Local order of orthorhombic weberite-type Y3TaO7 as determined by neutron total scattering and density functional theory calculations✰

Disorder in Ho2Ti2−xZrxO7: pyrochlore to defect fluorite solid solution series

“…This model is described in depth elsewhere. 45,46 This structure is very similar to Ccmm and has been previously used to describe the local atomic arrangement in A 3 BO 7 defect uorite materials. 43 The 16h oxygen site is split into two 8c sites and most cations and anions in the structure have more positional and vibrational degrees of freedom than in Ccmm.…”

“…25,31,35,40,41 Recent studies using neutron total scattering experiments with pair distribution function (PDF) analysis of disordered pyrochlore (e.g., Ho 2 Zr 2 O 7 ) have uncovered that the local atomic arrangement of the defect uorite phase is actually described by a partially ordered orthorhombic phase, 42 the structure of which can be described by a weberite-type (C222 1 ) structural model that is isostructural to Y 3 TaO 7 . [42][43][44][45][46][47] The weberite-type structure is another derivative of the uorite structure with a 2  ffiffiffi 2 p  ffiffiffi 2 p superstructure that contains a higher degree of ordered arrangements of different valence cations and ordered anion vacancies as compared with defect uorite but is distinct from pyrochlore (Fig. 1c).…”

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

“…The 8c sites are occupied completely by A 3+ cations forming edge-shared AO 7 polyhedral chains along the c axis and the chains in turn share edges along the b axis to form the AO 7 layer. AO 8 -BO 6 and AO 7 layers arrange alternately to form the overall structure (Gussev et al, 2020 (Shamblin et al, 2016a;Drey et al, 2020). So, the structure can be seen as an alternating arrangement of ordered and disordered layers in weberite-type, A 2 M 2 O 7 .…”

“…Understanding (Drey et al, 2020;Gussev et al, 2020). The crystal structures are drawn using the software VESTA (Momma and Izumi, 2008).…”

“…FIGURE 2 | Structure of weberite-type (A) Ho 3 TaO 7 and (B) Ho 2 Zr 2 O 7 , both forming in orthorhombic C222 1 space group. The (A/B)O 7 layer in which partial disorder between A and B cations is marked with blue polyhedra for clarity in (B).Figure has been drawn based on the crystallographic data from the literature(Drey et al, 2020;Gussev et al, 2020). The crystal structures are drawn using the software VESTA(Momma and Izumi, 2008).…”