ANSTO :: Browsing by Author "Smith, KL"

Browsing by Author "Smith, KL"

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Alternative Synroc formulations
(Cambridge University Press/Springer Nature, 2011-02-25) Vance, ER; Smith, KL; Thorogood, GJ; Begg, BD; Moricca, SA; Angel, PJ; Stewart, MWA; Ball, CJ
Perovskite is the least durable of the resistate minerals comprising Synroc-C and it is desirable to reduce its abundance in Synroc. Kinetic limitations and competition with Csapparently affect the incorporation of Sr into hollandite during hot-pressing at 1200°C/20 MPa so that ~ 10% of perovskite (a value below the percolation limit) is probably an optimum target. Zirconolite-rich Synroc formulations have been prepared for actinide-rich wastes. Background XRD and TEM studies have also been performed to study the crystal-chemical behaviour of Nd (a simulant of trivalent actinides) in zirconolite. Either rare-earth compensated perovskite or freudenbergite in Synroc can evidently be used to immobilise Na-bearing HLW. © 1992 Materials Research Society
ANSTO Nuclear Foresnics Research Facility: method development and applications
(Australian Nuclear Science and Technology Organisation, 2012-10-16) Wotherspoon, ATL; Hill, DM; Keegan, EA; Evans, T; Blagojevic, N; Loi, E; Toole, K; Griffiths, GJ; Smith, KL; Reinhard, MI
The IAEA defines nuclear forensic science, commonly shortened to “nuclear forensics” as ‘the scientific analysis of nuclear or other radioactive material, or of other evidence that is contaminated with radioactive material, in the context of legal proceedings, including administrative, civil, criminal or international law’1. In broad terms, the job of the nuclear forensic scientist is to support investigations that involve a nuclear security event. Nuclear forensic examinations will provide information to key questions posed by the investigative authority: What is it? How much is there? Is there any more out there? Is it ours? As an investigation proceeds other questions that may arise are; How old is it? What contaminants are present? Does it pose a threat? Who is responsible for the loss? Where did the material come from? Many of the techniques required to answer these questions are based on environmental radiochemistry. The Nuclear Forensic Research Facility (NFRF) at ANSTO is developing expertise in analysing nuclear and other radioactive material material based upon the precepts of the ‘model action plan’ of the International Technical Working Group for Nuclear Forensics (ITWG) and other best practices. We are also investigating the validity of traditional forensic techniques (like fingerprints and DNA) on evidence contaminated with radioactive material alongside more novel parameters, e.g. the isotopic composition at the ‘bulk’ material and the micro scale using advanced micro-analytical techniques. We are moving towards the integration of a range of radio analytical techniques such as mass spectrometry, electron microscopy and the simulation/modelling of material production signatures, to provide a range of different information streams to assist attribution. With each advance in our technical competencies we enhance our means to ensure the security of nuclear or other radioactive material.
