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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 Fm3¯$\bar{3}$m 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We refine the crystal structures of a systematic series of compounds with the general composition Ho (x) Yb (2-x) TiO 5 (x = 2, 1.6, 1.2, 1, 0.8, 0.4, 0) and Er 2 TiO 5 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 Kr 2+ 1 MeV ion-irradiation response of Ho 2 TiO 5 , HoYbTiO 5 , Yb 2 TiO 5 , and Er 2 TiO 5 , via the crystalline to amorphous transition observed by using the in-situ TEM approach. The critical dose of amorphisation, D c , was measured at various temperatures and used to calculate the critical temperature for maintaining crystallinity, T c . A trend of lower T c values with decreasing lanthanide radius is found. We describe a new approach for determining T c values using cross-sectional TEM analysis of ex-situ bulk irradiated, 1 MeV Se + , samples; Ho 2 TiO 5 , HoYbTiO 5 and Yb 2 TiO 5 . The results of D c and T c values using the two approaches vary; however the trends across the sample system remain the same. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In developing improvements in nuclear fuels, work has been conducted in replacing boron with lanthanides to act as neutron absorbent materials. To further this development for the first time the three major polymorphs of Dy 2 TiO 5 have been fabricated as bulk, single-phase materials in a systematic study. Crystal structure refinement has been carried out from powder x-ray diffraction data, with further structural detail attained via electron diffraction. A cubic phase, defect-pyrochlore, Fd-3m space group, was found with cell parameter a = 10.2996 (1) Å and oxygen x48f positional parameter = 0.331 (1). Dy 2 TiO 5 was also fabricated as a bulk, single-phase compound with hexagonal symmetry, P6 3 /mmc space group, with cell parameters a = b = 3.6307(2), c = 11.8963(8) Å. The radiation response for each of the polymorphs has been investigated in-situ via 1 MeV Kr – ion-irradiation and transmission electron microscopy characterisation at the IVEM-TANDEM facility, Argonne National Laboratory. Critical temperatures, T c , for maintaining crystallinity during irradiation were determined and showed Dy 2 TiO 5 with either orthorhombic or cubic symmetry to perform the best, with the lowest T c values of 711 and 761 K respectively when compared with the hexagonal form. These relatively low T c values may be attributed to different characteristics for each phase; high anti-site defect formation energy for the orthorhombic symmetry, and the ability to accommodate disorder for the cubic symmetry. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Using transmission electron microscopy we show that planar deformation lamellae occur within quartz in the substrate of a rock fulgurite, i.e., a lightning-derived glass. These lamellae exist only in a narrow zone adjacent to the quartz/fulgurite boundary and are comparable to planar deformation features ("shock lamellae") caused by hypervelocity impacts of extra-terrestrial objects. Our observations strongly suggest that the lamellae described here have been formed as a result of the fulgurite-producing lightning strike. This event must have generated a transient pressure pulse, whose magnitude, however, is uncertain at this stage. [ABSTRACT FROM AUTHOR]

A novel soft chemistry route was developed to synthesize Y 2 Hf x Ti 2− x O 7 (0≤ x ≤2.0) oxide solid solution. An aqueous solution containing reactants was produced to ensure the combustion reaction taking place at the molecular level. A suite of characterization techniques, including X-ray diffraction, Raman, transmission electron spectroscopy, as well as X-ray absorption near edge structure (XANES), is employed to investigate the structural and phase changes of the series. Both X-ray and electron diffraction patterns show that the Y 2 Hf x Ti 2− x O 7 system undergoes a clear composition-induced phase transition from ordered pyrochlore to disordered defect-fluorite at x ~1.5. On the other hand, Raman and XANES spectra reveal a gradual evolution of the local structure with the substitution of Hf for Ti. [ABSTRACT FROM AUTHOR]