Microstructural Evolution of Dy2O3-TiO2 Powder Mixtures during Ball Milling and Post-Milled Annealing

Abstract

The microstructural evolution of Dy2O3-TiO2 powder mixtures during ball milling and post-milled annealing was investigated using XRD, SEM, TEM, and DSC. At high ball-milling rotation speeds, the mixtures were fined, homogenized, nanocrystallized, and later completely amorphized, and the transformation of Dy2O3 from the cubic to the monoclinic crystal structure was observed. The amorphous transformation resulted from monoclinic Dy2O3, not from cubic Dy2O3. However, at low ball-milling rotation speeds, the mixtures were only fined and homogenized. An intermediate phase with a similar crystal structure to that of cubic Dy2TiO5 was detected in the amorphous mixtures annealed from 800 to 1000 °C, which was a metastable phase that transformed to orthorhombic Dy2TiO5 when the annealing temperature was above 1050 °C. However, at the same annealing temperatures, pyrochlore Dy2Ti2O7 initially formed and subsequently reacted with the remaining Dy2O3 to form orthorhombic Dy2TiO5 in the homogenous mixtures. The evolutionary mechanism of powder mixtures during ball milling and subsequent annealing was analyzed.

A2TiO5 (A = Dy, Gd, Er, Yb) at High Pressure

“…Patterns of the initial samples are highly crystalline A 2 TiO 5 phases with no unreacted products or other impurity phases. Lattice parameters from the refined XRD patterns are reported in Table and are in good agreement with previous investigations. ,,,,,,, …”

“…1 and are in good agreement with previous investigations. 2,12,13,34,35,21,20,36 In orthorhombic A 2 TiO 5 compounds, the A−O, A−A, and Ti−O bond distances increase with increasing A-site cation radius, evidenced by increases in PDF peak positions to higher r (Å) with lanthanide cation substitution (Figure 2a). The increase in the bond distances is attributed to the increased cationic size.…”

“…As is the case for the cubic phases, a metastable hexagonal polymorph can be recovered via high-temperature processing by changing the cooling rate. Such synthesis has been reported for Dy 2 TiO 5 , where a sol–gel technique was applied with various cooling rates. , …”

“…Such synthesis has been reported for Dy 2 TiO 5 , where a sol−gel technique was applied with various cooling rates. 20,21 Recently, Zhang et al reported the quenched hexagonal phases of o-Nd 2 TiO 5 and o-La 2 TiO 5 following compression to above 10 GPa and subsequent decompression. 22 The compounds undergo reconstructive phase transformations, and the quenchable hexagonal phase is isomorphic with the high-temperature polymorph of h-A 2 TiO 5 .…”

Dysprosium Incorporation for Phase Stabilization of Atomic-Layer-Deposited HfO2 Thin Films

“…Figure 1b shows that the Dy/(Dy + Hf) ratio for the 220), which were consistent with that of previous studies. 26,27 In the case of the 1:16 Dy-doped HfO 2 film, the polycrystalline structure of HfO 2 was changed to the preferred orientation of the monoclinic (−111) phase, while the intensity of monoclinic peaks including in (110), ( 111), (020), (120), and (−122) was significantly reduced. As the Dy concentration is increased to 1:2, a similar crystalline structure was observed as shown in Figure 2a with increased intensity.…”