Characterization and leaching behavior of plutonium-bearing Synroc-C
(Cambridge University Press/Springer Nature, 1996-02-05) Smith, KL; Lumpkin, GR; Blackford, MG; Hambley, M; Day, RA; Hart, KP; Jostsons, A
Synroc-C containing 10wt% simulated PW-4b-D HLW including 0.62 wt% 239Pu was subjected to MCC-1 type leach tests at 70°C in deionised water, silicate and carbonate leachates for 53 d and deionised water for 2472 d. The normalised total (i.e. unfiltered leachate + vessel wall) Pu leach rates in deionised water, silicate and carbonate leachates for periods up to 53 d were found to be of the order of 10-5, 10-4 and 10-4 g m-2 d-1 respectively. After 2472 d, the differential, normalised, Pu leach rate in deionised water dropped to ∼5 × 10-6 (total) and ∼5 × 10-8 (solution - after filtration through a 1000NMW filter) g m-2 d-1. SEM and AEM were used to characterise our starting material and investigate the secondary phases on the surfaces of leached Synroc-C discs. Calculated and measured normalised Pu leach rates are compared and the partitioning of Pu between zirconolite and perovskite is discussed. © Materials Research Society 1997
Characterization and leaching behavior of plutonium-bearing Synroc-C
(Materials Research Society, 1997-04-22) Smith, KL; Lumpkin, GR; Blackford, MH; Hambley, M; Day, RA; Hart, KP; Jostsons, A
Synroc-C containing 10wt% simulated PW-4b-D HLW including 0.62 wt% 239Pu was subjected to MCC-1 type leach tests at 70°C in deionised water, silicate and carbonate leachates for 53 d and deionised water for 2472 d. The normalised total (i.e. unfiltered leachate + vessel wall) Pu leach rates in deionised water, silicate and carbonate leachates for periods up to 53 d were found to be of the order of 10-5, 10-4 and 10-4 g m-2 d-1 respectively. After 2472 d, the differential, normalised, Pu leach rate in deionised water dropped to ∼5 × 10-6 (total) and ∼5 × 10-8 (solution - after filtration through a 1000NMW filter) g m-2 d-1. SEM and AEM were used to characterise our starting material and investigate the secondary phases on the surfaces of leached Synroc-C discs. Calculated and measured normalised Pu leach rates are compared and the partitioning of Pu between zirconolite and perovskite is discussed. © Materials Research Society 1997
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.
Dissolution of Synroc in deionised water at 150°C
(Materials Research Society (MRS)/Cambridge University Press/Springer Nature, 1996-02-15) Smith, KL; Colella, M; Thorogood, GJ; Blackford, MG; Lumpkin, GR; Hart, KP; Prince, KE; Loi, E; Jostsons, A
Synroc containing 20 wt% simulated high level waste (HLW) was subjected to two sets of leach tests at 150°C where the leachant was and was not replaced during the test (replacement and non-replacement testing). The leachant was a KH-phthalate buffered solution (pH 4.2). Samples were characterised before and after leach testing using SEM, AEM and SIMS. Elemental concentrations in leachates were measured using ICP-MS. In concert with the findings of i) a dissolution study of perovskite in a flowing leachant and ii) a previous Synroc dissolution study (wherein Synroc containing 10 wt% simulated HLW was subjected to periodic replacement, leach testing in deionised water at 150°C), the results of this study show that when the leachant replacement frequency is varied from 7 d to the duration of the test, there is no effect on leach rate or leaching mechanisms. © Materials Research Society 1997
HVEM-Tandem and EELS study of radiation damage in zirconolite
(Cambridge University Press, 1997-08-10) Smith, KL; Zaluzec, NJ; Lumpkin, GR
Zirconolite (CaZrTi2O7) is the major host phase for actinides in Synroc, a promising waste form for the immobilization of high-level radioactive waste. The effect of radiation damage on the structure and durability of zirconolite are important to predictive modeling of zirconolite`s behavior in the repository environment and risk assessment. In this study, radiation damage effects in zirconolite were investigated by irradiating samples with 1.5 MeV Kr+ ions using the HVEM-Tandem at Argonne National Laboratory (ANL) and energy loss electron spectroscopy (EELS). The HVEM-Tandem consists of a modified AEI high voltage transmission electron microscope interfaced to a 2 MV tandem ion accelerator. EELS spectra were collected using a Philips 420 TEM, operated at 120 kV, fitted with a Gatan Model 607 Serial EELS. EELS data were recorded at resolutions of {approximately} 1.0 eV and at a dispersion of about {approximately} 0.25 eV. Selected area diffraction patterns (SADs) of individual grains of various zirconolites were monitored as a function of dose to establish the critical dose for amorphization (D{sub c}). The authors found that (1) Dc(zirconolite) is independent of the atomic weight of dopants in zirconolite and the mean atomic weight of the sample and that (2) the Bragg reflections in SAD patterns which persist to the highest doses are firstly those resulting from the fluorite sublattice and secondly the four (110)-type reflections which lie on the innermost of the two diffuse rings representative of amorphous zirconolite. © 1997 Microscopy Society of America 1997
