situ bulk irradiated, 1 MeV Se+, samples; Ho2TiO5, HoYbTiO5 and Yb2TiO5. The results of Dc and Tc values using the two approaches vary; however the trends across the sample system remain the same. © 2018 Published by Elsevier B.V.
M(n+1)AXn phases are they tolerant/resistant to damage
(Australian Institute of Physics, 2011-02-03) Whittle, KR; Riley, DP; Blackford, MG; Aughterson, RD; Moricca, SA; Lumpkin, GR; Zaluzec, NJ
Ternary carbide materials have been proposed as having applications within the future nuclear technologies, both fusion (ITER/DEMO) and fission (Gen IV). These new designs require a material to have the ability to tolerate radiation damage to high levels, with a high level of predictability. As part of such a process two systems, specifically Ti3AlC2 and Ti3SiC2 have been studied to determine their radiation tolerance, using in-situ ion beam irradiation with 1 MeV Xe ions, coupled with transmission electron microscopy. Irradiations have shown that both systems show little amorphisation at 300K up to doses of at least 6.25 x 1015 ions cm-2 (~28-30 dpa). However, there is a subtle difference between Ti3AlC2 and Ti3SiC2, with Ti3SiC2 showing more evidence for damage. Further irradiations using 500 KeV Xe to fluences equivalent to 100 dpa have also been undertaken, with crystalline material visible and evidence of recrystallisation. Explanations and possible mechanisms for recovery from damage are presented, along with implications for future potential uses.
New pathway for the preparation of pyrochlore Nd2Zr2O7 nanoparticles
(Elsevier B.V., 2015-07-01) Kong, L; Karatchevtseva, I; Aughterson, RD; Davis, J; Zhang, YJ; Lumpkin, GR; Triani, G
Pyrochlore Nd2Zr2O7 nanoparticles were prepared by complex-precipitation in aqueous media, followed by calcination in MgO matrix and subsequent dissolution processing. A suite of characterization techniques, including X-ray diffraction, Raman, TEM, SEM, dynamic light scattering, and nitrogen sorption, was employed to investigate the structure and particle size of the synthesized nano materials. Results show that calcination at 1200 °C for 20 h forms Nd2Zr2O7 with pyrochlore structure. The matrix phase (MgO) had no effect on the formation of pyrochlore phase. The MgO phase was readily removed by dissolution at 0.5 M HNO3 aqueous solution; and the remaining pyrochlore Nd2Zr2O7 nanoparticles had a diameter of approximately 200 nm estimated by TEM and approximately 550 nm determined by light scattering due to slight aggregation. The bulk density of the pelletized powder reached approximately 99% of theoretical value, after uniaxial pressing at 2.0–2.5 MPa and sintering at 1400 °C for 48 h. © 2015 Elsevier B.V.
Novel complex ceramic oxides, Ln2TiO5 (Ln = La, Sm, Gd, Tb, Dy, Ho, Er, and Yb), for polyphase nuclear waste‐forms
(The American Ceramic Society, 2020-06-19) Aughterson, RD; Lumpkin, GR; Smith, KL; Cairney, JM
As part of a broader study of ceramic nuclear waste‐forms, four different lanthanide titanates were fabricated; La0.1Sm0.1Gd0.1Tb0.1Dy0.3Ho0.1Er0.2YbTiO5, Sm0.3Gd0.3Dy0.3Yb1.1TiO5, Sm0.1Gd0.4Dy0.4Yb1.1TiO5, and Sm0.2Gd0.2Dy0.2Yb1.4TiO5. The aim was to produce single‐phase novel materials with cubic symmetry, capable of incorporating a wide variety of cations and with acceptable radiation tolerance. The chemistry flexibility and radiation tolerance are some of the major desirable properties for nuclear waste‐form materials. By using multiple lanthanides the average lanthanide radius can be controlled and consequently the structure, along with properties such as radiation tolerance. The radiation tolerance was assessed using in situ 1 MeV krypton irradiation and transmission electron microscopy characterization. Those materials for which cubic symmetry was achieved displayed better radiation tolerance; a greater critical fluence of ions (Fc) was required for the crystalline to amorphous transition, and a lower temperature was required to maintain crystallinity (Tc) during irradiation. © 2020 The American Ceramic Society
Perspectives on pyrochlores, defect fluorites, and related compounds: building blocks for chemical diversity and functionality
(Frontiers Media S.A., 2021-11-12) Lumpkin, GR; Aughterson, RD
