Fluorite-pyrochlore phase transition in nanostructured Ln2Hf2O7 (Ln = La-Lu)

Modeling Disorder in Pyrochlores and Other Anion-Deficient Fluorite Structural Derivative Oxides

“…They have also attracted special interest as nuclear waste forms (Sickafus, 2000;Wang et al, 2000;Begg et al, 2001;Lian et al, 2003a;Lian et al, 2003b;Ewing et al, 2004;Helean et al, 2004;Lian et al, 2006;Lumpkin, 2006;Sickafus et al, 2007;Hartmann et al, 2011;Li et al, 2012;Sattonnay et al, 2013;Fischer et al, 2015;Raison and Haire, 2001;Lutique et al, 2003) and inert matrix fuel materials due to their high radiation tolerance. The high radiation tolerance of some pyrochlores is related to their ability to undergo an orderdisorder transition (Subramanian et al, 1983;Lang et al, 2010;Blanchard et al, 2012;Blanchard et al, 2013;FarmerMatt et al, 2014;Popov et al, 2016;Popov et al, 2018), i.e., a low thermodynamic barrier for transition from an ordered pyrochlore to a disordered fluorite structure. In contrast, pyrochlores that have high energy cost for the order-disorder transition would amorphize under irradiation (Sickafus, 2000).…”

Polymorphism in the family of Ln6−xMoO12−δ(Ln = La, Gd–Lu; x = 0, 0.5) oxygen ion- and proton-conducting materials

“…22 The morphotropy and polymorphism (thermodynamic phase and kinetic (growth-related) transitions) of the Ln 2 M 2 O 7 (Ln ¼ La-Lu; M ¼ Ti, Zr, Hf) rareearth pyrochlores have been analyzed in detail. 22,23 The purpose of this work was to study the formation of rareearth molybdate Ln 6Àx MoO 12Àd (Ln ¼ La, Gd, Dy, Ho, Er, Tm, Yb, Lu; x ¼ 0, 0.5) solid solutions in a wide temperature range, from 900 to 1650 C. To this end, precursors were synthesized using mechanical activation, a method that allows one to obtain homogeneous, highly dispersed oxide mixtures and occasionally leads to the formation of compounds at room temperature, i.e. ensures mechanochemical synthesis of mixed oxides.…”

A Comparison of Order-Disorder in Several Families of Cubic Oxides

“…Over the past two decades, there has been intense interest in defect chemistry, disorder, solid solution formation, and phase transitions in oxide pyrochlores ( Glerup et al, 2001 ; Shlyakhtina et al, 2004 ; Liu et al, 2004 ; Knee et al, 2005 ; Mandal et al, 2006 ; Matsuhira et al, 2007 ; Zhang et al, 2008 ; Clements et al, 2011 ; Wang et al, 2011 ; de los Reyes et al, 2013 ; Zhang et al, 2013 ; Zhang et al, 2014 ; Popov et al, 2016 ; Paul et al, 2016 ; Rittman et al, 2017a ; Rittman et al, 2017b ; Simeone et al, 2017 ; Ponnilavan et al, 2019 ; Popov et al, 2020 ; Marlton et al, 2021 ; Panghal et al, 2021 ). Because the pyrochlore structure is a derivative of fluorite, it belongs to a large family of related structures.…”