In situ radiation damage studies of Ca3Zr2FeAlSiO12 and Ca3Hf2FeAlSiO12
(Australian Institute of Nuclear Science and Engineering (AINSE), 2009-11-25) Whittle, KR; Blackford, MG; Smith, KL; Lumpkin, GR; Zaluzec, NJ
Garnets, A3B2C3O12, are considered to be potential host phases for the immobilization of high-level nuclear waste as they can accommodate a number of elements of interest, including Zr, Ti and Fe. The naturally occurring garnet, kimzeyite, Ca3(ZrTi)2(SiAlFe)O12, can contain ∼30wt% Zr. An understanding of the radiation tolerance of these materials is crucial to their potential use in nuclear waste immobilization. In this study two synthetic analogues of kimzeyite of composition Ca3(ZrTi)2(SiAlFe)O12 and Ca3Hf2FeAlSiO12 were monitored in situ during irradiation with 1.0 MeV Kr ions using the intermediate voltage electron microscope-tandem user facility (IVEM) at Argonne National Laboratory. The structure of these materials was previously determined by neutron diffraction and 57Fe Mössbauer spectroscopy. Ca3(ZrTi)2(SiAlFe)O12 and Ca3Hf2FeAlSiO12 have very similar structural properties with cubic la3d symmetry, the only significant difference being the presence of Zr and Hf, respectively on the 6 coordinated B sites. © 2009 AINSE
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.
Interface phenomena in synroc, a titanate-based nuclear waste ceramic
(Elsevier, 1995) Vance, ER; Ball, CJ; Blackford, MG; Day, RA; Lumpkin, GR; Smith, KL; Hart, KP; McGlinn, PJ; Thorogood, GJ
Several aspects of Synroc which fall into the broad class of interface phenomena are discussed. These are radiation damage processes which give rise to interfaces between damage tracks and neighbouring unirradiated material, intergranular films which have deleterious effects on chemical durability, and aqueous leaching of Synroc which takes place primarily at the interface between the solid and groundwater. © 1995 Elsevier B.V.
Investigating radiation damage in ceramics: the role of in situ microscopy
(Cambridge University Press, 2010-08-01) Smith, KL; Lumpkin, GR; Whittle, KR; Blackford, MG; Zaluzec, NJ
Radiation damage effects in ceramics are of interest in both current (e.g. nuclear waste forms) and next generation (Gen IV) nuclear technologies (e.g. transmutation targets, inert matrix fuels, waste forms etc.). The mechanisms of radiation damage production and recovery in ceramics often vary dependent on the damage source, e.g., energetic neutrons in reactor systems versus alpha recoil damage in nuclear waste forms. Furthermore, the kinetics of damage recovery are complicated by multiply activated processes and in certain cases, longer-term process may modify the structural state left by irradiation in the short term. Here, we review a selection of data collected by the current authors and associates, which highlight the roles played by in situ microscopy in unraveling the mechanisms of radiation damage in ceramics. In situ irradiation of a variety of ceramics (e.g. pyrochlores, perovskites, polymorphs of TiO2 and analogues etc.) have been carried out using the IVEM-Tandem Facility at Argonne National Laboratory [1-7]. The IVEM-Tandem Facility is comprised of an intermediate voltage TEM (IVEM), a Hitachi H-9000NAR, interfaced to two ion accelerators (at 30° to vertical). Specimens were generally prepared by crushing and suspending small fragments on holey carbon coated Cu grids. Samples were most often, irradiated using 1 MeV Kr ions at temperatures from 50 to 900K. Figure 1 shows (a) a bright field (BF) image and (b) selected area diffraction pattern (SADP) of a grain of a typical specimen (in this case TiO2) before in situ irradiation and (c) the SADP of the same grain after a series of irradiations. Multiple measurements were taken and averaged to ascertain the critical fluence (of particular ions) for amorphisation, Fc, of a given sample at various temperatures. Fc data were then were used to establish the critical temperature, Tc, of the particular sample, where Tc is the temperature at which the recovery process is at least equal to the damage rate (that is the temperature above which a sample can not be amorphised). IVEM-Tandem data on a range of pyrochlores with different compositions have been compiled and used to develop an empirical model that can predict the Tc values for many pyrochlores within +/- 80°C [2, 6]. IVEM-Tandem results for specific solid solution series of pyrochlores are informative and will be discussed more fully in the conference presentation. LaxSr1-3x/2TiO3 perovskites show a non-linear relationship for Tc with x [3]. In combination with other data, in situ TEM suggests that cubic perovskites in the 0
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.