In this article we provide some perspectives on a range of pyrochlore and defect fluorite type compounds with nominal A2B2O7, A2BO5, ABC2O7, and other stoichiometries. Typically, the phase transformations and stability fields in these systems are mapped as a function of the ionic radii of the A and B-site cations, e.g., the A/B cation radius ratio (rA/rB). This provides a useful guide to compatible structures and compositions for the development of advanced materials. Pyrochlore commonly transforms to a defect fluorite structure at high temperature in many systems; however, it is not uncommon to observe defect fluorite as the initial metastable phase at low temperature. The patterns of order-disorder observed in these materials are primarily due to the energetics of layer stacking, the defect formation and migration energies of cations and anions, or modulations of the parent cubic structure in 3 + n dimensional space. The first lead to predominantly non-cubic derivatives of the parent defect fluorite structure (e.g., zirconolite polytypes), the second control the order-disorder processes, and the latter lead to a variety of subtle additional scattering features within the cubic parent structure. Although the energetics of cation disorder and anion-vacancy disorder have become more accessible via atomistic approaches (e.g., MD and DFT), we continue to find interesting physical-chemical problems in these materials. For example, although there are significant differences in composition (Tb/Zr ratio and O content) between Tb2Zr2O7 and Tb2ZrO5, both of which are defect fluorites, we note that the modulations found in these two compounds by electron scattering are virtually identical with regard to the direction and magnitude of displacement from the normal Bragg diffracted beams. This suggests that neither the A/B cation ratio nor the oxygen stoichiometry have a significant effect on the modulations. The general observations on the systems of compounds noted in this paper rest primarily in the context of industrial materials for nuclear waste disposal, potential applications in inert matrix fuel designs, and other important technological applications such as ionic conductivity, electrical conductivity, and magnetism. Scientific advances in these areas have been underpinned by recent advances in ion irradiation, synchrotron X-ray, neutron scattering, and modelling and simulation capabilities. Furthermore, there has been some renewed interest in natural samples, e.g., Th-U zirconolite and pyrochlore as analogues for potential host phases in nuclear waste forms. In particular, the natural pyrochlores have provided additional details with regard to radiation damage ingrowth, percolation transitions, and the relationships between accumulated dose and physical properties including hardness, elastic modulus. Specific details of the thermal annealing of these samples have also been elucidated in considerable detail. © 2021 Lumpkin and Aughterson
The quantification of radiation damage in orthophosphates using confocal μ-luminescence spectroscopy of Nd3+
(Frontiers Media S.A., 2019-02-05) Lenz, C; Thorogood, GJ; Aughterson, RD; Ionescu, M; Gregg, DJ; Davis, J; Lumpkin, GR
In this study, we present a new concept based on the steady-state, laser-induced photoluminescence of Nd3+, which aims at a direct determination of the amorphous fraction f a in monazite- and xenotime-type orthophosphates on a micrometer scale. Polycrystalline, cold-pressed, sintered LaPO4, and YPO4 ceramics were exposed to quadruple Au-ion irradiation with ion energies 35 MeV (50% of the respective total fluence), 22 MeV (21%), 14 MeV (16%), and 7 MeV (13%). Total irradiation fluences were varied in the range 1.6 × 1013–6.5 × 1013 ions/cm2. Ion-irradiation resulted in amorphization and damage accumulation unto a depth of ~5 μm below the irradiated surfaces. The amorphous fraction created was quantified by means of surface-sensitive grazing-incidence X-ray diffraction and photoluminescence spectroscopy using state-of-the-art confocal spectrometers with spatial resolution in the μm range. Monazite-type LaPO4 was found to be more susceptible to ion-irradiation induced damage accumulation than xenotime-type YPO4. Transmission electron microscopy of lamella cut from irradiated surfaces with the focused-ion beam technique confirmed damage depth-profiles with those obtained from PL hyperspectral mapping. Potential analytical advantages that arise from an improved characterization and quantification of radiation damage (i.e., f a) on the μm-scale are discussed. © 2019 Lenz, Thorogood, Aughterson, Ionescu, Gregg, Davis and Lumpkin. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).

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