Study On The Microstructure And Radiation Effects Of Weberite-type Ln₃TaO₇?Ln:Rare Earth?

Weberite?Ln₃BO₇,where Ln represents rare earth;B=Ta,Nb,Sb,Mo?is a derivative structure of fluorite,which is regarded as a potential candidate on the disposal of the high level waste.Currently,researches on the weberites are mainly focused on their magnetic properties,while few studies on their irradiation effects and irradiation mechanical properties are available.Herein,to investigate the ion irradiation effects of the weberite is of importance.The work was divided into two sections.Firstly,high-temperature solid-state reaction was used to prepare several kind of Ln₃TaO₇?Ln=Y,Sm,Eu,Gd,Dy,Er,Tm,Lu?samples.The structural prosperities of Ln₃TaO₇ were characterized systematically by X-ray diffraction?XRD?,and Raman spectroscopy?Raman?,as well as Rietveld refinement method.Results showed that Ln₃Ta_<sub>O₇ underwent the transformation from orthogonal Ccmm?Ln=Y,Sm,Eu,Gd,Dy?structure to Fm3m?Ln=Er,Tm,Lu?cubic defect fluorite structure as the radius of lanthanide cations decreases.Meanwhile,the lattice parameter exhibited a decrease trend with the decreasing lanthanide cations radius regardless of in Ccmm or Fm^<sub>3^<sub>m structure.In addition,Raman spectroscopy analysis showed that the Raman vibration of Tm₃TaO₇ was different from Er₃TaO₇and Lu₃TaO₇ in the long-range disordered fluorite structure,which was similar Ccmm-like orthogonal structure vibration characteristics,indicating that Tm₃TaO₇ was presented as a disorder fluorite structure in the long-range,but was an order structure in the short-range.Secondly,the 6.5 MeV Xe²⁶⁺ions was used to irradiate the Ccmm structured Ln₃TaO₇?Ln=Y,Sm,Gd?.According to the grazing incidence X-ray diffraction?GIXRD?spectroscopy and nanoindentation techniques,the variations of structure and mechanical properties of Ccmm structured Ln₃TaO₇ was invesgated after ion beam irradiation.Results showed that under the irradiation of Xe²⁶⁺ion amorphous phase transition was appeared in none of three weberites when the irradiation dose is lower than 1×10¹⁵ ions/cm²?3.25 dpa?,however the volume swelling phenomenon were all appeared in different extents.Both Sm₃TaO₇ and Gd₃TaO₇ exhibited the most significant changes of lattice swelling rate at low doses(1×10¹⁴ ions/cm² and 4×10¹⁴ions/cm²);when the dose was 7×10¹⁴ ions/cm²,the swelling of Sm₃TaO₇ tended to be“saturated”gradually while the swelling of Gd₃TaO₇ was gradually flattened;At low dose(1×10¹⁴ ions/cm²and 4×10¹⁴ ions/cm²)the swelling of Y₃TaO₇ is not obvious.When the dose reaches 1×10¹⁵ions/cm² the swelling of Y₃TaO₇ was increased significantly,while it was still much smaller than that of Sm₃TaO₇ and Gd₃TaO₇,indicating that it possess the strongest anti-irradiation swelling ability.Furthermore,the variation of mechanical properties of Y₃TaO₇,Sm₃TaO₇ and Gd₃TaO₇irradiated by Xe²⁶⁺ions were not of significance,which had an extremely strong mechanical stability compared with the glass-cured substrates and metal tank materials.