Ion irradiation of ternary pyrochlore oxides
(American Chemical Society, 2009-07-14) Lumpkin, GR; Smith, KL; Blackford, MG; Whittle, KR; Harvey, EJ; Redfern, SAT; Zaluzec, NJ
Polycrystalline synthetic samples of Y2Ti2−xSnxO7 with x = 0.4, 0.8, 1.2, and 1.6, together with Nd2Zr2O7, Nd2Zr1.2Ti0.8O7, and La1.6Y0.4Hf2O7, were irradiated in situ in the intermediate voltage electron microscope (IVEM)-Tandem Facility at Argonne National Laboratory using 1.0 MeV Kr ions at temperatures of 50 to 650 K. Determination of the critical amorphization fluence (Fc) as a function of temperature has revealed a dramatic increase in radiation tolerance with increasing Sn content on the pyrochlore B site. Nonlinear least-squares analysis of the fluence-temperature curves gave critical temperatures (Tc) of 666 ± 4, 335 ± 12, and 251 ± 51 K for the Y2Ti2−xSnxO7 samples with x = 0.4, 0.8, and 1.2, respectively. The sample with x = 1.6 appears to disorder to a defect fluorite structure at a fluence below 1.25 × 1015 ions cm−2 and remains crystalline to 5 × 1015 ions cm−2 at 50 K. Additionally, the critical fluence-temperature response curves were determined for Nd2Zr1.2Ti0.8O7 and La1.6Y0.4Hf2O7, and we obtained Tc values of 685 ± 53 K and 473 ± 52 K, respectively, for these pyrochlores. Nd2Zr2O7 did not become amorphous after a fluence of 2.5 × 1015 ions cm−2 at 50 K, but there is evidence that it may amorphize at a higher fluence, with an estimated Tc of 135 K. The observed Tc results are discussed with respect to the predicted Tc values based upon a previously published empirical model (Lumpkin, G. R.; Pruneda, M.; Rios, S.; Smith, K. L.; Trachenko, K.; Whittle, K. R.; Zaluzec, N. J. J. Solid State Chem. 2007, 180, 1512). In the Y2Ti2−xSnxO7 pyrochlores, Tc appears to be linear with respect to composition, and is linear with respect to rA/rB and x(48f) for all samples investigated herein. © 2009, American Chemical Society
Ion irradiation of ternary pyrochlores
(Materials Research Society, 2008-12-01) Whittle, KR; Smith, KL; Blackford, MG; Redfern, SAT; Harvey, EJ; Zaluzec, NJ; Lumpkin, GR
Synthetic pyrochlore samples Y2Ti2-xSnxO7 (x=0.4, 0.8, 1.2, 1.6), Nd2Zr2O7, Nd2Zr1.2Ti0.8O7, and La1.6Y0.4Hf2O7, were irradiated in-situ using the IVEM-TANDEM microscope facility at the Argonne National Laboratory. The critical temperatures for amorphisation have revealed a dramatic increase in tolerance with increasing Sn content for the Y2Ti2-xSnxO7 series. This change has also found to be linear with increasing Sn content. Nd2Zr1.2Ti0.8O7 and La1.6Y0.4Hf2O7 were both found to amorphise, while Nd2Zr2O7 was found to be stable to high doses (2.5x10^15 ions cm-2). The observed results are presented with respect to previously published results for irradiation stability predictions and structural disorder. © Materials Research Society 2009
Ion irradiation of the TiO2 polymorphs and cassiterite
(Mineralogical Society of America, 2010-01) Lumpkin, GR; Blackford, MG; Smith, KL; Whittle, KR; Zaluzec, NJ; Ryan, EA; Baldo, P
