Crystal structure of fluorite-related Ln3SbO7 (Ln=La–Dy) ceramics studied by synchrotron X-ray diffraction and Raman scattering

Abstract

Ln 3 SbO 7 (Ln ¼La, Pr, Nd, Sm, Eu, Gd, Tb and Dy) ceramics were synthesized by solid-state reaction in optimized conditions of temperature and time to yield single-phase ceramics. The crystal structures of the obtained ceramics were investigated by synchrotron X-ray diffraction, second harmonic generation (SHG) and Raman scattering. All samples exhibited fluorite-type orthorhombic structures with different oxygen arrangements as a function of the ionic radius of the lanthanide metal. For ceramics with the largest ionic radii (La-Nd), the ceramics crystallized into the Cmcm space group, while the ceramics with intermediate and smallest ionic radii (Sm-Dy) exhibited a different crystal structure belonging to the same space group, described under the Ccmm setting. The results from SHG and Raman scattering confirmed these settings and ruled out any possibility for the non-centrosymmetric C222 1 space group describing the structure of the small ionic radii ceramics, solving a recent controversy in the literature. Besides, the Raman modes for all samples are reported for the first time, showing characteristic features for each group of samples.

Emergent order in the kagome Ising magnet Dy3Mg2Sb3O14

“…41)), a refined model of the magnetic Bragg scattering of Dy 3 SbO 7 was subtracted, as described in Supplementary Note 2 (we note that the orthorhombic crystal structure of Dy 3 SbO 7 (ref. 52) allowed the impurity Bragg peaks to be readily distinguished from sample peaks). The fit to neutron data of the Dy 3 SbO 7 magnetic-structure model is shown in Supplementary Fig.…”

Potential thermal barrier coating materials: RE3NbO7 (RE=La, Nd, Sm, Eu, Gd, Dy) ceramics

“…The crystal structures of RE 3 NbO 7 derive from the prototype (Fmm) by the following process. Four tetravalent cations (A 4+ ) are displaced by 3 trivalent RE 3+ and one pentavalent Nb 5+ , and one oxygen vacancy is produced in each unit cell to maintain electrical neutrality . The oxygen vacancy concentration is as high as 12.5% (1/8) in RE 3 NbO 7 , which is the strongest phonon scattering center among diverse lattice imperfections.…”

“…The oxygen vacancy concentration is as high as 12.5% (1/8) in RE 3 NbO 7 , which is the strongest phonon scattering center among diverse lattice imperfections. The chemical formula of weberite RE 3 NbO 7 is A 3+ A′ 3+ 2 B 5+ OO′ 4 O″ 2 □, when the chemical formula of fluorite RE 3 NbO 7 ceramics is A 3+ 3 B 5+ O 7 □ (□ represents oxygen vacancy) . In addition, each Nb coordinates with 6 O atoms to form NbO 6 octahedron in weberite RE 3 NbO 7 , which is called the framework structure.…”

Tantalatos e niobatos de terras raras luminescentes: síntese, propriedades e aplicações em fotônica

“…Estruturas cristalinas derivadas da fluorita (CaF2) têm recebido atenção considerável e estão sendo amplamente utilizadas como matrizes para os íons TR (MICHEL et al, 1976;ROSSELL, 1979b;a;KRIVOVICHEV, 1999;DOI et al, 2009;HINATSU et al, 2009;PAYNE et al, 2013;SIQUEIRA et al, 2013;WANG et al, 2014;FRANCIS et al, 2016), como por exemplo as estruturas do tipo pirocloro, weberita e a própria fluorita (cúbica).…”

“…e uma vacância de oxigênio aparece por célula de fluorita (CAI e NINO, 2009;HINATSU et al, 2009). As diferenças significativas entre os raios iônicos dos íons TR 3+ e M 5+ levam à um ordenamento no sítio do metal e assim a vacância de oxigênio é gerada no sítio do ânion (HINATSU et al, 2009;SIQUEIRA et al, 2013). Esta estrutura exibe configurações diferentes para os íons TR 3+ , íons coordenados a sete ou oito oxigênios que se encontram em cadeias paralelas com MO6 (CAI e NINO, 2009).…”