Browsing by Author "Cairney, JM"

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    Analytical techniques for probing small-scale layers that preserve information on gas–solid interactions
    (Mineralogical Society of America, 2018-11-01) Dalby, KN; Berger, JA; Brand, HEA; Cairney, JM; Eder, K; Eggins, SM; Herring, A; Hervig, RL; Kreider, PB; Mernagh, TB; Palm, AB; Renggli, CJ; Troitzsch, U; Yue, L; King, PL
    It has been 23 years (as we type) since Carroll and Holloway published the “Volatiles in Magmas” MSA volume (Carroll and Holloway 1994). The 1994 volume dealt with how to safely sample high-temperature gases and analytical methods for volatiles in glasses, which included secondary ion mass spectroscopy and vibrational spectroscopy. Since that time, some things have changed, and some have remained the same. There is still a disconnect between laboratory models of high-temperature gas–solid processes and field observations (Cashman et al. 2017), but we are starting to close that gap with rapid advances in technology. © 2018 Mineralogical Society of America
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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
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    The response of complex ceramic oxides exposed to ion-irradiation, compared using two TEM characterisation techniques; bulk, ex-situ, and thin crystal, in-situ
    (Australian Microscopy and Microanalysis Society, 2015-02-12) Aughterson, RD; Cairney, JM; Ridgway, MC; Zaluzec, NJ; Lumpkin, GR
    The response of materials exposed to high energy particles has been an active area of research for several decades, due both to potentially improved and detrimental effects on the material properties. 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]. Whilst there are many changes to the host material caused via the impact of accelerated ions the particular focus of this research is on the crystalline to amorphous transition. The amorphisation of the host material can lead to detrimental effects on its properties such as swelling, embrittlement, and micro-cracking leading to eventual structural failure. 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 Russian WWER type reactors for two decades 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 have indicated that the series ofLn2TiO5 compounds may take on a variety of crystal symmetries depending on the lanthanide size and fabrication conditions used [3, 4].Previous to any ion-irradiation exposure the materials of interest were tested for homogeneity of stoichiometry and crystallography. Characterisation was carried out via backscattered electron imaging (Z contrast) to highlight any variations in elemental composition. This was followed up with multiple spot analyses using energy dispersive x-ray spectroscopy to confirm the homogeneous nature of the material plus the stoichiometry. X-ray diffraction was used to determine the long range symmetry of the test materials plus confirm the single structure nature. Any materials found to have more than one crystal structure type or greater than 5% secondary phase were rejected for further ion-irradiation based experiments. The preliminary 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. The in-situ ion-irradiation 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 (refer to Figure 1). Further bulk Se+ ion-irradiation was carried out at the Australian National University using the TANDEM, heavy ion accelerator. The damage penetration depth was characterised ex-situ using cross-sectional TEM. The cross-sectional damage depth profile of the bulk sample was compared with simulation, SRIM (Stopping Range of Ions in Matter), based calculations and a critical dose of amorphisation value attained. By using these two TEM characterisation approaches the thin crystal in-situ results can be compared with the more “realistic” bulk approach. ©2015 Australian Microscopy and Microanalysis Society
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    TEM studies of ion-irradiation tolerance in Gd2TiO5
    (Australian Nanotechnology Network, 2012-02-07) Aughterson, RD; Cairney, JM; Gault, B; Ridgway, MC; Elliman, RG; Lumpkin, GR
    Gd2TiO5 has been identified as a potentially useful material for nuclear based applications such as burnable poison or constituent in waste-forms. A polycrystalline, single phase sample of Gd2TiO5 has been fabricated via the oxide-route reaction. The single phase status and chemical stoichiometry were confirmed using SEM backscattered images, EDS, and laboratory XRD. The structure was confirmed to be orthorhombic, Pnma, space group number 62. The suitability of use for this material in a radioactive environment was tested by in-situ measurement of the materials resistance to transformation from the crystalline to amorphous state via 1MeV Kr2+ ion-irradiation. The in-situ ion-irradiation was carried out using the intermediate voltage electron microscope (IVEM)-Tandem facility at Argonne National Laboratory. The critical dose, Dc, required to render the Gd2TiO5 completely amorphous was determined and the result is compared with other similarly tested materials. Further bulk gold ion-irradiation at various accelerating energies was carried out at the Australian National University using the TANDEM accelerator with damage penetration depth characterised using cross-sectional TEM.