Thin crystals of rutile, brookite, anatase, and cassiterite were irradiated in situ in the transmission electron microscope using 1.0 MeV Kr ions at 50–300 K. Synthetic rutile and natural cassiterite, with 0.1–0.2 wt% impurities, remain crystalline up to a fluence of 5 x 1015 ions cm–2 without evidence for amorphization at 50 K. Natural brookite and anatase, with 0.3–0.5 wt% impurities, become amorphous at fluences of 8.1 x 1014 and 2.3 x 1014 ions cm–2, respectively. We have also studied two natural rutile samples containing ~1.7 and 1.2 wt% impurities. These samples became amorphous at 9.2 x 1014 and 8.6 x 1014 ions cm–2 at 50 K, respectively. Further analyses of the fluence-temperature data for natural brookite, rutile, and anatase give critical amorphization temperatures of 168 ± 11, 209 ± 8, and 242 ± 6 K, respectively. Results are briefly discussed with respect to several criteria for radiation resistance, including aspects of the structure, bonding, and energetics of defect formation and migration. © 2010, Mineralogical Society of America
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.
Low pressure synchrotron x-ray powder diffraction of Cu5-xMxSbO6 (M=Cr, Mn, W)
(Australian Institute of Physics, 2016-02-04) Wilson, DJ; Söhnel, T; Smith, KL; Brand, HEA; Ulrich, C; Graham, PJ; Chang, FF; Allison, MC; Vyborna, NH
The large crystallographic and chemical diversity of copper-based metal oxides is one of their highlighting features and cause for pursuit into copper based material research. An interesting feature seen in copper based metal oxides is the coexistence of different copper oxidation states, in different crystallographic positions, within the same compound. This can lead to a mixture of magnetically active Cu2+ and magnetically inactive Cu1+ within the same compound, with different structural motifs. One interesting compound that demonstrates this coexistence of mixed copper oxidation states is Cu5SbO6, which crystallises in a modified delafossite structure type (CuFeO2). Here, the magnetically active brucite-like CuO2 layer was diluted in an ordered fashion with non-magnetic Sb5+. These layers were separated by linearly coordinated, magnetically inactive Cu1+. Rietveld refinements on a range of preparation temperatures revealed a low-temperature (LT) and high-temperature modification (HT) phase transition. This is related to an ordering (HT)/disordering (LT) effect of the Sb5+/Cu2+ brucite-like layers between the Cu1+ ions. Substituting the Cu2+ or Sb5+ in the layers with other transition metals (Cr, Mn, W) could present interesting changes to the properties of the material, and potentially influence the ordered/disordered stacking of the layers. By using solid-state Raman spectroscopy, we could show that this structure displayed a pressure-induced phase transition at room temperature for the ordered modification, which was not observed for the disordered modification. Lowering the pressure from ambient down to 20 mbar showed phonon modes at about 700 cm-1 and 550 cm-1 disappeared almost completely. Neutron powder diffraction experiments were conducted at atmospheric and low pressure on both ordered and disordered modifications. On analysis of the neutron diffraction patterns, we could show a very small shift in the reflections, and thus changes in the unit cell parameters, for the ordered modification, while these shifts were not observed for the disordered modification. These shifts should also be observed in synchrotron powder diffraction patterns. Therefore, we investigated the nature of this phase transition with variable pressure synchrotron X-ray powder diffraction.

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